Notices
Results 1 to 4 of 4

Thread: Thermal Conductivity Question

  1. #1 Thermal Conductivity Question 
    New Member
    Join Date
    Feb 2018
    Posts
    2
    I have been using a tabletop water bath for a while now. The water conveys the temperature beautifully, and my vessel ends up very close to the temperature setting on the water bath.

    For various reasons, evaporation/condensation was a problem, so I replaced the water with the beads sold by Lab Armor. They don't say, but I assume they are made of an aluminum alloy. The beads are approximately the size and dimension of smashed green peas. They do not convey the temperature to my vessel nearly as well as the water did. With the beads, the vessel is about 10C cooler at the same setting.

    Then, thinking that it must be an issue with air gaps and limited surface area contact, I tried common sand. Surprisingly, the sand performed almost exactly as the $450 Lab Armor beads.

    Neither the sand, nor the beads will suffice. Nor can I use water. Since aluminum has such a high K value, I am now considering buying very fine aluminum shot. The problem is that I can't really afford it, so I don't want to buy it if it's just going to perform similar to the beads, which I assume are basically aluminum.

    I am obviously not understanding something about thermal conductivity, because I thought that aluminum beads would convey heat at least as well as water, which has much lower thermal conductivity. Should the aluminum shot (400 microns diameter) convey the temperature better than the beads and the sand? Is there a better solution? Any guidance here would be greatly appreciated, because I'm at a loss. Thanks in advance.


    Last edited by BigDaddyPapa; February 1st, 2018 at 06:16 PM.
    Reply With Quote  
     

  2.  
     

  3. #2  
    Forum Isotope
    Join Date
    Feb 2012
    Location
    Western US
    Posts
    2,770
    Quote Originally Posted by BigDaddyPapa View Post
    I have been using a tabletop water bath for a while now. The water conveys the temperature beautifully, and my vessel ends up very close to the temperature setting on the water bath.

    For various reasons, evaporation/condensation was a problem, so I replaced the water with the beads sold by Lab Armor. They don't say, but I assume they are made of an aluminum alloy. The beads are approximately the size and dimension of smashed green peas. They do not convey the temperature to my vessel nearly as well as the water did. With the beads, the vessel is about 10C cooler at the same setting.

    Then, thinking that it must be an issue with air gaps and limited surface area contact, I tried common sand. Surprisingly, the sand performed almost exactly as the $450 Lab Armor beads.

    Neither the sand, nor the beads will suffice. Nor can I use water. Since aluminum has such a high K value, I am now considering buying very fine aluminum shot. The problem is that I can't really afford it, so I don't want to buy it if it's just going to perform similar to the beads, which I assume are basically aluminum.

    I am obviously not understanding something about thermal conductivity, because I thought that aluminum beads would convey heat at least as well as water, which has much lower thermal conductivity. Should the aluminum shot (400 microns diameter) convey the temperature better than the beads and the sand? Is there a better solution? Any guidance here would be greatly appreciated, because I'm at a loss. Thanks in advance.
    The problem is that air is five orders of magnitude less thermally conductive than aluminum. For that not to matter would require extremely intimate contact among all of the beads. You will not be able to achieve that result with ease, I'm afraid, if you continue to pursue a granular-solid approach. I would instead recommend an oil bath. There are many oils with far lower vapor pressure than water.


    Reply With Quote  
     

  4. #3  
    New Member
    Join Date
    Feb 2018
    Posts
    2
    tk421, thank you for that crystal clear answer. That is exactly what I needed to know.
    Reply With Quote  
     

  5. #4  
    exchemist
    Join Date
    May 2013
    Location
    London
    Posts
    2,873
    Quote Originally Posted by tk421 View Post
    Quote Originally Posted by BigDaddyPapa View Post
    I have been using a tabletop water bath for a while now. The water conveys the temperature beautifully, and my vessel ends up very close to the temperature setting on the water bath.

    For various reasons, evaporation/condensation was a problem, so I replaced the water with the beads sold by Lab Armor. They don't say, but I assume they are made of an aluminum alloy. The beads are approximately the size and dimension of smashed green peas. They do not convey the temperature to my vessel nearly as well as the water did. With the beads, the vessel is about 10C cooler at the same setting.

    Then, thinking that it must be an issue with air gaps and limited surface area contact, I tried common sand. Surprisingly, the sand performed almost exactly as the $450 Lab Armor beads.

    Neither the sand, nor the beads will suffice. Nor can I use water. Since aluminum has such a high K value, I am now considering buying very fine aluminum shot. The problem is that I can't really afford it, so I don't want to buy it if it's just going to perform similar to the beads, which I assume are basically aluminum.

    I am obviously not understanding something about thermal conductivity, because I thought that aluminum beads would convey heat at least as well as water, which has much lower thermal conductivity. Should the aluminum shot (400 microns diameter) convey the temperature better than the beads and the sand? Is there a better solution? Any guidance here would be greatly appreciated, because I'm at a loss. Thanks in advance.
    The problem is that air is five orders of magnitude less thermally conductive than aluminum. For that not to matter would require extremely intimate contact among all of the beads. You will not be able to achieve that result with ease, I'm afraid, if you continue to pursue a granular-solid approach. I would instead recommend an oil bath. There are many oils with far lower vapor pressure than water.
    Also, you won't get convection with a solid heat transfer medium. I'm fairly sure that convection is important to the heat transfer when liquids are used.

    In the lubs lab, we often used white oils in the temperature baths, usually with a pinch of BHT (Ionol or equivalent) to inhibit darkening with age. (We had a viscometer bath kept at 100C.)
    Reply With Quote  
     

Similar Threads

  1. Conductivity of limestone?
    By One beer in forum Earth Sciences
    Replies: 2
    Last Post: February 6th, 2014, 06:19 AM
  2. Ph and Conductivity
    By rauletechuleta in forum General Discussion
    Replies: 1
    Last Post: October 11th, 2012, 10:55 AM
  3. Conductivity Lab Question
    By Pierrotechnique in forum Chemistry
    Replies: 0
    Last Post: November 7th, 2011, 09:57 PM
  4. thermal conductivity
    By fatman57 in forum Chemistry
    Replies: 1
    Last Post: August 10th, 2011, 04:09 AM
  5. electrical and thermal conductivity
    By woody600 in forum Physics
    Replies: 4
    Last Post: March 3rd, 2009, 07:22 AM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •