Performance of tubular aluminum foam heat exchangers in multiple row bundles

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Abstract

Two sets of aluminum foam cylinders, 5 and 15 mm thick, are being tested in two-row and three-row bundles for their thermo-hydraulic performance. The bundles are formed using fixed transversal and longitudinal pitch distances and subject to airflow between 0.5 and 5.0 at 0.5 m s−1 interval under cross-flow. The effects of foam layer thickness and the number of row under staggered configuration are investigated. Thermo-hydraulic results are benchmarking against those of a conventional finned tube bundle of similar dimensions with pre-determined number of fins and assembled using the same pitch distances.

Keywords

Metal foams Heat exchangers Condensers Tube bank Tube bundle Cooling towers Cross-flow Geothermal 

List of symbols

A

Area (\(\hbox {m}^2\))

\(\bar{c}_{\mathrm{p}}\)

Specific heat capacity at constant pressure (J kg−1 K−1)

\(d_{\mathrm{f}}\)

Strut diameter (m)

\(d_{\mathrm{i}}\)

Core tube internal diameter (m)

\(d_{{\mathrm{o}}}\)

Core tube external diameter (m)

\(D_{\mathrm{i}}\)

Foam or fin annulus internal diameter \(= d_{{\mathrm{o}}}\) (m)

\(D_{\mathrm{o}}\)

Foam or fin annulus external diameter (m)

f

Friction factor (–)

H

Dimensional height (m)

h

Convective heat transfer coefficient (W \(\hbox {m}^{-2}\) K−1])

Kp

Pressure loss coefficient (–)

k

Thermal conductivity (W m−1 K−1)

L

Dimensional length (m)

\(\dot{m}\)

Mass flow rate (kg s−1)

Nu

Nusselt number (–)

P

Pressure (Pa)

\(\dot{Q}\)

Heat transfer rate (W)

R

Thermal resistance (K W−1)

Re

Reynolds number (–)

\(S_{\mathrm{L}}\)

Longitudinal pitch distance (m)

\(S_{\mathrm{T}}\)

Transversal pitch distance (m)

\(t_{\mathrm{f}}\)

Fin thickness (m)

\(t_{\mathrm{p}}\)

Fin pitch (m)

T

Temperature (K or \(^\circ\)C)

\(\vec {u}\)

Air velocity (m s−1)

U

Universal heat transfer coefficient (W \(\hbox {m}^{-2}\) K−1)

W

Dimensional width (m)

\(\hat{X}_{\mathrm{L}}\)

Ratio of longitudinal pitch to core diameter \(= S_{\mathrm{L}}/d_{\mathrm{o}}\) (–)

\(\hat{X}_{\mathrm{T}}\)

Ratio of transversal pitch to core diameter \(= S_{\mathrm{T}}/d_{\mathrm{o}}\)(–)

Abbreviations

FS

Full scale

HTC

Convective heat transfer coefficient (W \(\hbox {m}^{-2}\) K−1)

LMTD

Log mean temperature difference (K or \(^\circ\)C)

NTU

Number of transfer unit (–)

PID

Proportional–integral–derivative feedback control

PPI

Pores per inch [technically in\(^{-1}\), treated as (–)]

RTD

Resistance temperature detector

TCR

Thermal contact resistance (K/W)

Greek symbols

\(\Delta\)

Differential of

\(\epsilon\)

Heat exchanger efficiency (–)

\(\eta\)

Surface efficiency of aluminum foam (–)

\(\mu\)

Dynamic viscosity (Pa s)

\(\rho\)

Mass density (kg \(\hbox {m}^{-3}\))

\(\phi\)

Porosity (–)

\(\Omega ^*\)

Efficiency function of foam

Common Subscripts

a

Of the air

c

Of the colder fluid taking up heat

h

Of the hotter fluid losing heat

i

Of inside surface

max

The largest value

min

The smallest value

o

Of outside surface

s

Of a surface

t

Overall, total

\(\infty\)

Of the bulk air free flow stream

Notes

Acknowledgements

The principal author is grateful to QGECE for its financial support to this study. Both authors also express their gratitude to the following individuals: Professor Thomas Rösgen for setting up the PIV facility, giving initial tutorials, and providing supervision on related works in his lab at the Institut Für Fluiddynamik, ETH-Zurich; Mostafa Odabaee for his help in sourcing test specimens; Dr Morteza Khashehchi, who helped process PIV data for velocity check; Joy Wang and Peter Bleakley for helping with data logging instrument; Douglas Malcolm for helping with wind tunnel operation and air velocity PID control program; and lastly Berto Di Pasquale for general fabrication of in-house parts and accessories.

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2018

Authors and Affiliations

  1. 1.Queensland Geothermal Energy Centre of Excellence School of Mechanical and Mining EngineeringUniversity of QueenslandBrisbaneAustralia

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