Performance and Modeling of Thermosyphon Heat Exchangers for Solar Water Heaters

[+] Author and Article Information
S. D. Dahl, J. H. Davidson

Department of Mechanical Engineering, University of Minnesota, 111 Church Street, S. E. Minneapolis, MN 55455

J. Sol. Energy Eng 119(3), 193-200 (Aug 01, 1997) (8 pages) doi:10.1115/1.2888018 History: Received July 01, 1996; Revised March 01, 1997; Online February 14, 2008


Determining the performance of indirect solar heating systems that use thermosyphon heat exchangers requires knowledge of how thermosyphon flow rate and heat exchanger performance vary with operating conditions. In this paper, measured performance of a two-pass, tube-in-shell, double-wall heat exchanger is discussed in terms of modeling issues. Thermosyphon heat exchangers may operate in the developing, mixed convection regime where natural convection effects can significantly influence overall heat transfer and friction coefficients. Existing models which assume the thermal and hydraulic behaviors of thermosyphon heat exchangers are only functions of the thermosyphon and collector flow rates may not be suitable for all heat exchanger types. For example, the overall heat-transfer coefficient-area product for the two-pass, tube-in-shell heat exchanger is best expressed as a function of Reynolds, Grashof, and Prandtl numbers on the thermosyphon side of the heat exchanger. It is proposed that annual simulations of solar water heaters with thermosyphon heat exchangers use this type of relationship to characterize heat transfer in the heat exchanger.

Copyright © 1997 by The American Society of Mechanical Engineers
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