Abstract
The condensation rate of vapour bubbles is an important parameter to determine the condensation heat/mass transfer in subcooled boiling. It is defined by v_c=dR/dt where R is the bubble radius and t is time. In the definition, bubbles are assumed to have a spherical shape. Accurate measurement of v_c is required to understand the flow physics. Together with that, the measured data is needed for numerical prediction of the flow behaviors. A novel method has been developed in this study to measure v_c by using multiwave ultrasound. In the method, the velocity of the top and bottom interfaces of condensing moving bubbles are measured by using two ultrasonic frequencies (namely multiwave ultrasound). Thus v_c can be calculated based on the velocity difference between the two measurement lines. The accuracy of the measured data of v_c has been well confirmed by comparison with the result of the optical visualization and analysis of the subcooled boiling in a vertical pipe (at atmospheric pressure). The data of ohen can be exploited for the analysis of the interfacial heat transfer coefficient in subcooled flow boiling. Such measurements and analyses can be applied to the high temperature/pressure flow conditions in industrial and engineering practice.
