Suxin Qian

Design of a hydraulically driven compressive elastocaloric cooling system

This article presents the design of elastocaloric cooling system driven by hydraulic actuators. Ni-Ti tubes under axial compressive loading mode are used in the system to provide cooling and heating. Those Ni-Ti tubes are enclosed in four identical beds, which are driven by two one-way hydraulic cylinders. Operated under the single-stage reverse Brayton cycle, the system achieves heat transfer and heat recovery by using a sophisticated heat transfer fluid network controlled by solenoid valves. Two novel designs to improve the systems performance based on the lessons learned from the previous studies are applied to this prototype. Preliminary test results of the materials latent heat at a specific fluid flow rate and temperature difference agree well with the results reported in the literature. System coefficient of performance of 11.0 and temperature lift of 24.6 K are estimated based on a dynamic model developed in the previous study.

Elastocaloric effect in CuAlZn and CuAlMn shape memory alloys under compression

This paper reports the elastocaloric effect of two Cu-based shape memory alloys: Cu68Al16Zn16 (CuAlZn) and Cu73Al15Mn12 (CuAlMn), under compression at ambient temperature. The compression tests were conducted at two different rates to approach isothermal and adiabatic conditions. Upon unloading at a strain rate of 0.1 s−1 (adiabatic condition) from 4% strain, the highest adiabatic temperature changes (ΔTad) of 4.0 K for CuAlZn and 3.9 K for CuAlMn were obtained. The maximum stress and hysteresis at each strain were compared. The stress at the maximum recoverable strain of 4.0% for CuAlMn was 120 MPa, which is 70% smaller than that of CuAlZn. A smaller hysteresis for the CuAlMn alloy was also obtained, about 70% less compared with the CuAlZn alloy. The latent heat, determined by differential scanning calorimetry, was 4.3 J g−1 for the CuAlZn alloy and 5.0 J g−1 for the CuAlMn alloy. Potential coefficients of performance (COPmat) for these two alloys were calculated based on their physical properties of measured latent heat and hysteresis, and a COPmat of approximately 13.3 for CuAlMn was obtained. This article is part of the themed issue ‘Taking the temperature of phase transitions in cool materials’.

The mechanism of ΔT variation in coupled heat transfer and phase transformation for elastocaloric materials and its application in materials characterization

Elastocaloric cooling serves as a promising environmental friendly candidate with substantial energy saving potential as the next generation cooling technology for air-conditioning, refrigeration, and electronic cooling applications. The temperature change (ΔT) of elastocaloric materials is a direct measure of their elastocaloric effect, which scales proportionally with the device cooling performance based on this phenomenon. Here, the underlying physics between the measured ΔT and the adiabatic temperature span ΔTad is revealed by theoretical investigation of the simplified energy equation describing the coupled simultaneous heat transfer and phase transformation processes. The revealed relation of ΔT depends on a simple and symmetric non-linear function, which requires the introduction of an important dimensionless number Φ, defined as the ratio between convective heat transfer energy and variation of internal energy of the material. The theory was supported by more than 100 data points from the open li...

Combined caloric effects in a multiferroic Ni–Mn–Ga alloy with broad refrigeration temperature region

Solid-state refrigeration based on the caloric effects is promising to replace the traditional vapor-compressing refrigeration technology due to environmental protection and high efficiency. However, the narrow working temperature region has hindered the application of these refrigeration technologies. In this paper, we propose a method of combined caloric, through which a broad refrigeration region can be realized in a multiferroic alloy, Ni–Mn–Ga, by combining its elastocaloric and magnetocaloric effects. Moreover, the materials’ efficiency of elastocaloric effect has been greatly improved in our sample. These results illuminate a promising way to use multiferroic alloys for refrigeration with a broad refrigeration temperature region.

Experimental Study on Performance of a Residential Combined Cooling, Heating and Power System Under Varying Building Load

Trigeneration systems are closely associated with sorption cooling technology because prime mover waste heat can be recovered to produce cooling. The working pair and cycle type of the sorption cooling system needs to be matched to the waste heat temperature of the prime mover, as well as with the capacity and application of the trigeneration system. A residential trigeneration system with a 4 kWelec internal combustion engine, a 220 gallon (830 L) hot water tank and a 3 kW adsorption chiller powered by 70°C waste heat with separate sensible and latent cooling control strategy is presented in this study. Transient experiments were conducted under 5 day long hot water and space cooling load profiles from a simulated house to evaluate the performance from a practical perspective. The fuel consumption was measured and compared with that of two baseline systems. An analytical criterion was derived and discussed to further evaluate the trigeneration system with different loads under different climates. It was found that the presented residential trigeneration system could save about 30% of fuel consumption compared with conventional off-grid operation mode, but is not more fuel efficient than the conventional on-grid and vapor compression cooling combination.Copyright

Accurate prediction of work and coefficient of performance of elastocaloric materials with phase transformation kinetics

Elastocaloric cooling is a novel solid-state cooling technology based on the latent heat associated with martensitic phase transformation in shape memory alloys. The work associated with elastocaloric cooling cycle is determined based on the material physical properties as well as the operating temperatures. To predict the work accurately under common practical conditions, a 1-D dynamic model for the shape memory alloys with phase transformation kinetics for polycrystalline is developed in this study. The model is discretized and then implemented in MATLAB Simulink. Based on the physics of the phase transformation free energy, the model is capable to predict whether or not the local material would undergo transformation under the given stress and temperature condition. To validate the model, series of compressive loading-unloading tests for super-elastic Ni-Ti alloys were conducted under different temperatures. The test results and data from literature were compared to the model prediction, and the deviation is within 10%. The cycle work and coefficient of performance is demonstrated for a two-bed active elastocaloric regenerator system as an example and then compared with the conventional single-stage system.

Energy-efficient Elastocaloric Cooling by Flexibly and Reversibly Transferring Interface in Magnetic Shape Memory Alloys

Elastocaloric cooling is currently under extensive study owing to its great potential to replace the conventional vapor-compression technique. In this work, by employing multiscale characterization approaches, including in situ neutron diffraction in a loading frame, in situ transmission electron microscopy observation at different temperatures, in situ synchrotron X-ray Laue microdiffraction, and high-resolution infrared thermal imaging, we have investigated the thermal and stress-induced martensitic transformation, the stability of superelastic behavior and the associated elastocaloric effect for a Heusler-type Ni50.0Fe19.0Ga27.1Co3.9 single crystal. On the basis of transformation from cubic austenite into monoclinic martensite with a flexibly and reversibly transferring interface, this unique single crystal exhibits a giant elastocaloric effect of 11 K and ultralow fatigue behavior during above 12 000 mechanical cycles. The numerical simulation shows that the Ni50.0Fe19.0Ga27.1Co3.9 alloy offers 18% energy saving potential and 70% cooling capacity enhancement potential compared to the conventional shape-memory nitinol alloy in a single-stage elastocaloric cooling system, making it a great candidate for energy-efficient air conditioner applications.

Study on Performance Improvement of a Compressive Thermoelastic Cooling System Using Single Objective Optimization

Thermoelastic cooling, also known as elastocaloric cooling, is one alternative cooling technology aiming to reduce the use of global warming potential refrigerants in vapor compression cycles. The cooling is based on the latent heat associated with the martensitic phase change induced by stress in shape memory alloys, driven by either compression or tension. A few past studies have explored and proposed the cycle options and system setup of a compressive thermoelastic cooling system using nitinol tubes as working material. The system coefficient of performance (COP) and cooling capacity were predicted by a dynamic model based on the physics of the integrated complicated heat transfer process and martensitic phase change. This study aims to start the performance improvement studies via optimization using the model. The objective function of the optimization problem is COP. Design variables include a few important operating parameters, such as flow rates and cycle frequency. The previously developed dynamic model is used to evaluate the system performance for this study. It is estimated that the COP enhancement can be as large as 51% from the baseline design candidate. Finally, an updated performance improvement potential is presented to guide future studies.Copyright

Modeling and Optimization of a Novel Heat Recovery Design for Thermoelastic Cooling Systems

The traditional refrigerants used in the vapor compression cycles have significant environmental impacts due to their high global warming potential. To address this challenge, solid-sate cooling technologies without using any aforementioned fluids have been developed rapidly during the past decades. Thermoelastic cooling, a.k.a. elastocaloric cooling, is a new concept, and thus no systematic studies of it have been conducted to date. Heat recovery plays an important role in the performance of the cooling systems, affected by the parasitic internal latent heat loss inside the cycle. A novel heat recovery (HR) scheme was been proposed in our previous study to minimize such parasitic internal latent heat loss. The objective of this study is to further investigate the performance improvement potential of the proposed heat recovery method by introducing the optimization study using the previously validated heat recovery model. The dynamic model details are revisited. The assumptions behind the model are re-examined by using the real thermoelastic cooling prototype geometries and materials properties of nickel-titanium tubes. A multi-objective optimization problem was formulated for the model and solved by MatLab. The heat recovery efficiency and the heat recovery duration were used as optimization objectives. A well-spread Pareto solutions were obtained, and a final solution was chosen with a 6.7% penalty in HR efficiency but six times faster cycle.Copyright