Development of a phase change material (PCM)-based thermal switch

ABSTRACT

A thermal switch is an ON/OFF heat transfer control device which can be utilised in different modern fields such as cryogenics, solar energy systems, micro/nano-electronic cooling, the aerospace industry and building energy efficiency. In this study, paraffin wax is used to design and build a thermal switch based on phase change material (PCM). When the paraffin wax is heated and melts, one contact plate is pushed to make contact with another plate to turn the switch ON due to the pushing force generated by the volume expansion of the paraffin wax. Conversely, when the paraffin wax does not get enough heat to melt, the condition of the thermal switch is in the OFF state due to an air gap between the two plates. The ON/OFF thermal conductance ratio of the thermal switch is the major figure of merit and is investigated experimentally. The results show that the effective thermal conductivity of the PCM-based thermal switch in the ON state is recorded at 188.7 W/mK, while 6.2 W/mK is obtained in the OFF state. Therefore, the ON/OFF thermal conductance ratio is estimated at about 30.

KEYWORDS:

• Paraffin
• phase change material (PCM)
• thermal switch
• thermal conductivity
• thermal rectification

Acknowledgements

The authors would like to gratefully acknowledge Mr Yue Ren, an M.Sc. degree student who graduated from the Department of Mechanical Engineering at The Hong Kong University of Science and Technology (HKUST) in 2016, and Ms Stephanie Rawi, an undergraduate exchange student from the Universitas Indonesia, for their great support and cooperation in developing the PCM-based thermal switch.

Additional information

Notes on contributors

Xuanjie Wang

Mr Xuanjie Wang received his BEng degree in Energy, Power Systems and Automation from the Xi’an Jiaotong University in 2015 and obtained his M.Sc. degree in Mechanical Engineering from The Hong Kong University of Science and Technology (HKUST) in 2016. Currently, he is a Research Assistant in Ir Prof Christopher Chao’s research team. His research interests include heat transfer, phase change material, thermoelectric cooling, thermal switches and nanofluids.

Chi Yan Tso

Prof Chi Yan Tso received his BEng degree in Mechanical Engineering with first class honours, his M.Phil. degree in Environmental Engineering and his Ph.D. degree in Mechanical Engineering from the HKUST in 2010, 2012 and 2015, respectively. He is currently a Research Assistant Professor in the Department of Mechanical and Aerospace Engineering and a Junior Fellow at the HKUST Jockey Club Institute for Advanced Study (IAS). His work covers thermofluids, particularly in the fields of sustainable environment, heat transfer, adsorption technology, thermal rectification, nanofluids, passive radiative cooling and energy-related issues using numerical simulations as well as advanced experimental techniques.

Bhawat Traipattanakul

Mr Bhawat Traipattanakul received his BEng degree with first class honours in Mechanical Engineering from the King Mongkut’s University of Technology North Bangkok in Thailand in 2010, and his MEng degree in Energy Technology from the Asian Institute of Technology in Thailand in 2012. During his master’s study, he received a scholarship from Her Majesty the Queen of Thailand. He is currently a Ph.D. degree candidate in Mechanical Engineering at the HKUST. His research interests include thermal diodes, thermofluids, coalescing jumping droplets and heat transfer.

Christopher Y H Chao

Ir Prof Christopher Y H Chao graduated from The University of Hong Kong with first class honours in Mechanical Engineering in 1988. He obtained his master’s and doctoral degrees from the University of California at Berkeley, majoring in Thermosciences, in 1992 and 1994, respectively. He has a wide range of research interests in the areas of the built environment, energy and environmental engineering. Currently, he is a Chair Professor of Mechanical and Aerospace Engineering at the HKUST and has been the Head of Department since July 2014.