1. H. Niazmand, M. Charjouei Moghadam, A. Behravan
ENTECH '14 The International Energy Technologies Conference , Turkey, Istanbul, Dec 2014
Investigation on flow and heat transfer of CNT/transformer oil nanofluids
E. Ebrahimnia-Bajestan
Department of Energy, Graduate University of Advanced Technology Kerman, Iran
H. Niazmand, M. Charjouei Moghadam, A. Behravan

2. Overview Experimental Section Numerical Section
The flow and heat transfer of the CNT/transformer oil have been numerically simulated for the straight and 90° pipe employing the single-phase approach
CNT/Transformer Oil nanofluid is prepared in two volume fractions of and
The effect of Temperature and volume fractions is investigated on nanofluid Thermal conductivity and viscosity
The measured thermophysical properties have been used for developing the nanofluid thermophysical properties correlations that are employed in the numerical simulation

3. Introduction Transformer
main components of the electricity transmission networks
Heat production in wire and coil
Temperature rise:
Damages the paper insulation and liquid insulation medium
Is a limiting factor for transformer operation (breakdown)
Reduces the Lifetime of the transformer
Temperature control of the transformer is a essential need.
Transformer oil
electrical insulating medium
(Prevent electrical problems)
Heat transfer fluid

4. Introduction
Cooling Limitation: Low thermal conductivity of Transformer oil
Solution: Nanofluids
Nanofluids
Uniform and stable dispersion of nanoparticles into liquids

5. Literature review
Most of the studies in the literature are done on the water and ethylene glycol based nanofluids.
The oil based nanofluids are mostly been considered for their electrical and magnetic characteristics. (Jeon and Lee, 2014, Lee et al., 2012, Miao et al., 2013, Mansour et al., 2012, Timko et al., 2012, Dong et al., 2013)
Thermophysical properties of the oil based nanofluid
Investigator(s)
Base fluid
Particle type
Investigation
Botha et al., 2011
Transformer oil
Silver-Silica
Thermal conductivity increment and reduction in viscosity
Li et al., 2011
Copper
Both thermal conductivity and viscosity have increased
Singh and Kundan, 2013
Al2O3

6. Literature review convective heat transfer of oil based nanofluids.
Investigator(s)
Base fluid
Particle type
Geometery
Investigation
Liu, 2011
Transformer oil Cu
Straight pipe
Convective heat transfer of nanofluid at different flow temperatures and nanoparticle size was examined
Srinivasan and Saraswathi, 2012 BN
76% enhancement of the nanofluid convective heat transformer of with respect to its base fluid
CNT nanoparticles nanofluids used in different conditions
Investigator(s)
Base fluid
Particle type
Investigation
Nazari et al., 2014
Water and Ethylene glycol
Alumina and CNT
Comparing different types of nanofluids in CPU cooling
Ashtiani et al., 2012
Transformer oil
MW-CNT
Heat transfer characteristics of MW-CNT/transformer oil nanofluid inside flattened tubes under uniform wall temperature condition
Rahman et al., 2014
Water
CNT
Effect of solid volume fraction and tilt angle in a quarter circular solar thermal collectors filled with CNT–water nanofluid
Amiri et al., 2014
Pool Boiling heat transfer of CNT/water nanofluid
Chen and Xie, 2009
Oil
Optimized thermal conductivity enhancement

7. Challenges an motivations
Enhancement of low thermal conductivity of transformer oil
Natural or force convection of oil in transformers
heat transfer fluids with low viscosity
Thermophysical properties of oil based nanofluid
Convective heat transfer of oil based nanofluid
Outlines of this study:
Measurement of viscosity and thermal conductivity of CNT/transformer oil
Numerical study of convective heat transfer of the nanofluids employing measurement thermophysical data

8. Nanofluid Preparation using two-step method
Functionalized CNT
Surfactant free
Ultrasonication
(100W and 28kHz)
Different particle concentration of 0.001wt.% and 0.01wt% (0.0004vol.% and vol.%)

9. Thermophysical Properties Measurement
DV-III ultra viscometer for measuring nanofluid viscosity
KD2 Device for measuring nanofluid thermal conductivity

10. Viscosity measurement results and the correlated relation
Viscosity strongly decreases with temperature
No significant effect of particle concentration
Smaller pressure drops in higher volume fractions

11. Thermal conductivity measurement results and the correlated relation
The thermal conductivity increases with the increment of volume fractions because:
Higher thermal conductivity of CNTs in comparison with transformer oil
Brownian motion of nanoparticles into the base fluid
The bulk motion due to the Brownian motion of nanoparticles that results in a strong fluid mixing and heat transfer improvement
Shape effect of nanoparticles

12. Numerical Modeling Laminar forced convective heat transfer
Constant heat flux (3000 W/m2)
Single phase model
Proposed correlations for thermal conductivity and viscosity is applied
Both pipes have the same length (2.05m) and inner diameter (7.8mm)

13. The Governing equations
Continuity equation
Momentum equation
Energy equation

14. Nanofluid effective thermophysical properties relations used in the governing equations
Density
Heat Capacity
Thermal Conductivity
Viscosity

15. Thermophysical properties of the transformer oil and CNT
Thermophysical properties of the transformer oil have been obtained from the curve fitting to the measured data.
As for the density and specific heat, the curve fits have been done to the data of (Susa. 2005).
Thermophysical properties of nanoparicle
Particle Type
ρ (g/cm3)
K(W/mk)
Inner diameter (nm)
Outer diameter (nm)
Length
(µm)
CNT
2.1
2000
5-10
10-20 30

16. Numerical Model Validation
90 curved pipe:
Re = 300 , De = 122 , D = 8mm , Rϲ = 24mm , α = 1/6
VAN DE VOSSE, F., VAN STEENHOVEN, A., SEGAL, A. & JANSSEN, J A finite element analysis of the steady laminar entrance flow in a 90 curved tube. International journal for numerical methods in fluids, 9,

17. Results and discussion
velocity contours

18. Results and discussion
Temperature contours

19. Results and discussion
Averaged heat transfer coefficient versus Reynolds number for the straight pipe
Enhancement of heat transfer characteristics with Reynolds number and volume fraction

20. Results and discussion
Averaged heat transfer coefficient versus Reynolds number for the 90° curved pipe
Development of secondary flows in the curved pipe
Better mixing of the flow
Increased heat transfer

21. Results and discussion
The nanofluid heat transfer increment ratio with respect to the base fluid

22. Conclusion
Thermal conductivity of the CNT/Transformer oil nanofluid increases with volume fraction and temperature.
Viscosity of the CNT/Transformer oil nanofluid decreases with temperature and is not influenced by volume fraction which makes the usage of this kind of nanofluids more efficient in power transformers as a result of smaller pressure drops.
Convective heat transfer of the nanofluid is increased by using the nanofluid with respect to its base fluid.
The heat transfer enhancement is greater in the 90° curved pipe due to the development of secondary flows which results in the better mixing of the flow.

23. References
AMIRI, A., SHANBEDI, M., AMIRI, H., HERIS, S. Z., KAZI, S. N., CHEW, B. T. & ESHGHI, H Pool boiling heat transfer of CNT/water nanofluids. Applied Thermal Engineering, 71,
ASHTIANI, D., AKHAVAN-BEHABADI, M. A. & PAKDAMAN, M. F An experimental investigation on heat transfer characteristics of multi-walled CNT-heat transfer oil nanofluid flow inside flattened tubes under uniform wall temperature condition. International Communications in Heat and Mass Transfer, 39,
BOTHA, S. S., NDUNGU, P. & BLADERGROEN, B. J Physicochemical properties of oil-based nanofluids containing hybrid structures of silver nanoparticles supported on silica. Industrial & Engineering Chemistry Research, 50,
CHEN, L. & XIE, H Silicon oil based multiwalled carbon nanotubes nanofluid with optimized thermal conductivity enhancement. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 352,
DONG, M., SHEN, L., WANG, H., WANG, H. & MIAO, J Investigation on the electrical conductivity of transformer oil-based AlN nanofluid. Journal of Nanomaterials, 2013, 164.
JEON, H.-P. & LEE, J.-C Numerical simulation of particle concentration in dielectrophoretic flow for high voltage applications. Materials Research Bulletin, 58,
LEE, J.-C., SEO, H.-S. & KIM, Y.-J The increased dielectric breakdown voltage of transformer oil-based nanofluids by an external magnetic field. International Journal of Thermal Sciences, 62,
LI, D., XIE, W. & FANG, W Preparation and properties of copper-oil-based nanofluids. Nanoscale research letters, 6, 1-7.
LIU, K Heat transfer measurement in oil-based nanofluids. Doctor of Philosophy, University of Louisville.
MANSOUR, D.-E., ATIYA, E. G., KHATTAB, R. M. & AZMY, A. M. Year. Effect of titania nanoparticles on the dielectric properties of transformer oil-based nanofluids. In: Electrical Insulation and Dielectric Phenomena (CEIDP), 2012 Annual Report Conference on, IEEE,
MIAO, J., DONG, M., REN, M., WU, X., SHEN, L. & WANG, H Effect of nanoparticle polarization on relative permittivity of transformer oil-based nanofluids. Journal of Applied Physics, 113,
NAZARI, M., KARAMI, M. & ASHOURI, M Comparing the thermal performance of water, Ethylene Glycol, Alumina and CNT nanofluids in CPU cooling: Experimental study. Experimental Thermal and Fluid Science, 57,
RAHMAN, M. M., MOJUMDER, S., SAHA, S., MEKHILEF, S. & SAIDUR, R Effect of solid volume fraction and tilt angle in a quarter circular solar thermal collectors filled with CNT–water nanofluid. International Communications in Heat and Mass Transfer, 57,
SINGH, M. & KUNDAN, L Experimental Study on Thermal Conductivity and Viscosity of Al2O3-Nanotransformer Oil. IJTARME, 2.
SRINIVASAN, C. & SARASWATHI, R Nano-oil with high thermal conductivity and excellent electrical insulation properties for transformers. Curr Sci India, 102,
SUSA, D Dynamic thermal modelling of power
transformers. Doctor of Science, Helsinki University of Technology.
TIMKO, M., KOPCANSKY, P., MOLCAN, M., TOMCO, L., MARTON, K., MOLOKAC, S., RYBAR, P., STOIAN, F., HOLOTESCU, S. & TACULESCU, A Magnetodielectric Properties of Transformer Oil Based Magnetic Fluids. Acta Physica Polonica-Series A General Physics, 121, 1253.
VAN DE VOSSE, F., VAN STEENHOVEN, A., SEGAL, A. & JANSSEN, J A finite element analysis of the steady laminar entrance flow in a 90 curved tube. International journal for numerical methods in fluids, 9,

24. Thanks for your
Attention