Ice Chests and Refrigerators
Portable refrigerators are devices used to keep drinks, food and other temperature-sensitive materials cool on the go. They can range in complexity from simple ice chests to more complex thermoelectric and compressor-powered refrigerators. All three types of portable refrigerators rely on insulation. The refrigerator is a closed compartment with insulated sides which slow the movement of heat. When the refrigerator is closed, heat flows in very slowly. This allows the refrigerator to keep food cool without using much energy. In the case of ice chests, any heat that does leak in slowly melts the ice. The fridge remains at freezing temperature until enough heat leaks in to melt all the ice, a process which can take hours or even days.
Compressor-Powered Portable Refrigerators
The most efficient portable refrigerators use the same cooling method used in conventional household refrigerators and air-conditioners. A pump called a compressor pumps a fluid called refrigerant into a high-pressure chamber called the condenser, through a narrow valve and into a low-pressure chamber called the evaporator in a continuous circuit. The condenser is outside the refrigerator. When the refrigerant is pressurized inside of it, it rises in temperature. That excess heat leaks out of the compressor into the air. When the refrigerant flows into the low-pressure evaporator, the opposite thing happens: the refrigerant lowers in temperature. The evaporator is inside the refrigerator, and heat flows into it, cooling the portable fridge. Through this cycle, heat is continuously pumped out of the fridge and into the air outside, keeping the food inside nice and cool.
Thermoelectric refrigerators use a phenomenon called the Peltier Effect to supply cooling. When an electric current moves continuously between two different types of conductors, it creates a heat differential. One end of the Peltier cooler gets hot, and the other end gets cold. The cold end is placed inside the refrigerator, cooling the contents, while the hot end is placed outside, harmlessly radiating heat into the air. Because thermoelectric coolers have no bulky pumping unit, they are much lighter and more compact than compressor-powered units.. On the down side, they require more energy to run.