The Experts below are selected from a list of 12459 Experts worldwide ranked by ideXlab platform
J. S. Saini - One of the best experts on this subject based on the ideXlab platform.
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performance of artificially roughened solar air heaters a review
Renewable & Sustainable Energy Reviews, 2009Co-Authors: Vishavjeet Singh Hans, J. S. SainiAbstract:The conversion, utilization and recovery of energy invariably involve a heat exchange process, which makes it imperative to design more efficient heat exchanger. The use of artificial Roughness in different forms, shapes and sizes is the most common and effective way to improve the performance of a solar air heater. Several studies have been carried out to determine the effect of different Roughness Element geometries on heat transfer and friction in solar air heaters. This study reviews various Roughness Element geometries employed in solar air heaters for performance enhancement. Based on the correlations of heat transfer and friction factor developed by various investigators, an attempt has been made to compare the thermohydraulic performance of roughened solar air heaters.
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heat transfer and friction factor correlations for artificially roughened ducts with expanded metal mesh as Roughness Element
International Journal of Heat and Mass Transfer, 1997Co-Authors: R P Saini, J. S. SainiAbstract:Abstract An experimental investigation has been carried out for fully developed turbulent flow in a rectangular duct with large aspect ratio (11: 1) and having expanded metal mesh as artificial Roughness. The effect of expanded metal mesh geometry [i.e relative longway length of mesh (L/e), relative shortway length of mesh (S/e) and relative height of mesh (e/D)] on the heat transfer coefficient and friction factor has been investigated. The range of the system and operating parameters included L/e from 25 to 71.87, S/e from 15.62 to 46.87 and e/D from 0.012 to 0.039 for Reynolds numbers from 1900 to 13 000. Correlations for the Nusselt number and friction factor in terms of these parameters have been developed that can correlate the experimental data reasonably well.
R P Saini - One of the best experts on this subject based on the ideXlab platform.
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development of correlations for nusselt number and friction factor for solar air heater with roughened duct having arc shaped wire as artificial Roughness
Solar Energy, 2008Co-Authors: S K Saini, R P SainiAbstract:An experimental study has been carried out for enhancement of heat transfer coefficient of a solar air heater having roughened air duct provided with artificial Roughness in the form of arc-shape parallel wire as Roughness Element. Increment in friction factor by provided with such artificial Roughness Elements has also been studied. The effect of system parameters such as relative Roughness height (e/d) and arc angle (α/90) have been studied on Nusselt number (Nu) and friction factor (f) with Reynolds number (Re) varied from 2000 to 17000. Considerable enhancement in heat transfer coefficient has been achieved with such Roughness Element. Using experimental data correlations for Nusselt number and friction factor have also been developed for such solar air heaters, which gives a good agreement between predicted values and experimental values of Nusselt number and friction factor.
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heat transfer and friction factor correlations for artificially roughened ducts with expanded metal mesh as Roughness Element
International Journal of Heat and Mass Transfer, 1997Co-Authors: R P Saini, J. S. SainiAbstract:Abstract An experimental investigation has been carried out for fully developed turbulent flow in a rectangular duct with large aspect ratio (11: 1) and having expanded metal mesh as artificial Roughness. The effect of expanded metal mesh geometry [i.e relative longway length of mesh (L/e), relative shortway length of mesh (S/e) and relative height of mesh (e/D)] on the heat transfer coefficient and friction factor has been investigated. The range of the system and operating parameters included L/e from 25 to 71.87, S/e from 15.62 to 46.87 and e/D from 0.012 to 0.039 for Reynolds numbers from 1900 to 13 000. Correlations for the Nusselt number and friction factor in terms of these parameters have been developed that can correlate the experimental data reasonably well.
Krishnan Mahesh - One of the best experts on this subject based on the ideXlab platform.
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comparing experiment and computation of hypersonic laminar boundary layers with isolated Roughness
AIAA Aerospace Sciences Meeting (ASM), 2014Co-Authors: Brett F Bathel, Prahladh S Iyer, Krishnan Mahesh, Paul M Danehy, Jennifer A Inman, Stephen B Jones, Craig T JohansenAbstract:Streamwise velocity profile behavior in a hypersonic laminar boundary layer in the presence of an isolated Roughness Element is presented for an edge Mach number of 8.2. Two different Roughness Element types are considered: a 2-mm tall, 4-mm diameter cylinder, and a 2-mm radius hemisphere. Measurements of the streamwise velocity behavior using nitric oxide (NO) planar laser-induced fluorescence (PLIF) molecular tagging velocimetry (MTV) have been performed on a 20-degree wedge model. The top surface of this model acts as a flat-plate and is oriented at 5 degrees with respect to the freestream flow. Computations using direct numerical simulation (DNS) of these flows have been performed and are compared to the measured velocity profiles. Particular attention is given to the characteristics of velocity profiles immediately upstream and downstream of the Roughness Elements. In these regions, the streamwise flow can experience strong deceleration or acceleration. An analysis in which experimentally measured MTV profile displacements are compared with DNS particle displacements is performed to determine if the assumption of constant velocity over the duration of the MTV measurement is valid. This assumption is typically made when reporting MTV-measured velocity profiles, and may result in significant errors when comparing MTV measurements to computations in regions with strong deceleration or acceleration. The DNS computations with the cylindrical Roughness Element presented in this paper were performed with and without air injection from a rectangular slot upstream of the cylinder. This was done to determine the extent to which gas seeding in the MTV measurements perturbs the boundary layer flowfield.
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high speed boundary layer transition induced by a discrete Roughness Element
Journal of Fluid Mechanics, 2013Co-Authors: Prahladh S Iyer, Krishnan MaheshAbstract:Direct numerical simulation (DNS) is used to study laminar to turbulent transition induced by a discrete hemispherical Roughness Element in a high-speed laminar boundary layer. The simulations are performed under conditions matching the experiments of Danehy et al. ( AIAA Paper 2009–394, 2009) for free-stream Mach numbers of 3.37, 5.26 and 8.23. It is observed that the Mach 8.23 flow remains laminar downstream of the Roughness, while the lower Mach numbers undergo transition. The Mach 3.37 flow undergoes transition closer to the bump when compared with Mach 5.26, in agreement with experimental observations. Transition is accompanied by an increase in ${C}_{f} $ and ${C}_{h} $ (Stanton number). Even for the case that did not undergo transition (Mach 8.23), streamwise vortices induced by the Roughness cause a significant rise in ${C}_{f} $ until 20 $D$ downstream. The mean van Driest transformed velocity and Reynolds stress for Mach 3.37 and 5.26 show good agreement with available data. Temporal spectra of pressure for Mach 3.37 show that frequencies in the range of 10–1000 kHz are dominant. The transition process involves the following key Elements: upon interaction with the Roughness Element, the boundary layer separates to form a series of spanwise vortices upstream of the Roughness and a separation shear layer. The system of spanwise vortices wrap around the Roughness Element in the form of horseshoe/necklace vortices to yield a system of counter-rotating streamwise vortices downstream of the Element. These vortices are located beneath the separation shear layer and perturb it, which results in the formation of trains of hairpin-shaped vortices further downstream of the Roughness for the cases that undergo transition. These hairpins spread in the span with increasing downstream distance and the flow increasingly resembles a fully developed turbulent boundary layer. A local Reynolds number based on the wall properties is seen to correlate with the onset of transition for the cases considered.
Vishavjeet Singh Hans - One of the best experts on this subject based on the ideXlab platform.
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performance of artificially roughened solar air heaters a review
Renewable & Sustainable Energy Reviews, 2009Co-Authors: Vishavjeet Singh Hans, J. S. SainiAbstract:The conversion, utilization and recovery of energy invariably involve a heat exchange process, which makes it imperative to design more efficient heat exchanger. The use of artificial Roughness in different forms, shapes and sizes is the most common and effective way to improve the performance of a solar air heater. Several studies have been carried out to determine the effect of different Roughness Element geometries on heat transfer and friction in solar air heaters. This study reviews various Roughness Element geometries employed in solar air heaters for performance enhancement. Based on the correlations of heat transfer and friction factor developed by various investigators, an attempt has been made to compare the thermohydraulic performance of roughened solar air heaters.
Sunil Chamoli - One of the best experts on this subject based on the ideXlab platform.
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experimental and cfd investigation of convection heat transfer in solar air heater with reverse l shaped ribs
Solar Energy, 2016Co-Authors: Vipin B Gawande, D B Zodpe, A S Dhoble, Sunil ChamoliAbstract:Abstract A solar air heater is a thermal system which uses artificial Roughness in the form of repeated ribs on the absorber plate to enhance the heat transfer rate. Forced convection heat transfer of air in a solar air heater with reverse L-shaped ribs has been carried out experimentally and numerically. Thermal performance of solar air heater is studied with design variables such as relative Roughness pitch (7.14 ⩽ P / e ⩽ 17.86), Reynolds number (3800 ⩽ Re ⩽ 18,000), heat flux (1000 W/m 2 ) and constant relative Roughness height ( e / D = 0.042). A two dimensional CFD simulation is carried out with using CFD code, ANSYS FLUENT and RNG k – ɛ turbulence model, for solving turbulence terms in governing equations. The presence of reverse L-shaped rib shows a significant effect on heat transfer and friction factor characteristics, relative to change in relative Roughness pitch ( P / e ) and Reynolds number ( Re ). Thermo hydraulic performance parameter (T.H.P.P) of 1.90 considering heat transfer augmentation with same pumping power, has been evaluated for optimum configuration of the Roughness Element (reverse L-shaped rib) for artificially roughened solar air heater. It has been found that the numerical results are in good agreement with the experimental results for the range of parameters investigated. Correlations for Nusselt number and friction factor have been developed as a function of Roughness and flow parameters.
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experimental and cfd based thermal performance prediction of solar air heater provided with chamfered square rib as artificial Roughness
Journal of The Brazilian Society of Mechanical Sciences and Engineering, 2016Co-Authors: Vipin B Gawande, D B Zodpe, A S Dhoble, Sunil ChamoliAbstract:An experimental and two-dimensional computational fluid dynamics (CFD) analysis of a solar air heater has been carried out using chamfered square rib as artificial Roughness on the absorber plate. The relative Roughness pitch (P/e = 7.14–17.86), chamfer angle (α = 0°–40°), Reynolds number (Re = 3800–18,000) and relative Roughness height (e/D = 0.042) are chosen as design variables for analysis. A uniform heat flux of 1000 W/m2 is maintained on the surface of absorber plate. CFD code, ANSYS FLUENT 14.5 with renormalization group k-e model was chosen. An enhancement in Nusselt number and friction factor with decrease in relative Roughness pitch (P/e) is presented and discussed with reference to experimental and CFD analysis. The effect of chamfer angle and Reynolds number on enhancement of Nusselt number and friction factor is also presented. Optimum configuration of Roughness Element for artificially roughened solar air heater has been determined in terms of thermo-hydraulic performance parameter. The chamfer angle of 20° on square rib and relative Roughness pitch of 7.14 provide best thermo-hydraulic performance of 2.047 considering the maximum heat transfer and minimum pressure drop.
