RESEARCH PAPERS: Heat Exchangers

A Model for Condensate Retention on Plain-Fin Heat Exchangers

[+] Author and Article Information
A. I. ElSherbini2

Building and Energy Technologies Department, Kuwait Institute for Scientific Research, P.O. Box 24885 Safat, 13109, Kuwaitasherbini@kisr.edu.kw

A. M. Jacobi

Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801a-jacobi@uiuc.edu

The receding contact angle, θR, is not required, but can be incorporated—if know—into calculating Dmax.


Corresponding author.

J. Heat Transfer 128(5), 427-433 (Oct 19, 2005) (7 pages) doi:10.1115/1.2175091 History: Received January 23, 2005; Revised October 19, 2005

A model has been developed for predicting the amount of condensate retained as drops on the air-side of heat exchangers operating under dehumidifying conditions. For a coil with a given surface wettability, characterized by the advancing contact angle, the maximum diameter for a retained drop is obtained from a balance between gravitational and surface tension forces. A logarithmic function is used to describe the size-distribution of drops on fins, based on the fraction of fin-area covered by liquid. The volumes of individual drops are calculated by a geometric method for approximating the three-dimensional shapes of drops on vertical and inclined surfaces. The total volume of condensate accumulated on a coil is then found by multiplying the size-distribution and volume functions and integrating over all drop diameters. The model is successful in predicting measurements by other researchers of the mass of condensate retained on plain-fin heat exchangers. The critical fin spacing to avoid the formation of condensate bridges is also predicted.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

(a) Profile of a liquid drop fit by parts of two circles. (b) Contact line at the base of the drop. The two-circle method approximates the profiles and volumes of drops on vertical or inclined fins.

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Figure 2

Minimum contact angle, normalized by the maximum angle, as it varies with the Bond number for different liquids and surfaces. A single relation fits the data with a coefficient of determination r2=0.90.

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Figure 3

A force balance on a drop on an inclined fin, used to find the maximum drop diameter

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Figure 4

Size-distribution functions for drops condensing on plane surfaces, obtained by different researchers

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Figure 5

Heat-exchanger geometry used for comparing the model to measurements of retained condensate

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Figure 6

Predicted mass of condensate retained on heat exchangers compared to measurements reported by Shin and Ha (27) and Korte and Jacobi (6), and to an earlier model

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Figure 7

Critical fin spacing, beyond which condensate bridges cannot occur, as a function of the advancing contact angle




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