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Discussion “Pressure Drop During Refrigerant Condensation Inside Horizontal Smooth, Helical Microfin, and Herringbone Microfin Tubes” (, , , and , 2004, J. Heat Transfer, 126(5), pp. 687–696) OPEN ACCESS

[+] Author and Article Information
M. M. Awad

Faculty of Engineering and Applied Science,  Memorial University of Newfoundland, St. John’s, Newfoundland, A1B 3X5 Canadaawad@engr.mun.ca

J. Heat Transfer 130(1), 015501 (Jan 25, 2008) (1 page) doi:10.1115/1.2780189 History: Received March 20, 2007; Revised June 15, 2007; Published January 25, 2008
FIGURES IN THIS ARTICLE

In the paper “Pressure Drop During Refrigerant Condensation Inside Horizontal Smooth, Helical Microfin, and Herringbone Microfin Tubes” (Olivier, J. A., Liebenberg, L., Kedzierski, M. A., and Meyer, J. P., 2004, J. Heat Transfer, 126 (5), pp. 687–696), there are some errors in equations. The errors will be summarized first. After that, a general expression for the liquid-only friction factor fLo will be presented because the general form presented in this paper, Eq. (16), is not valid for helical microfin tubes.

Equation (4) for the momentum pressure drop Δpm must be written as follows:Display Formula

Δpm=G2{[(1x)2ρL(1ε)+x2ρVε]out[(1x)2ρL(1ε)+x2ρVε]in}
(4)

The error in Eq. 4 is clearly a typographical error considering that the exponent a is not in the Nomenclature and the parameter a is not used elsewhere in the manuscript. In addition, the model will faithfully predict the measurements given in the original paper once all of the other corrections have been incorporated.

In Eq. 7, for the definition of the Froude rate, it is better to use the subscript V not v for vapor to use a consistent style of writing the parameters in the whole paperDisplay Formula

Ft=[G2x3(1x)ρV2gDi]12
(7)

The line after Eq. (9) must be written as “with the two-phase multiplier being that of Souza et al.  [16].” Reference [16] is Souza, A. L., Chato, J. C., Wattelet, J. P., and Christoffersen, B. R., 1993, “Pressure Drop During Two-Phase Flow of Pure Refrigerants and Refrigerant-Oil Mixtures in Horizontal Smooth Tubes,” ASME Heat Transfer With Alternate Refrigerants, HTD, 243 , pp. 35–41.

Equation (10) is applicable only for the range FrL>0.7, where the Froude number is defined as

FrL=G2ρL2gDi

Equation (12) for helical microfin tubes must be written as follows:Display Formula

fLo=0.046ReL0.2(DiDe)1(AAn)0.5(secβ)0.75
(12)
whereDisplay Formula
AAn=14entπDi2cosβ
(13)

Equation (14) for herringbone microfin tubes must be written as follows:Display Formula

fLo=0.046ReL0.2(DiDe)1(AAn)0.5(2secβ)1.1
(14)
whereDisplay Formula
AAn=12entπDi2cosβ
(15)

The general form of Eq. (16) is not valid for helical microfin tubes because the term ent is multiplied by 1 in Eq. (16), while the term ent is multiplied by 4 in Eqs. (12) and (13).

Based on Eqs. (12)–(15), the following general form for helical microfin tubes and for herringbone microfin tubes is presented as

fLo=0.046ReL0.2(DiDe)1(14entπDi2Xcosβ)0.5(Xsecβ)Y

For helical microfin tubes,

X=1
Y=0.75

For herringbone microfin tubes,

X=2
Y=1.1

The term 4X in the general form for helical microfin tubes and for herringbone microfin tubes can be written in different ways, such as 23X, 62X, or 3!2X.

Copyright © 2008 by American Society of Mechanical Engineers
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