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The influence of secondary refrigerant air chiller U-bends on fluid temperature profile and downstream heat transfer for laminar flow conditions.

Author(s) : CLARKE R., FINN D. P.

Type of article: Article

Summary

This paper describes numerical investigations, using computational fluid dynamics, conducted to examine the heat transfer mechanisms by which air-chiller U-bends cause enhanced downstream internal convection, where single phase secondary refrigerants under laminar conditions are employed as the heat exchanger fluid. The numerical model, created using FLUENT, consists of a single heat exchanger tube pass incorporating an inlet pipe, a U-bend and an outlet pipe. The model was validated using experimental data from the literature. Numerical investigations indicate that within the U-bend, secondary flows partially invert temperature profiles resulting in a significant localised decrease in average fluid temperature at the pipe surface. As a result, downstream heat transfer enhancement is observed, the magnitude of which can exceed that typical of a pipe combined entry condition in some circumstances by greater than 20% for up to 20 pipe diameters downstream. Heat transfer enhancement was found to increase with increasing U-bend radius, but to decrease with increasing heat exchanger pipe radius and internal Reynolds number. A simple technique based on quantification of the degree of temperature inversion at the U-bend is proposed which provides a mechanism by which heat transfer enhancement can be estimated. [Reprinted with permission from Elsevier. Copyright, 2007].

Details

  • Original title: The influence of secondary refrigerant air chiller U-bends on fluid temperature profile and downstream heat transfer for laminar flow conditions.
  • Record ID : 2008-1290
  • Languages: English
  • Source: International Journal of Heat and Mass Transfer - vol. 51 - n. 3-4
  • Publication date: 2008/02

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