An accurate wall temperature measurement using infrared thermometry with enhanced two-phase flow visualization in a convective boiling system

This paper presents an experimental strategy to achieve the accurate wall temperature measurement using infrared (IR) thermometry with the enhanced flow visualization. Our particular interest is focused on the measurement of two-phase flow parameters in a convective boiling system which involves a large heated area. For the present application, the important issues such as the design of test section and material selection were discussed along with our decision-making process. Then, the IR-based temperature tracking algorithm was established based on the multi-layer heater wall design proposed. To apply this algorithm, however, the optical properties of materials must be identified first. Thus, the optical features of selected materials, e.g., soda-lime glass and indium-tin-oxide (ITO) were investigated and the measured values were validated through experiments. The wall temperature tracking algorithm on the proposed heater wall design was validated both for steady-state and transient conditions. Also, such algorithm was proved to be applicable for the heat flux measurement. Finally, the feasibility of the present approach was demonstrated through a subcooled flow boiling experiment. The results showed that both the hydrodynamic motions of bubble and the corresponding wall temperature can be captured with high fidelity using the measurement strategy presented, from which the interrelation between the sliding vapor bubbles and the wall heat transfer were discussed. (authors)