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Laminar natural convection within long vertical uniformly heated parallel-plate channels and circular tubes

The problem of simple mathematical models of laminar natural convective
flow within a long vertical parallel-plate channels and circular tubes kept at
uniformly heated walls is revisited to seek a clear physical understanding of heat
transfer mechanisms. A series solution method to analyze the fully developed flow
and an integral solution method to analyze the developing flow are used. Chapters
3, 4, and 5 of this dissertation constitute a series of three-paper manuscripts for
submission to archival journals.
The channels and circular tubes considered here are assumed to be
sufficiently long to yield a fully developed flow thermally as well as
hydrodynamically before the exit is encountered. In such fully developed flow
situation, the fluid mass flow rate naturally induced into the channel due to
buoyancy is found to be a function of the wall heating condition. The predicted
average Nusselt number as a function of GrPrD/L not only agrees with the existing
literature but also is found to be in a functional form comparable to that proposed
by Elenbaas (1942 a and b). Our results show that, in spite of being driven by
buoyancy (rather than by a pump or a blower), the flow and heat transfer
characteristics in the fully developed regime are essentially the same as those of
fully developed laminar forced convection in which the flow is externally driven.
This observation is confirmed to be valid also in the study (Chapter 5) of
laminar natural convection in the developing (entrance) region within a long
vertical parallel-plate channel and circular tube. The mass flow rate, which has to
remain invariant with axial location even in the entry region, is determined by the
flow in the fully developed region. This is the same mechanism involved in forced
convection in which the fluid outside the developing boundary layers (i.e. the core
flow) is forced to accelerate in the entrance region. The entrance length of channel
natural convection is also discovered to be about the same as that in forced
convection. / Graduation date: 2001
Date27 June 2000
CreatorsVorayos, Nat
ContributorsKanury, A. Murty
Source SetsOregon State University
Detected LanguageEnglish

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