Experimental and Numerical Investigation of Effect of Inclination on sCO2 Heat Transfer in a Circular Pipe

Supercritical carbon dioxide (sCO2) can be utilized as a working fluid in various thermal systems including large scale power cycles; portable power production units, centralized coolant systems and standalone cooling devices. However,the lack of accurate prediction tools such as heat transfer coefficient correlations, and insufficient research studies about the mechanisms controlling heat transfer processes, are hindering its practical realization for key energy and cooling systems. The overall objective of this study is to extend fundamental knowledge about heat transfer and fluid dynamic processes in conduits pertinent to sCO2 with an emphasis on flow inclination and directional effects. This paper present the a study on effects of gravity, buoyancy on sCO2 flow at temperature near and away from the pseudocritical temperature. The experimental setup consists of a high temperature and pressure sCO2 heat transfer loop and flow testing facility. Recently researched sCO2 heat exchangers can have tubes oriented at different angles such as 45° or 90° to horizontal. For optimized design of efficient and cost-effective turbo-machinery components utilizing sCO2 as the heat transfer fluid, an understanding of convective heat transfer inside a tube/pipe is equally as important as external heat transfer. This paper presents an experimental and numerical study on sCO2 heat transfer at various inclinations with angles ranging from 0° (horizontal) to 90° (vertical) along with upward and downward flow direction with different inlet temperature. Thermocouple based temperature measurement is utilized at multiple locations within the test section axially and circumferentially to study the temperature distributions on the tube surface. Computational Fluid dynamics (CFD) simulations have been performed using ANSYS Fluent to complement experimental data. The CFD and experiment have been analysed against known Gnielinski nusselt number correlation.