Teaching technique for internal forced convection flows through tubes cooled or heated by external natural convection. II. Vertical orientation
✍ Scribed by Ulises Lacoa; Antonio Campo
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 157 KB
- Volume
- 5
- Category
- Article
- ISSN
- 1061-3773
No coin nor oath required. For personal study only.
✦ Synopsis
This article is concerned with a distinct instructional technique that facilitates the examination of laminar forced convection flow through a vertical pipe exposed to an external natural convection environment. Literally, one particular case corresponds to external forced convective cooling, which is invariant with the tube orientation. Another particular case corresponds to external natural convection cooling, which depends on the tube orientation. For both cases, a simple one-dimensional (1-D) lumped formulation enabled the determination of the mean bulk and wall temperature distributions of the internal fluid flow as well as the total rate of heat transfer in a finite tube length within the region of thermal development.
Streamwise-mean values for the internal Nusselt numbers have been taken from standard correlation equations reported in undergraduate textbooks on heat transfer. Meanwhile, streamwise-mean values for the external Nusselt numbers have been extracted from articles published in the open literature. The combination of both Nusselt numbers leads to the calculation of a streamwise-mean, equivalent Nusselt number, which serves to regulate the thermal interaction between the two fluid streams. Representative results for a selected combination of internal and external fluids, expressed in terms of their thermal conductivity ratios, are discussed at length. The computed thermal quantities (global and local) based on a 1-D lumped model compared favorably with those based on a more general and rigorous 2-D differential model, which inevitably necessitated a finite-difference methodology and a personal computer.