natural coolant material

Hey everyone. I am searching for a material that serves as a natural coolant (keeps cool). Through material libraries, I have come across Bismuth, and Peltier Modules, which are somewhat expensive thermo-electric materials. I was wondering if anyone had advice for new resources (other than material libraries) or other materials that naturally keep cool. These could be low-tech materials or natural coolants. For instance, a cucumber has coolant properties because it is comprised of 90% water. Lots of coolants involve the evaporation of water through a channel or tube, but many of these concepts are patented. Any direction would be appreciated.

that them there seems to be a problem… I think I have an idea that we can talk about over lunch, but maybe tomorrow because I already ate a hot pocket today.

I think that I am confused by your question. Are you looking for a natural coolant - like a thermal fluid that runs through a heat exchanger. Or are you looking for different types of “natural” cooling methods.

I think we need to know more about our application to help you. What do you need to cool, why do you need to utilize “natural” cooling?

As for thermal fluids, there are an number of natural fluids that can act as a thermal fluid - the most obvious being water. There are other less common thermal fluids that are non-reactive like glycerin - these are used because they can be chilled to lower temperatures than water because they have a lower freezing point.

If you are looking for other cooling methods. Well they are all based on removing energy from a system. A thermo electric cooler utilizes a semiconductor to remove energy (heat) from a system, but that energy still needs to be disappated. Usually this is done with a chiller (which would require a thermal fluid) or by convection (using fins/fan).

Another cooling method is known as vacuum cooling - to accomplish this you need to pull a vacuum on a closed system, as the pressure in the system approaches zero the phase transition point for water changes. To allow for the water on the surface on a item to vaporize into a gas, energy is removed from the item that the water is on. This energy comes in the form of heat. This is how large groups of crops are cooled.

There are many “natural” forms of cooling. Lets hear more about your problem…

Hot pocket? That has HOT in the name. It won,t work. Maybe if you could use a cold pocket and put that in your project… Sleep on it and let me know how it works out.

Ceramic (stoneware, not enameled) filled with water will wick and evaporate.

Peltier junctions are excellent, but you need to have a cooling system on the other side (all they do is transfer heat – one side gets hot and one gets cool – so you can use them to heat and cool by reversing the voltage. Very useful benefit). This means fans, heat sinks, more power, etc.

Chemical packs are also a possibility, but not usually reusable.

I haven’t really looked beyond those – peltier junctions are actually a lot more useful than you seem to think.

I suggest using WATER… or maybe ICE

What about cooling materials with pressure. Don’t some pressurized gasses cool under pressure?

Gases cool when they are depressurized (and, contrarily, they heat up when they’re put under pressure. Feel the cylinder of your bicycle pump after you’ve used it to pump a tire).

That’s the concept behind a refrigerator/air conditioner: gas under pressure in a tube is carefully depressurized, turning cold. It cools the environment around it by absorbing heat. The gas, now at room temperature, is pressurized again, heating it up. It’s then cooled back to room temperature (the radiator coils on the back of a fridge, or the outside half of an A/C), then sent through the system.

FWIW, the reason gas cools when released from pressure is because the atoms are crammed together at a certain density, and this allows for a given amount of particle motion at a given temperature. When the container is expanded, the atoms have have much more space to move in, but as they move these greater distances they use more energy than they needed for the smaller distances…end result is that the gas cools off dramatically according to PV = nRT.

That’s all the thermodynamics for today. :slight_smile:

Thank you all for your comments. Here are some more specifics on the project:

A low-tech way to actively keep the surface of a fabric cool.

In summary, the idea is to take a piece of foam, saturate it with water, and put it in a fabric casing or vessel. Once a part of the body comes in contact with the surface, heat is pulled away from the body’s surface due to the conductive properties of water. Your body is the conductive heat source, the water-saturated foam is the heat sink, and the underside fabric disperses the heat. The problem is that the water can start smelling moldy.

We are investigating other materials with similar properties to water that are neither toxic, nor generate mold over time. We don’t want anything that needs to be refrigerated like some gels, and certainly nothing electrical.

Have you looked into acids? Acids are conductive right? Or is it Alkalines?

You may want to look into some of the carbon fibers that are available. Some fiber types are capable of very impressive thermal conductivity, but there may be issues with directional thermal flow.

Cytec’s P-120S fiber seems to have high conductivity with no mention of longitudinal-only conductivity. I’d get more information from them on that though. Thier customer service is fairly fast and friendly and they don’t deal through distributors.