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Porous Media

Forced Convection Heat Transfer in Spray Formed Copper and Nickel Foam Heat Exchanger Tubes

[+] Author and Article Information
Nicholas Tsolas

Sanjeev Chandra

Department of Mechanical and Industrial Engineering, Centre for Advanced Coating Technologies,  University of Toronto, Toronto, ON, M5S 3G8, Canada

J. Heat Transfer 134(6), 062602 (May 08, 2012) (10 pages) doi:10.1115/1.4006015 History: Received March 18, 2011; Revised November 16, 2011; Published May 08, 2012; Online May 08, 2012

A thermal spray coating process was used to deposit dense 2 mm thick metal skins on the surfaces of square cross-section channels (300 mm × 20 mm × 20 mm) of nickel and copper foams with 10 and 40 PPI (pores per inch) pore densities. A heater was wrapped around the channels to apply surface heat-fluxes varying from 427 to 6846 W/m2 . Compressed air was blown through the channels at flow rates of 5–80 l/min. Foam and fluid temperature distributions along the length of the channel and the pressure drop across it were measured. The foam was modeled as a porous medium and properties such as permeability K and inertial coefficient CF were determined from the experimental data. Local and average convective heat transfer coefficients were calculated from air and foam temperature measurements. Nusselt numbers were calculated and correlated in terms of the Reynolds, Prandtl, and Darcy numbers. Heat transfer to air flowing through a 10 PPI foam channel was shown to have increased nearly seven times compared to that of hollow tube with the same dimensions.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Successive stages during deposition of thermal spray coating on a metal foam channel

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Figure 2

Cross sections through 10 PPI and 40 PPI Ni metal foam samples with stainless steel skins. The samples are 20 mm wide, with approximately 1.2 mm thick skin.

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Figure 3

(a) Schematic of the experimental apparatus and (b) detailed view of the thermocouples

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Figure 4

Pictures of typical open-cell metal foams with 40 PPI and 10 PPI pore sizes

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Figure 5

(a) SEM images of the foam fiber cross section and pore with defined hydraulic diameters and (b) definition of foam fiber and pore diameter in a cubic model of metal foams

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Figure 6

Variation of experimentally measured pressure gradient with average fluid velocity in the nickel foam channels. The experimental uncertainty is ±81 Pa/m in the pressure gradient and ±0.06 m/s in fluid flow velocity measurements.

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Figure 7

Friction factor variation with Reynolds number

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Figure 8

Experimentally measured temperatures of (a) the channel wall and (b) the bulk fluid, plotted as a function of the axial distance from the inlet of a 10 PPI nickel foam channel. The heat flux was 3851 ± 64.5 W/m2 . The experimental uncertainties are ±2.6 °C in the temperature measurement and ±0.5 mm in the length measurement.

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Figure 9

Convective heat transfer coefficient variation with average fluid flow velocity for nickel foams for varying heat flux. The experimental uncertainty is ±0.06 m/s in the fluid flow velocity measurements, whereas the maximum uncertainty in the heat transfer coefficient is ±13%.

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Figure 10

Convective heat transfer coefficient variation with average fluid flow velocity for copper foams for varying heat flux. The experimental uncertainty is ±0.06 m/s in the fluid flow velocity measurements, whereas the maximum uncertainty in the heat transfer coefficient is ±14%.

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Figure 11

Volumetric heat transfer coefficient variation with average fluid velocity for nickel foams with varying heat flux. The experimental uncertainty is ±0.06 m/s in the fluid flow velocity measurements, whereas the maximum uncertainty in the volumetric heat transfer coefficient is ±9%.

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Figure 12

Volumetric heat transfer coefficient variation with average flow velocity for copper foams with varying heat flux. The experimental uncertainty is ±0.06 m/s in the fluid flow velocity measurements, whereas the maximum uncertainty in the volumetric heat transfer coefficient is ±4%.

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Figure 13

Heat transfer enhancement with 10 PPI nickel and copper foam channels compared to a hollow tube with the same dimensions

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Figure 14

Average Nusselt number as a function of the Reynolds, Prandtl, and Darcy numbers for nickel and copper metal foams of 10 and 40 PPI pore densities

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