Enhancement of gallium phase-change heat transfer by copper foam and ultrasonic vibration

In this study, the effects of copper foam and ultrasonic vibration on the melting process of low-melting gallium in a rectangular vessel were experimentally investigated. The effective thermal conductivity, heating wall temperature, most melting duration, and total melting duration during the gallium's melting process were examined for various heating powers. We found that a portion of the gallium remained solid in the corners of the vessel in the late melting stage, and melting the remaining solid portion accounted for approximately 28% of the total melting duration of the pure gallium. In our test, the corresponding heating wall temperature rose significantly during this stage, which reduced the usable volume of the vessel. However, by the addition of copper foam and ultrasonic waves the remaining solid portion was greatly reduced, and the heating wall temperature was controlled. The total melting time for the gallium with added copper foam and ultrasonic waves was reduced by 10% and 17%, respectively, below that for the pure gallium melting process. When heat was added using ultrasonic waves for a long period of the melting process, the temperature of the heating surface was consistently lower than a pure gallium heat regenerator without ultrasonic waves. This would enhance the value of workable condition power for devices.