Measurements have been made of the fully developed and entrance-region heat transfer characteristics of a hydrodynamically-developed flow of oil and water in an electrically-heated tube. The Prandtl number range was 3-75. The effect of variable fluid properties was isolated by varying the local wall-to-bulk temperature difference at fixed values of the local Reynolds and Prandtl numbers. It was found that both the Sieder-Tate and the Colburn corrections overestimated the effect of variable fluid properties. Constant-property heat transfer results were deduced by extrapolating the measured heat transfer coefficients to the condition of zero wall-to-bulk temperature difference. Except at low Reynolds numbers for the oil tests (Pr = 48 and 75), the constant-property results were underestimated by the Dittus-Boelter equation Nu = 0·023 Re0·8 Pr0·4. Local heat transfer coefficients were measured in the thermal entrance region. The thermal entrance length, defined in terms of a 5 per cent approach to fully developed conditions, ranged from 1·25 to 3·75 diameters depending upon the Reynolds and Prandtl numbers. Analytical results, computed as an extension of an earlier investigation by Sparrow et al. are presented for a wide range of Reynolds and Prandtl numbers.
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Acknowledgement-Thea uthors gratefully acknowledge the cooperation of the Monsanto Chemical Company, particularly Mr. MALCOLM MCEWEN and Mr. DONALD E. ROUSHo f the Organic ChemicalsD ivision, in supplyingt he Therminol FR-2 oil. In this connection, thanks are also extendedt o Mr. HORACEL . SMITH,J r., President,S mitherm Division, Hupp Corporation, The numericals olutionsw ere programmedb y Dr. S. H. LIN. This researchw as supported in part by the Atomic Energy Commission under Contract AT(1 l-1)-659. Additional acknowledgemenist also extended to the Electra-Motive Division of General Motors Corporation for its generousf ellowship support to J. A. Malina.