Study on the heat transfer characteristics of the annular fin under dry-surface, partially wet-surface, and fully wet-surface conditions

doi:10.1016/j.icheatmasstransfer.2005.08.009

International Communications in Heat and Mass Transfer

Volume 33, Issue 1, January 2006, Pages 112-121

https://doi.org/10.1016/j.icheatmasstransfer.2005.08.009 Get rights and content

Abstract

In the present study, theoretical results of the heat transfer characteristics and the fin efficiency of the annular fin are presented. Annular fin under dry-surface conditions, partially wet-surface conditions, and fully wet-surface conditions are investigated. The mathematical models based on the conservation equations of energy and mass are developed and solved by the central finite difference method to obtain temperature distribution along the fin. Effects of inlet condition of working fluids and the fin dimensions on the heat transfer characteristics and fin efficiency are considered. The results obtained from the model are validated by comparing with those obtained from the other researchers. There is a reasonable agreement between the results obtained from the present model and those obtained from the other model.

Introduction

Finned-tube heat exchangers are widely used in applications for air cooling and dehumidifying heat recovery process. Heat and mass transfer occur simultaneously when the coil surface temperature is below the dew point temperature of the air being cooled. In general, heat transfer process of finned-tube heat exchanger under wet-surface conditions is more complex than that under dry-surface conditions. There are many works had been reported on heat transfer and flow characteristics. Coney and Sheppard [1] predicted the fin effectiveness, fin temperature distribution, and condensate film thickness in a laminar humid air cross flow. Mirth and Ramadhyani [2] used the dry-surface heat transfer correlations for predicting the chilled-water cooling-coil performance under condensing conditions. Kaxeminejad [3] analyzed a one-dimensional conduction heat transfer of a cooling and dehumidifying fin assembly. The effects of the relative humidity, dry bulb temperature, and cold fluid temperature on the temperature distribution and also on the augmentation factor were considered. Thombre and Sukhatme [4] experimentally studied the fully developed heat transfer and friction factor characteristics of shrouded fin arrays in the turbulent flow region. Srinivasan and Shah [5] determined the fin efficiency in two-phase flow applications. Salah El-Din [6] developed analytical solutions for predicting the performance of the fully and partially wet fin assembly. Rosario and Rahman [7], [8] studied effects of relative humidity, dry bulb temperature of air, and cold fluid temperature inside the coil on the performance of the heat exchanger under dehumidification conditions. Laing et al. [9] developed the mathematical model for predicting the wet-surface fin efficiency of a plate-fin-tube heat exchanger. Kundu [10] analyzed the performance and optimization of a cooling and dehumidifying straight taper longitudinal fin. Mokheimer [11] studied the performance of annulus fins of different profiles subject to locally variable heat transfer coefficient.

Although some studies have been performed for the heat transfer characteristics of the annular fin, there still remains room to discuss. The purpose of this paper is to theoretically study the heat transfer characteristics and performance of the annular fin under dry-surface conditions, partially wet-surface conditions, and fully wet-surface conditions. Effects of relevant parameters on the temperature distribution and fin efficiency are considered.

Section snippets

Mathematical modelling

As shown in Fig. 1, the heat transfer characteristics of annular finned-tube assembly under dry-surface conditions, partially wet-surface conditions, and fully wet-surface conditions can be determined by the conservation equations of energy and mass. The mathematical model is based on that of Rosario and Rahman [7], [8] and Kraus et al. [12] with the following main assumptions:

–
Thermal resistance of the condensate is not included.
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The thermal conductivity of the fin and wall are constant.
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The

Solution method

An annular fin is divided into various segments along the radial direction as shown in Fig. 1. Eqs. (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), (16), (17), (18), (19), (20), (21), (22) are written in dimensionless forms as in Eqs. (23), (24), (25), (26), (27), (28), (29), (30), (31), (32), (33), (34), (35), (36), (37), (38), (39), (40), (41), (42), (43), (44), (45). These equations are solved simultaneously by using the implicit central finite different

Results and discussion

In the following sections, results of the effects of flow conditions and fin dimensions on the temperature distribution along the tube wall and fin are presented. Verification of the present mathematical model is performed by comparison with the results obtained from other researchers. Fig. 2 shows the comparison between the results obtained from the model and those obtained from the other researchers [13], [14] under fully wet-surface conditions. The fin efficiency can be calculated from Eq.

Conclusion

The predicted results of the heat transfer characteristics of the annular fin under dry-surface conditions, partially wet-surface conditions, and fully wet-surface conditions are presented. The results obtained from the model are validated by comparing with those obtained from the other researchers. The effects of inlet condition of both working fluids and the fin dimensions are discussed. There is reasonable agreement between the results obtained from the present model and those obtained the

References (14)

D.R. Mirth et al.
Prediction of cooling-coil performance under condensing conditions
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(1993)
H. Kazeminejad
Analysis of one-dimensional fin assembly heat transfer with dehumidification
Int. J. Heat Mass Transfer
(1995)
S.B. Thombre et al.
Turbulent flow heat transfer and friction factor characteristics of shrouded fin arrays with uninterrupted fins
Exp. Therm. Fluid Sci.
(1995)
V. Srinivasan et al.
Fin efficiency of extended surfaces in two-phase flow
Int. J. Heat Fluid Flow
(1997)
M.M. Salah El-Din
Performance analysis of partially-wet fin assembly
Appl. Therm. Eng.
(1998)
L. Rosario et al.
Analysis of heat transfer in a partially wet radial fin assembly during dehumidification
Int. J. Heat Fluid Flow
(1999)
B. Kundu
An analytical study of the effect of dehumidification of air on the performance and optimization of straight tapered fins
Int. Commun. Heat Mass Transf.
(2002)

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Citation Excerpt :
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^☆: Communicated by W.J. Minkowycz.

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Study on the heat transfer characteristics of the annular fin under dry-surface, partially wet-surface, and fully wet-surface conditions☆

Abstract

Introduction

Section snippets

Mathematical modelling

Solution method

Results and discussion

Conclusion

Int. J. Heat Fluid Flow

Int. J. Heat Mass Transfer

Exp. Therm. Fluid Sci.

Int. J. Heat Fluid Flow

Appl. Therm. Eng.

Int. J. Heat Fluid Flow

Int. Commun. Heat Mass Transf.