Roller-Cam-Driven Compressive Elastocaloric Device: A Breakthrough in High Cooling Power Density

Academic Background

With the intensification of global climate change, traditional vapor compression (VC) refrigeration technology has faced increasing criticism due to its use of refrigerants such as hydrofluorocarbons (HFCs), which have a high global warming potential (GWP). To address this environmental issue, researchers have been exploring more eco-friendly refrigeration alternatives. Elastocaloric cooling, a refrigeration technology based on solid-state materials, has garnered significant attention due to its zero carbon emissions and high energy efficiency potential. Elastocaloric cooling achieves refrigeration through stress-induced phase transitions in materials, particularly utilizing the heat release and absorption during the phase transitions of shape memory alloys (SMAs) such as nickel-titanium alloys (NiTi).

However, despite the excellent performance of existing elastocaloric cooling devices, their large volume has hindered their widespread practical application. This is primarily due to the bulky actuators required to load the solid refrigerants, limiting the compactness and cooling power density (CPD) of the devices. To tackle this issue, researchers have focused on developing more compact elastocaloric cooling devices to reduce device volume and improve cooling power density.

Source of the Paper

This paper was co-authored by Jiongjiong Zhang (张炯炯), Siyuan Cheng (程思远), and Qingping Sun (孙庆平), affiliated with the Department of Mechanical and Aerospace Engineering at the Hong Kong University of Science and Technology, the Department of Physics at the Southern University of Science and Technology, and the School of Mechanical Engineering at Hebei University of Science and Technology, respectively. The paper was published on May 16, 2025, in the journal Device, titled Roller-Cam-Driven Compressive Elastocaloric Device with High Cooling Power Density.

Research Content

a) Research Process and Methodology

The core of this study is the development of a roller-cam-driven elastocaloric cooling device aimed at reducing device volume and improving cooling power density. The research process includes the following key steps:

1. Device Design and Construction: The researchers designed a compact roller-cam-driven device using a small rotary motor instead of traditional linear actuators. The rotary motor offers higher power density and mechanical efficiency, thereby reducing the overall device volume. The core components of the device include the roller cam, linear actuators, and regenerator. The regenerator employs multiple NiTi tubes with finned internal walls as the refrigerant.

2. Material and Structural Optimization: To optimize cooling performance, the researchers measured the material properties of the NiTi tubes and designed efficient fin structures to enhance heat transfer efficiency. Through cyclic training and stress-strain testing, the phase transition temperature range and fatigue life of the material were determined.

3. Cooling Performance Testing: The device was cyclically operated to test the system’s temperature span and cooling power. Experiments were conducted at various fluid velocities and operating frequencies to obtain the optimal cooling performance. The temperature span and cooling power of the device were measured using heat exchangers and water bath control systems.

b) Key Research Findings

1. Cooling Power Density: The device achieved a maximum no-load temperature span of 27.4 K and a maximum cooling power of 40.6 W, corresponding to a volumetric cooling power density of 1.4 W/L. This value significantly exceeds that of existing elastocaloric cooling devices.

2. Fatigue Life: The finned NiTi tubes used in the device demonstrated exceptional fatigue life, surpassing 2×10^7 cycles, indicating potential for long-term use.

3. Efficiency and Performance: The coefficient of performance (COP) of the device showed a declining trend between 0.31 and 0.42 Hz, but as the operating frequency increased further, the cooling power increased, leading to a slight improvement in COP.

c) Conclusions and Significance

This study has significantly enhanced the cooling power density of elastocaloric cooling devices to 1.4 W/L by developing a compact roller-cam-driven device, while achieving a temperature span of up to 27.4 K and a fatigue life of 2×10^7 cycles. This research provides new insights into the practical application of elastocaloric cooling technology, demonstrating that the use of small rotary motors and optimized material structures can significantly improve the compactness and cooling performance of devices.

d) Research Highlights

1. High Cooling Power Density: Through the compact roller-cam-driven design, the device achieved a cooling power density of 1.4 W/L, significantly higher than existing elastocaloric cooling devices.

2. Exceptional Fatigue Life: The finned NiTi tubes exhibited a fatigue life exceeding 2×10^7 cycles under cyclic loading, indicating potential for long-term use.

3. Innovative Design and Optimization: The use of a small rotary motor instead of traditional linear actuators, combined with fin structures to optimize heat transfer efficiency, represents two major innovations in this study.

e) Other Valuable Information

The study also highlights that while the cooling power density of the device has significantly improved, it still falls short of commercial vapor compression refrigeration technology (>10 W/L). Future research could explore novel shape memory alloy materials, such as nickel-manganese-tin alloys (Ni-Mn-Sn), which require lower stress during phase transitions, aiding in the development of more compact and efficient elastocaloric cooling devices.

Summary

Through innovative roller-cam-driven design and material optimization, this study successfully developed a compact and efficient elastocaloric cooling device. The device not only boasts high cooling power density and exceptional fatigue life but also provides a new technical route for zero-carbon-emission refrigeration technology. Future research can further optimize the mechanical structure and material performance of the device based on these findings, promoting the widespread application of elastocaloric cooling technology in practical settings.