Electric Cooling Squeezes New Benchmark

Have you ever wondered how modern refrigeration worked? This week, in light of a recent development in electric refrigeration, we have occasion to learn about the wonderful technology behind refrigeration. Researchers from the Johns Hopkins Applied Physics Laboratory (APL) have discovered a 70% more efficient way to build electrothermal cooling cells. The technology in question has been dubbed, “controlled hierarchically engineered superlattice structures” (CHESS) by APL researchers.

If what the researchers say is true, this new development could revolutionize EVs, refrigerator systems, and prosthetic devices forever after. Modern refrigeration has typically relied on two principles: Emile Clapeyron’s ideal gas law and Jean Charles Athanase Peltier’s Peltier effect. Modern refrigeration mostly uses vapor compression cycles (relying on thermodynamics of phase change and pressure/temperature relationships), while electrothermal cooling uses the properties of different metals under electrical load. Both have their own advantages and drawbacks.

Compression refrigeration is highly efficient when compared to electrothermal cooling. It utilizes a liquid with a low boiling point at regular pressure, but a higher boiling temperature at greater pressures. This system relies on the properties of certain liquids called refrigerants. When it is under lower pressure, the liquid has a boiling point below room temperature and evaporates, drawing heat into itself. The gas then condenses into a liquid again under a higher pressure, radiating heat. Such a process is energy efficient, yet lacks scalability (the ability to make a system work on a macro or micro scale). If your fridge were flipped upside down, it would need a couple of hours for the oil to settle before it is used, because the compressor relies on a well of oil to lubricate itself. Peltier devices operate just as well upside down as right side up, weighing a fraction of the compressors’ weight.

The Peltier effect is a phenomenon that utilizes two conductors with different conductivities to distribute charge unequally on both sides of the device. For example, say one side is copper, and the other side is gold. The different concentrations of energy create differences in the temperature of the two sides of the device. The proximity of the hot and cold sides, however, eventually brings the cool side hotter than ambient room temperature when more current is run through it. A heat-sink, a larger object of conductive material and surface area, is crucial in order to expel unwanted heat from the hot side. The current Peltier device is called a bulk thermoelectric device, while the newer version is called a thin film thermoelectric device, TFTEC for short. The TFTEC tech produced by Johns Hopkins set a new record for thermoelectric cooling efficiency.

Bulk Peltier devices have an efficiency of around 10% when they are cooling significantly below ambient temperature. This means for every 10 degrees of cooling, there is 100 degrees of heating on the warm side. The 70% increase in efficiency by this new CHESS TFTEC model would make for an efficiency of 17% during significant heat pumping activity. This is a far cry from the efficiency of typical compression refrigerators, but it is a new record for Peltier devices. They are collaborating with Samsung to test, validate, and scale these devices in more realistic settings. We await further good news on the subject!

Read more about CHESS Nano Film here.