Device Model for a Solid-State Barocaloric Refrigerator

Abstract

Solid-state refrigeration represents a promising alternative to vapor compression cooling systems. Solid-state devices based on magnetocaloric, electrocaloric and elastocaloric effects have demonstrated the ability to achieve high-efficiency, reliable and environment-friendly refrigeration. Cooling devices based on the barocaloric effect – entropy change due to applied hydrostatic pressure, however, have not yet been realized despite the significant promise shown in material-level studies. As a step towards demonstrating a practical cooling system, this work presents a thermodynamic and heat transfer model for a barocaloric refrigerator. The model simulates transient thermal transport within the solid refrigerant and heat exchange with hot and cold thermal reservoirs during reversed Brayton refrigeration cycle operation. We use the model to evaluate the specific cooling power (SCP) and coefficient of performance (COP) of the device comprising nitrile butadiene rubber (NBR) as a representative barocaloric refrigerant. We used experimentally validated barocaloric properties of NBR to quantify the contribution of different operating parameters including cycle frequency, applied pressure, operating temperatures, and heat transfer coefficient. The results show that a barocaloric refrigerator operating with a temperature span of 2.4 K and 0.1 GPa applied pressure can achieve an SCP of 0.024 W g-1 at 10 mHz cycle frequency and a COP as high as 5.5 at 1 mHz cycle frequency – exceeding that of conventional vapor compression refrigerators. In addition, to identify key refrigerant properties, we quantified the effect of bulk modulus, thermal expansion coefficient, heat capacity, and thermal conductivity on device performance. The results highlight the trade-off between different material properties to maximize the barocaloric response, while minimizing mechanical work and improving thermal transport. This work demonstrates the promise of solid-state cooling devices based on soft barocaloric materials and provides a framework to quantify its performance at the device-level.

Keywords: solid-state refrigeration, barocaloric cooling, heat pump, device modeling, elastomers