Study on Thermal Diode Tanks (TDT) for Refrigeration and Air-Conditioning (RAC) Systems

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dc.contributor.advisorHu, Eric
dc.contributor.advisorChen, Lei
dc.contributor.authorWang, Mingzhen
dc.contributor.schoolSchool of Electrical and Mechanical Engineering
dc.date.issued2024
dc.description.abstractThe escalating challenge of global warming, coupled with rapid economic development, has fueled an unprecedented surge in the construction of public infrastructure. This surge has also heightened the demand for Heating, Ventilation, and Air-conditioning (HVAC) systems. The 20th century witnessed the evolution of HVAC, with Refrigeration and Air-conditioning (RAC) becoming a ubiquitous commercial offering for urbanized residences and buildings. Densely populated areas, characterized by a temperate climate featuring significant day-to-night temperature variations, experience substantial cooling demands during the daytime. To address this, the Thermal Diode Tank (TDT) emerges as a novel technology that can be applied in RAC systems to improve their performances. The TDT, essentially an insulated water tank equipped with heat pipes, releases heat to the environment when its water temperature exceeds the ambient temperature. However, the tank does not absorb heat from the surroundings when the ambient temperature is higher. Placing a TDT outdoors overnight would decrease the temperature of water to the minimum ambient temperature of the night. If the water is then used for an RAC system as the cooling water during the subsequent day, the integrated system can potentially yield a higher Coefficient of Performance (COP) compared to a standard RAC system. The conventional gravity heat pipe of a TDT acts as a thermal diode to dissipate heat through convection heat transfer at its condensation section. As the TDT woks mainly at night, a novel heat pipe that incorporates radiation heat transfer at the heat pipe condenser section was proposed in this study to allow radiation heat exchange with night sky. This innovative Radiation-enhanced Heat Pipe (RHP) is capable of simultaneous radiation and convection heat transfer mechanism. A Radiation-enhanced Thermal Diode Tank (RTDT) is defined by a TDT equipped with an RHP, while a Convection Thermal Diode Tank (CTDT) represents a TDT coupled with a Convective Heat Pipe (CHP). It has been found the RTDT was capable to produce water at lower than minimum night ambient temperature in some cases, of which the CTDT was incapable. This study systematically explored the performance of an RTDT in cooling water production and energy-saving potential when integrated with a standard RAC system. The correlations between design and operational parameters of TDT assisted RAC (TDT-RAC) system and its performance have been studied. The study found that RTDT indeed had a better water-cooling performance than CTDT, which is also a better choice for cooling and storing water at a lower temperature. The RTDT could also lower the water temperature below the minimum ambient temperature, but it is impractical. Simulation models for both RTDT and CTDT have been developed and validated by the experiment to assess their performance in cooling water production. Thermal stratification inside a TDT has been thoroughly investigated by CFD, in order to determine the optimal TDT structure for cooling water storage. It was found that by applying positive thermal stratification inside the tank, the performance of the TDT itself and the system could be improved. A vertical tank configuration also enhances the TDT performance in water-cooling. Additionally, the impacts of weather conditions, regions, room temperature setpoints and RHP radiative surface areas on the RTDT-RAC system performance have been studied by utilizing TRNSYS. A high hourly COP of 5.3 could be achieved by the RTDT-RAC system, with up to 40% reduction in energy consumption compared to the reference system. A Bi-functional Thermal Diode Tank (BTDT) is also proposed to improve the heating and cooling performances of heat pumps in both summer and winter, which exhibited superior performance over the reference system, achieving an 8% Energy Saving Percentage (ESP) for heating and an impressive 39.75% ESP for cooling. The peak ESPs observed were 31.6% for heating and 41.2% for cooling.
dc.description.dissertationThesis (Ph.D.) -- University of Adelaide, School of Electrical and Mechanical Engineering, 2024en
dc.identifier.urihttps://hdl.handle.net/2440/144158
dc.language.isoen
dc.provenanceThis electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legalsen
dc.titleStudy on Thermal Diode Tanks (TDT) for Refrigeration and Air-Conditioning (RAC) Systems
dc.typeThesisen

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