Experimental study of a low-cost reversible thermal diode for advanced heat manipulation

A low-cost reversible thermal diode was fabricated by a copper tube loop incorporating a valve in the top channel for advanced thermal management. The inner surface of one vertical tube was treated to superhydrophobic, while that of the other vertical tube was modified to superhydrophilic and further loaded with a superhydrophilic copper mesh for water wicking. Furthermore, the valve in the top channel can behave as a switch to control the hot vapor flow between the two vertical tubes. Then, different heat powers from 5 W to 15 W were applied to investigate the rectification effect of the thermal diode under low (30 %), medium (50 %), and high (70 %) filling ratios (FR) of the working fluid. The results showed that its rectification ratio could exceed 2.8 with the help of the control valve at FR = 30 %. Furthermore, the rectification effect could be reversed by the valve without flipping the thermal diode. In reversible working mode, the reversed heat transport could reach twice of the forward heat transport at FR = 50 %. Therefore, owning to the reversible heat transfer capacity, this study can guide the advanced thermal diode design for unstable waste heat recovery, solar energy harvesting, building energy management, etc.