What is overheating in refrigeration

Protection against overheating

A chemical protection suit with a built-in cooling unit - that sounds bizarre, but will be presented as a top development at this year's Interschutz. Chemical protective suits completely cover the body of the firefighter, there is no exchange between the outside atmosphere and the inside of the suit. Consequence: The heat produced by the firefighter cannot escape, and the air in the suit heats up alarmingly after just a few minutes. Sebastian-Heinz Pohr from Entrak in Wendelstein, Bavaria, suggests internal cooling as a solution.

"This device works on the principle of melting enthalpy, ie when phase change materials change their state, like ice. Ice melts into water, then it absorbs energy, so it cools, so we use this effect to cool the inside of protective suits. We suck the air, lead it through the device and release it cooled and dried inside the suit. "

The principle is simple, but works well: The warm air is pumped through an ice-cold salt solution - the storage medium -, cooled there and blown back into the suit via a small fan. The output is around 300 watts in half an hour. Pohr:

"That is already a high cooling performance, if you consider that a person produces 300 to 350 watts of energy during heavy physical exertion, then we set this level of cooling against it."

After an hour at the latest, the cooling effect is used up and the firefighter has to interrupt his work. He would have to do that anyway, because his oxygen supplies only last for a good hour. The amount of air you breathe and the performance of the cooling unit are matched to one another. The term "cool" is a bit misleading in this context. Pohr:

"We stay about ten degrees Celsius below the temperature that would set itself if it didn't cool down. And that's a lot: We have temperatures in protective suits that can easily rise to 40 or 45 degrees, which is then above body temperature, if we can then cool down to about 30 degrees, then there is again enough temperature gradient that the person can experience a cooling there. "

A firefighter also has to protect himself from heat, but this time from the outside, during the extinguishing. Depending on the fire, the outside temperature can rise to a few hundred degrees. Ordinary fabric would catch fire immediately. Dr. Yves Bader from the Du Pont de Nemours company in Geneva through a multi-layer textile system.

"It's a bit like a double window that protects me from the heat from the outside: We have multilayer systems so that we get a temperature difference between the individual layers. This gradually reduces the temperature down to the body. On the other hand, we want that the layers are so permeable that the body vapors find their way out again. "

What Yves Bader uses different materials for: on the outside high-strength and non-flammable Kevlar, on the inside several layers of air and moisture-permeable synthetic fabric. The heat is reflected on the outside, and inside it cools down from layer to layer.