A scale analysis of the transient discharge of a fully mixed thermal storage vessel with an immersed single-tube heat exchanger is extended to provide a generalized expression for the transient natural convection Nusselt number for heat exchangers comprising many tubes. The transient Nusselt number is expressed in terms of the Rayleigh number at the initiation of the discharge (or charge) process and easily measured geometric parameters. Nusselt numbers measured for a 240-tube heat exchanger immersed in a fully mixed storage vessel are well correlated in the proposed form. The applicability of the approach to thermally stratified storage fluids is evaluated for both a single-tube and the 240-tube bundle. For heat exchangers of practical size for solar systems, for example the 240-tube bundle, buoyancy driven flow within the storage is sufficient to mix an initially stratified fluid. In this case, Nusselt numbers during the discharge process are predicted accurately by the proposed transient formulation. However, if the storage fluid remains stratified during discharge, as is the case for an initially stratified vessel with a single-tube heat exchanger, the transient formulation is not recommended.
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Research Papers
Transient Natural Convection Heat Transfer Correlations for Tube Bundles Immersed in a Thermal Storage
Yan Su,
Yan Su
Department of Mechanical Engineering,
University of Minnesota
, 111 Church Street S.E., Minneapolis, MN 55455
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Jane H. Davidson
Jane H. Davidson
Department of Mechanical Engineering,
e-mail: jhd@me.umn.edu
University of Minnesota
, 111 Church Street S.E., Minneapolis, MN 55455
Search for other works by this author on:
Yan Su
Department of Mechanical Engineering,
University of Minnesota
, 111 Church Street S.E., Minneapolis, MN 55455
Jane H. Davidson
Department of Mechanical Engineering,
University of Minnesota
, 111 Church Street S.E., Minneapolis, MN 55455e-mail: jhd@me.umn.edu
J. Sol. Energy Eng. May 2007, 129(2): 210-214 (5 pages)
Published Online: December 8, 2005
Article history
Received:
June 20, 2005
Revised:
December 8, 2005
Citation
Su, Y., and Davidson, J. H. (December 8, 2005). "Transient Natural Convection Heat Transfer Correlations for Tube Bundles Immersed in a Thermal Storage." ASME. J. Sol. Energy Eng. May 2007; 129(2): 210–214. https://doi.org/10.1115/1.2710492
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