Experimental study on thermal performance of a novel micro channel separated heat pipe system coupled with radiative sky cooling

A novel micro channel separated heat pipe system coupled with radiative sky cooling is proposed to reduce the cooling energy consumption in data centers. The system can operate in two modes, including the conventional heat pipe mode and the coupled heat pipe mode with radiative sky cooling. Two prototype systems with different structures of radiative cooling heat exchanger (RCHE) were designed, built and experimentally tested. The surface of RCHE is pained with a spectrally selective absorbing material, which has a low absorptivity in the solar irradiation band and a high emissivity in the atmospheric window band. The temperatures of air and refrigerant along with the refrigerant pressure were measured. The subcooling degree, cooling capacity and energy efficiency ratio (EER) were calculated and analyzed. Experimental results indicate that compared to the conventional system, refrigerant can be cooled further in the coupled system due to the assistant cooling by the RCHE through radiating heat to the cold outer space, with a higher subcooling degree at the inlet of evaporator by 0.4 °C on average. Moreover, the coupled system had 18.91% more cooling capacity and higher EER. Then, the performances of the coupled system with different structures of RCHE were compared. It was observed that 10.7% more cooling capacity and higher EER were obtained by the coil tube structure coupled system over the parallel tube structure coupled system.