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ABSTRACT

Frost formation occurs on evaporator fin surfaces of heat pumps in heating mode when the surface temperature is below the frost point and the moisture content is sufficiently high. This frost on fin surfaces can significantly degrade the performance of air-source heat pump systems. This paper studies a novel mechanical defrosting approach for heat exchanger fins through integrating shape morphing cells in the fins. The shape morphing defrosting strategy relies on embedded structures with negative stiffness characteristics. These structures can undergo snap-through and suddenly release energy upon actuation. The snap-through induces out of plane displacements and vibrations to break and shed the accumulated frost. We modify flat fin geometry and introduce bistability in the heat exchanger fins. The bistable characteristics of modified copper-coated aluminum and weld steel fins are experimentally investigated. The defrosting performance of the fins is studied by forming glazelike ice using thermoelectric devices. The energy needed for mechanical and thermal defrosting strategy is experimentally found and a direct comparison is carried out between the strategies.