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

Conference · Thu Jul 01 04:00:00 EDT 1999

OSTI ID:20030569

Dahl, S; Davidson, J

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% ethylene glycol is circulated in the tubes. Actual Nusselt numbers are within 15% 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.

• Research Organization: Univ. of Minnesota, Minneapolis, MN (US)
• OSTI ID: 20030569
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
FORCED CONVECTION
HEAT EXCHANGERS
HEAT FLUX
NATURAL CONVECTION
NUSSELT NUMBER
SOLAR WATER HEATERS
THERMOSYPHONS