- Researchers demonstrate a new cooling system with 2 different kinds of thermoelectric materials.
- It accelerates heat more efficiently in its natural direction – from a hot object to the relatively cool surroundings.
As computer chips, lasers, batteries, and high-power electronics evolve toward more compact design with higher power densities, they require more sophisticated thermal management technology. These devices use thermoelectric cooling to remove heat from hot objects.
Unlike thermodynamics problems, these so-called Peltier cooler are optimized to keep a cold object cold. Most commercial Peltier coolers are portable refrigeration elements like camping fridges or beverage coolers. They work by drawing heat from cold area to hot area (naturally heat moves from hot to cold).
However, in the ‘active cooling’ mechanism, natural heat flow is accelerated from a hot object to a relatively cool region. In this case, the aim is to maximize the heat drained from the hot reservoir while minimizing the temperature drop.
Recently, physicists at Ohio State University and the University of Virginia came up with a new design principle for thermoelectric instruments that is tuned for battery and computer applications. They demonstrated a cooling system with 2 different kinds of thermoelectric materials.
How Did They Do It?
To design effective thermoelectric cooling devices, the research team selected material based on a figure of merit named zT, which is used to determine the performance of thermoelectric modules, including refrigeration modules.
Material carrying a lot of heat (due to electric currents) would have a high zT. These materials typically have low thermal conductivity, thus they do not allow heat to flow back through the equipment into the cold object. However, heat dissipates naturally when the object is hot.
Consider a normal cooling condition where a hot object is attached to thermoelectric equipment enclosed by a relatively cold reservoir. When voltage is applied, electrons and holes (charge carriers that carry heat) flow from the hot region to the cold region.
Difference between active cooling and refrigeration | Courtesy of researchers
To make cooling more efficient, the team developed a new figure of merit called effective thermal conductivity. It represents the sum of active thermal conductivity (turn on when the voltage is applied) and passive (normal) thermal conductivity.
They used two kinds of materials with large effective thermal conductivities –
- Magnon-drag metals (cobalt), in which electrons interact with magnons and carries some extra heat.
- Kondo-effect metals (cerium-palladium), in which electrons strongly interact with each other, increasing the heat associated with each conducting electron (hole).
Researchers used these materials to construct a Peltier cooler and placed it between cold and hot reservoirs. They then tested the device in passive and active mode.
When 5-ampere current was applied, the device drained out nearly 0.1 watts more heat from the hot reservoir that it did with zero current. Based on temperature difference, the active mode registered 1000 watts/meter-kelvin, while the passive mode reached 40 watts/meter-kelvin.
These kinds of dual-mode coolers could be beneficial for processors. It could work in passive mode when the number of computing processes is less, and switch to active mode when CPU usage is high.