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Modeling of irreversibility factors for nanofluid flow in different channels regarding nanoparticle arrangement

Particle migration and channel size considerations
  • Saeed Heshmatian
  • Mehdi Bahiraei
  • Mohammad Amani
Article
  • 9 Downloads

Abstract

Irreversibility factors for the TiO2–water nanofluid flow are evaluated through entropy generation rates caused by friction and heat transfer by taking into account nanoparticle migration. Effects of three factors of viscosity gradient, non-uniform shear rate and Brownian diffusion are considered. The investigations are performed in both conventional channels and minichannels since the channel size has the considerable effects of on entropy generation. Influence of particle migration on the irreversibility factors is more noticeable in smaller channels such that with considering particle migration, the maximum thermal entropy generation rate increases about 51% for 0.2 mm channel, while this increment is almost 16% for 1 mm channel. Unlike results are obtained for conventional channels and minichannels, such that total entropy generation intensifies in minichannels and reduces in conventional channels by particle concentration increment. Friction is main factor in entropy generation for minichannels, while heat transfer demonstrates a higher contribution in conventional channels. The optimal channel size where minimum entropy generation occurs is obtained which is dependent on Reynolds number. Therefore, for lower Reynolds number, optimal case occurs at smaller channel size. Furthermore, diagrams of total entropy generation show minimum (optimal) point for 3 mm channel, while they demonstrate the constant trends for other channels.

Keywords

Entropy generation Nanofluid Particle migration Irreversibility Second law of thermodynamics 

List of symbols

A

Area (m2)

Be

Bejan number

cp

Specific heat/J kg−1 K−1

Db

Brownian diffusion coefficient/m2s−1

dp

Diameter of nanoparticles (m)

J

Total particle flux/ms−1

Jµ

particle flux due to viscosity gradient/ms−1

Jc

Particle flux due to non-uniform shear rate/ms−1

Jb

Particle flux due to Brownian motion/ms−1

Kc

Constant

Kµ

Constant

k

Thermal conductivity/W m−1 K−1

kB

Boltzmann’s constant/J K−1

P

Pressure (Pa)

R

Radius of tube (m)

Re

Reynolds number

r

Radial coordinate

\( \dot{S}_{g,f}^{{{\prime \prime \prime }}} \)

Local frictional entropy generation rate/W m−3 K−1

\( \dot{S}_{g,f}^{{{\prime \prime \prime }}} \)

Local thermal entropy generation rate/W m−3 K−1

\( \dot{S}_{g,t}^{{{\prime \prime \prime }}} \)

Total entropy generation rate/W m−3 K−1

T

Temperature (K)

v

Velocity/ms−1

Greek letters

\( \dot{\gamma } \)

Shear rate s−1

μ

Dynamic viscosity/kg m 1s−1

ρ

Density/kg m−3

φ

Volume concentration

φm

Mean volume concentration

Subscripts

f

Base fluid

p

Particles

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2018

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringKermanshah University of TechnologyKermanshahIran
  2. 2.Mechanical and Energy Engineering DepartmentShahid Beheshti UniversityTehranIran

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