Feasibility study of a defrosting method at thin frost moment based on temperature difference recognition

Abstract

In the frosting-defrosting cycle of an air-source heat pump, it is crucial to determine the defrosting start time reasonably to enhance efficient operation. A straightforward defrosting control strategy for thin frost moments, based on temperature difference recognition proposed. This method was implemented while ensuring that the reduction in the heat transfer rate remained within a certain ratio, thereby avoiding a rapid decline in heat transfer efficiency. For the experiments, bare aluminum, hydrophilic, and superhydrophobic heat exchangers were set up, and the defrosting effect was explored by varying the thin frost moment point and melting temperature. The experimental results indicate that the method effectively improves the rate of heat acquisition (ROHA) of a single cycle compared with defrosting under complete frost blockage, irrespective of the surface properties. Superhydrophobic heat exchangers prove to be the most suitable choice. When the heat transfer rate decayed by 25%, the defrosting energy consumption of the superhydrophobic heat exchangers was lower by 37.2% and 29.9%, and the ROHA was higher by 11.3% and 11.7%, respectively, compared to those of the hydrophilic and bare aluminum heat exchangers. Throughout cyclic operation, the superhydrophobic surfaces demonstrated stable performance. However, the high-efficiency heat transfer times of the hydrophilic and bare aluminum heat exchangers were only 73.8% and 54.4%, respectively, of the superhydrophobic heat exchangers, due to the influence of water stagnation. Under the control of this defrosting strategy, the superhydrophobic heat exchanger can achieve low-temperature defrosting and reduce the energy consumption of defrosting medium preparation while ensuring a certain ROHA. This defrosting method holds potential for engineering applications.