S-ST-1-14 CFD Study of Single-Phase Laminar Mixed Convection in Inclined Tubes
To gain insight into the thermal-hydraulic phenomena associated with mixed convection in internal flows, we used computational fluid dynamics (CFD) to conduct a parametric study of single-phase laminar liquid flows in inclined tubes with isothermal, uniform wall temperatures (UWT). Both heating and cooling processes were simulated to isolate the effects of inclination angle on tubeside heat transfer in the presence of buoyancy-induced aiding and opposing flow. Twenty-six simulations were conducted in a fully three-dimensional computational domain modeled after a single tube 17 mm in diameter and 4.5 m long, using tube orientations from 0 (horizontal flow) to ±90 degrees (vertical aiding and opposing flow). This study revealed that for the range of parameters studied, the overall tubeside heat transfer coefficient was actually maximized at tube inclinations of approximately +15 degrees for heating and −15 degrees for cooling. Comparisons showed good agreement between the CFD results and predictions from Xist® 6 for the vertical aiding upflow heating case; however, significant differences were found for the horizontal and other vertical flow conditions. This investigation should serve as a starting point for future experimental and additional numerical investigations into inclined tube flows with mixed convection.