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Sizing of heat exchangers with non-uniform coefficients

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Abstract

A technique is presented to include the effects of a non-uniform, overall heat transfer coefficient in double-pipe heat exchanger analysis using the effectiveness (or efficiency) method. The local overall coefficient is permitted to vary with the local temperature difference between the two fluids according to (T−t)n, where the exponent “n” assumes individual values for various physical situations. A procedure is provided to estimate the appropriate value of “n” for a particular problem. The development provides a correction factor to the ordinary results of the effectiveness method for uniform overall coefficients.

Zusammenfassung

Für die Berücksichtigung des Einflusses eines nicht-konstanten Gesamtwärmeübergangskoeffizienten in Doppelwand-Wärmetauschern wird ein Verfahren erläutert, daß die Effektivitäts(oder Wirkungsgrad-)Methode verwendet. Der lokale Wärmeübergangskoeffizient kann sich dabei mit der lokalen Temperaturdifferenz zwischen den beiden Fluiden nach der Funktion (T-t)n ändern, wobei der Exponent „n“ individuelle Größen bei verschiedenen physikalischen Situationen berücksichtigt. Es wird ein Verfahren für die Abschätzung des geeigneten Zahlenwertes für „n“ für ein) spezielles Problem angegeben. Das Ergebnis der Untersuchung ist ein Korrekturfaktor zu den gewöhnlichen Ergebnissen der Wirkungsgrad-Methode bei konstanten Wärmeübertragungskoeffizienten.

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Abbreviations

a:

constants

b:

constants

MC W/m2-°K:

thermal capacity rate of hot fluid

mc W/m2-°K:

thermal capacity rate of cold fluid

Ntu:

number of transfer units

n:

exponent

R:

ratio of thermal capacity rates

T °K:

temperature of hot fluid

t °K:

temperature of cold fluid

U W/m2-°K:

overall heat transfer coefficient

Ur :

ratio of overall heat transfer coefficients

Ψ :

dimensionless temperature difference

θ°K:

temperature difference

0:

non-uniform coefficient case

1:

fluid inlet conditions

i:

intermediate point

max:

maximum value

min:

minimum value

References

  1. Kumar, C. A.: Sizing of Heat Exchangers with Non-Uniform Coefficients. Unpublished M. S. Thesis, University of Houston, Dec 1971.

  2. Kays, W. M., London, A. L.: Compact Heat Exchangers, McGraw-Hill, 1964.

  3. Carey, J. R.: Fast, Convenient Approach to Sizing Heat Exchangers, Chem. Eng. Vol. 66, No. 10, May 1959, 169–174.

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  4. Peters, D. L.: Heat Exchanger Design with Transfer Coefficient Varying with Temperature or Length of Flow Path. Wärme- und Stoffübertragung 3 (1970) 220–226.

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Author information

Authors and Affiliations

  1. Mechanical Engineering Dpmt., University of Houston, 77004, Houston, Texas

    J. E. Cox

  2. Continental Carbon Co, P.O. Box 22085, 77027, Houston, Texas

    C. A. Kumar

Authors
  1. J. E. Cox
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  2. C. A. Kumar
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Cox, J.E., Kumar, C.A. Sizing of heat exchangers with non-uniform coefficients. Wärme- und Stoffübertragung 6, 1–2 (1973). https://doi.org/10.1007/BF01270698

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  • DOI: https://doi.org/10.1007/BF01270698

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