Thread: Propylene Glycol Used as a Heat Transfer Fluid.

To All:

We are working on a science project involving solar energy. This project is basically a take on the thermosiphon system. To quickly explain we have a solar collector made from copper tubing. 24" x 24" with 4 vertical tubes 20" long. Connected at the top and bottom of each of the 4 verticals by 1/2" copper tubing with one 3/4" tube extending from the middle vertically about 4 feet to a heat sink? This is where the heat transfer fluid should transfer its heat to the heat sink and then on to a small water resevoir where hot water can be drawn off. Voila hot water.

Only problem is we are trying to find out the percentage of Glycol we should use. (if this was the experiment then we would do that). We could use 100% or use a percentage similar to what is in a automobile 50/50.

Another question is the amount we should use. Full or something lessor.

The principal is based on the sunlamp heats the solar collector the transfer fluid heats and the hot gas rises (since heat rises) and transfers its heat to the heat sink which then tranfers its heat to the water. cooled the transfer fluid turns back to a liquid and returns to the bottom to begin its process all over.

Mike

I'm so not an expert on this subject, however I was under the impression oils transfered heat better? If not I would love to know the transfer ratio's of different compounds.

How about some form of liquid silver

I'm sure someone on this forum has a clue about your question.

I am assuming that propylene glycol has a fairly low specific heat. You would want to use a lot of it at 100% solution. Antifreeze/water is mixed in a car to prevent the water from boiling and there being gas flowing through the radiator (this would obviously break it). Since you are dealing with a solar collector you won't have that problem so you want as high a percentage of propylene glycol as possible, otherwise it would be like sticking a bucket of water in the sun and using the heat generated from that to heat another bucket of water. Extremely inefficient. You want to fill the reservoir with propylene glycol so that it gives off more heat, it will take longer to heat up initially but once it gets going it will give the heat off faster.

Sorry it took me so long to reply to this question, I was trying to figure out what excatly the experiment was. It would work a lot better if you set copper pipes out in the sun and ran water through them. Less heat loss through radiation.

Well if you were trying to collect heat wouldn't you use a black collector and insulated mirrorized glass tuding as the transfer with a vacum layer? The idea being to collect as much heat as possible and not loose it in transfer. As to the exact type of liquid to be used, that I'm not sure of. I think you would also want to run it in a humid area.

What liquid has the best thermal transfer ratio?

I think the original question was hat percentage of propylene glycol to use, not how to design the collector or what alterntive materials to use. I'd use ethylene glycol, myself, at 50:50.

The propylene glycol is nore Green, and almost as good. Use 50:50 in copper, particularly if you have dissimilar metal contacts anywhere.

An more efficient collector using prabolic mirrors and such, would boil the propylene glycol pretty quickly, so you'd quickly need something with a higher bp and pretty damned good heat transfer -- at least by my experience -- least you melt the collector. Sodium works well in higher tempertures.

But there are also considerations of what mechanism will be used to extract the work from the transfer material...phase changes make heat capacity seem trivial.

But back to metals: they rock. Depending upon your budget, you might toy with room temperature liquid metal eutectics...