Heat transfer and rheological properties of transformer oil-oxidized MWCNT nanofluid


Power transformers play a key role in power and electrical industries and thus boosting their efficiency is necessary. In this study, the effect of oxidized multi-walled carbon nanotubes on transformer oil thermophysical properties was experimentally investigated. The maximum amount of carbon nanotubes was chosen up to 0.01 mass% to assure the maximum purity of transformer oil. Heat transfer characteristics of transformer oil and nanofluids in two cases of free and forced convection were studied. Breakdown voltage, flash point, pour point, density, electrical and thermal conductivities, viscosity and shear stress, as eight important quality parameters, were determined. According to the experimental results, the Breakdown voltage decreased through concentration increasing. Electrical conductivity is not changed considerable with increasing concentration and temperature. Thermal conductivity of nanofluids and transformer oil changed with increasing temperature and concentration. Furthermore, at all concentrations and temperatures, the viscosity of the nanofluids was lower than that of transformer oil.

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A :

Heat transfer area (m2)

I :

Current (A)

V :

Voltage (V)

Q :

Input power (W)

T h :

Temperature of the oil (°C)

T c :

Temperature of the wall  (°C)

L :

The distance between the cold and hot walls (m)

C P :

Specific heat of oil (J kg−1 K−1)

g :

Gravity force (m s−2)

h :

Heat transfer coefficient (W m−2 K−1)

k :

Thermal conductivity (W m−1 K−1)

Nu :

Nusselt number

Pr :

Prandtel number

Gr :

Grashof number

Ra :

Rayleigh number


Volumetric expansion coefficient

ρ :

Density (g cm−3)

μ :

Dynamic viscosity (Pa s)

ν :

Kinematic viscosity (cP)

τ :

Shear stress (Pa)

γ :

Shear rate (s−1)


Multi-walled carbon nanotube


Transformer oil


Breakdown voltage/kV


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The authors are grateful for the financial support of the Iran Nanotechnology Initiative Council as well as Niroonamad Khorasan for analyzing breakdown voltage test.

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Correspondence to Saeed Zeinali Heris.

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Beheshti, A., Shanbedi, M. & Heris, S.Z. Heat transfer and rheological properties of transformer oil-oxidized MWCNT nanofluid. J Therm Anal Calorim 118, 1451–1460 (2014). https://doi.org/10.1007/s10973-014-4048-0

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  • Thermodynamic properties
  • Electrochemical measurements
  • Dielectric properties
  • Thermal conductivity
  • Energy storage
  • Nanostructures