Mechanical Defrosting

Project Description: 

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. Metal working is used to manufacture fins exhibiting multistable behavior (bistable and metastable) 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. The mechanical defrosting approach on average consumes 81.09 less energy, requires 10.84 times less power and is 8.26 times faster. ​

The mechanical defrosting is highly effective for solid frost. The highly ductile nature of porous frost requires conversion to solid frost which can then be shed using a thermo-mechanical defrosting strategy.

In this project we developed the technology from concept to Technology Readiness Level 3. We secured several grants from Center for High Performance Buildings (CHPB) and collaborated with industry professionals to ensure design for manufacturability and assembly (DFMA). This research led to a utility patent (US20230015420A1) and several provisional patents.

Publications:

• A. Thakkar, J. Ma, J. E. Braun, W. T. Horton, A. F. Arrieta. Energy-efficient defrosting of heat exchanger fins with embedded negative stiffness structures. Applied Thermal Engineering, 2023

• A. Thakkar, J. Ma, J. E. Braun, W. T. Horton, A. Arrieta. Frost formation in evaporator fins with embedded negative stiffness structures. 18th International Refrigeration and Air Conditioning Conference, 2021

• A. Thakkar, J. Ma, J. E. Braun, W. T. Horton, A. Arrieta. De-Icing in heat pump fins using shape morphing. ASHRAE Annual Transactions, 2021

• A. Thakkar, J. Braun, T. Horton and A. Arrieta. Thermo-Mechanical Strategy for Defrosting of Porous Frost. (To be submitted in ASHRAE Transactions)