## THERMAL SCIENCE

International Scientific Journal

### EFFECT OF FLOW SEPARATION OF TIO2 NANOFLUID ON HEAT TRANSFER IN THE ANNULAR SPACE OF TWO CONCENTRIC CYLINDERS

**ABSTRACT**

In the wake of energy crises the researchers are encouraged to explore new ways of enhancement in thermal performance of heat exchanging equipment. In current research, SST K-ω model and finite volume method, were employed to augment heat transfer in to separation flow of TiO2/nanofluid in the annular space of two concentric cylinders. In the present investigation TiO2 nanoparticles of volume fractions 0.5%-2% at Reynolds number range of 10000-40000 and contraction ratios from 1 to 2 were considered at constant heat flux boundary condition. Simulation results reveal that, the highest enhancement in heat transfer coefficient is corresponding to the annular pipe with contraction ratio of 2 due to the generated recirculation flow zone that begins after the separation point on the wall. Further, the surface heat transfer coefficient enhances with the increase of nanoparticles volume fraction and Reynolds number. The velocity distribution profile before and after the steps, reveals that increasing of the height of step and Reynolds number, recirculation regions also increases. Numerical results indicate that, the highest pressure drop occurs at Re=40000 and contraction ratio of 2.

**KEYWORDS**

PAPER SUBMITTED: 2018-07-09

PAPER REVISED: 2019-07-25

PAPER ACCEPTED: 2019-08-08

PUBLISHED ONLINE: 2019-09-15

**THERMAL SCIENCE** YEAR

**2020**, VOLUME

**24**, ISSUE

**Issue 2**, PAGES [1007 - 1018]

- Abu Mulaweh, H.I., 2005, " Turbulent mixed convection flow over a forward facing step the effect of step heights," International Journal of Thermal Sciences, 44(2), pp.155 162.
- Orselli, R.M., and De Lemos, M.J.S., 2005, "Sudden contraction in a turbulent with a porous insert," L atin American Journal of Solids and Structures, 2, pp.269 290.
- Gandjalikhan Nassab , S.A., Moosavi, Hosseini Sarvari , R.S.M., 2009, "Turbulent forced convection flow adjacent to inclined forward step in a duct," International Journal of Thermal Scienc es, 48(7), pp. 1319 1326.
- Armaly, B.F., Durst, F., Pereira , J.C.F., Schönung , B., 1983, "Experimental and theoretical investigation of backward facing step flow," Journal of Fluid Mechanics, 127, pp.473 496.
- Lee, T., Mateescu, , D., 1998, " Experimental and numerical investigation of 2 d backward facing step flow," Journal of Fluids and Structures, 12(6), pp. 703 716.
- Hussein Togun, HI Abu Mulaweh, SN Kazi, A Badarudin, 2016, "Numerical simulation of heat transfer and separation Al2O3/nanoflui d flow in concentric annular pipe," International Communications in Heat and Mass Transfer, 71, pp. 108 117.
- Togun, H., Abdulrazzaq, T., Kazi, S.bdulrazzaq, T., Kazi, S., Badarudin, A., 2013, ", Badarudin, A., 2013, "Augmented of Turbulent Heat Augmented of Turbulent Heat Transfer in an Annular Pipe with Abrupt ExpansionTransfer in an Annular Pipe with Abrupt Expansion," ," TThermalhermal SSciencecience 2020, pp. , pp. 16211621--16321632
- Togun H, Tuqa A, Kazi SN, Badarudin A, Ariffin MKA. 20166, "Heat transfer to laminar flow over , "Heat transfer to laminar flow over a double backwarda double backward--facing step," Int J Mech Aerosp Manuf Ind Sci Eng World Acad Sci Eng Technol, facing step," Int J Mech Aerosp Manuf Ind Sci Eng World Acad Sci Eng Technol, 10 pp. 11710 pp. 117--22.22.
- Oon, C. S, Hussein Togun, S. N. Kazi, A. Badarudin, M. N. M. Zubir, E. Sadeghinezhad,2013, " Hussein Togun, S. N. Kazi, A. Badarudin, M. N. M. Zubir, E. Sadeghinezhad,2013, " Computational simulation of heat transfer to separation fluid flow in an annular passage," Computational simulation of heat transfer to separation fluid flow in an annular passage," International Communications in Heat and Mass Transfer, 46(0), pp. 92International Communications in Heat and Mass Transfer, 46(0), pp. 92--96.96.
- Togun, H.,Ahmed Jassim Shkarah, S. N. Kazi, A. Badarudin, 2013, "CFD Simulation of Heat n, H.,Ahmed Jassim Shkarah, S. N. Kazi, A. Badarudin, 2013, "CFD Simulation of Heat Transfer and Turbulent Fluid Flow over a Double ForwardTransfer and Turbulent Fluid Flow over a Double Forward--Facing Step," Mathematical Problems in Facing Step," Mathematical Problems in Engineering, 2013, pp. 10.Engineering, 2013, pp. 10.
- Tuqa Abdulrazzaq, Hussein Togun, M. K. A. Ariffin, A.B. S. N. Kazi, N. M Adam, S. ffin, A.B. S. N. Kazi, N. M Adam, S. Masuri,2014, " Heat Transfer and Turbulent Fluid Flow over Vertical Double ForwardMasuri,2014, " Heat Transfer and Turbulent Fluid Flow over Vertical Double Forward--Facing Step, Facing Step, World Academy of Science," Engineering and Technology, 86, pp. 722World Academy of Science," Engineering and Technology, 86, pp. 722--726.726.
- Hussein Togun, SN Kazi, A Badarudin, 2017, "Turbulent heat transfer to separation nanofluid rbulent heat transfer to separation nanofluid flow in annular concentric pipe," International Journal of Thermal Sciences,117, pp. 14flow in annular concentric pipe," International Journal of Thermal Sciences,117, pp. 14--2525
- Yılmaz, I.l., H.F. Öztop, 2006, "Turbulence forced convection heat transfer over double forward facing step flow,"facing step flow," International Communications in Heat and Mass Transfer, 33(4), pp.508International Communications in Heat and Mass Transfer, 33(4), pp.508--517.517.
- Oztop, H.F., K.S. Mushatet, İ. Yılmaz, 2012, "Analysis of turbulent flow and heat transfer over a double forward facing step with obstacles," International Communications in Hdouble forward facing step with obstacles," International Communications in Heat and Mass Transfer, eat and Mass Transfer, 39(9),pp. 139539(9),pp. 1395--1403.1403.
- Neary V.S., F. Sotiropoulos, 1996, "Numerical investigation of laminar flows through 90--degree degree diversions of rectangular crossdiversions of rectangular cross--section," Computers & Fluids, 25(2), pp.95section," Computers & Fluids, 25(2), pp.95--118.118.
- N.K.A. J.G. Barbosa Saldana, V. Sarin, Numerical simulation of mixed convective flow over a Saldana, V. Sarin, Numerical simulation of mixed convective flow over a threethree--dimensional horizontal backward facingdimensional horizontal backward facing--step, Journal of Heat Transfer 127 (2005) 1027step, Journal of Heat Transfer 127 (2005) 1027--1036.1036.
- Nada, S.A., 2008, "Experimental investigation of natural convection heat transfer in horizontal in horizontal and inclined annular fluid layers," Heat Mass Transfer 44, pp. 929and inclined annular fluid layers," Heat Mass Transfer 44, pp. 929--936.936.
- Kherbeet, A.S, H.A. Mohammed, B.H. Salman, 2012, "The effect of nanofluids flow on mixed convection heat transfer over microscale backwardconvection heat transfer over microscale backward--facing step," Internatiofacing step," International Journal of Heat and nal Journal of Heat and Mass Transfer, 55(21Mass Transfer, 55(21--22), pp. 587022), pp. 5870--5881.5881.
- Manca, O., S. Nardini, D. Ricci, 2012, "A numerical study of nanofluid forced convection in ribbed channels," Applied Thermal Engineering, 37(0), pp. 280ribbed channels," Applied Thermal Engineering, 37(0), pp. 280--292.292.
- Menter, F.R. , 1994, " Two" Two--equation eddyequation eddy--viscosity turbulence models for engineering viscosity turbulence models for engineering applications," AIAA Journal, 32(8), pp. 1598applications," AIAA Journal, 32(8), pp. 1598--1605.1605.
- Klinzing, W.P., E.M. Sparrow,2009, " Evaluation of Turbulence Models for External Flows," Numerical Heat Transfer, Part A: ApplicationsNumerical Heat Transfer, Part A: Applications, 55(3), pp. 205, 55(3), pp. 205--228.228.
- Tseng, Y.S., Y.M. Ferng, C.H. Lin, 2014, "Investigating flow and heat transfer characteristics in a fuel bundle with splita fuel bundle with split--vane pair grids by CFD methodology," Annals of Nuclear Energy, 64(0), pp. vane pair grids by CFD methodology," Annals of Nuclear Energy, 64(0), pp. 9393--99.99.
- Lancial, N., F. Beaubert, S. Harmand, G. Rolland, 2013, "Effects of a turbulent wall jet on heat aubert, S. Harmand, G. Rolland, 2013, "Effects of a turbulent wall jet on heat transfer over a nontransfer over a non--confined backwardconfined backward--facing step," International Journal of Heat and Fluid Flow, facing step," International Journal of Heat and Fluid Flow, 44(0), pp. 33644(0), pp. 336--347.347.
- Dutta, R.,A. Dewan, B. Srinivasan, 2013, " Comparison of various integration to wall (ITW) of various integration to wall (ITW) RANS models for predicting turbulent slot jet impingement heat transfer," International Journal of RANS models for predicting turbulent slot jet impingement heat transfer," International Journal of Heat and Mass Transfer, 65(0), pp.750Heat and Mass Transfer, 65(0), pp.750--764.764.
- Vajjha, R. S., D.K. Das, 2009, "Experimental determination of thermal conductivity of three nductivity of three nanofluids and development of new correlations," International Journal of Heat and Mass Transfer, nanofluids and development of new correlations," International Journal of Heat and Mass Transfer, 52(2152(21--22), pp. 467522), pp. 4675--4682.4682.
- Xuan, Y. , W. Roetzel, 2000, " Conceptions for heat transfer correlation of nanofluids," International JouInternational Journal of Heat and Mass Transfer, 43(19), pp.3701rnal of Heat and Mass Transfer, 43(19), pp.3701--3707.3707.
- Wang, H.L. B.--X., X.F. Peng, 2000, "Research on the heatX., X.F. Peng, 2000, "Research on the heat--conduction enhancement for liquid conduction enhancement for liquid with nanowith nano--particle suspensions, General Paper (Gparticle suspensions, General Paper (G--1), "International Symposium on Thermal Science 1), "International Symposium on Thermal Science and Engand Engineering (TSE2002), Beijing.ineering (TSE2002), Beijing.
- Brinkman, H.C. , 1952, "The Viscosity of Concentrated Suspensions and Solutions," The Journal of Chemical Physics, 20(4), pp. 571of Chemical Physics, 20(4), pp. 571--571.571.
- Togun, H., Tuqa Abdulrazzaq, A.B. S. N. Kazi, 2014, "Numerical study of turbulent heat transfer heat transfer in annular pipe with sudden contraction," Applied mechanics and materials. , 465in annular pipe with sudden contraction," Applied mechanics and materials. , 465--466,pp. 461466,pp. 461--466.466.