Nanojet impingement cooling of an isothermal surface in a partially porous medium under the impact of an inclined magnet
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Nanojet impingement cooling of an isothermal surface in a partially porous medium under the impact of an inclined magnetic field Fatih Selimefendigil1 • Hakan F. O¨ztop2 Received: 25 July 2019 / Accepted: 13 September 2019 Akade´miai Kiado´, Budapest, Hungary 2019
Abstract In this study, jet impingement heat transfer characteristics for a layered nanofluid and porous domains under the effects of inclined uniform magnetic field are examined by using Galerkin weighted residual finite element method. Effects of various pertinent parameters such as Reynolds number (between 100 and 500), Hartmann number (between 0 and 6), magnetic inclination angle (between 0 and 90), Darcy number (between 104 and 102 ) and height of porous layer (between 0.25 H and 4 H) on the fluid flow and heat transfer are analyzed. It was observed that local and average heat transfer rate enhance when the value of Reynolds number, magnetic field inclination angle and permeability of the porous layer increase, while the impact is reversed for magnetic field strength. Magnetic field inclination angle has more influence on the convective heat transfer features as compared to strength, and for a horizontally aligned magnetic field heat transfer process is inefficient. When cases in the absence and presence of magnetic field (at Hartmann number of 6) are compared, 28% of reduction in the average heat transfer is obtained. An optimum value of porous layer height is observed where the highest heat transfer rates are achieved. Keywords MHD nanofluid Jet impingement Finite element method Porous medium List of symbols B0 Magnetic field strength Da Darcy number Ha Hartmann number H Separating distance between plates h Local heat transfer coefficient k Thermal conductivity L Plate length n Unit normal vector Nus Local Nusselt number Num Average Nusselt number p Pressure Pr Prandtl number Re Reynolds number T Temperature & Fatih Selimefendigil [email protected] ¨ ztop Hakan F. O [email protected] 1
Department of Mechanical Engineering, Celal Bayar University, 45140 Manisa, Turkey
2
Department of Mechanical Engineering, Technology Faculty, Fırat University, 23119 Elazig, Turkey
u, v w x, y
xy velocity components Slot width Cartesian coordinates
Greek characters a Thermal diffusivity c Magnetic field inclination angle Porosity h Non-dimensional temperature j Permeability m Kinematic viscosity q Density of the fluid r Electrical conductivity / Solid volume fraction Subscripts c Cold h Hot m Average nf Nanofluid w Wall
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N. Selimefendigil, H. F. Öztop
Introduction
Table 1 Grid independence study (Ha ¼ 3, c ¼ 45 , Da ¼ 5 103 , h ¼ H)
Jet impingement cooling has many applications such as in drying, glass annealing, turbine blade cooling and many others. Nanofluids technology is successfully implemented in jet flow applications. The nanofluids which are composed of nanosized particles and base fluid such as water, ethylene glycol, refrigerants, mineral oil provide higher heat
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