Buckling prevention of a single long NiTi tube compressive elastocaloric regenerator

A single long NiTi tube compressive elastocaloric regenerator: experimental results

“…The compressive elastocaloric regenerator developed by Cheng et al [32] was adopted in this study. A commercially available superelastic polycrystalline long NiTi shape memory alloy tube (outer diameter 5.00 ± 0.02 mm, wall thickness 1.00 ± 0.02 mm, and initial length 305.00 ± 0.03 mm) wire-cut from a straight original tube (VascoTube, Lot # 11488-99) using the electrical discharge machining technique was used as the elastocaloric solid refrigerant in the cooler.…”

“…transfer fluid direction was controlled by four check valves (Runze, RZ-CV014, PVDF). More details about the structure and novel designs of the regenerator can be found elsewhere (Cheng et al [29,32]). The hot heat transfer fluid loop was connected with the syringe pump using an adapter (Runze, WZ-048L-PTFE, 1/4 inch-28 UNF).…”

“…The ε flow and U were 1 and 4.2, respectively. In all the experiments in this work, the maximum applied strain of the compressive elastocaloric regenerator was set as 2.5%, because a large applied strain significantly contributed in achieving a large temperature span [6,32,42]. It can be seen from figure 7 that the temperature span, specific cooling power and coefficient of performance all decreased as the cycle time increased at the parameters listed above, indicating the dominance of the decrease of operation frequency due to the increase of cycle time over the heat transfer enhancement from the NiTi tube to the heat transfer fluid due to the increase of heat transfer fluid flow time.…”

“…Elastocaloric cooling and heat pumping is an alternative cooling technology to current vapor-compression systems that has the potential to be efficient and environmentally friendly [1][2][3][4]. Researchers and engineers among the world have been actively developing tensile [5][6][7][8][9][10][11][12][13][14][15][16], compressive [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], bending [34][35][36], and twisting [37] elastocaloric cooling and heat pumping prototypes recently, and a high fatigue life have been demonstrated for compressive elastocaloric prototypes utilizing NiTi shape memory alloys as solid-state refrigerants [28,30,31,33,[38][39][40][41]. Development of an efficient operation strategy, including achieving a large temperature span, specific cooling power, and coefficient of performance for compressive el...…”

“…Our group has also studied the effect of heat transfer fluid velocity on the specific cooling power of internally grooved NiTi tubes under compression (Zhang et al [31,33]) and NiTi sheets under bending (Li et al [35]) and found that a proper heat transfer fluid velocity was required to maximize the specific cooling power of the NiTi elastocaloric refrigerant under a fixed temperature lift. Recently our group has proposed a novel concept called the 'single-long-tube compression' [28,29,32] to achieve the elastocaloric cooling at a low specific driving force and a long-term durability. Systematic investigations of the dependences of the cooling performance on operation parameters are required to explore the optimum strategy in the operation of the single long tube compressive elastocaloric regenerator, which is still not available in the literature so far.…”