Thermoelastic Cooling Constitutive Model And Numerical Analysis Of Shape Memory Alloy

In the past decade,more efficient and environmentally friendly refrigeration technology has developed rapidly to solve the problem that the annual refrigeration energy consumption accounts for about one fifth of the global power resources.A British scientist named Quarini put forward the basic principle of thermoelastic cooling technology in 2004.The US Department of Energy listed it as the refrigeration technology with the most energy-saving potential among more than 20 new refrigeration technologies in 2004,and its energy efficiency ratio(EER)is expected to reach 12,which is 3.8 times that of traditional vapor compression refrigeration technology.At present,thermoelastic cooling technology has become a new interdisciplinary research hotspot.Shape memory alloy(SMA)is a kind of solid-state refrigeration technology,which is driven by the stress field to produce phase transformation of SMA material,resulting in the increase of entropy,resulting in the elastocaloric effect and absorbing heat from the outside.SMA is widely used in many engineering fields for its excellent shape memory properties,super elasticity,biocompatibility and high damping.It can undergo phase transformation and absorb or release latent heat under uniaxial load.The phase transformation process can be driven not only by stress but also by temperature.The constitutive model of thermomechanical coupling effect can describe and predict the deformation characteristics of structure or device SMA under various complex thermo-mechanical loads.However,the research on thermo-mechanical coupling constitutive model of SMA is not comprehensive,so it is necessary to establish a thermo-mechanical coupling constitutive model based on SMA phase transition mechanism to analyze the thermoelastic cooling process and cooling performance of SMA.This paper takes SMA as the research object,analyzes thermoelastic cooling principle,establishes the thermo-mechanical coupling constitutive model,and numerical analysis was carried out uses MATLAB software.According to the realizable refrigeration system,establishes the cop mathematical model of thermoelastic cooling performance,and analyzes the cooling capacity of the system.The main work is as follows:1.The basic properties of SMA materials are studied and the mechanism of elastocaloric effect is analyzed.The physical properties of elastocaloric effect of SMA are analyzed by isothermal entropy change and adiabatic temperature variation,and the characterization method of elastocaloric effect of SMA is described.2.In the macro scale,a thermo-mechanical coupling constitutive model is established for a One-dimensional SMA tube under convection heat transfer conditions through summarizing the existing SMA uniaxial loading experiments,and the thermodynamic driving force equation,temperature balance equation and internal variable evolution equation of inelastic phase transition mechanism are derived.A closed equation system of one-dimensional thermo-mechanical deformation behavior of SMA tube is established according to the specific geometry of SMA bed of the thermoelastic cooling refrigerator.The temperature field of SMA tube is solved by using the finite difference method(TDMA).The model is validated by simulating and predicting the super elastic and shape memory effect of SMA under different loading rates.Furthermore,the model is used to predict the cooling capacity of SMA.3.The thermo-mechanical coupling constitutive model is simulated to analyze the influence of key parameters on the deformation behavior of SMA,and the simulation results show that a same SMA material can show shape memory effect,hyperelasticity or partial shape memory effect and partial hyperelasticity under different ambient temperature.The cooling performance of SMA is affected by external factors(such as strain rate,ambient temperature,convective heat transfer coefficient).If the material parameters and external factors are selected reasonably,the temperature drop of SMA can reach 10 ? 30 K.4.Several kinds of thermoelastic cooling cycles and their realizable refrigeration systems are introduced.Based on the temperature entropy diagram and the stress-strain diagram,the cycle processes of single-stage Brayton cycle and single-stage Stirling cycle are analyzed.The mathematical model of COP of Brayton cycle cooling system is derived.This model can be used as a simple calculation tool for the study of COP in the future.Based on the established dynamic COP mathematical model,the key parameters(heat transfer efficiency,heat recovery efficiency and system temperature difference)were analyzed.The results show that larger heat transfer efficiency,larger regenerative efficiency and smaller temperature difference are beneficial to improve COP of thermoelastic cooling system.