Natural convective heat transfer in uniformly heated vertical pipe annuli

Abstract

AbstractNatural convective heat transfer in vertical concentric pipe annuli is investigated both numerically and experimentally for a fluid having a Prandtl number of 0.7. Numerical calculations for three cases of different heating conditions for pipes (heated inner pipe, heated outer pipe, both pipes heated) are made of laminar flows for different inner‐to‐outer‐pipe diameter ratios di/do from 0.2 to 0.8. For each case, the thermal entrance length x/b at the modified Grashof numbers Gr*=102 to 5 × 105 is well correlated with Grashof number Gr* and annulus length to clearance ratio L/b. Local Nusselt numbers Nui and Nuo in the thermally fully developed region have certain constant values dependent on the diameter ratio di/do, regardless of Gr* and L/b. Average Nusselt numbers Nui and Nuo in the thermal entrance region are also independent of Gr* and L/b. © 2001 Scripta Technica, Heat Trans Asian Res, 30(8): 676–688, 2001