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Abstract
The aim of this article is to analyze the elastocaloric effect of a commercial Ni-Ti plate for its application in a cooling device. In the first part, the article shows numerical results of the cooling characteristics of a regenerator-based elastocaloric cooling device with different thickness of the Ni-Ti plates based on a previously developed numerical model. It is shown that such a device (with a plate thickness of 0.1 mm) can produce a specific cooling power up to 7 kW/kg and coefficient of performance values up to 5 at the 30 K of the temperature span. In the second part of the article, a testing and analysis of the elastocaloric effect of the Ni-Ti plate using infrared thermography is shown. Prior to the elastocaloric testing, the sample was mechanically polished and subjected to 200 loading–unloading cycles at a slow strain-rate and 10,000 loading–unloading cycles at high strain-rate to stabilize its superelastic behavior and evaluate its fatigue life. When the functional and structural stability was reached and relatively good fatigue resistance was proven, the elastocaloric effect of the sample was studied with an infrared camera as a function of strain-rate and applied strain. It is shown that the adiabatic conditions are well approximated at strain-rates above 0.1 s−1. The largest adiabatic temperature change of 14 K during loading and 12.5 K during unloading were measured at the applied strain of 4.2% (at a strain-rate of 0.33 s−1). The homogeneity of the elastocaloric effect and the temperature irreversibilities during unloading are presented and discussed. It can be concluded that thin Ni-Ti plates with suitable austenitic finish temperature are good candidates to be applied in a proof-of-concept regenerator-based cooling device.
Nomenclature
| Af | = | austenitic finish temperature [°C] |
| Aht | = | total heat transfer area in regenerator [m2] |
| C | = | specific heat [J·kg·K−1] |
| COP | = | coefficient of performance |
| CHEX | = | cold-side heat exchanger |
| dh | = | hydraulic diameter [m] |
| eCE | = | elastocaloric effect |
| f | = | friction factor |
| heff | = | effective heat transfer coefficient [W·m−2·K−1] |
| HHEX | = | hot-side heat exchanger |
| keff | = | effective heat conduction coefficient [W·m−1·K−1] |
| L | = | regenerator's length |
| m | = | mass of elastocaloric material [kg] |
| = | mass-flow rate [kg·s−1] | |
| s | = | entropy [J·kg−1·K−1] |
| T | = | temperature [K] |
| ΔTad | = | adiabatic temperature change [K] |
| t | = | time [s] |
| v | = | velocity [m·s−1] |
| ϵ | = | strain [%] |
| ρ | = | material's desnity [kg·m−3] |
| σ | = | stress [Mpa] |
| φ | = | regenerator's porosity [%] |
Subscripts:
| f | = | fluid |
| s | = | solid |