Two-phase flow regime identification through local temperature mapping

Two-phase flows underpin some of our most ubiquitous technologies, ranging from micro-scale liquid-liquid cooling of electronics to macro-scale liquid-vapour boiling and condensation in thermal power plants. Establishing the morphology of a two-phase flow, under a prescribed set of conditions, is considered particularly important in the design stage. As the pressure loss and heat transfer characteristics of a two-phase flow are intimately linked to the fluidic arrangement, knowledge of the prevailing flow topology enhances understanding, and can lead to the development of flow-specific correlations and/or models. This paper presents a novel experimental measurement technique for identifying the predominant two-phase flow regime in a circular tube. Specifically, the investigation presented in this paper focuses on condensing flows of steam, at typical Rankine cycle cooling conditions. However, it is proposed that the experimental arrangement and methodology can be applied to any two-phase flow scenario. The approach presented herein employs a temperature measurement platform - composed from localised instrumentation - to measure the temperature drop, associated with the presence of a liquid phase, at any point in the tube. Through analysis and interpretation of local temperature difference measurements around the inside tube circumference, and along the tube length, the predominant flow regime can be identified. In this study, measurements were taken from a 25 mm internal diameter round tube, with steam flow rates in the range of 0.42–0.94 g·s^-1. The flow regime was seen to transition from an annular-type profile nearest the tube inlet to a stratified-wavy topology towards the tube exit in all instances.