The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
R P Vedula - One of the best experts on this subject based on the ideXlab platform.
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local effectiveness and nusselt number distributions for a rectangular jet impinging on a cylindrical convex surface at different angles
International Journal of Thermal Sciences, 2018Co-Authors: Satyanand Abraham, R P VedulaAbstract:Abstract Local effectiveness and Nusselt number distribution measurements for heated rectangular jets impinging perpendicularly and obliquely on a cylindrical convex surface are reported here. The jets exit from a rectangular nozzle of height ‘H’ and width ‘W’ with aspect ratios, H/W, equal to 10 and 5 and the corresponding the curvature ratios (ratio of Hydraulic Diameter of nozzle to Diameter of the impinging convex surface), b/D, were equal to 0.083 and 0.076. Studies were conducted for non dimensional jet-to-target distances, L/b, equal to 2, 3, 4 and 5, and for inclination of jet axis with the convex target surface, θ, equal to 0°, 30° and 45°. The Reynolds numbers, Re (based on average exit velocity of jet and Hydraulic Diameter of nozzle) was kept constant at 17000. The entrainment of the fluid from the surroundings into the walljet from the top surface and edge regions, which is symmetric on the either side of the impingement zone for perpendicular impingement, gives a ‘rhombus like’ shape for the effectiveness contours. However, the entrainment is asymmetric for oblique impingement, with the drop in effectiveness rapid in the uphill side and gradual in the downhill side, giving the effectiveness contours a ‘kite like’ shape. The fluid entrainment from the top surface and edge regions influence the Nusselt number distribution also. The relatively higher mixing of the jet fluid with the ambient at the edge regions increases the turbulence and thereby increases the Nusselt number at these locations, resulting in contour shapes different from those observed for the effectiveness.
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influence of rib height on the local heat transfer distribution and pressure drop in a square channel with 90 continuous and 60 v broken ribs
Applied Thermal Engineering, 2009Co-Authors: V Sriharsha, S V Prabhu, R P VedulaAbstract:Internal channel cooling is employed in advanced gas turbines blade to allow high inlet temperatures so as to achieve high thrust/weight ratios and low specific fuel consumption. The objective of the present work is to study the effect of rib height to the Hydraulic Diameter ratio on the local heat transfer distributions in a double wall ribbed square channel with 90° continuous attached and 60° V-broken ribs. The effect of detachment of the rib in case of broken ribs on the heat transfer characteristics is also presented. Reynolds number based on duct Hydraulic Diameter is ranging from 10,000 to 30,000. A thin stainless steel foil of 0.05 mm thickness is used as heater and infrared thermography technique is used to obtain the local temperature distribution on the surface. The images are captured in the periodically fully developed region of the channel. It is observed that the heat transfer augmentations in the channel with 90° continuous attached ribs increase with increase in the rib height to Hydraulic Diameter ratio (e/D) but only at the cost of the pressure drop across the test section. The enhancements caused by 60° V-broken ribs are higher than those of 90° continuous attached ribs and also result in lower pressure drops. But, with an increase in the rib height, the enhancements are found to decrease in channel with broken ribs. The effect of detachment incase of broken ribs is not distinctly observed. The heat transfer characteristics degraded with increase in the rib height in both attached and detached broken ribbed cases.
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local heat transfer distribution in a square channel with 90 continuous 90 saw tooth profiled and 60 broken ribs
Experimental Thermal and Fluid Science, 2008Co-Authors: Abhishek Gupta, V Sriharsha, S V Prabhu, R P VedulaAbstract:Abstract Internal channel cooling is employed in advanced gas turbines blade to allow high inlet temperatures so as to achieve high thrust/weight ratios and low specific fuel consumption. The objective of the present study is to measure the local heat transfer distributions in a double wall ribbed square channel with 90° continuous, 90 ° saw tooth profiled and 60° V-broken ribs. Comparison is made between the 90 ° continuous ribs ( P/e = 7 and 10 for a e/D = 0.15) and 90 ° saw tooth profiled rib configurations ( P/e = 7 for an e/D = 0.15) for the same rib height to the Hydraulic Diameter ratio ( e/D ). The effect of pitch to rib height ratio ( P/e = 7.5,10 and 12) of 60° V-broken ribbed channel with a constant rib height to Hydraulic Diameter ratio ( e/D ) of 0.0625 on the local heat transfer distribution is studied. The Reynolds number based on duct Hydraulic Diameter is ranging from 10,000 to 30,000. A thin stainless steel foil of 0.05 mm thickness is used as heater and infrared thermography technique is used to obtain the local temperature distribution on the surface. The images are captured in the periodically fully developed region of the channel. It is observed that the heat transfer augmentations in the channel with 90 ° saw tooth profiled ribs are comparable with those of 90 ° continuous ribs. The enhancements caused by 60° V-broken ribs are higher than those of 90 ° continuous ribs. The effect of pitch to the rib height ratio ( P/e ) is not significant for channel with 60° V-broken ribs for a given rib height to Hydraulic Diameter ratio ( e/D = 0.0625).
Amirah M Sahar - One of the best experts on this subject based on the ideXlab platform.
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effect of Hydraulic Diameter and aspect ratio on single phase flow and heat transfer in a rectangular microchannel
Applied Thermal Engineering, 2017Co-Authors: Amirah M Sahar, J G Wissink, Mohamed M Mahmoud, T G Karayiannis, Mohamad Ashrul S IshakAbstract:Abstract The effect of aspect ratio and Hydraulic Diameter on single phase flow and heat transfer in a single microchannel was investigated numerically and the results are presented in this paper. Previously, many studies in literature investigating the effect of geometrical parameters reached contradictory conclusions leaving some phenomena unexplained. Additionally, most researchers studied the effect of channel geometry by varying the channel height for a constant channel width or varying the width for a constant height. This means that the Hydraulic Diameter and aspect ratio vary simultaneously, which makes it difficult to identify the relative importance of the aspect ratio and the Hydraulic Diameter. In the present study, the effect of Hydraulic Diameter was studied by varying the channel width and depth while keeping the aspect ratio constant. The range of Hydraulic Diameters was 0.1–1 mm and the aspect ratio was fixed at 1. In the second set of simulations, the aspect ratio ranged from 0.39 to 10 while the Hydraulic Diameter was kept constant at 0.56 mm. The simulations were performed using the CFD software package ANSYS Fluent 14.5. The geometry investigated in this study includes symmetrical cylindrical inlet and outlet plenums and a microchannel. The fluid entered and left the channel vertically from the top in a direction normal to the channel axis. The dimensions of the inlet/outlet plenums (Diameter and height measured from the channel bottom surface) were kept constant while the width and depth of the channel were varied. The simulations were conducted for a range of Reynolds numbers (Re = 100–2000) and water was used as the working fluid. A three dimensional thin wall model was used to avoid conjugate heat transfer effects. A constant heat-flux boundary condition was applied at the bottom and vertical side walls of the channel, while the upper wall was considered adiabatic. The friction factor was found to decrease slightly with aspect ratio up to AR ≈ 2 after which it increased with increasing aspect ratio. The results demonstrated that the slope of the velocity profile at the channel wall changes significantly with aspect ratio for AR > 2. The effect of the aspect ratio and Hydraulic Diameter on the dimensionless hydrodynamic entry length is not significant. Also, the aspect ratio does not affect the heat transfer coefficient while the dimensionless Nusselt number increases with increasing Hydraulic Diameter. The friction factor was found to increase with increasing Hydraulic Diameter.
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single phase flow pressure drop and heat transfer in rectangular metallic microchannels
Applied Thermal Engineering, 2016Co-Authors: Amirah M Sahar, J G Wissink, Mohamed M Mahmoud, Mehmed Rafet Ozdemir, Ekhlas M Fayyadh, T G KarayiannisAbstract:Abstract Numerical simulations were performed using Fluent 14.5 to investigate single phase flow and conjugate heat transfer in copper rectangular microchannels. Two different configurations were simulated: (1) single channel with Hydraulic Diameter of 0.561 mm and (2) multichannel configuration consisting of inlet and outlet manifolds and 25 channels with Hydraulic Diameter of 0.409 mm. In the single channel configuration, four numerical models were investigated namely, 2D thin-wall, 3D thin-wall (heated from the bottom), 3D thin-wall (three side heated) and 3D full conjugate models. In the multichannel configuration, only 3D full conjugate model was used. The simulation results of the single channel configuration were validated using experimental data of water as a test fluid while the results of the multichannel configuration were validated using experimental data of R134a refrigerant. In the multichannel configuration, flow distribution among the channels was also investigated. The 3D thin-wall model simulation was conducted at thermal boundary conditions similar to those assumed in the experimental data reduction (uniform heat flux) and showed excellent agreement with the experimental data. However, the results of the 3D full conjugate model demonstrated that there is a significant conjugate effect and the heat flux is not uniformly distributed along the channel resulting in significant deviation compared to the experimental data (more than 50%). Also, the results demonstrated that there is a significant difference between the 3D thin-wall and full conjugate models. The simulation of the multichannel configuration with an inlet manifold having gradual decrease in cross sectional area achieved very reasonable uniform flow distribution among the channels which will provide uniform heat transfer rates across the base of the microchannels.
Mohamed M Mahmoud - One of the best experts on this subject based on the ideXlab platform.
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effect of Hydraulic Diameter and aspect ratio on single phase flow and heat transfer in a rectangular microchannel
Applied Thermal Engineering, 2017Co-Authors: Amirah M Sahar, J G Wissink, Mohamed M Mahmoud, T G Karayiannis, Mohamad Ashrul S IshakAbstract:Abstract The effect of aspect ratio and Hydraulic Diameter on single phase flow and heat transfer in a single microchannel was investigated numerically and the results are presented in this paper. Previously, many studies in literature investigating the effect of geometrical parameters reached contradictory conclusions leaving some phenomena unexplained. Additionally, most researchers studied the effect of channel geometry by varying the channel height for a constant channel width or varying the width for a constant height. This means that the Hydraulic Diameter and aspect ratio vary simultaneously, which makes it difficult to identify the relative importance of the aspect ratio and the Hydraulic Diameter. In the present study, the effect of Hydraulic Diameter was studied by varying the channel width and depth while keeping the aspect ratio constant. The range of Hydraulic Diameters was 0.1–1 mm and the aspect ratio was fixed at 1. In the second set of simulations, the aspect ratio ranged from 0.39 to 10 while the Hydraulic Diameter was kept constant at 0.56 mm. The simulations were performed using the CFD software package ANSYS Fluent 14.5. The geometry investigated in this study includes symmetrical cylindrical inlet and outlet plenums and a microchannel. The fluid entered and left the channel vertically from the top in a direction normal to the channel axis. The dimensions of the inlet/outlet plenums (Diameter and height measured from the channel bottom surface) were kept constant while the width and depth of the channel were varied. The simulations were conducted for a range of Reynolds numbers (Re = 100–2000) and water was used as the working fluid. A three dimensional thin wall model was used to avoid conjugate heat transfer effects. A constant heat-flux boundary condition was applied at the bottom and vertical side walls of the channel, while the upper wall was considered adiabatic. The friction factor was found to decrease slightly with aspect ratio up to AR ≈ 2 after which it increased with increasing aspect ratio. The results demonstrated that the slope of the velocity profile at the channel wall changes significantly with aspect ratio for AR > 2. The effect of the aspect ratio and Hydraulic Diameter on the dimensionless hydrodynamic entry length is not significant. Also, the aspect ratio does not affect the heat transfer coefficient while the dimensionless Nusselt number increases with increasing Hydraulic Diameter. The friction factor was found to increase with increasing Hydraulic Diameter.
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single phase flow pressure drop and heat transfer in rectangular metallic microchannels
Applied Thermal Engineering, 2016Co-Authors: Amirah M Sahar, J G Wissink, Mohamed M Mahmoud, Mehmed Rafet Ozdemir, Ekhlas M Fayyadh, T G KarayiannisAbstract:Abstract Numerical simulations were performed using Fluent 14.5 to investigate single phase flow and conjugate heat transfer in copper rectangular microchannels. Two different configurations were simulated: (1) single channel with Hydraulic Diameter of 0.561 mm and (2) multichannel configuration consisting of inlet and outlet manifolds and 25 channels with Hydraulic Diameter of 0.409 mm. In the single channel configuration, four numerical models were investigated namely, 2D thin-wall, 3D thin-wall (heated from the bottom), 3D thin-wall (three side heated) and 3D full conjugate models. In the multichannel configuration, only 3D full conjugate model was used. The simulation results of the single channel configuration were validated using experimental data of water as a test fluid while the results of the multichannel configuration were validated using experimental data of R134a refrigerant. In the multichannel configuration, flow distribution among the channels was also investigated. The 3D thin-wall model simulation was conducted at thermal boundary conditions similar to those assumed in the experimental data reduction (uniform heat flux) and showed excellent agreement with the experimental data. However, the results of the 3D full conjugate model demonstrated that there is a significant conjugate effect and the heat flux is not uniformly distributed along the channel resulting in significant deviation compared to the experimental data (more than 50%). Also, the results demonstrated that there is a significant difference between the 3D thin-wall and full conjugate models. The simulation of the multichannel configuration with an inlet manifold having gradual decrease in cross sectional area achieved very reasonable uniform flow distribution among the channels which will provide uniform heat transfer rates across the base of the microchannels.
Satyender Singh - One of the best experts on this subject based on the ideXlab platform.
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experimental and numerical investigations of a single and double pass porous serpentine wavy wiremesh packed bed solar air heater
Renewable Energy, 2020Co-Authors: Satyender SinghAbstract:Abstract This research work presents the thermal performance investigation of a porous serpentine wavy wiremesh packed bed solar air heater, experimentally and numerically. Experimental results revealed the best thermal and thermoHydraulic efficiencies for 93% porous double pass serpentine packed bed solar air heater and found to be about 80% and 74%, respectively, which is about 18% and 17% high compared to single pass, respectively. Whereas, numerical investigation is carried out on a CFD tool and the results are validated with experimental data. The range of porosity from 85% to 95%, wavelength from 0.05 m to 0.075 m, amplitude from 0.012 m to 0.016 m, Hydraulic Diameter from 0.025 m to 0.046 m and mass flow rate from 0.01 to 0.05 kg/s is considered to obtain optimum values for geometrical and flow parameters on the basis of THPP and exergy efficiency. The numerical results present the maximum 24.33% better thermoHydraulic performance for serpentine packed bed solar air heater when compared to flat packed bed solar air heater. The wavelength of 0.075 m, amplitude of 0.012 m, Hydraulic Diameter of 0.0835 m, porosity of 90%, and mass flow rate of 0.03 kg/s is obtained as the optimum configuration.
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thermal performance analysis of semicircular and triangular cross sectioned duct solar air heaters under external recycle
Journal of energy storage, 2018Co-Authors: Satyender SinghAbstract:Abstract The present work is focused on the analytical and numerical investigations related to thermal and thermoHydraulic efficiencies of a solar air heater (SAH) with semicircular (Model-I) and triangular (Model-II) cross-sectioned ducts. V-down rib roughness is considered on the bottom side of the absorber plate under the external recycle operation and effect on the thermal performance is analyzed using the analytical investigation. It is observed that the employment of recycle operation substantially improves the thermal performance of these two SAH models as compared to the single-pass operation (without recycle). The external recycle of the air exiting from the SAH outlet increases the heat extraction rate and strengthen the heat transfer coefficient for the air flowing through the roughened SAH duct and further increases the thermal performance. Moreover, SAH models are operated for different Hydraulic Diameters. Whereas, the best results of thermal performance are obtained at the least value of the Hydraulic Diameter. It is predicted from the analytical investigation that the Model-I of the semicircular duct with recycle is 3% and 17% efficient in thermal efficiency as compared to Model-II of the triangular duct with and without recycle, respectively, at a Hydraulic Diameter of 0.06 m. While, the maximum value of the thermal and thermoHydraulic efficiencies obtained for Model-I with recycle operation is found to be 75% and 72%, respectively. Although, the numerical investigation is carried out using Ansys-Fluent software to clearly present the associated air heating and pressure drop reduction abilities of both the solar air heater ducts.
T G Karayiannis - One of the best experts on this subject based on the ideXlab platform.
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effect of Hydraulic Diameter and aspect ratio on single phase flow and heat transfer in a rectangular microchannel
Applied Thermal Engineering, 2017Co-Authors: Amirah M Sahar, J G Wissink, Mohamed M Mahmoud, T G Karayiannis, Mohamad Ashrul S IshakAbstract:Abstract The effect of aspect ratio and Hydraulic Diameter on single phase flow and heat transfer in a single microchannel was investigated numerically and the results are presented in this paper. Previously, many studies in literature investigating the effect of geometrical parameters reached contradictory conclusions leaving some phenomena unexplained. Additionally, most researchers studied the effect of channel geometry by varying the channel height for a constant channel width or varying the width for a constant height. This means that the Hydraulic Diameter and aspect ratio vary simultaneously, which makes it difficult to identify the relative importance of the aspect ratio and the Hydraulic Diameter. In the present study, the effect of Hydraulic Diameter was studied by varying the channel width and depth while keeping the aspect ratio constant. The range of Hydraulic Diameters was 0.1–1 mm and the aspect ratio was fixed at 1. In the second set of simulations, the aspect ratio ranged from 0.39 to 10 while the Hydraulic Diameter was kept constant at 0.56 mm. The simulations were performed using the CFD software package ANSYS Fluent 14.5. The geometry investigated in this study includes symmetrical cylindrical inlet and outlet plenums and a microchannel. The fluid entered and left the channel vertically from the top in a direction normal to the channel axis. The dimensions of the inlet/outlet plenums (Diameter and height measured from the channel bottom surface) were kept constant while the width and depth of the channel were varied. The simulations were conducted for a range of Reynolds numbers (Re = 100–2000) and water was used as the working fluid. A three dimensional thin wall model was used to avoid conjugate heat transfer effects. A constant heat-flux boundary condition was applied at the bottom and vertical side walls of the channel, while the upper wall was considered adiabatic. The friction factor was found to decrease slightly with aspect ratio up to AR ≈ 2 after which it increased with increasing aspect ratio. The results demonstrated that the slope of the velocity profile at the channel wall changes significantly with aspect ratio for AR > 2. The effect of the aspect ratio and Hydraulic Diameter on the dimensionless hydrodynamic entry length is not significant. Also, the aspect ratio does not affect the heat transfer coefficient while the dimensionless Nusselt number increases with increasing Hydraulic Diameter. The friction factor was found to increase with increasing Hydraulic Diameter.
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single phase flow pressure drop and heat transfer in rectangular metallic microchannels
Applied Thermal Engineering, 2016Co-Authors: Amirah M Sahar, J G Wissink, Mohamed M Mahmoud, Mehmed Rafet Ozdemir, Ekhlas M Fayyadh, T G KarayiannisAbstract:Abstract Numerical simulations were performed using Fluent 14.5 to investigate single phase flow and conjugate heat transfer in copper rectangular microchannels. Two different configurations were simulated: (1) single channel with Hydraulic Diameter of 0.561 mm and (2) multichannel configuration consisting of inlet and outlet manifolds and 25 channels with Hydraulic Diameter of 0.409 mm. In the single channel configuration, four numerical models were investigated namely, 2D thin-wall, 3D thin-wall (heated from the bottom), 3D thin-wall (three side heated) and 3D full conjugate models. In the multichannel configuration, only 3D full conjugate model was used. The simulation results of the single channel configuration were validated using experimental data of water as a test fluid while the results of the multichannel configuration were validated using experimental data of R134a refrigerant. In the multichannel configuration, flow distribution among the channels was also investigated. The 3D thin-wall model simulation was conducted at thermal boundary conditions similar to those assumed in the experimental data reduction (uniform heat flux) and showed excellent agreement with the experimental data. However, the results of the 3D full conjugate model demonstrated that there is a significant conjugate effect and the heat flux is not uniformly distributed along the channel resulting in significant deviation compared to the experimental data (more than 50%). Also, the results demonstrated that there is a significant difference between the 3D thin-wall and full conjugate models. The simulation of the multichannel configuration with an inlet manifold having gradual decrease in cross sectional area achieved very reasonable uniform flow distribution among the channels which will provide uniform heat transfer rates across the base of the microchannels.
