The Experts below are selected from a list of 3684 Experts worldwide ranked by ideXlab platform
Najib Laraqi - One of the best experts on this subject based on the ideXlab platform.
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Analytical computation of transient heat transfer and macro-Constriction Resistance applied to thermal spraying processes
Comptes Rendus Mécanique, 2012Co-Authors: Najib Laraqi, M. El GanaouiAbstract:Abstract An analytical solution of the thermal macro-Constriction Resistance is derived by using the Hankel finite transform and the Duhamel theorem leading to a simple expression of the solution as a serial expansion with fast convergence. The application concerns the thermal macro-Constriction Resistance estimate during the spreading and coated formation involved in thermal spraying process. In such a process, the heat flux reaches a few hundreds of W / mm 2 while the spreading duration is extremely short (about μs). The phenomena of thermal macro-Constriction deposit/substrate interface play are of primary importance because they control the coating cooling and the thermo-mechanical behavior of the deposited layer, as well. The effect of the spreading velocity on the thermal macro-Constriction Resistance has been studied. Results show the existence of a critical threshold of spreading velocity for which the transient problem has to be considered. On the other side (below the threshold) the study state regime should be sufficient for the macro-Constriction estimate.
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temperature and thermal Resistance in frictional devices
Applied Thermal Engineering, 2004Co-Authors: Najib Laraqi, A Bairi, L SeguiAbstract:Exact analytical solutions are developed to calculate the three-dimensional temperature distribution and the thermal Constriction Resistance due to moving heat sources on semi-infinite bodies. Three configurations are studied: (a) rectangular source on a rectangular prism, (b) elliptic source on a rectangular prism and (c) eccentric circular source on a rotating cylinder. By varying the values of geometric parameters in the provided solutions, we get the solution for various particular cases (e.g., unique or multiple: strip, rectangular, square, elliptic and circular moving heat sources). The proposed analytical models also allow to calculate the flash and average temperatures regardless the Peclet number value. Some comparisons with available models are presented. For each configuration, we provide some results given the thermal Constriction Resistance (or the average contact temperature) as a function of geometric parameters and velocity.
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The Thermal Constriction Resistance for an Eccentric Spot on a Circular Heat Flux Tube
Journal of Heat Transfer, 2004Co-Authors: A. Baïri, Najib LaraqiAbstract:An analytical solution is proposed to calculate the thermal Constriction Resistance for an eccentric circular spot with uniform flux on a semi-infinite circular heat flux tube. This solution is developed using the finite coterie Fourier transform and the finite Hankel transform. It allows to calculate the stationary three-dimensional temperature distribution and the thermal Constriction Resistance
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thermal Resistance for random contacts on the surface of a semi infinite heat flux tube
Journal of Heat Transfer-transactions of The Asme, 2003Co-Authors: Najib LaraqiAbstract:Analytical solution is developed to calculate the thermal Constriction Resistance for contacts randomly distributed on the surface of a laterally insulated semi-infinite square prism. The contacts are modeled by circular spots with different radii and uniform heat flux. We analyze the evolution of the thermal Constriction Resistance as a function of the number of contacts, the relative contact size, and the dispersion of radii of spots
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Theory of thermal Resistance between solids with randomly sized and located contacts
International Journal of Heat and Mass Transfer, 2002Co-Authors: Najib Laraqi, Abderrahmane BaïriAbstract:Abstract Linear superposition method is used to determine an analytical solution of the thermal Constriction Resistance adapted to random contacts. The contact area is constituted of numerous disks which have different radii and are randomly distributed over a square or circular area. The developed solution is easy to use and allows to consider numerous contacts at a reasonable computing time. The disks can be distributed in entire contact surface or located in a specific region. The results are in an excellent agreement with available data in the literature for identical and regular contacts. The model is used to study the thermal Constriction Resistance evolution as a function of contact disorders, number and sizes of disks and relative contact size area. The results are compared to the model of regular contacts.
Hossein Shokouhmand - One of the best experts on this subject based on the ideXlab platform.
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assessment of temperature dependent conductivity effects on the thermal spreading Constriction Resistance of semiconductors
Journal of Thermophysics and Heat Transfer, 2012Co-Authors: Yousef Rahmani, Hossein ShokouhmandAbstract:Thermal spreading Resistance takes placewhenever heat flow leaves a source of finite area and enters awider area. The present study aims to obtain the thermal spreading/Constriction Resistance models of some semiconductor materials with temperature-dependent thermal conductivity. A steady-state nonlinear heat conduction equation of the problem is transformed into the Laplace equation via the Kirchhoff transformation. The concepts of individual isotropic half-space and heat-flux tube are used in this study. The spreading Resistances of the semiconductor materials in arbitrary temperature andheat-flux ranges are compared to each other. Results indicate that spreading/ Constriction Resistance is affected by the temperature-dependent conductivity of semiconductor materials. The conductivity dependence of spreading/Constriction Resistance becomesmore significant as the difference between the temperatures of contact surface and convenient thermal sink becomes more evident.
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a numerical study of thermal spreading Constriction Resistance of silicon
Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2012Co-Authors: Yousef Rahmani, Hossein ShokouhmandAbstract:Thermal spreading or Constriction Resistances exist whenever heat flows from one region to another in different cross sectional areas. In this study, the ideas of Isotropic half-space and Heat flux tube are numerically modeled in order to estimate the thermal spreading/Constriction Resistance. Furthermore, the thermal spreading Resistances of the Silicon in arbitrary temperature and heat flux ranges are calculated for assessing the temperature-dependent thermal conductivity effects. Finally, different sizes of contact area in the Heat flux tube pattern are used to obtain the effect of contact size on the thermal spreading/Constriction Resistance. Results clearly indicate that the thermal spreading/Constriction Resistance is affected by the temperature-dependent conductivity of solids, shape of contact surface, size of contact and boundary conditions.
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A numerical study of thermal spreading/Constriction Resistance of silicon
13th InterSociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2012Co-Authors: Yousef Rahmani, Hossein ShokouhmandAbstract:Thermal spreading or Constriction Resistances exist whenever heat flows from one region to another in different cross sectional areas. In this study, the ideas of Isotropic half-space and Heat flux tube are numerically modeled in order to estimate the thermal spreading/Constriction Resistance. Furthermore, the thermal spreading Resistances of the Silicon in arbitrary temperature and heat flux ranges are calculated for assessing the temperature-dependent thermal conductivity effects. Finally, different sizes of contact area in the Heat flux tube pattern are used to obtain the effect of contact size on the thermal spreading/Constriction Resistance. Results clearly indicate that the thermal spreading/Constriction Resistance is affected by the temperature-dependent conductivity of solids, shape of contact surface, size of contact and boundary conditions.
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Assessment of Temperature-Dependent Conductivity Effects on the Thermal Spreading/Constriction Resistance of Semiconductors
Journal of Thermophysics and Heat Transfer, 2012Co-Authors: Yousef Rahmani, Hossein ShokouhmandAbstract:Thermal spreading Resistance takes placewhenever heat flow leaves a source of finite area and enters awider area. The present study aims to obtain the thermal spreading/Constriction Resistance models of some semiconductor materials with temperature-dependent thermal conductivity. A steady-state nonlinear heat conduction equation of the problem is transformed into the Laplace equation via the Kirchhoff transformation. The concepts of individual isotropic half-space and heat-flux tube are used in this study. The spreading Resistances of the semiconductor materials in arbitrary temperature andheat-flux ranges are compared to each other. Results indicate that spreading/ Constriction Resistance is affected by the temperature-dependent conductivity of semiconductor materials. The conductivity dependence of spreading/Constriction Resistance becomesmore significant as the difference between the temperatures of contact surface and convenient thermal sink becomes more evident.
S.s. Kulkarni - One of the best experts on this subject based on the ideXlab platform.
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Analysis of transport through thin film composite membranes using an improved Wheatstone bridge Resistance model
Journal of Membrane Science, 1997Co-Authors: S.k. Karode, S.s. KulkarniAbstract:Abstract The two-dimensional Wheatstone bridge Resistance analog model for permeation through thin film composite (TFC) membranes proposed by Karode et al. [5] has been extended to also include the cases where the coating layer thickness is of similar magnitude as the pore radius in the support matrix. The effect of the Constriction Resistance, i.e. the Resistance encountered by the permeating species in traveling in a radial direction to find a pore to diffuse through is highlighted by considering three generic types of TFC membranes: (i) TFC membranes where the support has very low surface porosity; (ii) TFC membranes with moderate support layer surface porosity; and (iii) TFC membranes incorporating an intermediate gutter layer between the top coating and the bottom support. The model predictions are compared with experimental data reported in literature and various effects are highlighted by considering a few hypothetical cases. The calculations indicate that PRISM type membranes do not require pore filling in order to achieve a composite selectivity close to that of the support material as the high Constriction Resistance due to low surface porosity effectively prevents transport along the less permselective pathway. In case of less permeable but highly selective top layers, the Constriction Resistance can be significantly decreased by the gutter layer concept resulting in higher permeabilities and selectivities controlled by the coating layer. In general, the Constriction Resistance becomes dominant when the permeability of the top layer is low or when the support surface porosity is low.
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An improved model incorporating Constriction Resistance in transport through thin film composite membranes
Journal of Membrane Science, 1996Co-Authors: S.k. Karode, V.s. Patwardhan, S.s. KulkarniAbstract:Abstract An improved Wheatstone bridge Resistance model for diffusion through a thin film composite (TFC) membrane has been proposed. The Constriction Resistance encountered by the diffusing species in seeking out a pore in the support membrane to diffuse through is quantified. This Resistance model has been validated for a range of parameters against a rigorous two dimensional numerical analysis of the diffusion process through a TFC membrane. An analytical solution has also been developed for the case when the support membrane matrix can be considered to be impermeable. It is shown that when the support membrane surface porosity is greater than 10−3 but less than 0.6, the accurate prediction of flux through a TFC membrane requires a two dimensional analysis. It is shown that the improved Wheatstone bridge model with Constriction Resistance is accurate through the entire range of parameters.
S. H.-k. Lee - One of the best experts on this subject based on the ideXlab platform.
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Transient effect on the Constriction Resistance between spheres
Computational Mechanics, 2000Co-Authors: W.w.m. Siu, S. H.-k. LeeAbstract:Systems of contacting spheres are common in engineering applications where the heat transfer analysis can be quite cumbersome due to the transient behavior and the complex geometrical arrangement. As a result, most of the previous works, in this area, have adopted the porous media approach. However, this approach requires the length scale of the representative cell to be roughly three orders of magnitude larger than the size of the spheres. Constriction Resistance relations could be useful in accurately computing the temperature distribution within systems of contacting spheres, however many of the requisite relations are not available. Thus, the objective of this study is to develop these relations. In this study, the transient, three-dimensional conduction equation was solved using a finite volume scheme and a non-uniform grid. From the resulting temperature distributions, the steady-state and transient Constriction Resistance of one-sphere and two-sphere systems were computed and correlated. The results also showed, for the first time, the critical parameters below which the transient variations must be considered.
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Effective conductivity computation of a packed bed using Constriction Resistance and contact angle effects
International Journal of Heat and Mass Transfer, 2000Co-Authors: W.w.m. Siu, S. H.-k. LeeAbstract:Abstract Effective conductivity computation is a major component in the study of conduction within a porous medium, consisting of packed spheres. For packings with porosity lower than 0.47, previous studies typically model the packed bed as an arrangement of cylinders with connecting webs. Not only does such system deviate from the actual structure, but its usage also requires empirically determined parameters. An alternative method is herein presented, and is valid for packed beds of porosity below 0.5, and where the conductivity of the sphere is much larger than that of the surrounding matrix. The present method approximates the packed bed as packed sphere systems consisting of different unit cells, and then using the presently computed relations to obtain the effective thermal conductivity. The relations were derived from Constriction Resistance relations, accounting for the angles formed between the contacting spheres. The results show for the first time, the necessity of properly accounting for these contact angles. Accounting for the contact angle, the effective thermal conductivity was computed for seven packed beds with porosities ranging from 0.18 to 0.47. The results were in excellent agreement with previous experimental and numerical work.
Yousef Rahmani - One of the best experts on this subject based on the ideXlab platform.
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assessment of temperature dependent conductivity effects on the thermal spreading Constriction Resistance of semiconductors
Journal of Thermophysics and Heat Transfer, 2012Co-Authors: Yousef Rahmani, Hossein ShokouhmandAbstract:Thermal spreading Resistance takes placewhenever heat flow leaves a source of finite area and enters awider area. The present study aims to obtain the thermal spreading/Constriction Resistance models of some semiconductor materials with temperature-dependent thermal conductivity. A steady-state nonlinear heat conduction equation of the problem is transformed into the Laplace equation via the Kirchhoff transformation. The concepts of individual isotropic half-space and heat-flux tube are used in this study. The spreading Resistances of the semiconductor materials in arbitrary temperature andheat-flux ranges are compared to each other. Results indicate that spreading/ Constriction Resistance is affected by the temperature-dependent conductivity of semiconductor materials. The conductivity dependence of spreading/Constriction Resistance becomesmore significant as the difference between the temperatures of contact surface and convenient thermal sink becomes more evident.
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a numerical study of thermal spreading Constriction Resistance of silicon
Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2012Co-Authors: Yousef Rahmani, Hossein ShokouhmandAbstract:Thermal spreading or Constriction Resistances exist whenever heat flows from one region to another in different cross sectional areas. In this study, the ideas of Isotropic half-space and Heat flux tube are numerically modeled in order to estimate the thermal spreading/Constriction Resistance. Furthermore, the thermal spreading Resistances of the Silicon in arbitrary temperature and heat flux ranges are calculated for assessing the temperature-dependent thermal conductivity effects. Finally, different sizes of contact area in the Heat flux tube pattern are used to obtain the effect of contact size on the thermal spreading/Constriction Resistance. Results clearly indicate that the thermal spreading/Constriction Resistance is affected by the temperature-dependent conductivity of solids, shape of contact surface, size of contact and boundary conditions.
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A numerical study of thermal spreading/Constriction Resistance of silicon
13th InterSociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2012Co-Authors: Yousef Rahmani, Hossein ShokouhmandAbstract:Thermal spreading or Constriction Resistances exist whenever heat flows from one region to another in different cross sectional areas. In this study, the ideas of Isotropic half-space and Heat flux tube are numerically modeled in order to estimate the thermal spreading/Constriction Resistance. Furthermore, the thermal spreading Resistances of the Silicon in arbitrary temperature and heat flux ranges are calculated for assessing the temperature-dependent thermal conductivity effects. Finally, different sizes of contact area in the Heat flux tube pattern are used to obtain the effect of contact size on the thermal spreading/Constriction Resistance. Results clearly indicate that the thermal spreading/Constriction Resistance is affected by the temperature-dependent conductivity of solids, shape of contact surface, size of contact and boundary conditions.
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Assessment of Temperature-Dependent Conductivity Effects on the Thermal Spreading/Constriction Resistance of Semiconductors
Journal of Thermophysics and Heat Transfer, 2012Co-Authors: Yousef Rahmani, Hossein ShokouhmandAbstract:Thermal spreading Resistance takes placewhenever heat flow leaves a source of finite area and enters awider area. The present study aims to obtain the thermal spreading/Constriction Resistance models of some semiconductor materials with temperature-dependent thermal conductivity. A steady-state nonlinear heat conduction equation of the problem is transformed into the Laplace equation via the Kirchhoff transformation. The concepts of individual isotropic half-space and heat-flux tube are used in this study. The spreading Resistances of the semiconductor materials in arbitrary temperature andheat-flux ranges are compared to each other. Results indicate that spreading/ Constriction Resistance is affected by the temperature-dependent conductivity of semiconductor materials. The conductivity dependence of spreading/Constriction Resistance becomesmore significant as the difference between the temperatures of contact surface and convenient thermal sink becomes more evident.