Porosity effect on thermal and fluid dynamic behaviors of a compact heat exchanger in aluminum foam

Porosity effect on thermal and fluid dynamic behaviors of a compact heat exchanger in aluminum foam

Bernardo BuonomoAnna di Pasqua Davide Ercole Oronzio Manca

Dipartimento di Ingegneria, Università degli Studi della Campania “L. Vanvitelli”, Real Casa dell’Annunziata, Via Roma 29, Aversa, Italy

Corresponding Author Email: 
bernardo.buonomo@unicampania.it
Page: 
305-322
|
DOI: 
https://doi.org/10.3166/ RCMA.28.305-322
| |
Published: 
30 September 2018
| Citation

ACCESS

Abstract: 

Metal foams are a relatively recent category of materials used in different applications, such as: compact heat sinks, geothermal operations, heat exchanger and solar thermal plants. The use of metal foams in heat exchangers gives it efficiency, compact and light for the open porosity, a high thermal conductivity and a large accessible surface area per unit volume.

A numerical study has been conducted to evaluate the thermal and fluid dynamic behaviors of a tubular aluminum foam heat exchanger. The thermal non-equilibrium energy condition is considered to execute two-dimensional simulations on metal foam heat exchanger. The examined foams are characterized by distinct porosity, from 0.90 to about 0.97, for different values of pores per inch, equal to 5, 10, 20 and 40. Different air flow rates and an assigned surface tube temperature are imposed. The results are given in terms of heat transfer coefficient and local Nusselt number evaluated on the external surface of the tube. Typical global parameters in a compact heat exchanger, such as effectiveness and NTU, are showed. Moreover, local air temperature and velocity profiles are presented in the cross section, between two consecutive tubes. Finally, the Energy Performance Ratio (EPR) is showed in order to demonstrate the effectiveness of the metal foams.

Keywords: 

aluminum foam, heat exchanger, heat transfer enhancement

1. Introduction
2. Governing equations and physical model
3. Numerical model
4. Results and discussions
5. Conclusions
Nomenclature

A

cross section, m2

CF

drag factor coefficient

cp

specific heat, J kg-1 K-1

d

tube diameter, m

df

dp

fiber diameter, m

pore diameter, m

f

friction factor

h

heat transfer coefficient, W m-2 K-1

hsf

interfacial heat transfer coefficient, W m-2 K-1

H

half pitch, m

Htot

heat exchanger height, m

j

Colburn factor

k

thermal conductivity, W m-1 K-1

K

porous permeability, m2

L

thickness of porous media, m

$\dot{m}$  

 

mass flow rate, kg s-1

Nu

Nusselt number

NTU

number transfer of units

p

static pressure, Pa

Pr

Prandtl number

Q

heat transfer rate, W

r

radius tube, m

Re

Reynolds number

s

curvilinear abscissa, m

T

Temperature, K

u

x-velocity, m s-1

u0

inlet air velocity, m s-1

v

y-velocity, m s-1

x

Cartesian axis direction, m

y

Cartesian axis direction, m

 

Greek symbols

 

 

asf

specific surface area density, m-1

Δ

difference

ɛ

effectiveness

µ

dynamic viscosity, kg m-1 s-1

ρ

density, kg m-3

f

porosity

w

number of pores per inch, m-1

 

Subscripts

 

0

inlet condition

clean

system without foam

d

tube diameter

df

fiber diameter

eff

effective

f

fluid phase of metal foam

mf

metal foam

s

solid phase of metal foam

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