Natural convective heat transfer in uniformly heated vertical pipe annuli

✍ Scribed by Koki Takahashi; Takuya Morikawa; Yutaka Harada; Naozo Hattori

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 217 KB
• Volume: 30
• Category: Article
• ISSN: 1099-2871
• DOI: 10.1002/htj.10013

✦ Synopsis

Natural 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 d i /do from 0.2 to 0.8. For each case, the thermal entrance length x/b at the modified Grashof numbers Gr * = 10 2 to 5 × 10 5 is well correlated with Grashof number Gr * and annulus length to clearance ratio L/b. Local Nusselt numbers Nu i and Nu o in the thermally fully developed region have certain constant values dependent on the diameter ratio d i / d o , regardless of Gr * and L/b. Average Nusselt numbers Nu i ___ and Nu o ___ _ in the thermal entrance region are also independent of Gr * and L/b.