Heat and Mass Transfer

, Volume 41, Issue 7, pp 583–593

3D Numerical heat transfer and fluid flow analysis in plate-fin and tube heat exchangers with electrohydrodynamic enhancement

Original

Abstract

Three-dimensional laminar fluid flow and heat transfer over a four-row plate-fin and tube heat exchanger with electrohydrodynamic (EHD) wire electrodes are studied numerically. The effects of different electrode arrangements (square and diagonal), tube pitch arrangements (in-line and staggered) and applied voltage (VE=0–16 kV) are investigated in detail for the Reynolds number range (based on the fin spacing and frontal velocity) ranging from 100 to 1,000. It is found that the EHD enhancement is more effective for lower Re and higher applied voltage. The case of staggered tube pitch with square wire electrode arrangement gives the best heat transfer augmentation. For VE=16 kV and Re = 100, this study identifies a maximum improvement of 218% in the average Nusselt number and a reduction in fin area of 56% as compared that without EHD enhancement.

Keywords

3D Electrohydrodynamics (EHD) Plate-fin Tube heat exchanger 

List of symbols

Cp

Pressure drop coefficient, 2(pinp)/ρ uin2

D

Tube diameter (m)

E

Electric field strength (V m−1)

f

Fanning friction factor, 2·(pinp)/ρ uin2H/4L

f0

Fanning friction factor for flow without EHD

FE

EHD (N m−3)

g

Acceleration due to gravity (m s−2)

h

Heat transfer coefficient (W m−2 °C−1)

\(\bar h\)

Average heat transfer coefficient (W m−2°C−1)

H

Fin spacing (m)

i

Current density (A m−2)

j

Colburn factor \(\overline {{\text{Nu}}} /\left( {\operatorname{Re} \Pr ^{1/3} } \right)\)

j0

Colburn factor for flow without EHD

k

Thermal conductivity (W m−1°C−1)

L

Flow length (m)

n

Direction normal to the surface

Nu

Local Nusselt number, h·H/k

\(\overline {{\text{Nu}}}\)

Average Nusselt number, \(\bar h \cdot H/k\)

P

Pressure (Pa)

Pr

Prandtl number, ν/α

q

Electric charge density (Cm−3)

Re

Reynolds number, Uin·H

SL

Tube pitch for longitudinal direction (m)

ST

Tube pitch for transverse direction (m)

Tw

Wall temperature (K)

T

Temperature (K)

Tb

Bulk mean temperature (K)

Tin

Inlet temperature (K)

Uin

Frontal velocity (m s−1)

u

Fluid velocity (m s−1)

V

Voltage (V)

VE

Voltage at wire electrode (V)

X, Y, Z

Coordinates

Greek symbols

α

Thermal diffusivity (m2 s−1)

ɛ

Fluid permittivity (F m−1)

σE

Electrical conductivity ( m−1)

ρ

Fluid density (kg m−3)

ν

Kinematic viscosity (m2 s−1)

μ

Dynamic viscosity (N s m−1)

Θ

Dimensionless temperature, (TTin)/(TwTin)

Θb

Dimensionless bulk mean temperature, (TbTin)/(TwTin)

Subscript

0

Without electric field

Superscript

vectors

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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringNational Cheng-Kung UniversityTainanTaiwan

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