Energy-Efficient Defrosting in Heat Exchanger Fins with Embedded Negative Stiffness Structures

Abstract

Frost formation in heat pump fin surfaces during cold climate conditions can significantly degrade the performance of air-source heat pumps. Typical thermal defrosting methods are energetically expensive and can cause thermal discomfort. This research investigates a novel mechanical defrosting solution for heat exchanger fins using multistable shape morphing cells integrated into the fins. We use bending (metalworking) to manufacture fins exhibiting multistable behavior (bistable and metastable) out of three materials by plastically deforming selective regions of a laser-cut flat fin precursor. These structures undergo snap-through and suddenly release energy upon actuation, the induced out-of-plane displacements and vibrations can be used to break and shed frost. We experimentally characterize the bistable behavior (actuating forces, stored and released strain energy) of the three sets of bistable and metastable fins to evaluate their mechanical defrosting potential. Using finite element analysis, we characterize the dynamic response of the fins under various boundary conditions. The defrosting performance of the fins is studied by forming glaze-like ice using thermoelectric devices. We experimentally investigate the influence of different boundary conditions on the percentage of ice shed from the fin surface, and measure and compare the power and energy consumption due to mechanical and thermal defrosting. We demonstrate the technological feasibility of the energetically efficient mechanical defrosting approach and make recommendations on fin design and boundary conditions to maximize the defrosting performance.

Keywords: Deicing, Mechanical Defrosting, Thermal Defrosting, Metallic Bistable Structures, Metallic Metamaterials