Radiation-enhanced thermal diode tank (RTDT) for refrigeration and air-conditioning (RAC) systems

Abstract

A Thermal Diode Tank (TDT) is invented for energy conserving purposes that can passively produce cooling water at a minimum night ambient temperature. The TDT is an insulated water tank equipped with heat pipes, which provides unidirectional heat transfer from the TDT water to its surroundings. The conventional heat pipes dissipate heat mainly by convection heat transfer, which are termed Convective Heat Pipes (CHPs), and a TDT equipped with CHPs is a Convection TDT (CTDT). To promote the TDT performance in generating cooling water at a lower temperature, a Radiation-enhanced Heat Pipe (RHP) is proposed with a flattened hollow cuboid as its condenser section to radiate heat to the night sky, while maintaining the convection heat transfer with air. Such a Radiation-enhanced TDT (RTDT) is expected to have a better water-cooling performance than CTDT currently obtains, and could potentially cool the water below the minimum ambient temperature. In this paper, performance simulation models for both RTDT and CTDT have been developed and validated by the experiment. The results reveal that the RTDT generates colder water than CTDT does, and the heat transfer capacity of the RTDT is approximately twice as high as that of the CTDT if they are made from the same quantity of materials. It is found not advisable to promote the TDT performance by increasing the air circulation at the heat pipe condenser. However, analysis shows that increasing the heat pipe condenser area dominantly contributes to the enhancement of TDT performance, especially for RTDT.