The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Ahmad Arabkoohsa - One of the best experts on this subject based on the ideXlab platform.
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a new version of a low concentration evacuated tube solar collector optical and thermal investigation
Solar Energy, 2019Co-Authors: Mavd De Paula Ribeiro Teles, K. A.r. Ismail, Ahmad ArabkoohsaAbstract:Abstract This work is focused on investigating the performance of a new version of evacuated tube solar collector with and without solar tracking system. The evacuated tube solar collector is composed of an absorbing copper tube positioned eccentrically inside a transparent glass cover tube which has a reflective film insert on its inner surface and vacuum in eccentric Annular Space. Modeling of the proposed evacuated tube collector is based on the conservation equations of mass, momentum and energy and discretized by using the finite volumes method. A home-built numerical code is developed, tested and its grid size optimized. This code is validated against available experimental and numerical results. Effects of the tilt angle and tracking systems are also evaluated. The results showed maximum and minimum daily efficiencies of the collector of about 73% and 42%, respectively. The annual efficiency of this collector was evaluated as 61.5% for the city of Sao Luis, Brazil. The new contributions from the present work include the reflective film, the eccentricity of the absorber and the presence of vacuum in the Annular Space. The reflective film helps to keep the absorber at uniform temperature and reduce thermal induced stress. The eccentricity is introduced to create concentration effect which helps to increase the outlet temperature of the working fluid and reduce the mass of the collector system. The presence of vacuum in the eccentric Annular Space reduces effectively the thermal losses, improves the efficiency.
Mavd De Paula Ribeiro Teles - One of the best experts on this subject based on the ideXlab platform.
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a new version of a low concentration evacuated tube solar collector optical and thermal investigation
Solar Energy, 2019Co-Authors: Mavd De Paula Ribeiro Teles, K. A.r. Ismail, Ahmad ArabkoohsaAbstract:Abstract This work is focused on investigating the performance of a new version of evacuated tube solar collector with and without solar tracking system. The evacuated tube solar collector is composed of an absorbing copper tube positioned eccentrically inside a transparent glass cover tube which has a reflective film insert on its inner surface and vacuum in eccentric Annular Space. Modeling of the proposed evacuated tube collector is based on the conservation equations of mass, momentum and energy and discretized by using the finite volumes method. A home-built numerical code is developed, tested and its grid size optimized. This code is validated against available experimental and numerical results. Effects of the tilt angle and tracking systems are also evaluated. The results showed maximum and minimum daily efficiencies of the collector of about 73% and 42%, respectively. The annual efficiency of this collector was evaluated as 61.5% for the city of Sao Luis, Brazil. The new contributions from the present work include the reflective film, the eccentricity of the absorber and the presence of vacuum in the Annular Space. The reflective film helps to keep the absorber at uniform temperature and reduce thermal induced stress. The eccentricity is introduced to create concentration effect which helps to increase the outlet temperature of the working fluid and reduce the mass of the collector system. The presence of vacuum in the eccentric Annular Space reduces effectively the thermal losses, improves the efficiency.
Jian Zhang - One of the best experts on this subject based on the ideXlab platform.
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studies on strongly swirling flows in the full Space of a volute cyclone separator
Aiche Journal, 2005Co-Authors: Liyuan Hu, Lixing Zhou, Jian ZhangAbstract:The three-dimensional (3-D) strongly swirling turbulent flows in the full Space of a volute cyclone separator was measured using laser Doppler velocimetry (LDV), and was simulated using an improved Reynolds stress equation model by modifying the empirical constants in the isotropization of production and convection model (IPCM) + wall pressure–strain term of the Reynolds stress equation, incorporated into the platform of FLUENT 6.0. Predicted Reynolds stress model (RSM) velocities are more reasonable than those obtained previously. The specific features of turbulent flows in the separation Space, dust hopper, Annular Space, and the outlet tube are different. The results show that the time-averaged tangential velocity profiles in the separation Space have a typical Rankine-vortex structure. In some regions, such as the entrance, the vicinity of the top of the Annular Space, the inner vortex-flow region, the vicinity of the discharge port, the vicinity of the wall, the intersection part between the upward and downward flows, the turbulent intensity is very large and changes sharply; the turbulence is anisotropic in most regions, but the magnitudes of three RSM velocity components are of the same order of magnitude. The distribution of time-averaged tangential velocity is asymmetric in the Annular Space. The longitudinal secondary vortexes exist near the top of the dust hopper and the top of the cyclone. The distribution of time-averaged axial velocity in the exit tube is entirely different from that in the separation Space. © 2005 American Institute of Chemical Engineers AIChE J, 51: 740–749, 2005
K. A.r. Ismail - One of the best experts on this subject based on the ideXlab platform.
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a new version of a low concentration evacuated tube solar collector optical and thermal investigation
Solar Energy, 2019Co-Authors: Mavd De Paula Ribeiro Teles, K. A.r. Ismail, Ahmad ArabkoohsaAbstract:Abstract This work is focused on investigating the performance of a new version of evacuated tube solar collector with and without solar tracking system. The evacuated tube solar collector is composed of an absorbing copper tube positioned eccentrically inside a transparent glass cover tube which has a reflective film insert on its inner surface and vacuum in eccentric Annular Space. Modeling of the proposed evacuated tube collector is based on the conservation equations of mass, momentum and energy and discretized by using the finite volumes method. A home-built numerical code is developed, tested and its grid size optimized. This code is validated against available experimental and numerical results. Effects of the tilt angle and tracking systems are also evaluated. The results showed maximum and minimum daily efficiencies of the collector of about 73% and 42%, respectively. The annual efficiency of this collector was evaluated as 61.5% for the city of Sao Luis, Brazil. The new contributions from the present work include the reflective film, the eccentricity of the absorber and the presence of vacuum in the Annular Space. The reflective film helps to keep the absorber at uniform temperature and reduce thermal induced stress. The eccentricity is introduced to create concentration effect which helps to increase the outlet temperature of the working fluid and reduce the mass of the collector system. The presence of vacuum in the eccentric Annular Space reduces effectively the thermal losses, improves the efficiency.
Luis Fernando Alzuguir Azevedo - One of the best experts on this subject based on the ideXlab platform.
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Taylor-Couette Instabilities in Flows of Newtonian and Power-Law Liquids in the Presence of Partial Annulus Obstruction
Journal of Fluids Engineering-transactions of The Asme, 2005Co-Authors: Bruno Venturini Loureiro, P. R. De Souza Mendes, Luis Fernando Alzuguir AzevedoAbstract:The flow inside a horizontal annulus due to the inner cylinder rotation is studied. The bottom of the Annular Space is partially blocked by a plate parallel to the axis of rotation, thereby destroying the circumferential symmetry of the Annular Space geometry. This flow configuration is encountered in the drilling process of horizontal petroleum wells, where a bed of cuttings is deposited at the bottom part of the annulus. The velocity field for this flow was obtained both numerically and experimentally. In the numerical work, the equations which govern the three-dimensional, laminar flow of both Newtonian and power-law liquids were solved via a finite-volume technique. In the experimental research, the instantaneous and time-averaged flow fields over two-dimensional meridional sections of the Annular Space were measured employing the particle image velocimetry (PIV) technique, also both for Newtonian and power-law liquids. Attention was focused on the determination of the onset of secondary flow in the form of distorted Taylor vortices
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Characterization of Fluid Flow and Taylor Vortex Onset in Partially-Obstructed Annular Space With Inner Cylinder Rotation
Volume!, 2004Co-Authors: Bruno Venturini Loureiro, P. R. Souza Mendes, Luis Fernando Alzuguir AzevedoAbstract:The present work studies the characteristics of the flow field inside an Annular Space formed by two concentric cylinders with rotation of the inner cylinder. The Annular Space was partially blocked by a plate parallel to the axis of rotation, thereby destroying the circumferential symmetry of the Annular Space geometry. This flow configuration encounters application on the modeling of drilling of horizontal petroleum wells where a bed of cuttings is formed at the bottom part of the annulus. This bed was modeled in the present work by a flat plate inserted into the Annular Space. The velocity field was investigated both numerically and experimentally. The equations governing the three-dimensional, laminar flow of a Newtonian fluid were solved via a finite-volume technique. The instantaneous and time-averaged flow fields over two-dimensional meridional sections of the Annular Space were measured employing the particle image velocimetry technique (PIV). Attention was focused on the determination of the onset of secondary flow in the form of distorted Taylor vortices. The results demonstrated that the critical rotational Reynolds number is directly influenced by the degree of obstruction of the flow given by the cylinder-to-plate gap. The smaller the gap, the larger the critical Taylor number. The gap dimensions control the width of the vortices. The calculated steady state axial flow profiles results agreed well with measurements. Transitions values of the rotational Reynolds numbers were also well predicted by the computations. Differences were found between measured and predicted values for the length of the Taylor vortices. Transverse flow maps revealed a complex interaction between Taylor vortices and zones of recirculating flow, for moderate to high degrees of flow obstruction.Copyright © 2004 by ASME
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TAYLOR-COUETTE INSTABILITIES IN PARTIALLY-OBSTRUCTED Annular SpaceS WITH INNER CYLINDER ROTATION
Fluids Engineering, 2004Co-Authors: Bruno Venturini Loureiro, Paulo R. De Souza Mendes, Luis Fernando Alzuguir AzevedoAbstract:The flow inside a horizontal annulus due to the inner cylinder rotation is studied. The bottom of the Annular Space is partially blocked by a plate parallel to the axis of rotation, thereby destroying the circumferential symmetry of the Annular Space geometry. This flow configuration the drilling process of horizontal petroleum wells, where a bed of cuttings is deposited at the bottom part of the annulus. The velocity field for this flow was obtained both numerically and experimentally. In the numerical work, the equations which govern the three-dimensional, laminar flow of both Newtonian and power-law liquids were solved via a finite-volume technique. In the experimental research, the instantaneous and time-averaged flow fields over two-dimensional meridional sections of the Annular Space were measured employing the particle image velocimetry (PIV) technique. Attention was focused on the determination of the onset of secondary flow in the form of distorted Taylor vortices. The results showed that the critical rotational Reynolds number is directly influenced by the degree of obstruction of the flow. The influence of the obstruction is more perceptible in Newtonian than non-Newtonian fluids. The larger is the obstruction, the larger is the critical Taylor number. The height of the obstruction also controls the width of the vortices. The calculated steady state axial velocity profiles agreed well with the corresponding measurements. Transition values of the rotational Reynolds number are also well predicted by the computations. However, the measured and predicted values for the vortex size do not agree as well. Transverse flow maps revealed a complex interaction between the Taylor vortices and the zones of recirculating flow, for moderate to high degrees of flow obstruction.Copyright © 2004 by ASME
