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Thread: New here need help about condensation!

  1. #1 New here need help about condensation! 
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    Hi, like what the title said, I'm new here, only registered a few seconds ago. So sometime ago I was brainstorming if condensation only occurs on hard/solid surfaces. I know condensation occurs when the water vapor is cooled and/or compressed to its saturation limit, but why do I only see them condensing on hard surfaces like bottles, pot lids, tin cans, etc. and not on a liquid's surface? I did my research about it and only to find out that condensation is the collection of droplets on a cool surface. So guys, does condensation occur on anything if the condition(s) are met but we just can't see it or they only occur on solid surfaces? Thanks very much!


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    It is an interesting question. I can recall absolutely nothing in textbooks, or the like, about moisture condensing on liquids. However, if the liquids are suffciently cool I cannot think of any reason this would not occur. Why do we not see it? You have suggested the explanation yourself - water condensing on water will simply not be noticeable. I suggest placing a chilled glass of brandy in a room where condensation is taking place and observing the result. (Use an inexpensive brandy.)


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    It is an interesting question. I think there are multiple things going on. It is partly that condensation will be more noticeable on a smooth surface (I'm sure there is all sort of interesting physics behind why it forms droplets, the size of them, etc). But also, many smooth surfaces will be things like metal which conducts heat well, or glass, which doesn't conduct heat so well but is usually thing. This is important because it is not enough for the surface to be cold, but it has to be a good conductor to absorb the heat from condensing the water. Many rough surfaces tend to be things like plastic or fur, which don't conduct heat. But if water did condense on a matt surface, then maybe it would spread out rather than form drops and just be less visible.

    As for condensation on the surface of a liquid, I would be pretty sure it happens. But it might be tricky to observe.
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    Quote Originally Posted by molecool View Post
    Hi, like what the title said, I'm new here, only registered a few seconds ago. So sometime ago I was brainstorming if condensation only occurs on hard/solid surfaces. I know condensation occurs when the water vapor is cooled and/or compressed to its saturation limit, but why do I only see them condensing on hard surfaces like bottles, pot lids, tin cans, etc. and not on a liquid's surface? I did my research about it and only to find out that condensation is the collection of droplets on a cool surface. So guys, does condensation occur on anything if the condition(s) are met but we just can't see it or they only occur on solid surfaces? Thanks very much!
    If liquid (or a condensable gas) hits a liquid surface and they are miscible (or the incoming molecule has a large enough accomodation coefficient) they coalesce, and the "condensing" liquid enters the bulk of the liquid (if diffusion is fast enough) so you won't see any "condensation" (but you will see the volume of the liquid go up). If the two liquids are not miscible (like some of the experiments I'm doing on aerosol particles) you can get a liquid-liquid phase seperated system where the "condensation" if it occurs will appear as a thin layer on top of the original liquid, probably you have never noticed this as the amount of condensation will probably be small compared to the volume of liquid it is condensing on to and most liquids are miscible with small amounts of water to some degree (even if they form emulsions rather than true solutions).


    I'm currently doing experiments on liquid-liquid phase separation in micron sized droplets (we are trying to figure out how mixed organic/inorganic particles behave in the atmosphere) and we see this type of behaviour. If we have a droplet containing water and small amounts of an inorganic salt and a long chain organic that is slightly soluble in water (a polyol or similar) at high humidity the particle is a one phase homogeneous system and if you increase the humidity in the gas surrounding it, water "condenses" onto the surface, enters the dropet and you can see the droplet size increase and the chemicals in it become more dilute. At low relative humidity the organic and aqueous phases separate with the organic layer on the outside, now as you increase the RH, if the organic is hydrophobic enough water uptake can be slowed by the organic coating on the surface and you can get a system where you have an aqueous core surrounded by an organic layer which is itself surrounded by an annulus of water. It's pretty cool stuff and I'm still trying to make sense of some of our data but I thought it was relevant to your question.
    Last edited by PhDemon; February 5th, 2014 at 06:43 AM. Reason: clarity
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    I see condensation on glass...when you wash it and turn it....also on metal, and I have seen it on plastic, and occasionally on really cold ice cream....on liquids? I don't believe I ever have.
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    My impression was that "condensation" on the surface of a liquid occurs all the time, but it isn't often referred to in that way. At any temperature, an equilibrium will exist between the rate of evaporation from a liquid and the rate of condensation on it, so condensation will be happening continuously. At equilibrium, there will be no increase in the mass of liquid of course, but if the temperature of the liquid were to suddenly fall for some reason, the rate of condensation would exceed the rate of evaporation and the mass of liquid would increase.
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    Pretty much spot on, but as a minor nit-pick there are factors other than temperature (such as partial pressure of the condensable gas in the surrounding medium, surface tension of the liquid, diffusion coefficients of the condensable species etc.) that can affect the condensation and evaporation rates from liquid surfaces.
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    There is a possible puzzle if we consider different immiscible liquids. For example, if one were to expose the surface of a bowl of oil which is at 5 C to a humid atmosphere at 30 C, would water from the atmosphere condense on the oil? It's a scenario which I don't think I have ever witnessed, but I expect that condensation would occur.
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    It would, I tried to explain it in post#4 above. You would get either a) a thin layer of water on top of the oil which would be easy to miss, or b) the water would enter the bulk as small aqueous globules suspended in the oil.
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    Quote Originally Posted by PhDemon View Post
    It would, I tried to explain it in post#4 above. You would get either a) a thin layer of water on top of the oil which would be easy to miss, or b) the water would enter the bulk as small aqueous globules suspended in the oil.
    Or would sink through the oil to form as a layer below it.

    One problem with observing water condensation on oil is that oils and greases do not attract water so the water will preferentially condense on the walls of the container instead of the surface of the oil.

    edit: we use hydrophobics like glycerine or glycol to prevent condensation on windows and bathroom mirrors. Even soap works in a pinch.
    Last edited by dan hunter; February 5th, 2014 at 11:34 AM.
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    True, if the water was denser than the organic and could diffuse through it effectively.

    Also true, I'm not used to thinking about containers, I'm used to experiments on levitated particles...
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    Quote Originally Posted by PhDemon View Post
    True, if the water was denser than the organic and could diffuse through it effectively.

    Also true, I'm not used to thinking about containers, I'm used to experiments on levitated particles...
    I find the idea of naturally occuring emulsions interesting though. I assume you are describing an emulsion when you say "small aqueous globules suspended in the oil."
    I have never seen emulsions formed without mechanical agitation of some sort, and in my experience emulsions are not stable unless either the water fraction or the oil fraction droplets are very small (like in homogonized milk) or the emulsion relies on emulsifying agents (like egg yolk is used in mayonaise). Even the formation of that white sludge in engines is condensed water agitated in the crankcase by the crankshaft, fed through the oil pump, and sheared into the oil as it goes through the bearings.

    So what you are noticing in levitated particles of oil might be very interesting indeed. I would be curious about what area and thickness a water film on a particle is when the water surface tension draws the water into a sphere instead of a film on the oil droplet, and vice versa.

    edit: I reread #4. Yes, very interesting.
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    We do see these type of natural emulsions in our droplets under certain experimental conditions (they may be less common in bulk liquids and as you say agitation is often needed to make them). We are currently trying to figure out a way of getting the film thickness (actually for what we are looking at at the minute it is the film thickness of an organic around an aqueous core) from our Raman spectra, we have a tame theoretician/computer modeller writing some code for this, at the moment I'm calculating asynchronous mode offsets (a mode offset is the relative shift of TE and TM resonant modes in the particle, i.e. the distance the small spikes are from the middle position between the large spikes in the figure 2 in this paper, if the particle is "core-shell" these offsets increase as the film thickness increases) to try and figure it out which isn't great. I have also been trying to figure it out using the dry mass ratio of the substances in the particles and a thermodynamic model (such as E-AIM or AIOMFAC) to calculate how much water each component will take up as a function of relative humidity, from this, assuming that when phase separation occurs the water associated with each phase is the same as it would be in a pure component aerosol (a bit of an iffy assumption TBH) and calculating the volume fraction of each phase you can get a theoretical film thickness as a function of water activity which we can compare with our experimental data to see if it makes sense (so far no luck, the agreement isn't great, probably due to some iffy assumptions so I'm waiting for the code from our modeller).
    Last edited by PhDemon; February 7th, 2014 at 09:02 AM.
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    Probing aerosol dynamics by....
    Reid, Mitchem, Hopkins, Ward
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    "Reid" is my boss. This paper was written before I started working here but it was one I had to hand to illustrate some of the things I mentioned. More recently we've used it to develop a new way of accurately measuring low vapour pressures (A new approach to determine vapour pressures and hygroscopicities of aqueous aerosols containing semi-volatile organic compounds - Physical Chemistry Chemical Physics (RSC Publishing)) I'm the 2nd author...

    The phase separation stuff is still very much work in progress and won't be published for a while (there are two more to write with data I already have and understand first as well as needing to do more experimental work).
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    Quote Originally Posted by Strange View Post
    It is partly that condensation will be more noticeable on a smooth surface (I'm sure there is all sort of interesting physics behind why it forms droplets, the size of them, etc).
    The layer of condensation made up of small droplets is a puzzle. It suggests some kind of nucleation and, as water molecules are electrical dipoles, an electrical effect could be the cause of the nucleation. However, whilst there could be a non-uniform distribution of charge on a glass surface (non-uniform on a scale approximating to the size of droplets), it is unlikely that a similar non-uniform distribution of charge would exist on a metal surface, because such a surface would, of course, be conducting - droplet layers also form on smooth metal surfaces.
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    Clouds, mists and fogs are all forms of condenasation where there is no surface. Heterogeneous nucleation is when there is dust and salts in the air that the water can condense onto. So long as the temperature is below the dewpoint and the air is saturated it will condense on dust particle.

    If the temperature drops to -40degrees it can be cold enough for homogeneous condensation. That is where the droplets forn without any seed or surface for them to start on.
    The relative humidity has to be about 700% and the water vapor in the air is actually supercooled.
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    Quote Originally Posted by molecool View Post
    Hi, like what the title said, I'm new here, only registered a few seconds ago. So sometime ago I was brainstorming if condensation only occurs on hard/solid surfaces. I know condensation occurs when the water vapor is cooled and/or compressed to its saturation limit, but why do I only see them condensing on hard surfaces like bottles, pot lids, tin cans, etc. and not on a liquid's surface? I did my research about it and only to find out that condensation is the collection of droplets on a cool surface. So guys, does condensation occur on anything if the condition(s) are met but we just can't see it or they only occur on solid surfaces? Thanks very much!
    How about rain, snow, fog, etc.?
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    Hello once again, I'm back and WOW, to be honest I'm surprised by the number of replies. I really, really appreciate all your replies and because of that I'm much more relieved now. I even did an experiment yesterday with a glass of ice cold soy milk (which I never drink anyway). After like 1-2 hours, I was amazed at how the liquid level rose. It rose up to at least half a centimetre and of course, the soy milk turned a little diluted. Once again I thank you all for your replies, I've read all of them and I'm impressed!

    TL;DR : Thanks for all your replies! Love them!

    Another question : Why doesn't the water vapor in a bottle left at room temperature condense on the inside of the bottle instead of on the water? Surely water vapor will condense on anything if the air is saturated, am I right?

    Quote Originally Posted by mathman View Post
    Quote Originally Posted by molecool View Post
    Hi, like what the title said, I'm new here, only registered a few seconds ago. So sometime ago I was brainstorming if condensation only occurs on hard/solid surfaces. I know condensation occurs when the water vapor is cooled and/or compressed to its saturation limit, but why do I only see them condensing on hard surfaces like bottles, pot lids, tin cans, etc. and not on a liquid's surface? I did my research about it and only to find out that condensation is the collection of droplets on a cool surface. So guys, does condensation occur on anything if the condition(s) are met but we just can't see it or they only occur on solid surfaces? Thanks very much!
    How about rain, snow, fog, etc.?
    Good idea mathman, I didn't think about that.
    Last edited by molecool; February 6th, 2014 at 05:19 AM.
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    Quote Originally Posted by JonG View Post
    There is a possible puzzle if we consider different immiscible liquids. For example, if one were to expose the surface of a bowl of oil which is at 5 C to a humid atmosphere at 30 C, would water from the atmosphere condense on the oil? It's a scenario which I don't think I have ever witnessed, but I expect that condensation would occur.
    There would be condensation but water would sink in the oil so the condensate would appear at the bottom of the container of oil.
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  22. #21  
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    Quote Originally Posted by molecool View Post
    Hello once again, I'm back and WOW, to be honest I'm surprised by the number of replies. I really, really appreciate all your replies and because of that I'm much more relieved now. I even did an experiment yesterday with a glass of ice cold soy milk (which I never drink anyway). After like 1-2 hours, I was amazed at how the liquid level rose. It rose up to at least half a centimetre and of course, the soy milk turned a little diluted. Once again I thank you all for your replies, I've read all of them and I'm impressed!

    TL;DR : Thanks for all your replies! Love them!

    Another question : Why doesn't the water vapor in a bottle left at room temperature condense on the inside of the bottle instead of on the water? Surely water vapor will condense on anything if the air is saturated, am I right?

    Quote Originally Posted by mathman View Post
    Quote Originally Posted by molecool View Post
    Hi, like what the title said, I'm new here, only registered a few seconds ago. So sometime ago I was brainstorming if condensation only occurs on hard/solid surfaces. I know condensation occurs when the water vapor is cooled and/or compressed to its saturation limit, but why do I only see them condensing on hard surfaces like bottles, pot lids, tin cans, etc. and not on a liquid's surface? I did my research about it and only to find out that condensation is the collection of droplets on a cool surface. So guys, does condensation occur on anything if the condition(s) are met but we just can't see it or they only occur on solid surfaces? Thanks very much!
    How about rain, snow, fog, etc.?
    Good idea mathman, I didn't think about that.
    Bump.
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    Quote Originally Posted by dan hunter View Post
    Clouds, mists and fogs are all forms of condenasation where there is no surface. Heterogeneous nucleation is when there is dust and salts in the air that the water can condense onto. So long as the temperature is below the dewpoint and the air is saturated it will condense on dust particle. .
    Just to nitpick, or rather to be accurate: a dust particle is a surface. From the POV of a water molecule it is a huge surface, so extensive that some water molecules have formed a Flat Dust Society.
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    OK John, I thought the rest of my post covered that. It seems I didn't explain it right.
    The point is that homogeneous condensation will occour when the temperature and humidity are both at the critical point. Temperature below critical and humidity above critical.
    In other words super cooled vapour at supersaturation will self seed droplets (which will most likely flash freeze into ices). At -40 you can get ice fogs that look like diamond dust floating in the air.
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    Quote Originally Posted by dan hunter View Post
    OK John, I thought the rest of my post covered that. It seems I didn't explain it right.
    The point is that homogeneous condensation will occour when the temperature and humidity are both at the critical point. Temperature below critical and humidity above critical.
    In other words super cooled vapour at supersaturation will self seed droplets (which will most likely flash freeze into ices). At -40 you can get ice fogs that look like diamond dust floating in the air.
    Why can't water vapor condense on themselves to form droplets then falls down to the ground due to gravity?
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    Quote Originally Posted by molecool View Post
    Why can't water vapor condense on themselves to form droplets then falls down to the ground due to gravity?
    Uhm... is that a joke? Like, er, you know, rain?
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    Quote Originally Posted by molecool View Post
    Quote Originally Posted by molecool View Post
    Hello once again, I'm back and WOW, to be honest I'm surprised by the number of replies. I really, really appreciate all your replies and because of that I'm much more relieved now. I even did an experiment yesterday with a glass of ice cold soy milk (which I never drink anyway). After like 1-2 hours, I was amazed at how the liquid level rose. It rose up to at least half a centimetre and of course, the soy milk turned a little diluted. Once again I thank you all for your replies, I've read all of them and I'm impressed!

    TL;DR : Thanks for all your replies! Love them!

    Another question : Why doesn't the water vapor in a bottle left at room temperature condense on the inside of the bottle instead of on the water? Surely water vapor will condense on anything if the air is saturated, am I right?

    Quote Originally Posted by mathman View Post
    Quote Originally Posted by molecool View Post
    Hi, like what the title said, I'm new here, only registered a few seconds ago. So sometime ago I was brainstorming if condensation only occurs on hard/solid surfaces. I know condensation occurs when the water vapor is cooled and/or compressed to its saturation limit, but why do I only see them condensing on hard surfaces like bottles, pot lids, tin cans, etc. and not on a liquid's surface? I did my research about it and only to find out that condensation is the collection of droplets on a cool surface. So guys, does condensation occur on anything if the condition(s) are met but we just can't see it or they only occur on solid surfaces? Thanks very much!
    How about rain, snow, fog, etc.?
    Good idea mathman, I didn't think about that.
    Bump.
    As you imply, it will only condense on a surface that is below the "dew point" (the temperature at which the air inside the bottle becomes saturated with water vapour.) As air cools, its ability to "dissolve" water vapour decreases. Eventually a point is reached where it cannot hold the water vapour it contains and then condensation will begin which is how clouds, fog and indeed dew, form - hence the name.

    If the surface of your bottle is above the dew point you won't get any condensation. The more water vapour there is in the air, the higher the dew point will be, but the concentration of water vapour will be determined by the temperature of the liquid providing the source of vapour. So, if you have a warm liquid in a cold bottle, you will see condensation, but if you have cold liquid in a warm bottle, you won't.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by molecool View Post
    Why can't water vapor condense on themselves to form droplets then falls down to the ground due to gravity?
    Uhm... is that a joke? Like, er, you know, rain?
    No, I understand his question.
    xxxx.....
    ....xxxx
    ERRRRR... I guess I didn't understand the question.
    Last edited by dan hunter; February 7th, 2014 at 04:49 AM.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by molecool View Post
    Why can't water vapor condense on themselves to form droplets then falls down to the ground due to gravity?
    Uhm... is that a joke? Like, er, you know, rain?
    I mean at sea level? Why won't clouds form down here anyway? I'm sorry that I didn't state my question clearly, but then again, why wouldn't water vapor hydrogen bond and condense on themselves instead of condensing on something?

    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Quote Originally Posted by molecool View Post
    Hello once again, I'm back and WOW, to be honest I'm surprised by the number of replies. I really, really appreciate all your replies and because of that I'm much more relieved now. I even did an experiment yesterday with a glass of ice cold soy milk (which I never drink anyway). After like 1-2 hours, I was amazed at how the liquid level rose. It rose up to at least half a centimetre and of course, the soy milk turned a little diluted. Once again I thank you all for your replies, I've read all of them and I'm impressed!

    TL;DR : Thanks for all your replies! Love them!

    Another question : Why doesn't the water vapor in a bottle left at room temperature condense on the inside of the bottle instead of on the water? Surely water vapor will condense on anything if the air is saturated, am I right?

    Quote Originally Posted by mathman View Post
    Quote Originally Posted by molecool View Post
    Hi, like what the title said, I'm new here, only registered a few seconds ago. So sometime ago I was brainstorming if condensation only occurs on hard/solid surfaces. I know condensation occurs when the water vapor is cooled and/or compressed to its saturation limit, but why do I only see them condensing on hard surfaces like bottles, pot lids, tin cans, etc. and not on a liquid's surface? I did my research about it and only to find out that condensation is the collection of droplets on a cool surface. So guys, does condensation occur on anything if the condition(s) are met but we just can't see it or they only occur on solid surfaces? Thanks very much!
    How about rain, snow, fog, etc.?
    Good idea mathman, I didn't think about that.
    Bump.
    It will only condense on a surface that is below the "dew point". This is the temperature at which the air inside the bottle becomes saturated with water vapour. As air cools, its ability to "dissolve" water vapour decreases. Eventually a point is reached where it cannot hold the water vapour it contains and then condensation will begin. This is how clouds, fog and indeed dew, form - hence the name.

    If the surface of your bottle is above the dew point you won't get any condensation. The more water vapour there is in the air, the higher the dew point will be, but the concentration of water vapour will be determined by the temperature of the liquid providing the source of vapour. So, if you have a warn liquid in a cld bottle, you will see condensation, but if you have cold liquid in a warm bottle, you won't.

    Yes, yes! That's it! Finally a clear answer!
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    Quote Originally Posted by molecool View Post
    I mean at sea level? Why won't clouds form down here?
    They do: we call it fog! Also, there are some buildings that are large enough to form clouds and rain (I have read that this could happen in the big hangar at the NASA Ames Research Center... is it still there, I wonder...)
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    Quote Originally Posted by dan hunter View Post
    Clouds, mists and fogs are all forms of condenasation where there is no surface.
    Not really correct in most situations for the atmosphere. Clouds, mist and fogs all had a surface, specifically and generically known as a cloud condensation nuclei, which serve as the surface. Without one, condensation can happen but must reach, depending on temperature and air movement, more than 300%, of what we consider the saturation point. Some aerosols, however, are particularly effective cloud condensation nuclei; sea salts are the most common example of such hydroscopic aerosols, which is why condensation in the form of sea fogs can start to form at about 80% relative humidity (saturation) as well as why sea fogs are the most dense (e.g. colloquially called pea soup fog).

    The OPs difference in condensation point is really about which surface is most receptive to condensation.
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    Quote Originally Posted by Lynx_Fox View Post
    Quote Originally Posted by dan hunter View Post
    Clouds, mists and fogs are all forms of condenasation where there is no surface.
    Not really correct in most situations for the atmosphere. Clouds, mist and fogs all had a surface, specifically and generically known as a cloud condensation nuclei, which serve as the surface. Without one, condensation can happen but must reach, depending on temperature and air movement, more than 300%, of what we consider the saturation point. Some aerosols, however, are particularly effective cloud condensation nuclei; sea salts are the most common example of such hydroscopic aerosols, which is why condensation in the form of sea fogs can start to form at about 80% relative humidity (saturation) as well as why sea fogs are the most dense (e.g. colloquially called pea soup fog).

    The OPs difference in condensation point is really about which surface is most receptive to condensation.
    This is interesting. You seem to be saying that if one has hygroscopic nuclei present, then condensation can occur even though the air is not 100% saturated with water vapour, i.e. you get condensation above the dew point. I did not know this, though I suppose one can rationalise it, inasmuch as the hygroscopic material presumably provides a lower energy configuration for the molecules than a pure liquid would, and so the effective dew point is raised.

    I suppose also - thinking about it further - that I should not be surprised, as this is actually just the inverse of the well known phenomenon of boiling point elevation: when you add salt to water the BP goes up, for the same reason.


    Does this sound right?
    Last edited by exchemist; February 7th, 2014 at 09:43 AM. Reason: wrong word
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    Quote Originally Posted by exchemist View Post

    This is interesting. You seem to be saying that if one has hygroscopic nuclei present, then condensation can occur even though the air is not 100% saturated with water vapour, i.e. you get condensation above the dew point.
    Yes, and it's pretty commonly seen as haze over salty seas.

    The reverse is true as well, where there's a lack of aerosols there's not condensation well above "100%" saturation--it's pretty uncommon in the atmosphere.



    I suppose also - thinking about it further - that I should not be surprised, as this is actually just the inverse of the well known phenomenon of boiling point elevation: when you add salt to water the BP goes up, for the same reason.
    Will give it more thought, but I wouldn't connect it too far, boiling and evaporation are substantively different processes.
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    Quote Originally Posted by Lynx_Fox View Post
    Quote Originally Posted by exchemist View Post

    This is interesting. You seem to be saying that if one has hygroscopic nuclei present, then condensation can occur even though the air is not 100% saturated with water vapour, i.e. you get condensation above the dew point.
    Yes, and it's pretty commonly seen as haze over salty seas.

    The reverse is true as well, where there's a lack of aerosols there's not condensation well above "100%" saturation--it's pretty uncommon in the atmosphere.



    I suppose also - thinking about it further - that I should not be surprised, as this is actually just the inverse of the well known phenomenon of boiling point elevation: when you add salt to water the BP goes up, for the same reason.
    Will give it more thought, but I wouldn't connect it too far, boiling and evaporation are substantively different processes.
    What I mean is the general principle of hygroscopic salts providing a lower energy state for water molecules, hence making them more reluctant to disaggregate into the vapour phase.
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    Middle of summer....humid day in Northern Coastal California.....(very Northern).....you look at the grass on the golf course and it is like a stage play with the mist coming out of the ground?

    Is that the mixture of warmth in the air (humidity) and the water in the grass (soil?)
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    Guys, I thought of 2 interesting questions :

    For example, there is a closed container/pot/bottle filled with water and both the water and the vapor have met their equilibrium and reached the dewpoint temperature (which is the temperature in which the rate of condensation equals the rate of evaporation).

    Then I happen to heat up the container, increasing the rate of evaporation and exceeding the rate of condensation. However, there is still vapor above the water. So will there be excess pressure when the heated water tries to evaporate through the saturated air in the container?

    Also, if vapor can condense onto the surface of a liquid like we said earlier, can warm vapor condense onto cooler vapor in the air (or at least transfer heat)? After all, they're just water (assuming the vapor is just water molecules) in gaseous state. I mean, what's the big deal between vapor and water, right?

    Thank you very much!

    Last edited by molecool; February 8th, 2014 at 09:46 AM.
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    Quote Originally Posted by molecool View Post
    Guys, I thought of 2 interesting questions :

    For example, there is a closed container/pot/bottle filled with water and both the water and the vapor have met their equilibrium and reached the dewpoint temperature (which is the temperature in which the rate of condensation equals the rate of evaporation).

    Then I happen to heat up the container, increasing the rate of evaporation and exceeding the rate of condensation. However, there is still vapor above the water. So will there be excess pressure when the heated water tries to evaporate through the saturated air in the container?

    Also, if vapor can condense onto the surface of a liquid like we said earlier, can warm vapor condense onto cooler vapor in the air (or at least transfer heat)? After all, they're just water (assuming the vapor is just water molecules) in gaseous state. I mean, what's the big deal between vapor and water.

    Thank you very much!

    Yes, an excess pressure will develop above the liquid as you raise the temperature of the container. This will arise both from the rise in temperature of the air and from the increase in vapour pressure of the liquid.

    Warm vapour can certainly condense in cooler air (e.g. fog), but can't condense on it as, being a gas, it has no surface.

    And yes of course heat exchange takes place all the time between portions of substances that are at different temperatures and in contact with each other. In a way, that is what we mean by different temperatures.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Guys, I thought of 2 interesting questions :

    For example, there is a closed container/pot/bottle filled with water and both the water and the vapor have met their equilibrium and reached the dewpoint temperature (which is the temperature in which the rate of condensation equals the rate of evaporation).

    Then I happen to heat up the container, increasing the rate of evaporation and exceeding the rate of condensation. However, there is still vapor above the water. So will there be excess pressure when the heated water tries to evaporate through the saturated air in the container?

    Also, if vapor can condense onto the surface of a liquid like we said earlier, can warm vapor condense onto cooler vapor in the air (or at least transfer heat)? After all, they're just water (assuming the vapor is just water molecules) in gaseous state. I mean, what's the big deal between vapor and water.

    Thank you very much!

    Yes, an excess pressure will develop above the liquid as you raise the temperature of the container. This will arise both from the rise in temperature of the air and from the increase in vapour pressure of the liquid.

    Warm vapour can certainly condense in cooler air (e.g. fog), but can't condense on it as, being a gas, it has no surface.

    And yes of course heat exchange takes place all the time between portions of substances that are at different temperatures and in contact with each other. In a way, that is what we mean by different temperatures.
    Ok, thanks! But what do you mean condense in and condense on?
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    Quote Originally Posted by molecool View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Guys, I thought of 2 interesting questions :

    For example, there is a closed container/pot/bottle filled with water and both the water and the vapor have met their equilibrium and reached the dewpoint temperature (which is the temperature in which the rate of condensation equals the rate of evaporation).

    Then I happen to heat up the container, increasing the rate of evaporation and exceeding the rate of condensation. However, there is still vapor above the water. So will there be excess pressure when the heated water tries to evaporate through the saturated air in the container?

    Also, if vapor can condense onto the surface of a liquid like we said earlier, can warm vapor condense onto cooler vapor in the air (or at least transfer heat)? After all, they're just water (assuming the vapor is just water molecules) in gaseous state. I mean, what's the big deal between vapor and water.

    Thank you very much!

    Yes, an excess pressure will develop above the liquid as you raise the temperature of the container. This will arise both from the rise in temperature of the air and from the increase in vapour pressure of the liquid.

    Warm vapour can certainly condense in cooler air (e.g. fog), but can't condense on it as, being a gas, it has no surface.

    And yes of course heat exchange takes place all the time between portions of substances that are at different temperatures and in contact with each other. In a way, that is what we mean by different temperatures.
    Ok, thanks! But what do you mean condense in and condense on?
    Well, "on" implies the existence of a surface. For example, dew condenses "on" cold grass, a cold car roof, etc, while fog condenses "in" cold air.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Guys, I thought of 2 interesting questions :

    For example, there is a closed container/pot/bottle filled with water and both the water and the vapor have met their equilibrium and reached the dewpoint temperature (which is the temperature in which the rate of condensation equals the rate of evaporation).

    Then I happen to heat up the container, increasing the rate of evaporation and exceeding the rate of condensation. However, there is still vapor above the water. So will there be excess pressure when the heated water tries to evaporate through the saturated air in the container?

    Also, if vapor can condense onto the surface of a liquid like we said earlier, can warm vapor condense onto cooler vapor in the air (or at least transfer heat)? After all, they're just water (assuming the vapor is just water molecules) in gaseous state. I mean, what's the big deal between vapor and water.

    Thank you very much!

    Yes, an excess pressure will develop above the liquid as you raise the temperature of the container. This will arise both from the rise in temperature of the air and from the increase in vapour pressure of the liquid.

    Warm vapour can certainly condense in cooler air (e.g. fog), but can't condense on it as, being a gas, it has no surface.

    And yes of course heat exchange takes place all the time between portions of substances that are at different temperatures and in contact with each other. In a way, that is what we mean by different temperatures.
    Ok, thanks! But what do you mean condense in and condense on?
    Well, "on" implies the existence of a surface. For example, dew condenses "on" cold grass, a cold car roof, etc, while fog condenses "in" cold air.
    So basically "on" means the condensation on a solid/liquid surface while "in" means condensation in air/gas?
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    It's basically the difference between homogeneous nucleation and heterogeneous nucleation.
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    Quote Originally Posted by molecool View Post
    Ok, thanks! But what do you mean condense in and condense on?
    It's a false distinction in the atmosphere--condensation almost always happens on solid or liquid aerosol surfaces--often too small to see with the naked eye.
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    Quote Originally Posted by Lynx_Fox View Post
    Quote Originally Posted by molecool View Post
    Ok, thanks! But what do you mean condense in and condense on?
    It's a false distinction in the atmosphere--condensation almost always happens on solid or liquid aerosol surfaces--often too small to see with the naked eye.
    So can vapor be classified as liquid aerosol as it is just water molecules?

    Quote Originally Posted by exchemist View Post
    So, if you have a warm liquid in a cold bottle, you will see condensation, but if you have cold liquid in a warm bottle, you won't.
    What if you have liquid in a bottle and both of them are at the dew point temperature? Will you see condensation on the surface of the bottle?
    Last edited by molecool; February 9th, 2014 at 02:37 AM.
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    Quote Originally Posted by molecool View Post
    Quote Originally Posted by Lynx_Fox View Post
    Quote Originally Posted by molecool View Post
    Ok, thanks! But what do you mean condense in and condense on?
    It's a false distinction in the atmosphere--condensation almost always happens on solid or liquid aerosol surfaces--often too small to see with the naked eye.
    So can vapor be classified as liquid aerosol as it is just water molecules?

    Quote Originally Posted by exchemist View Post
    So, if you have a warm liquid in a cold bottle, you will see condensation, but if you have cold liquid in a warm bottle, you won't.
    What if you have liquid in a bottle and both of them are at the dew point temperature? Will you see condensation on the surface of the bottle?
    Yr 1st) No, that's not what he's saying. He's saying in practice there are almost always solid or liquid particles i.e. impurities, that serve as nuclei for condensation, even if you can't see them. He's speaking as a meteorologist, talking about real world conditions in the atmosphere. But a vapour is a gas, not an aerosol.

    Yr 2nd) If everything is at the dew point, it is on the point of condensing. You won't notice any condensation until the temperature falls an infinitesimal amount further.
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    I take it my question didn't have merit.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Quote Originally Posted by Lynx_Fox View Post
    Quote Originally Posted by molecool View Post
    Ok, thanks! But what do you mean condense in and condense on?
    It's a false distinction in the atmosphere--condensation almost always happens on solid or liquid aerosol surfaces--often too small to see with the naked eye.
    So can vapor be classified as liquid aerosol as it is just water molecules?

    Quote Originally Posted by exchemist View Post
    So, if you have a warm liquid in a cold bottle, you will see condensation, but if you have cold liquid in a warm bottle, you won't.
    What if you have liquid in a bottle and both of them are at the dew point temperature? Will you see condensation on the surface of the bottle?
    Yr 1st) No, that's not what he's saying. He's saying in practice there are almost always solid or liquid particles i.e. impurities, that serve as nuclei for condensation, even if you can't see them. He's speaking as a meteorologist, talking about real world conditions in the atmosphere. But a vapour is a gas, not an aerosol.

    Yr 2nd) If everything is at the dew point, it is on the point of condensing. You won't notice any condensation until the temperature falls an infinitesimal amount further.
    Thanks a lot again! But actually, about the 2nd question, I meant can you notice condensation on the dry internal surface of the bottle if everything is on the point of condensing?
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    Quote Originally Posted by babe View Post
    Middle of summer....humid day in Northern Coastal California.....(very Northern).....you look at the grass on the golf course and it is like a stage play with the mist coming out of the ground?

    Is that the mixture of warmth in the air (humidity) and the water in the grass (soil?)
    That would be the layer of air closest to the cold ground exceeding the dew point. Overnight, if it is clear, the ground cools by radiation and can end up colder than the air above it.
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    Quote Originally Posted by babe View Post
    I take it my question didn't have merit.
    No it was just overlooked - I've now replied.
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    Quote Originally Posted by babe View Post
    I take it my question didn't have merit.
    It's roughly the same process. What we see as morning steam rising off plants and ground is because there's a thin layer of sun warmed air within the lower couple feet. That thin layer of warmer air means higher evaporation from the ground and many plants opening up their stomata and releasing even more water vapor. That layer is also unstable and mixes upwards and rapidly cools (usually referred to as the surface boundary layer by meteorologist) . As it cools we start to see condensation as the temperature of those little sun warmed eddies drops below the dew point again.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by babe View Post
    Middle of summer....humid day in Northern Coastal California.....(very Northern).....you look at the grass on the golf course and it is like a stage play with the mist coming out of the ground?

    Is that the mixture of warmth in the air (humidity) and the water in the grass (soil?)
    That would be the layer of air closest to the cold ground exceeding the dew point. Overnight, if it is clear, the ground cools by radiation and can end up colder than the air above it.
    Mahalo! That really makes sense!!
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    Quote Originally Posted by Lynx_Fox View Post
    Quote Originally Posted by babe View Post
    I take it my question didn't have merit.
    It's roughly the same process. What we see as morning steam rising off plants and ground is because there's a thin layer of sun warmed air within the lower couple feet. That thin layer of warmer air means higher evaporation from the ground and many plants opening up their stomata and releasing even more water vapor. That layer is also unstable and mixes upwards and rapidly cools (usually referred to as the surface boundary layer by meteorologist) . As it cools we start to see condensation as the temperature of those little sun warmed eddies drops below the dew point again.
    Thank to you also!! Makes sese!!!
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    Why does condensation need a surface though? To transfer heat? Or?
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    Quote Originally Posted by molecool View Post
    Why does condensation need a surface though? To transfer heat? Or?
    Well no, you do not need a surface. For example you can make a fog appear in in pure cold air. In this case, the latent heat is transferred to the air rather than to a surface. However, as Lynx Fox has pointed out, in the real world there are nearly always solid particles in the air and the surface that these provide is helpful to condensation in another way. They act as condensation nuclei. These help the condensation process to start.

    Very pure humid air can be cooled some way below its dew point without any condensation, due to the absence of condensation nuclei. This is what is known as "supercooling". Although, thermodynamically, the molecules should start to condense, it is far easier for a molecule to attach itself to a group of molecules that are already in the liquid state than it is for the first pair of slow-moving molecules to stick together. When the first pair of them tries, due to their relative speed they tend to come unstuck again, whereas if a single slow-moving molecule encounters a mass of molecules that are already stuck together as a liquid, the energy of its motion can be more easily spread among the others when it hits, making it less likely to bounce off. Nuclei have surfaces and edges that a few water molecules stick to (get "adsorbed" on) and their slow-moving comrades can then bump into them and have a better chance of staying stuck.

    This illustrates another concept that is useful to know in physics and even more in chemistry, which is the distinction between thermodynamic and kinetic stability. Although the slow-moving vapour phase molecules thermodynamically can and should lose energy by collapsing into a liquid state, the lack of a mechanism to help them do it can delay the process. Hence supercooling.

    Just, as, thermodynamically, a newspaper in your hand is thermodynamically unstable compared to the water and CO2 it can make by burning in the air, but, (thankfully) there is a kinetic barrier to this happening - until you apply a lighted match.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Why does condensation need a surface though? To transfer heat? Or?
    Well no, you do not need a surface. For example you can make a fog appear in in pure cold air. In this case, the latent heat is transferred to the air rather than to a surface. However, as Lynx Fox has pointed out, in the real world there are nearly always solid particles in the air and the surface that these provide is helpful to condensation in another way. They act as condensation nuclei. These help the condensation process to start.

    Very pure humid air can be cooled some way below its dew point without any condensation, due to the absence of condensation nuclei. This is what is known as "supercooling". Although, thermodynamically, the molecules should start to condense, it is far easier for a molecule to attach itself to a group of molecules that are already in the liquid state than it is for the first pair of slow-moving molecules to stick together. When the first pair of them tries, due to their relative speed they tend to come unstuck again, whereas if a single slow-moving molecule encounters a mass of molecules that are already stuck together as a liquid, the energy of its motion can be more easily spread among the others when it hits, making it less likely to bounce off. Nuclei have surfaces and edges that a few water molecules stick to (get "adsorbed" on) and their slow-moving comrades can then bump into them and have a better chance of staying stuck.

    This illustrates another concept that is useful to know in physics and even more in chemistry, which is the distinction between thermodynamic and kinetic stability. Although the slow-moving vapour phase molecules thermodynamically can and should lose energy by collapsing into a liquid state, the lack of a mechanism to help them do it can delay the process. Hence supercooling.

    Just, as, thermodynamically, a newspaper in your hand is thermodynamically unstable compared to the water and CO2 it can make by burning in the air, but, (thankfully) there is a kinetic barrier to this happening - until you apply a lighted match.
    I see, so in the absence of a surface, condensation will only occur waaaay below the dewpoint but if there's a surface it will occur much easily?

    Thanks btw.
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    Quote Originally Posted by molecool View Post
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by molecool View Post
    Why does condensation need a surface though? To transfer heat? Or?
    Well no, you do not need a surface. For example you can make a fog appear in in pure cold air. In this case, the latent heat is transferred to the air rather than to a surface. However, as Lynx Fox has pointed out, in the real world there are nearly always solid particles in the air and the surface that these provide is helpful to condensation in another way. They act as condensation nuclei. These help the condensation process to start.

    Very pure humid air can be cooled some way below its dew point without any condensation, due to the absence of condensation nuclei. This is what is known as "supercooling". Although, thermodynamically, the molecules should start to condense, it is far easier for a molecule to attach itself to a group of molecules that are already in the liquid state than it is for the first pair of slow-moving molecules to stick together. When the first pair of them tries, due to their relative speed they tend to come unstuck again, whereas if a single slow-moving molecule encounters a mass of molecules that are already stuck together as a liquid, the energy of its motion can be more easily spread among the others when it hits, making it less likely to bounce off. Nuclei have surfaces and edges that a few water molecules stick to (get "adsorbed" on) and their slow-moving comrades can then bump into them and have a better chance of staying stuck.

    This illustrates another concept that is useful to know in physics and even more in chemistry, which is the distinction between thermodynamic and kinetic stability. Although the slow-moving vapour phase molecules thermodynamically can and should lose energy by collapsing into a liquid state, the lack of a mechanism to help them do it can delay the process. Hence supercooling.

    Just, as, thermodynamically, a newspaper in your hand is thermodynamically unstable compared to the water and CO2 it can make by burning in the air, but, (thankfully) there is a kinetic barrier to this happening - until you apply a lighted match.
    I see, so in the absence of a surface, condensation will only occur waaaay below the dewpoint but if there's a surface it will occur much easily?

    Thanks btw.
    Yes, though I'm not sure exactly how far below. I imagine it may depend on the vapour involved and a lot of other things. We may have people on this forum that can answer that, but I'm not expert on it.
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    Quote Originally Posted by molecool View Post
    I see, so in the absence of a surface, condensation will only occur waaaay below the dewpoint but if there's a surface it will occur much easily?

    Thanks btw.
    You got it.
    Think about a jet flying in the higher atmosphere.
    The moisture is there and it is cold but not condensed because there is not enough dust up there for it to condense on.
    The jet's kerosene burning motors effectively inject carbon particles (soot) into the atmosphere which the moisture condenses on and gives us those long thin clouds we call vapour trails.
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    Quote Originally Posted by dan hunter View Post
    Quote Originally Posted by molecool View Post
    I see, so in the absence of a surface, condensation will only occur waaaay below the dewpoint but if there's a surface it will occur much easily?

    Thanks btw.
    You got it.
    Think about a jet flying in the higher atmosphere.
    The moisture is there and it is cold but not condensed because there is not enough dust up there for it to condense on.
    The jet's kerosene burning motors effectively inject carbon particles (soot) into the atmosphere which the moisture condenses on and gives us those long thin clouds we call vapour trails.
    I was going to say surely it is the water vapour in the exhaust that is responsible, but then I checked and find it is both the water vapour and the soot particles acting as nuclei : Contrail - Wikipedia, the free encyclopedia
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    Yup. Considering how far most jets fly and the amount of fuel they carry and how much water vapour it would take to create their trails.
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    Bravo! Thanks a lot, you guys!!!!!!!!
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    Quote Originally Posted by dan hunter View Post
    Quote Originally Posted by molecool View Post
    I see, so in the absence of a surface, condensation will only occur waaaay below the dewpoint but if there's a surface it will occur much easily?

    Thanks btw.
    You got it.
    Think about a jet flying in the higher atmosphere.
    The moisture is there and it is cold but not condensed because there is not enough dust up there for it to condense on.
    The jet's kerosene burning motors effectively inject carbon particles (soot) into the atmosphere which the moisture condenses on and gives us those long thin clouds we call vapour trails.
    Question....they how do you get "Ice on the Wings" of an airplane......usually it's our 32 seat prop we have to fly from SFO to ACV....
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  61. #60  
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by dan hunter View Post
    Quote Originally Posted by molecool View Post
    I see, so in the absence of a surface, condensation will only occur waaaay below the dewpoint but if there's a surface it will occur much easily?

    Thanks btw.
    You got it.
    Think about a jet flying in the higher atmosphere.
    The moisture is there and it is cold but not condensed because there is not enough dust up there for it to condense on.
    The jet's kerosene burning motors effectively inject carbon particles (soot) into the atmosphere which the moisture condenses on and gives us those long thin clouds we call vapour trails.
    I was going to say surely it is the water vapour in the exhaust that is responsible, but then I checked and find it is both the water vapour and the soot particles acting as nuclei : Contrail - Wikipedia, the free encyclopedia
    Wait, I suppose you mean water droplets, right? Because vapor can't condense on itself unless supercooled/supersaturated.
    Last edited by molecool; February 13th, 2014 at 08:30 AM.
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  62. #61  
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    At the altitude aircraft fly (~10 km) it would be supercooled...

    Temperature in the Stratosphere - Windows to the Universe
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  63. #62  
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    The temperature is only one part of the equation. The humidity level has to be supercritical too. Often the homogeneous nucleation particles are under 5 nanometers and evaporate again instead of stabilizing or growing.
    Homogeneous nucleation is not very common though, and it might be better not to get sidetracked by it. Please forget I ever mentioned it.

    ahrens chapter 6
    HOMOGENEOUS NUCLEATION

    Homogeneous nucleation occurs when the water vapor molecules condense and form a cloud droplet. To do this requires an environmental temperature of -40C and saturated air, or relative humidity of several hundred percent.
    Vapour trails, contrails, whatever you like to call them are mostly the atmosphere in the air condensing on the pollution being spewed out the tailpipes of the jet planes. The mixing condensation from the water left in the exhaust is also forms nuclei for the moisture in the atmosphere to condense on. In addition to the carbon soot the exhaust carries sulfur compounds like H2SO4 which can attract water molecules and form condensation nuclei.
    molecool likes this.
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  64. #63  
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    [QUOTE=babe;525331
    Question....they how do you get "Ice on the Wings" of an airplane......usually it's our 32 seat prop we have to fly from SFO to ACV....[/QUOTE]
    Cold air at high altitude, moisture in the cold air waiting for something to condense on.
    The motion and pressure difference across the wing contribute to the effect.

    This link is to a pdf download about it.
    Aircraft Icing - Flight Training - AOPA

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  65. #64  
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    [QUOTE=dan hunter;525401]
    Quote Originally Posted by babe;525331
    Question....they how do you get "Ice on the Wings" of an airplane......usually it's our 32 seat prop we have to fly from SFO to ACV....[/QUOTE
    Cold air at high altitude, moisture in the cold air waiting for something to condense on.
    The motion and pressure difference across the wing contribute to the effect.

    This link is to a pdf download about it.
    Aircraft Icing - Flight Training - AOPA
    but ours gets it on the GROUND at ACV and they have to DE ICE the plane.....it's freaking prop...on the ground and iced!......I am not talking at high altitude...I am just curious!

    I appreciate EVERY answer!
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    Quote Originally Posted by dan hunter View Post
    The temperature is only one part of the equation. The humidity level has to be supercritical too. Often the homogeneous nucleation particles are under 5 nanometers and evaporate again instead of stabilizing or growing.
    Homogeneous nucleation is not very common though, and it might be better not to get sidetracked by it. Please forget I ever mentioned it.

    ahrens chapter 6
    HOMOGENEOUS NUCLEATION

    Homogeneous nucleation occurs when the water vapor molecules condense and form a cloud droplet. To do this requires an environmental temperature of -40C and saturated air, or relative humidity of several hundred percent.
    Vapour trails, contrails, whatever you like to call them are mostly the atmosphere in the air condensing on the pollution being spewed out the tailpipes of the jet planes. The mixing condensation from the water left in the exhaust is also forms nuclei for the moisture in the atmosphere to condense on. In addition to the carbon soot the exhaust carries sulfur compounds like H2SO4 which can attract water molecules and form condensation nuclei.
    But then I thought when the warm vapor from the exhaust meets negative temperatures it is already way below the dewpoint temperature and thus supersaturated? In this case it doesn't need particles to condense on, does it? And I don't understand "mixing condensation"? There is condensed water in the exhaust too?
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  67. #66  
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    Quote Originally Posted by molecool View Post
    Quote Originally Posted by dan hunter View Post
    The temperature is only one part of the equation. The humidity level has to be supercritical too. Often the homogeneous nucleation particles are under 5 nanometers and evaporate again instead of stabilizing or growing.
    Homogeneous nucleation is not very common though, and it might be better not to get sidetracked by it. Please forget I ever mentioned it.

    ahrens chapter 6
    HOMOGENEOUS NUCLEATION

    Homogeneous nucleation occurs when the water vapor molecules condense and form a cloud droplet. To do this requires an environmental temperature of -40C and saturated air, or relative humidity of several hundred percent.
    Vapour trails, contrails, whatever you like to call them are mostly the atmosphere in the air condensing on the pollution being spewed out the tailpipes of the jet planes. The mixing condensation from the water left in the exhaust is also forms nuclei for the moisture in the atmosphere to condense on. In addition to the carbon soot the exhaust carries sulfur compounds like H2SO4 which can attract water molecules and form condensation nuclei.
    But then I thought when the warm vapor from the exhaust meets negative temperatures it is already way below the dewpoint temperature and thus supersaturated? In this case it doesn't need particles to condense on, does it? And I don't understand "mixing condensation"? There is condensed water in the exhaust too?
    Mixing condensation, forget I mentioned it. I was using the words in a nonstandard way. It a concept usually used in meteorology but not much anywhere else. It has to do when you mix warm moist air with cold dry air and what the new dew point is.

    Yes the exhaust is moist. I guess you have never noticed the water dripping out of the tailpipe of a car on a cold day. Same type of thing.

    Anyway, you have managed to keep this thread going a very long time.
    Have fun, I'm done.
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