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Research Papers: Heat Transfer Enhancement

# Performance of Aluminum and Carbon Foams for Air Side Heat Transfer Augmentation

[+] Author and Article Information
Patrick T. Garrity, Renwei Mei

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611

James F. Klausner1

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611klaus@ufl.edu

1

Corresponding author.

J. Heat Transfer 132(12), 121901 (Sep 17, 2010) (9 pages) doi:10.1115/1.4002172 History: Received March 12, 2009; Revised June 14, 2010; Published September 17, 2010; Online September 17, 2010

## Abstract

The air side heat transfer performance of three aluminum foam samples and three modified carbon foam samples are examined for comparison with multilouvered fins often found in compact heat exchangers. The aluminum foam samples have a bulk density of $216 kg/m3$ with pore sizes of 0.5, 1, and 2 mm. The modified carbon foam samples have bulk densities of $284$, $317$, and $400 kg/m3$ and machined flow passages of 3.2 mm in diameter. The samples were placed in a forced convection arrangement using a foil heater as the heat source and ambient air as the sink. A constant heat flux of $9.77 kW/m2$ is applied throughout the experiments with the mean air velocity ranging from 1 to 6 m/s as the control parameter. The steady volume-averaged momentum equation and a two-equation nonequilibrium heat transfer model are employed to extract the volumetric heat transfer coefficients. Pressure drop measurements are correlated with the Darcy–Forcheimer relation. Empirical heat transfer correlations for the aluminum and carbon foam samples are provided. Using a hypothetical heat exchanger considering only the thermal resistance between the ambient air and the outer tube wall, the air side performance for each sample is modeled based on the local heat transfer coefficients and friction factors obtained from experiments. The performance of each sample is evaluated based on a coefficient of performance (COP, defined as the ratio of the total heat removed to the electrical input of the blower), compactness factor (CF, defined as the total heat removed per unit volume), and power density (PD, defined as the total heat removed per unit mass). Results show the carbon foam samples provide significant improvement in CF but the COP and PD are considerably lower than that for comparable multilouvered fin heat exchangers.

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## Figures

Figure 1

Foam samples: (a) aluminum, 10 PPI, 20 PPI, and 40 PPI (from top to bottom) and (b) carbon, L1A, D1, and L1 (from top to bottom)

Figure 2

Experimental facility used to measure the heat transfer augmentation performance of carbon and aluminum foams in a convection arrangement

Figure 3

Axial pressure and upper wall temperature variation for 10 PPI aluminum foam sample um=1.13 m/s

Figure 4

Carbon foam pressure gradient variation with respect to mean air velocity

Figure 5

Aluminum foam pressure gradient variation with respect to mean air velocity

Figure 6

Foam upper wall temperature variation with respect to mean air velocity for all carbon and aluminum foam samples

Figure 7

Dimensionless velocity profile of air flowing through the channel

Figure 8

Dimensionless temperature profiles within the channel: (a) solid and (b) fluid

Figure 9

Carbon foam volumetric heat transfer coefficient variation with respect to mean fluid velocity

Figure 10

Aluminum foam volumetric heat transfer coefficient variation with respect to mean fluid velocity

Figure 16

Comparison of compactness factor for louvered fin and foam configurations

Figure 17

Comparison of power density for louvered fin and foam configurations

Figure 15

Comparison of coefficient of performance for louvered fin and foam configurations

Figure 14

Depiction of louvered fin geometric parameters

Figure 13

Hypothetical heat exchanger in cross flow with (a) louvered fin and (b) carbon/aluminum foam configurations

Figure 12

Nusselt number correlation for carbon foams

Figure 11

Nusselt number correlation for aluminum foams showing a transition to thermal equilibrium conditions

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