Impact of hysteresis on caloric cooling performance

M Masche,J Tušek,L Ianniciello,K Engelbrecht

doi:10.1016/j.ijrefrig.2020.10.012

Abstract

• 1D regenerator model with hysteresis is used to assess caloric cooler's performance. • Modeling of six hypothetical materials with different caloric properties. • Effect of hysteresis is greater on coefficient of performance than on cooling power. • Materials with low isothermal entropy change are very sensitive to hysteresis. • Materials with low specific heat can tolerate high hysteresis values. Caloric cooling relies on reversible temperature changes in solids driven by an externally applied field, such as a magnetic field, electric field, uniaxial stress or hydrostatic pressure. Materials exhibiting such a solid-state caloric effect may provide the basis for an alternative to conventional vapor compression technologies. First-order phase transition materials are promising caloric materials, as they yield large reported adiabatic temperature changes compared to second-order phase transition materials, but exhibit hysteresis behavior that leads to possible degradation in the cooling performance. This work quantifies numerically the impact of hysteresis on the performance of a cooling cycle using different modeled caloric materials and a regenerator with a fixed geometry. A previously developed 1D active regenerator model has been used with an additional hysteresis term to predict how modeled materials with a range of realistic hysteresis values affect the cooling performance. The performance is quantified in terms of cooling power, coefficient of performance (COP), and second-law efficiency for a range of operating conditions. The model shows that hysteresis reduces efficiency, with COP falling by up to 50% as the hysteresis entropy generation ( q hys ) increases from 0.5% to 1%. At higher working frequencies, the cooling performance decreases further due to increased internal heating of the material. Regenerator beds using materials with lower specific heat and higher isothermal entropy change are less affected by hysteresis. Low specific heat materials show positive COP and cooling power up to 2% of q hys whereas high specific heat materials cannot tolerate more than 0.04% of q hys .

Highlights

Research on alternative cooling techniques based on solid-state refrigerants, generally called caloric cooling, has received interest recently thanks to reports on attractive caloric properties that can be used for solid state cooling
Because the focus of this paper is to study how material properties influence active magnetic regenerator (AMR) performance generally, a 1D model that neglects thermal losses has been implemented. 1D models have been shown to capture an acceptable level of system detail while using considerably less computing power than 2D and 3D and are a good choice for this study
Intrinsic hysteresis in materials with a first-order phase transition is a large issue that limits their application in solid-state cooling devices

Summary

Introduction

Research on alternative cooling techniques based on solid-state refrigerants, generally called caloric cooling, has received interest recently thanks to reports on attractive caloric properties that can be used for solid state cooling. Cycles built around the temperature increase/decrease of materials associated with the application/removal of an external field could have the potential to become a more efficient alternative to conventional vapor compression cooling technologies (Bansal et al, 2012; Qian et al, 2016b). Caloric properties exist for ferroic materials (i.e. the caloric materials) that exhibit a reversible temperature change, known as the caloric effect, when an external field is applied. Depending on the external field, the caloric effect is either magnetocaloric (magnetic field), electrocaloric (electric field), barocaloric (hydrostatic pressure) or elastocaloric (uniaxial stress). Caloric effects are interesting in materials that exhibit multiple-coupled ferroic properties. Those materials are called multiferroics and are discussed by Fähler et al, (2012). The coupling of caloric effects within the same material can improve the system performance

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