Experimental investigation on the defrosting performance of a finned-tube evaporator using intermittent ultrasonic vibration

When an air-source heat pump (ASHP) was operated in heating mode under certain ambient conditions, frost always accumulated on the fin surface of its outdoor coil. Frosting may increase the energy consumption and deteriorate the performance of the ASHP, and hence, periodic defrosting is necessary. In this study, a new defrosting method using intermittent ultrasonic vibration was investigated. First, the vibration attenuation characteristics of a double-row outdoor coil and the frost growth characteristics under different ambient conditions were determined. Next, the average frost thickness with and without the application of intermittent ultrasonic vibration was calculated using MATLAB software. Finally, the decrease in defrosting energy consumption, the increase in heating capacity, and the increase in the coefficient of performance were analysed. The experimental results indicate that intermittent ultrasonic vibration could effectively remove the frost accumulated on the fin surface, and the effective defrosting area of an single ultrasonic transducer was 0.165m2 for a double-row finned-tube evaporator on which an ultrasonic transducer with a rated power of 50W and resonant frequency of 40kHz was applied. The defrosting energy consumption of the ASHP unit with ultrasonic vibration was 3.14–5.46% lower than that without ultrasonic vibration, whereas the heating capacity increased by 2.2–9.03% and the COP increased by 6.51–15.33%. In addition, the thermal comfort of the indoor side was clearly improved.

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