Cooling vests for hot weather

 Cooling vests are designed to keep you cool when its hot. 

If you have to work outside or you want to play or exercise outside in hot weather, a cooling vest can keep you cool and comfortable. 

A cooling vest can also keep you cool and comfortable inside your home if your house does not have air conditioning. 

Many cooling vests have pockets to hold removable inserts filled with a phase change material, and others have these inserts sewn into them.

thermapparel - one of its Cooling Vests for Women

A phase change material we are all familiar with is water. Water (the liquid phase of this material) freezes, turning into ice (the solid phase of this material) at 0°C. 

Water ice also melts, changing from its solid phase back into its liquid phase (water) at the same temperature, at 0°C. 

Water ice would be a great phase change material in a cooling vest for a polar bear living in a warm climate. 

Why a phase change material is good at keeping you cool

You could put a jacket in your freezer overnight to wear the next day, and it would keep you cool - briefly.Your body and outside air would soon heat the jacket, and it would lose its ability to cool you after a few minutes. 

If you place 1 kg of crushed ice in a saucepan and place it on a hotplate on the stove, the ice will begin to melt as heat is added. This is the ice changing phase - melting into water.

As long as there is some ice left, you can continue to add heat, and the temperature will stay at 0°C. 

This is one thing a phase change material does well to keep you cool for longer. As long as some of it is solid, the temperature will stay constant while it absorbs heat, keeping you cool.

The other thing about phase change materials when they are melting from solid to liquid, is that they absorb a lot of heat. And remember, they do not increase in temperature. 

If there is no phase change, any heat added will cause a liquid to steadily increase in temperature. For example, adding heat to 1 kilogram of water at 20°C will increase its temperature steadily. The water will get to 30°C after absorbing a little over 40 kilojoules (heat energy).

Melting 1 kilogram of ice absorbs over 330 kilojoules (heat energy) before it has all melted. The entire time the heat is being absorbed, temperature of the remaining ice and the water from the ice that melted stays constant, at 0°C. 

 

For humans, a more suitable phase change material is one that melts at a temperature around 18°C. 

Cooling vests are even available for dogs - whether they are working dogs on farms and have to work when it is hot, or pets that need exercise even when it is hot outside.