Mixed Convection in a Vertical Parallel Plate Microchannel With Asymmetric Wall Heat Fluxes

2006 ◽  
Vol 129 (8) ◽  
pp. 1091-1095 ◽  
Author(s):  
Mete Avcı ◽  
Orhan Aydın
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Parallel Plate ◽  
Temperature Jump ◽  
Velocity Slip ◽  
Heat Fluxes ◽  
Limiting Case ◽  
Convection Parameter

In this study, exact analytical results are presented for fully developed mixed convective heat transfer of a Newtonian fluid in an open-ended vertical parallel plate microchannel with asymmetric wall heating at uniform heat fluxes. The velocity slip and the temperature jump at the wall are included in the formulation. The effects of the modified mixed convection parameter, Grq∕Re, the Knudsen number, Kn, and the ratio of wall heat flux, rq=q1∕q2, on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu=f(Grq∕Re,Kn,rq) expression is developed. For, the limiting case of Kn=0, the results are found to be in an excellent agreement with those in the existing literature.

Mixed Convection in a Vertical Parallel Plate Microchannel

2006 ◽  
Vol 129 (2) ◽  
pp. 162-166 ◽  
Author(s):  
Mete Avcı ◽  
Orhan Aydın
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Newtonian Fluid ◽  
Wall Temperature ◽  
Parallel Plate ◽  
Temperature Jump ◽  
Velocity Slip ◽  
Convection Parameter

In this study, fully developed mixed convective heat transfer of a Newtonian fluid in an open-ended vertical parallel plate microchannel is analytically investigated by taking the velocity slip and the temperature jump at the wall into account. The effects of the mixed convection parameter, Gr/Re, the Knudsen number, Kn, and the ratio of wall temperature difference, rT, on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu=f(Gr∕Re,Kn,rT) expression is developed.

Mixed Convection in a Vertical Microannulus Between Two Concentric Microtubes

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Mete Avcı ◽  
Orhan Aydın
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Temperature Jump ◽  
Slip Flow ◽  
Velocity Slip ◽  
Slip Flow Regime ◽  
Convection Parameter ◽  
Rarefaction Effects

In this study, fully developed mixed convective heat transfer of a Newtonian fluid in a vertical microannulus between two concentric microtubes is analytically investigated by taking the velocity slip and the temperature jump at the wall into account. The effects of the mixed convection parameter Gr/Re, the Knudsen number Kn, and the aspect ratio r* on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu=f(Gr∕Re,Kn,r*) expression is developed. It is disclosed that increasing Gr/Re enhances heat transfer while rarefaction effects considered by the velocity slip and the temperature jump in the slip flow regime decreases it.

scholarly journals Gas Microflows in the Slip Flow Regime: A Critical Review on Convective Heat Transfer

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Stéphane Colin
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Flow Regime ◽  
Convective Heat ◽  
Temperature Jump ◽  
Numerical Models ◽  
Slip Flow ◽  
Velocity Slip ◽  
Constant Wall Temperature ◽  
Slip Flow Regime

Accurate modeling of gas microvection is crucial for a lot of MEMS applications (microheat exchangers, pressure gauges, fluidic microactuators for active control of aerodynamic flows, mass flow and temperature microsensors, micropumps, and microsystems for mixing or separation for local gas analysis, mass spectrometers, vacuum, and dosing valves…). Gas flows in microsystems are often in the slip flow regime, characterized by a moderate rarefaction with a Knudsen number of the order of 10−2–10−1. In this regime, velocity slip and temperature jump at the walls play a major role in heat transfer. This paper presents a state of the art review on convective heat transfer in microchannels, focusing on rarefaction effects in the slip flow regime. Analytical and numerical models are compared for various microchannel geometries and heat transfer conditions (constant heat flux or constant wall temperature). The validity of simplifying assumptions is detailed and the role played by the kind of velocity slip and temperature jump boundary conditions is shown. The influence of specific effects, such as viscous dissipation, axial conduction and variable fluid properties is also discussed.

Steady fully developed mixed convection flow in a vertical parallel plate microchannel with bilateral heating and filled with porous material

2012 ◽  
Vol 227 (1) ◽  
pp. 56-66 ◽  
Author(s):  
Basant K Jha ◽  
Deborah Daramola ◽  
Abiodun O Ajibade
Keyword(s):  
Mixed Convection ◽  
Parallel Plate ◽  
Velocity Slip ◽  
Darcy Number ◽  
Closed Form Expression ◽  
Convection Flow ◽  
Governing Equations ◽  
Undetermined Coefficient ◽  
Convection Parameter ◽  
Bilateral Heating

This study investigated analytically the hydrodynamic and thermal behaviour of a fully developed laminar, viscous, incompressible fluid in a vertical parallel plate microchannel taking into account the velocity slip and thermal jump at the walls. The governing equations are expressed in a dimensionless form using the dimensionless quantities. The method of undetermined coefficient was employed to obtain the closed-form expression for velocity, which is used to determine the skin friction. The solution obtained is then presented graphically and the results are discussed for various dimensionless parameters entering the problem. During the course of investigation, it is found that the critical values of the mixed convection parameter Gre (which is the ratio of the Grashof number Gr to the Reynolds number Re) led to flow reversal decrease with increase in Darcy number, while it increases with increase in Knudsen number Kn. Also, the Nusselt number Nu is found to increase with increasing Darcy number.

MIXED CONVECTIVE SLIP FLOWS IN A VERTICAL PARALLEL PLATE MICROCHANNEL WITH SYMMETRIC AND ASYMMETRIC WALL HEAT FLUXES

2012 ◽  
Vol 36 (3) ◽  
pp. 207-218 ◽  
Author(s):  
Hamid Niazmand ◽  
Behnam Rahimi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Friction Coefficient ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Parallel Plate ◽  
Flux Ratio ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Slip Flows

Mixed convective gaseous slip flows in an open-ended vertical parallel-plate channel with symmetric and asymmetric wall heat fluxes are numerically investigated. Buoyancy effects on developing and fully developed solutions are studied using the SIMPLE algorithm. The velocity and temperature fields are examined for different values of Knudsen number, mixed convection parameter and heat flux ratio. It is found that increasing Gr/Re leads to an increase in the heat transfer rate and friction coefficient. Also, rarefaction effects decrease the heat transfer rate and friction coefficient. The friction coefficient decreases with an increase in heat flux ratio.

Numerical Investigation on Nanofluid Mixed Convection in Triangular Ducts Heated by a Uniform Heat Flux

2012 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci ◽  
S. Tamburrino
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Numerical Investigation ◽  
Convective Heat ◽  
Richardson Number ◽  
Uniform Heat Flux ◽  
Working Fluids ◽  
Laminar Mixed Convection

Heat transfer enhancement technology covers a very important role in designing efficient heating and cooling equipments. This goal can be achieved by means of different techniques. Convective heat transfer can be improved actively or passively, for example, by adopting special surfaces or by increasing the thermal conductivity of the working fluids. Thus, the use of suspended solid nanoparticles in the working fluids can be taken into account. In this paper a numerical investigation on laminar mixed convection with Al2O3/water based nanofluids in a triangular channel is presented. A uniform and constant heat flux on the channel surfaces is assumed and the single-phase model approach has been employed in order to describe the nanofluid behaviour. The analysis has been performed in the steady state regime for particle size in nanofluids equal to 30 nm. The CFD code Fluent has been employed in order to solve the three-dimensional numerical model and different Richardson number values and nanoparticle volume fractions have been considered. Results are presented for the fully developed regime flow. The increase of average convective heat transfer coefficients and Nusselt number values for increasing values of Richardson number and particle concentration is observed by analyzing the obtained results. However, also wall shear stress and required pumping power profiles increase as expected.

Mechanisms of Heat and Mass Transfer for Thin-Film Evaporation With Velocity Slip and Temperature Jump

2019 ◽  
Author(s):  
Xiu Xiao ◽  
Chunji Yan ◽  
Yulong Ji
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Jump ◽  
Slip Length ◽  
Velocity Slip ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Solid Liquid Interface ◽  
Solid Liquid

Abstract Velocity slip and temperature jump at the solid-liquid interface are important phenomena in microchannel heat transfer. A comprehensive mathematical model considering both velocity slip condition and temperature jump at the solid-liquid interface is developed to understand the mechanisms of heat and mass transfer during thin-film evaporation in this paper. The model structure is established based on the lubrication theory, Clausius-Clapeyron equation and Young-Laplace equation. To better formulate the film evaporation process, three dimensionless parameters representing the effects of slip length coefficient, temperature jump and wall superheat degree respectively, are introduced in the present model. The analytical solution provides insight of film thickness and heat transfer characteristics for the evaporating thin film. It shows that as the slip length and temperature jump coefficient decrease, the length of evaporating thin film region is shortened and the location of maximum heat flux moves closer to the initial evaporating point. The effect of slip condition on heat flux is small, but the increase of temperature jump can reduce the peak heat flux significantly. Furthermore, the analysis on the three thermal resistances which are caused by temperature jump, conduction through liquid film and evaporation on liquid-vapor interface result in a better understanding for effective heat transfer during thin-film evaporation.

Slip Flow Heat Transfer in Annular Microchannels With Constant Heat Flux

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Zhipeng Duan ◽  
Y. S. Muzychka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Knudsen Number ◽  
Temperature Jump ◽  
Slip Flow ◽  
Velocity Slip ◽  
Heat Transfer Characteristics ◽  
Uniform Wall ◽  
Flow Heat ◽  
Uniform Wall Heat Flux

Microscale fluid dynamics has received intensive interest due to the emergence of microelectromechanical systems technology. When the mean free path of the gas is comparable to the channel’s characteristic dimension, the continuum assumption is no longer valid and velocity slip and temperature jump may occur at the duct walls. Slip flow heat transfer in annular microchannels has been examined. The effects of velocity slip and temperature jump on the hydrodynamically and thermally fully developed heat transfer characteristics for laminar flow have been studied analytically. The analysis is carried out for both uniform wall heat flux on one wall, adiabatic on the other wall, and uniform wall heat flux on both walls. The results indicate that the slip flow Nusselt numbers are lower than those for continuum flow and decrease with an increase in Knudsen number for most practical engineering applications. The effects of Knudsen number, radius ratio, and heat flux ratio on heat transfer characteristics are discussed, respectively.

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