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Sadik Kakac - One of the best experts on this subject based on the ideXlab platform.
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slip flow heat transfer in microtubes with axial conduction and viscous dissipation an extended graetz problem
International Journal of Thermal Sciences, 2009Co-Authors: Barbaros Çetin, Almila G. Yazicioglu, Sadik KakacAbstract:This study is an extension of the Graetz problem to include the Rarefaction Effect, viscous dissipation term and axial conduction with constant-wall-heat-flux thermal boundary condition. The energy equation is solved analytically by using general eigenfunction expansion. The temperature distribution and the local Nusselt number are determined in terms of confluent hypergeometric functions. The Effects of the Rarefaction, axial conduction and viscous dissipation on the local Nusselt number are discussed in terms of dimensionless parameters such as the Knudsen number, Peclet number and Brinkman number.
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Fluid flow in microtubes with axial conduction including Rarefaction and viscous dissipation
International Communications in Heat and Mass Transfer, 2008Co-Authors: Barbaros Çetin, Almila G. Yazicioglu, Sadik KakacAbstract:Abstract Graetz problem inside the microtube is revisited considering Rarefaction Effect, viscous dissipation term and axial conduction in the fluid for uniform wall temperature boundary condition in the slip flow regime. The flow is assumed to be hydrodynamically fully developed, thermally developing, and the velocity profile is solved analytically. The temperature field is determined by the numerical solution of the energy equation. The Rarefaction Effect is imposed to the problem via velocity-slip and temperature jump boundary conditions. The local and fully developed Nu numbers are obtained in terms of dimensionless parameters; Pe , Kn , Br , κ . Fully developed Nu numbers and the thermal entrance length are found to increase by the presence of the finite axial conduction.
Almila G. Yazicioglu - One of the best experts on this subject based on the ideXlab platform.
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Effect of Surface Roughness in Parallel-Plate Microchannels on Heat Transfer
Numerical Heat Transfer Part A: Applications, 2009Co-Authors: Metin Bilgehan Turgay, Almila G. YaziciogluAbstract:In this study, the Effect of surface roughness on convective heat transfer in two-dimensional parallel plate microchannels is analyzed numerically for steady-state, single-phase, developing, and laminar air flow in the slip flow regime. Slip velocity and temperature jump at wall boundaries are imposed to observe the Rarefaction Effect. The Effect of triangular roughness elements on Nusselt number are compared to cases with smooth surfaces. The results indicate that increasing surface roughness reduces heat transfer in continuum. However, in slip flow regime, an increase in the Nusselt number with increasing roughness height is observed; this increase being more pronounced at low rarefied flows. It is also found that the presence of axial conduction and viscous dissipation have increasing Effects on heat transfer in smooth and rough channels, compared to cases where they are neglected.
Giulio Croce - One of the best experts on this subject based on the ideXlab platform.
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Effect of surface roughness: comparison between continuum and kinetic approaches
Journal of Physics: Conference Series, 2012Co-Authors: Olga Rovenskaya, Giulio CroceAbstract:In the present work a numerical analysis of the flow field in rough microchannels is carried out using two approaches: Navier-Stokes equations provided with first order slip-boundary condition and kinetic S-model equation with Maxwell diffuse reflecting boundary condition. An implicit scheme is used for the solution of S-model equation and an algorithm allowing massive parallelization in both physical and velocity spaces has been developed. The roughness geometry is modelled as a series of triangular obstructions with relative roughness e equals to 1.25%, 2.5% and 5%. A wide range of Mach numbers is considered, from nearly incompressible to chocked flow conditions and a Reynolds number up to 170. To estimate Rarefaction Effect the flow at Knudsen number ranging from 0.01 to 0.08 and fixed pressure ratio has been considered. Accuracy and discrepancies between full Navier - Stokes and S-model solutions are discussed, assessing the range of applicability of first order slip condition in rough geometries. The Effect of the roughness is discussed via Poiseuille number as a function of local Knudsen and Mach numbers.
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Compressibility and Rarefaction Effect on heat transfer in rough microchannels
International Journal of Thermal Sciences, 2009Co-Authors: Giulio Croce, Paola D'agaroAbstract:Abstract High pressure drop and high length to hydraulic diameter ratios yield significant compressibility Effects in microchannel flows, which compete with Rarefaction phenomena at the smaller scale. In such regimes, flow field and temperature field are no longer decoupled. In presence of significant heat transfer, and combined with the Effect of viscous dissipation, this yields to a quite complex thermo-fluid dynamic problem. A finite volume compressible solver, including generalized Maxwell slip flow and temperature jump boundary conditions suitable for arbitrary geometries, is adopted. Roughness geometry is modeled as a series of triangular shaped obstructions, and relative roughness from 0% to 2.65% were considered. The chosen geometry allows for direct comparison with pressure drop computations carried out, in a previous paper, under adiabatic conditions. A wide range of Mach number is considered, from nearly incompressible to chocked flow conditions. Flow conditions with Reynolds number up to around 300 were computed. The outlet Knudsen number corresponding to the chosen range of Mach and Reynolds number ranges from very low value to around 0.05, and the competing Effects of Rarefaction, compressibility and roughness are investigated in detail. Compressibility is found to be the most dominant Effect at high Mach number, yielding even inversion of heat flux, while roughness has a strong Effect in the case of rarefied flow. Furthermore, the mutual interaction between heat transfer and pressure drop is highlighted, comparing Poiseuille number values for both cooled and heated flows with previous adiabatic computations.
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Compressibility and Rarefaction Effect on Heat Transfer in Rough Microchannels
ASME 5th International Conference on Nanochannels Microchannels and Minichannels, 2007Co-Authors: Giulio Croce, Paola D'agaroAbstract:High pressure drop and high length to hydraulic diameter ratios yield significant compressibility Effects in microchannel flows, which compete with Rarefaction phenomena at the smaller scale. In such regimes, flow field and temperature field are no longer decoupled. In presence of significant heat transfer, and combined with the Effect of viscous dissipation, this yields to a quite complex thermo-fluid dynamic problem. A finite volume compressible solver, including generalized Maxwell slip flow and temperature jump boundary conditions suitable for arbitrary geometries, is adopted. Roughness geometry is modeled as a series of triangular shaped obstructions, and relative roughness from 0% to 2.65% were considered. The chosen geometry allows for direct comparison with pressure drop computations carried out, in a previous paper, under adiabatic conditions. A wide range of Mach number is considered, from nearly incompressible to chocked flow conditions. Flow conditions with Reynolds number up to around 300 were computed. The outlet Knudsen number corresponding to the chosen range of Mach and Reynolds number ranges from very low value to around 0.05, and the competing Effects of Rarefaction, compressibility and roughness are investigated in detail. Compressibility is found to be the most dominant Effect at high Mach number, yielding even inversion of heat flux, while roughness has a strong Effect in the case of rarefied flow. Furthermore, the mutual interaction between heat transfer and pressure drop is highlighted, comparing Poiseuille number values for both cooled and heated flows with previous adiabatic computations.Copyright © 2007 by ASME
Barbaros Çetin - One of the best experts on this subject based on the ideXlab platform.
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analysis of heat transfer and entropy generation for a low peclet number microtube flow using a second order slip model an extended graetz problem
Journal of Engineering Mathematics, 2014Co-Authors: Barbaros Çetin, Soheila ZeinaliAbstract:The classical Graetz problem, which is the problem of the hydrodynamically developed, thermally developinglaminarflowofanincompressiblefluidinsideatubeneglectingaxialconductionandviscousdissipation, is one of the fundamental problems of internal-flow studies. This study is an extension of the Graetz problem to includetheRarefactionEffect,viscousdissipationtermandaxialconductionwithaconstantwalltemperaturethermal boundary condition. The energy equation is solved to determine the temperature field analytically using general eigenfunction expansion with a fully developed velocity profile. To analyze the low-Peclet-number nature of the flow, the flow domain is extended from −∞ to +∞ .T o model the Rarefaction Effect, as econd-order slip model is implemented. The temperature distribution, local Nusselt number, and local entropy generation are determined in terms of confluent hypergeometric functions. This kind of theoretical study is important for a fundamental understanding of the convective heat transfer characteristics of flows at the microscale and for the optimum design of thermal systems, which includes convective heat transfer at the microscale, especially operating at low Reynolds numbers.
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Effect of Thermal Creep on Heat Transfer for a Two-Dimensional Microchannel Flow: An Analytical Approach
Journal of Heat Transfer, 2013Co-Authors: Barbaros ÇetinAbstract:In this paper, velocity profile, temperature profile, and the corresponding Poiseuille and Nusselt numbers for a flow in a microtube and in a slit-channel are derived analytically with an isoflux thermal boundary condition. The flow is assumed to be hydrodynamically and thermally fully developed. The Effects of Rarefaction, viscous dissipation, axial conduction are included in the analysis. For the implementation of the Rarefaction Effect, two different second-order slip models (Karniadakis and Deissler model) are used for the slip-flow and temperature-jump boundary conditions together with the thermal creep at the wall. The Effect of the thermal creep on the Poiseuille and Nusselt numbers are discussed. The results of the present study are important (i) to gain the fundamental understanding of the Effect of thermal creep on convective heat transfer characteristics of a microchannel fluid flow and (ii) for the optimum design of thermal systems which includes convective heat transfer in a microchannel especially operating at low Reynolds numbers. [DOI: 10.1115/1.4024504]
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Evaluation of Nusselt Number for a Flow in a Microtube With Second-Order Model Including Thermal Creep
ASME 2012 10th International Conference on Nanochannels Microchannels and Minichannels, 2012Co-Authors: Barbaros ÇetinAbstract:In this paper, Nusselt number for a flow in a microtube is determined analytically with a constant wall heat flux thermal boundary condition. The flow assumed to be incompressible, laminar, hydrodynamically and thermally fully-developed. The thermo-physical properties of the fluid are assumed to be constant. The Effect of Rarefaction, viscous dissipation, axial conduction, which are important at the microscale, are included in the analysis. For the implementation of the Rarefaction Effect, two different second-order slip models are used for the slip-flow and temperature-jump boundary conditions together with the thermal creep at the wall. Closed form solutions for the fully-developed temperature profile and Nusselt number are derived as a function of Knudsen number, Brinkman number and Peclet number.Copyright © 2012 by ASME
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EVALUATION OF NUSSELT NUMBER FOR A FLOW IN A MICROTUBE USING SECOND-ORDER SLIP MODEL
Thermal Science, 2011Co-Authors: Barbaros Çetin, Özgür BayerAbstract:In this paper, the fully-developed temperature profile and corresponding Nusselt value is determined analytically for a gaseous flow in a microtube with a thermal boundary condition of constant wall heat flux. The flow assumed to be laminar, and hydrodynamically and thermally fully developed. The fluid is assumed to be constant property and incompressible. The Effect of Rarefaction, viscous dissipation and axial conduction, which are important at the microscale, are included in the analysis. Second-order slip model is used for the slip-flow and temperature jump boundary conditions for the implementation of the Rarefaction Effect. Closed form solutions for the temperature field and the fully-developed Nusselt number is derived as a function of Knudsen number, Brinkman number and Peclet number.
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slip flow heat transfer in microtubes with axial conduction and viscous dissipation an extended graetz problem
International Journal of Thermal Sciences, 2009Co-Authors: Barbaros Çetin, Almila G. Yazicioglu, Sadik KakacAbstract:This study is an extension of the Graetz problem to include the Rarefaction Effect, viscous dissipation term and axial conduction with constant-wall-heat-flux thermal boundary condition. The energy equation is solved analytically by using general eigenfunction expansion. The temperature distribution and the local Nusselt number are determined in terms of confluent hypergeometric functions. The Effects of the Rarefaction, axial conduction and viscous dissipation on the local Nusselt number are discussed in terms of dimensionless parameters such as the Knudsen number, Peclet number and Brinkman number.
Yoshinori Inoue - One of the best experts on this subject based on the ideXlab platform.
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quasisteady streaming with Rarefaction Effect induced by asymmetric sawtooth like plane waves
Physics of Fluids, 1996Co-Authors: Takeru Yano, Yoshinori InoueAbstract:The nonlinear plane acoustic wave emitted from a harmonically oscillating plate into an ideal gas of semi‐infinite extent develops into a sawtooth‐like wave, as long as the energy dissipation is negligibly small everywhere except for discontinuous shock fronts. The present authors have recently studied the strongly nonlinear propagation process and, in particular, numerically shown that, contrary to the result of the conventional weakly nonlinear theory, streaming (mean mass flow) due to shocks occurs in the direction of wave propagation, and thereby the gas near the plate is rarefied as time proceeds [J. Acoust. Soc. Am. 94, 1632 (1993)]. In this paper, the analysis of strongly nonlinear problem is advanced by extending the numerical computation up to about 190 periods of oscillation of plate, which is about three times longer than the previous one. It is demonstrated that, in the course of time, a quasisteady state is established, where a low‐density and high‐entropy region formed near the plate continu...
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Quasisteady streaming with Rarefaction Effect induced by asymmetric sawtooth‐like plane waves
Physics of Fluids, 1996Co-Authors: Takeru Yano, Yoshinori InoueAbstract:The nonlinear plane acoustic wave emitted from a harmonically oscillating plate into an ideal gas of semi‐infinite extent develops into a sawtooth‐like wave, as long as the energy dissipation is negligibly small everywhere except for discontinuous shock fronts. The present authors have recently studied the strongly nonlinear propagation process and, in particular, numerically shown that, contrary to the result of the conventional weakly nonlinear theory, streaming (mean mass flow) due to shocks occurs in the direction of wave propagation, and thereby the gas near the plate is rarefied as time proceeds [J. Acoust. Soc. Am. 94, 1632 (1993)]. In this paper, the analysis of strongly nonlinear problem is advanced by extending the numerical computation up to about 190 periods of oscillation of plate, which is about three times longer than the previous one. It is demonstrated that, in the course of time, a quasisteady state is established, where a low‐density and high‐entropy region formed near the plate continu...
