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Research Papers

Fin Effects in Flow Channels of Plate-Fin Compact Heat Exchanger Cores

[+] Author and Article Information
R. M. Manglik1

Thermal-Fluids and Thermal Processing Laboratory, College of Engineering and Applied Science,  University of Cincinnati, Cincinnati, OH 45221-0072Raj.Manglik@uc.edu

O. A. Huzayyin, M. A. Jog

Thermal-Fluids and Thermal Processing Laboratory, College of Engineering and Applied Science,  University of Cincinnati, Cincinnati, OH 45221-0072

See Robinson Fin Machines, Inc., at the following URL: http://www.robfin.com/Home/tabid/2036/Default.aspx

1

Corresponding author.

J. Thermal Sci. Eng. Appl 3(4), 041004 (Oct 28, 2011) (9 pages) doi:10.1115/1.4004844 History: Received June 10, 2011; Revised August 10, 2011; Accepted August 11, 2011; Published October 28, 2011; Online October 28, 2011

Abstract

The fin effects on laminar forced convection of air in the interfin passages of plate-fin heat exchangers are investigated. Steady state fully developed flows in rectangular, trapezoidal, and triangular plate-fin channels are considered. With H1 and T conditions at the partition plates, the conjugate conduction–convection fin problem is solved computationally. The fin effects on the convective Nusselt number are shown to scale by a new dimensionless parameter Ω, which accounts for the attendant fin material and size; its limits describe perfectly conducting and nonconducting fins. Ineffective fins and the consequent reduction in the convective heat transfer coefficient are most pronounced in low fin density cores with longer fins in low-conductivity metal (stainless steel). However, with increasing fin density and shorter fins, the convection performance is virtually the same as that with 100% fin efficiency; the same is the case when fins are made of very high conductivity metal (copper). These results provide design insights for optimizing the conjugate fin-conduction and fluid-flow convection performance in plate-fin compact heat exchangers.

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Figures

Figure 1

Plate-fin type heat exchanger cores: (a) typical configurations made of copper, aluminum, and steel (image courtesy Robinson Fin Machine), and common interfin passage geometries (b) rectangular, (c) trapezoidal, and (d) triangular)

Figure 2

Schematic representation of thermal boundary conditions at plate-fin flow channel walls: (a) ideal and fundamental boundary conditions and (b) actual conditions that account for conjugate fin-conduction and its effectiveness

Figure 3

Variation of fully developed laminar flow Nu with aspect ratio γ of a rectangular (φ = 90 deg) interfin channel with ηf  ∼ 1 and ηf  ∼ 0 fins for both T and H1 conditions

Figure 4

Variation of fully developed laminar flow Nu with aspect ratio γ of a trapezoidal (φ = 75 deg) interfin channel with ηf  ∼ 1 and ηf  ∼ 0 fins for both T and H1 conditions

Figure 5

Variation of fully developed laminar flow Nu with aspect ratio γ of a triangular interfin channel with ηf  ∼ 1 and ηf  ∼ 0 fins for both T and H1 conditions

Figure 6

(a) Generalized interfin channel geometry and coordinate system, (b) computational domain in transformed coordinates, and (c) conduction–convection fin thermal energy balance

Figure 7

Typical fin temperature variation with Ω and ηf in plate-fin channels with H1 thermal condition at partition plates: (a) on fin surface of a rectangular channel and (b) on fin surface of a trapezoidal channel

Figure 8

Effect of height and density of plate fins made of stainless steel on the variation of (Nu/Nu1 ) with fin parameter Ω and H1 thermal condition at partition plates: (a) rectangular duct, φ = 90 deg and (b) trapezoidal duct with φ = 75 deg

Figure 9

Effect of height and density of plate fins made of stainless steel on the variation of (Nu/Nu1 ) with fin parameter Ω and T thermal condition at partition plates: (a) rectangular duct, φ = 90 deg and (b) trapezoidal duct with φ = 75 deg

Figure 10

Effect of height and density of plate fins made of copper on the variation of (Nu/Nu1 ) with fin parameter Ω and H1 thermal condition at partition plates: (a) rectangular duct, φ = 90 deg and (b) trapezoidal duct with φ = 75 deg

Figure 11

Effect of height and density of plate fins made of copper on the variation of (Nu/Nu1 ) with fin parameter Ω and T thermal condition at partition plates: (a) rectangular duct, φ = 90 deg and (b) trapezoidal duct with φ = 75 deg

Figure 12

Variation in ER with fin density for typical plate-fin channels made in stainless steel of different rectangular and trapezoidal flow cross-section aspect ratio γ

Figure 13

Variation in ER with fin density for typical plate-fin channels made in copper of different rectangular and trapezoidal flow cross-section aspect ratio γ

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