Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
8
6
2016
NUMERICAL INVESTIGATION OF ROUND TURBULENT SWIRLING JET IMPINGEMENT HEAT TRANSFER FROM A HOT SURFACE
489-507
Muhammad Ali Rob
Sharif
Aerospace Engineering and Mechanics Department, The University of Alabama, Tuscaloosa, Alabama, USA
Numerical investigation of heat transfer from a heated plane circular surface due to round turbulent submerged swirling jet impingement is conducted in this study. A round swirling turbulent jet is impinging normally on a concentric circular hot plane surface. The axisymmetric flow domain is bounded by the hot impingement surface and the jet exit plane. The flow is characterized by the jet exit Reynolds number (Re), the jet exit swirl number (Sw) representing the swirl strength of the inlet flow, and the nondimensional distance of separation from the jet exit to the impingement plate (H). The commercial CFD code ANSYS Fluent along with the transition SST k-ω turbulence model is used for the computations. In order to select a suitable turbulence model for the computations, the performance of a few turbulence models in the computation of round impinging jet heat transfer were validated against experimental data, and the transition SST k-ω model was selected. Computations are performed for many arrangements of the above-mentioned parameters and critical analysis of the heat transfer process is performed. The results indicate negative effect on heat transfer when swirl is present. For low- to mid-range swirl strength when Sw ≤ 0.77, the average Nusselt number drops mildly as Sw is increased from 0 (nonswirling case). When Sw ≥ 1, the average Nusselt number increases mildly with increasing Sw but remains less than that for the nonswirling case. Also when Sw ≤ 0.77, the average Nusselt number increases mildly with increasing jet-to-target separation distance (2 ≤ H ≤ 10). On the other hand, when Sw ≥ 1.00, the average Nusselt number moderately drops as H increases.
NON-SIMILAR SOLUTION OF STEADY MHD MIXED CONVECTION FLOW OVER A ROTATING SPHERE
509-523
J.
Rajakumar
Department of Mathematics, National Institute of Technology Tiruchirappalli, Tiruchirappalli − 620015, Tamilnadu, India
P.
Saikrishnan
Department of Mathematics, National Institute of Technology Tiruchirappalli, Tiruchirappalli − 620015, Tamilnadu, India
Ali J.
Chamkha
Department of Mechanical Engineering, Prince Sultan Endowment for Energy and
Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952, Kingdom of Saudi
Arabia; RAK Research and Innovation Center, American University of Ras Al Khaimah, United Arab Emirates, 10021
Ali F.
Al-Mudhaf
Manufacturing Engineering Department, The Public Authority for Applied Education and Training, P. O. Box 42325, Shuweikh, 70654 Kuwait
An analysis is accomplished to investigate the features of heat transfer and fluid flow of a steady laminar magnetohydrodynamics (MHD) mixed convection flow of water around a rotating sphere. The transformed governing equations of the non-similar boundary layers are solved by an implicit finite difference method along with the quasi-linearization technique. It is perceived that both the local friction coefficients in the x and y directions and the heat transfer coefficient are increasing and the point of separation is delayed with increasing magnetic parameter, suction parameter, and buoyancy force.
LAMINARIZATION OF TURBULENT FLOW IN ASYMMETRICALLY HEATED VERTICAL CHANNEL
525-541
Biswadip
Shome
Global Technology and Engineering Center, Offices No. 501 & No. 502, D Block, Weikfield IT Citi Info Park, Pune-Nagar Road, Pune, India 411014
Laminarization of turbulent flow of helium in an asymmetrically heated vertical channel was investigated using a low-Reynolds number turbulence model. The investigation was done for inlet Reynolds number ranging from 4000 to 10000, nondimensional wall heat flux ranging from 0.001 to 0.006, and wall heat flux ratio ranging from 0 to 1. A laminarization criterion, based on the ration of turbulence production to turbulence dissipation rate, has been developed as a function of inlet Reynolds number, nondimensional wall heat flux, and wall heat flux ratio. An increase in asymmetry of the wall heat flux is seen to arrest laminarization. The results predict a reduction in the Nusselt number as compared to the constant property turbulent flow results, ranging from as much as 57% reduction for inlet Reynolds number of 4000 to 19% reduction for inlet Reynolds number of 10000.
JOINT INFLUENCE OF HIGH ENTROPY LAYER AND GOERTLER VORTICES ON HEAT TRANSFER IN SUPERSONIC COMPRESSION RAMP FLOW
543-553
Pavel Vladimirovich
Chuvakhov
Central Aerohydromynamic Institute, 1 Zhukovskogo str., Zhukovsky, Moscos reg., 140180, Russia; and Moscow Institute of Physics and Technology (State University), 9 Institutskiy per., Dolgoprudny, Moscow reg., 141700, Russia
Ivan Vladimirovich
Egorov
Central Aerohydrodynamic Institute (TsAGI), 1, Zhukovsky Str., Zhukovsky,
Moscow Region, 140180, Russian Federation
H.
Olivier
RWTH Aachen University, 52056 Aachen, Germany
A.
Roghelia
RWTH Aachen University, 52056 Aachen, Germany
The joint influence of a small bluntness-generated high entropy layer and Goertler vortices is investigated numerically for a laminar supersonic compression ramp flow at free stream Mach number M∞ = 8 and Reynolds number ReL ~ 3.71 × 105 based on flat plate length. Beside the fact that Goertler vortices result in spanwise variation of the heat flux coefficient with respect to its average level, they are also found to increase the average level. The high entropy layer is shown to dramatically reduce heat flux and its spanwise variations due to vortices in the reattachment region, with Goertler vortices suppressed.
NATURAL CONVECTION OF A HYBRID NANOFLUID-FILLED TRIANGULAR ANNULUS WITH AN OPENING
555-566
Fatih
Selimefendigil
Mechanical Engineering Department, Celal Bayar University, Manisa, 45140, Turkey
Ali J.
Chamkha
Department of Mechanical Engineering, Prince Sultan Endowment for Energy and
Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952, Kingdom of Saudi
Arabia; RAK Research and Innovation Center, American University of Ras Al Khaimah, United Arab Emirates, 10021
Natural convection of an Al2O3/ Cu-water hybrid nanofluid filled triangular annular cavity was numerically investigated. The inner and outer surfaces of the concentric triangular cavities are isothermal, and an opening is considered in the inclined side wall of the outer triangle. The governing equations are solved with the finite element method. The influence of the Rayleigh number (between 104 and 5 × 105), opening ratio (between 0 and 0.625), and solid volume fraction of the nanoparticles (between 0 and 0.02) on the fluid flow and heat transfer was considered. It was observed that the Nusselt number is enhanced with the Rayleigh number and opening ratio. The effects of the opening ratio on the heat transfer enhancement is more effective for higher values of Rayleigh numbers. The increment in the average heat transfer versus the solid nanoparticle volume fraction shows a linear relation, and the slope of the linear curve is higher for the solid volume fraction with higher thermal conductivity.
EVALUATION OF TURBULENCE MODELS FOR NATURAL AND FORCED CONVECTION FROM FLAT PLATES
567-582
Ahmed
Kalendar
Department of Mechanical Power and Refrigeration, College of Technological Studies-PAAET, Shuwaikh, Kuwait
Abdulrahim
Kalendar
Department of Mechanical Power and Refrigeration, College of Technological Studies-PAAET, Shuwaikh, Kuwait
Yousuf
Alhendal
Department of Mechanical Power and Refrigeration, College of Technological Studies-PAAET, Shuwaikh, Kuwait
Because forced and natural convective flows over relatively wide flat plates have been widely studied, there are many empirical equations available to estimate the heat transfer rates in such situations. However, it is not clear which turbulence model should be used when numerically calculating the heat transfer rate in situations involving laminar, transitional, and turbulent flows. Furthermore, because of the differences among the results given by the various available empirical correlation equations, the selection of a turbulence model and the estimation of the accuracy of numerical results can be rather difficult. Laminar, transitional, and turbulent natural and forced convective heat transfer from isothermal and constant surface heat flux plates has been considered. It has been assumed that the flow is steady, and symmetrical about the center plane of the plate. The governing equations have been numerically solved using the commercial CFD code FLUENT. Results have only been obtained for a Prandtl number of 0.7. Rayleigh numbers between 106 and 1012, heat flux Rayleigh numbers between 107 and 1015, and Reynolds numbers between 103 and 107 have been considered. Numerical results for natural and forced convective flows have been obtained using six turbulence models and the numerical results have been compared with the results given by existing empirical equations in the different flow regions considered. These available data made it possible to establish new reliable correlations for natural convective heat transfer in transitional flow regions.
CONTENTS VOLUME 8, 2016
583-589