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The new heat pump, developed by a research group in Israel, consists of a speaker, a resonator and a thermoacoustic core placed inside the resonator.
A research group from the Technion – Israel Institute of Technology has developed a novel phase change thermoacoustic heat pump (PTHP) concept for residential and industrial heat pumping.
"Phase-change acoustic conversion offers great potential for clean and efficient cooling technology, which can be powered by a hybrid source of electricity or, more importantly, heat," said lead author of the research, Guy Ramon, a pv magazine . “The use of acoustics greatly simplifies the construction of devices, reducing the need for moving parts, and the presence of phase shifting dramatically increases the power density of these devices, while using sustainable materials.”
The acoustically driven system uses a binary mixture of an inert and reactive component as the working fluid that undergoes condensation and evaporation during the thermoacoustic cycle. Atmospheric air is used as the inert gas, while water or isopropanol is used as the reactive component.
The heat pump consists of a speaker, a resonator, and a thermoacoustic core placed inside the resonator. The core includes a cold heat exchanger, a stack, and an ambient heat exchanger.
“The length and diameter of the resonator are 0.88 m and 47 mm, respectively, and the stack is a 600 cell per square inch piece of ceramic honeycomb with a length of 95 mm,” the researchers explained. "The ambient heat exchanger is of the plate-fin type, with a gap of 2 mm and a fin width of 0.7 mm."
The system incorporates a cold heat exchanger made of 0.5mm thick nickel-chromium wire and is embedded within a 3D printed skeleton. It is used to provide the heat load to the system, which in turn is driven by a speaker at the resonant frequency of the system, which is 86 Hz.
The system works in four steps. Initially, the mixture of the reactive component and the inert gas moves towards the region of low pressure. The reduced partial pressure then drives the evaporation of the reactive component which carries with it the latent heat. In the third step, the mixture undergoes the reverse processes of the first two steps and the reactive component condenses on the solid, transferring latent heat. Finally, the acoustic power is consumed to pump heat against the temperature gradient.
The research group compared the performance of the heat pump with that of a reference device without phase change. He found that the heat pump can achieve a coefficient of performance (COP) greater than 40% with a mixture of air and isopropanol at a concentration of 0.8.
“Our experimental results show that higher cooling power and higher COP can be obtained with phase change when the temperature difference is below a critical value, verifying that phase change improves heat pumping. thermoacoustic," he said. “However, when the temperature difference increases to exceed the critical value, the performance is worse than that of the equivalent classical thermoacoustic heat pump, because the time-averaged mass flow reverses its direction and transports heat against the direction of heat pumping.
The novel heat pump concept was presented in the paper “ Environmentally-sound: An listening-driven heat pump based on phase change ”, published in Energy Conversion and Management. “The patented technology is now entering the initial stages of commercialization,” Ramón stated, adding that more research is still required for the proper realization of its full potential. |
