Numerical investigation of flow development and thermal boundary condition effects on local sCO2 heat transfer trends in circular tubes

Abstract

This paper presents numerical results for the effects of flow development length and thermal boundary conditions on local sCO2 heat transfer and flow performance in horizontal circular tubes. For the development length study, the tubes consist of various lengths of adiabatic sections and were connected by a fixed-length heat transfer section. An adiabatic entry region with lengths between 0 and 1000 mm, followed by a 500 mm long heat transfer section were tested. Boundary conditions including heat flux, mass flux, and inlet temperature were varied. Centerline velocity and local heat transfer rate were compared to investigate the impact of the length of adiabatic development section. To study the effects of thermal boundary conditions on sCO2 flows, a single tube (with and without a surrounding wall) and an idealized tube-in-tube heat exchanger were implemented. A uniform heat flux and uniform temperature boundary condition were applied to the single tubes, while the tube-in-tube heat exchanger had an inherent conjugate boundary condition. The resulting local sCO2 heat transfer coefficients for the different thermal boundary condition cases were compared.