Applicability of uniform heat flux Nusselt number correlations to thermosyphon heat exchangers for solar water heaters

Journal Article · Sat May 01 04:00:00 EDT 1999 · Journal of Solar Energy Engineering

DOI:https://doi.org/10.1115/1.2888151· OSTI ID:354271

Dahl, S; Davidson, J ^[1]

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1. Univ. of Minnesota, Minneapolis, MN (United States). Mechanical Engineering Dept.

Nusselt numbers are measured in three counterflow tube-in-shell heat exchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heat exchangers were previously developed in Dahl and Davidson (1998) from data obtained in carefully controlled experiments with uniform heat flux at the tube walls. The data presented in this paper confirm that the uniform heat flux correlations apply under more realistic conditions. Water flows in the shell and 50 percent ethylene glycol circulates in the tubes. Actual Nusselt numbers are within 15 percent of the values predicted for a constant heat flux boundary condition. The data reconfirm the importance of mixed convection in determining heat transfer rates. Under most operating conditions, natural convection heat transfer accounts for more than half of the total heat transfer rate.

• Sponsoring Organization: USDOE
• OSTI ID: 354271
• Journal Information: Journal of Solar Energy Engineering, Journal Name: Journal of Solar Energy Engineering Journal Issue: 2 Vol. 121; ISSN JSEEDO; ISSN 0199-6231
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
COUNTERFLOW SYSTEMS
HEAT EXCHANGERS
HEAT FLUX
NUSSELT NUMBER
SOLAR WATER HEATERS
THERMOSYPHONS