Abstract
This work presents a cell model for predicting the thermal conductivity of nanofluids. Effects due to the high specific surface area of the mono-dispersed nanoparticles and the micro-convective heat transfer enhancement associated with the Brownian motion of particles are addressed in detail. Novelty of the paper lies in its prediction of the non-linear dependence of thermal conductivity of nanofluids on particle volume fraction at low particle concentrations. The model is found to correctly predict the trends observed in experimental data over a wide range of particle sizes, temperatures and particle concentrations.
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Abbreviations
- A m :
-
Heat transfer area per particle for conduction through liquid medium (m2)
- A pc :
-
Volume averaged cross-sectional area for conduction through nanoparticle (m2)
- A ps :
-
Surface area of nanoparticle (m2)
- c :
-
Empirical constant
- d p :
-
Average particle diameter (m)
- dT/dx :
-
Temperature gradient (K/m)
- h :
-
Convective heat transfer coefficient (W/m2 K)
- k b :
-
Boltzmann constant (J/K)
- k m :
-
Thermal conductivity of liquid medium (W/m K)
- k p :
-
Thermal conductivity of particle (W/m K)
- l :
-
Length scale of the unit cell (m)
- Nu :
-
Nusselt number
- n :
-
Number of nanoparticles per unit volume of nanofluid
- Pe :
-
Peclet number
- q m :
-
Heat flux in liquid medium by conduction (W/m2)
- q nf :
-
Overall heat flux in nanofluid (W/m2)
- R c :
-
Thermal resistance of micro-convection (K/W)
- R eff :
-
Effective thermal resistance of the nanofluid system (K/W)
- R m :
-
Thermal resistance of conduction in liquid medium (K/W)
- R p :
-
Thermal resistance of a particle (K/W)
- T :
-
Temperature (K)
- u p :
-
Particle velocity due to Brownian motion (m/s)
- eff:
-
Effective
- m:
-
Liquid medium
- nf:
-
Nanofluid
- p:
-
Particle
- α:
-
Thermal diffusivity (m2/s)
- ɛ:
-
Particle volume fraction
- η:
-
Dynamic viscosity (N s/m2)
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Acknowledgements
The authors acknowledge the support from Defence Research and Development Organisation (DRDO) and Department of Science and Technology (DST), Government of India, for the present research work.
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Patel, H.E., Sundararajan, T. & Das, S.K. A cell model approach for thermal conductivity of nanofluids. J Nanopart Res 10, 87–97 (2008). https://doi.org/10.1007/s11051-007-9236-4
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DOI: https://doi.org/10.1007/s11051-007-9236-4