A new performance evaluation method and its application in fin-tube surface design of small diameter tube

Abstract

In this paper, a simple yet efficient performance comparison method is proposed based on the assumptions of constant properties and identical frontal area. For this method, no correlations are required, and a small number of discrete data are sufficient. To illustrate the feasibility of the proposed approach, a new slotted fin with 4 mm tubes is designed to replace the original louvered fin with tubes of 7 mm. The orthogonal design method is adopted in the fin design to reduce the number of computational cases significantly, and yet a nearly optimum combination of major geometric factors can still be obtained. The reasonable parametric combination of 3 global parameters is obtained by analyzing the numerical results of 16 plain plate fins. Based on this result, 3 new slotted fins with different fin pitches are studied. The slotted fin with a fin pitch of 1.4 mm is recommended after considering the heat transfer, comprehensive performance, and cost of material and operation. The result shows that compared with the original louvered fin, the recommended fin not only increases the heat transfer rate by 2.2%, 22.5%, and 13.7% under an identical flow rate, identical pressure drop, and identical pumping power constraint, respectively, but also saves approximately 36% of the copper tube materials.

Key words： performance evaluation; orthogonal design; small-diameter tube

Acknowledgements

This work was supported by the National Basic Research Program of China (No. 2007CB206902). The computations were conducted at Xi’an Node of National High-Performance Computing Cluster of China.

Notation

Ac	frontal cross-section area/m2
cp	specific heat/(kJ·kg-1·K-1)
L	orthogonal array or straight line
p	pressure/Pa
P	pumping power/W
T	temperature/K
u, v, w	velocity component in Cartesian coordinates system/(m·s-1)
ui	velocity component in Cartesian coordinates system/(m·s-1)
V	inlet velocity of fluid/(m·s-1)
x, y, z	coordinate component in Cartesian coordinates system
xi	coordinate component in Cartesian coordinates system

Greek symbols

Δp	fluid pressure drop between inlet and outlet/Pa
ΔT	fluid temperature difference between inlet and outlet/K
Φ	heat transfer rate/W
η	dynamic viscosity/(kg·m-1·s-1)
λ	thermal conductivity of fluid/(W·m-1·K-1)
ρ	fluid density/(kg·m-1)

Subscripts

1,2	code for fin for comparison
a, b, c	code for straight line
i	summation Indicators
k	free Indicators
w	tube wall

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