Development of an Approach to Measure the Inner Wall Temperature of a Tubular Window for Experiments of Two-Phase Flow Heat Transfer on the China Space Station

Observation of vapor-liquid two-phase flow patterns in a tube, together with precision measurement of the inner wall temperature of the tube is a key technique for studying the heat transfer of phase change of the two-phase flow. For the experimental study of the in-tube two-phase flow and phase-change heat transfer in microgravity on the China Space Station (CSS), a platinum thin film about 40 nm in thickness is coated on the inner wall of a quartz tube, allowing for observing flow patterns of the fluid, heating the fluid passing through, and measuring the temperature of the platinum film itself. To verify that the platinum film can measure the temperature of itself while it is working as a heater simultaneously, experiment was conducted on a selected tubular window. It showed quite acceptable precision and repeatability of the temperature measurement (0.1 ℃) at a current density of less than 4kA/cm² for calibration and remained 0.2 ℃ for applied current up to 0.7A (70kA/cm²) when it worked as a heater. After the current of 0.7A was applied for about 6 h, the slope and intercept of the linear temperature-resistance relationship of the platinum film change (i.e., the room-temperature resistance increases by 2Ω). Such platinum film can be served as a thermometer after a second in-situ calibration, with a precision kept within 0.1 ℃.