Development of Boiling and Two-phase Flow Experiments on Board ISS: Temperature Data Derivation and Image Analysis of a Transparent Heated Short Tube in the Glass Heated Section

Abstract

In order to clarify flow behavior and heat transfer characteristics of flow boiling in microgravity, the boiling and two-phase flow experimental facility which will be conducted in International Space Station (ISS) is developed. The glass heated section as an evaporating test section is installed in this facility, and the heated section is consisted of three transparent heated tubes which have different heated length, 50 mm, 50 mm and 5 mm, respectively. The transparent heated tube is made by Pyrex glass and the inner wall of the tube is covered by extremely thin gold film as using not only a heater but also resistance thermometer; that is, the tube can be measured the averaged inner wall temperature of the entire heated area. In addition, gas-liquid behavior of flow boiling can be observed through the gold film. The transparent heated short tube, which has 5 mm heated length and 4 mm inner diameter is a newly developed for third segment of the heated section of ISS experiment. In this study, derivation of the inner wall temperature and image analysis of flow behavior by using the short tube is described. Then the relation between heat transfer characteristics and flow behavior by using this tube is discussed. As a result of single-phase heat transfer experiment, the electrode resistance of the heated tube should be considered for estimation of the inner wall temperature of the short tube. Nusselt number considered the resistance of the electrode part has a good agreement with existing correlations compeared to Nusselt number derived from total resistance of the tube. By using the image analysis, useful information such as liquid film thickness of annular flow and passing of disturbance wave can be obtained with heat transfer characteristics data simultaneously. The results indicates that the heat transfer in the liquid film region of slug flow is insignificantly small compeared to turbulent liquid flow at the wake of slug under the conditions of this study.