## 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

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

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