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When the mean free path of the gas is comparable to the channel’s characteristic dimension, the continuum assumption is no longer valid and velocity slip and temperature jump may occur at the duct walls.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.

Variable Property Effects in Simultaneously Developing Gaseous Slip-Flow in Rectangular Microchannels With Prescribed Wall Heat Flux

2010 ◽  
Author(s):  
Azad Qazi Zade ◽  
Metin Renksizbulut ◽  
Jacob Friedman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Knudsen Number ◽  
Thermophysical Properties ◽  
Slip Flow ◽  
Wall Heat Flux ◽  
Heat Transfer Characteristics ◽  
Rectangular Microchannels ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The effects of variable physical properties on the flow and heat transfer characteristics of simultaneously developing slip-flow in rectangular microchannels with constant wall heat flux are numerically investigated. A co-located finite-volume method is used in order to solve the mass, momentum and energy equations in their most general form. Thermophysical properties of the flowing gas are functions of temperature, while density and Knudsen number are allowed to change with both pressure and temperature. Different Knudsen numbers are considered in order to study the effects of slip-flow. Simulations indicate that the constant physical property assumption can result in under/over-prediction of the local friction and heat transfer coefficients depending on the problem configuration. Density and thermophysical property variations have significant effects on predicting flow and heat transfer characteristics since the gas temperature constantly changes as a result of the applied wall heat flux. Heat transfer coefficient is affected both due to the change in the velocity field and change in thermophysical properties. Also temperature dependence of the local Knudsen number can significantly alter the friction coefficients due to its strong dependence on slip conditions. The degree of discrepancy varies for different cases depending on the Knudsen number, and the applied heat flux strength and direction (cooling versus heating).

Heat transfer characteristics of slip flow over solid spheres

2016 ◽  
Vol 230 (19) ◽  
pp. 3431-3441 ◽  
Author(s):  
Morteza Anbarsooz ◽  
Hamid Niazmand
Keyword(s):  
Knudsen Number ◽  
Temperature Jump ◽  
Slip Flow ◽  
Velocity Slip ◽  
Reynolds Numbers ◽  
Solid Sphere ◽  
Maximum Temperature ◽  
Heat Transfer Characteristics ◽  
Prandtl Numbers ◽  
Thermal Wake

In this study, heat transfer characteristics of slip flow over an isolated impermeable solid sphere are investigated numerically. An isothermal solid sphere is considered at intermediate Reynolds numbers (0 ≤ Re ≤ 50) for Prandtl numbers in the range of 0.7–7.0. The Navier–Stokes and energy equations are solved by a control volume technique in conjunction with the velocity slip and temperature jump boundary conditions. It was found that the size of the thermal wake region according to the Knudsen number depends on the Prandtl number. At lower Prandtl numbers (0.7 ≤ Pr ≤ 2.0), the thermal wake region shrinks as the Knudsen number increases, while at higher Prandtl numbers, it grows as the Knudsen number increases. The maximum temperature jump occurs at the front stagnation point where the local Nusselt is itself maximum, owing to the maximum temperature gradient at this point. The results show that due to the opposing effects of the velocity slip and temperature jump, the average Nusselt number variation with the Knudsen number depends nonlinearly on both the Prandtl and Reynolds numbers. Furthermore, for the limiting case of Re → 0, an analytical solution for the problem is presented which has also served as a validation case.

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.

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.

Investigation of Heat Transfer Over a Rotating Disk in Case of Temperature and Velocity Jump Conditions by Using Differential Transform Method

2010 ◽  
Author(s):  
A. Y. Gunes ◽  
G. Komurgoz ◽  
A. Arikoglu ◽  
I. Ozkol
Keyword(s):  
Heat Transfer ◽  
Knudsen Number ◽  
Temperature Jump ◽  
Velocity Slip ◽  
Rotating Disk ◽  
Jump Conditions ◽  
Governing Equations ◽  
Transform Method ◽  
Differential Transform ◽  
Velocity Jump

The energy crisis in the last two decades has turned the attention of scientific and engineering communities to redesigned and developed heat-fluid interaction systems. All of the details in analyses are reconsidered to reduce energy consumption. The present work examines the effects of temperature and velocity jump conditions on heat transfer, fluid flow over a single rotating disk. The flow due to rotating disks is of great interest in thermal engineering as it appears in many industrial and engineering applications such as gas turbine engines and micropumps. The related equation of flow, which is nonlinear and coupled, and heat transfer governing equations are reduced to ordinary differential equations by applying the so-called classical approach which was first introduced by Von Karman. Instead of this approach, a pure numerical one, the recently developed popular semi numerical analytical technique differential transform method (DTM), with Benton transformation, is employed to solve the reduced governing equations under the assumptions of velocity-slip and temperature jump conditions on the disk surface. The solution is valid for continuum and slip-flow regime which has a Knudsen number smaller than 0.1. The results attained for various physical cases are interpreted by using non-dimensional parameters related to flow and temperature fields. Velocity and temperature profiles are presented graphically. The effect of various parameters such as the Knudsen Number (Kn), Reynolds Number (Re) and Nusselt Numbers (Nu) are examined. The observed physical consequences are the velocity slip and temperature jump at the wall becoming strongly dependant on the Knudsen number. It is also observed that the temperature jump and velocity jump conditions have nonlinear effects on slip; these effects are investigated with great details and presented graphically.

Three Dimensional Numerical Analysis of Laminar Slip-Flow Heat Transfer in Rectangular Microchannels

2008 ◽  
Author(s):  
H. D. Madhawa Hettiarachchi ◽  
Mihajlo Golubovic ◽  
William M. Worek
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Temperature Jump ◽  
Slip Flow ◽  
Three Dimensional ◽  
Velocity Slip ◽  
Thermal Boundary Condition ◽  
Navier Stokes ◽  
Constant Wall Temperature ◽  
Rectangular Microchannels

Slip-flow and heat transfer in rectangular microchannels are studied numerically for constant wall temperature (T) and constant wall heat flux (H2) boundary conditions under thermally developing flow. Navier-Stokes and energy equations with velocity slip and temperature jump at the boundary are solved using finite volume method in a three dimensional cartesian coordinate system. A modified convection-diffusion coefficient at the wall-fluid interface is defined to incorporate the temperature-jump boundary condition. Validity of the numerical simulation procedure is stabilized. The effect of rarefaction on heat transfer in the entrance region is analyzed in detail. The velocity slip has an increasing effect on the Nusselt (Nu) number whereas temperature jump has a decreasing effect, and the combined effect could result increase or decrease in the Nu number. For the range of parameters considered, there could be high as 15% increase or low as 50% decrease in fully developed Nu is plausible for T thermal boundary condition while it could be high as 20% or low as 35% for H2 thermal boundary condition.

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