Sharif Digital Repository

The present investigation considers the thermally developing electroosmotic flow of power-law fluids through a parallel plate microchannel. Both the viscous dissipation and Joule heating effects are taken into account and a step change in wall temperature is considered to represent physically conceivable thermal entrance conditions. Expressions for the dimensionless temperature and Nusselt number in the form of infinite series are presented. In general, the resultant eigenvalue problem is solved numerically; nevertheless, an analytical solution is presented for the regions close to the entrance. A parametric study reveals that increasing amounts of the Peclet number result in higher wall... 

In the present work, the second law of thermodynamics analysis has been carried out for steady-state fully developed laminar gas flow in a parallel plate microchannel with asymmetrically heated walls. The rarefaction effects as well as viscous heating effects are taken into consideration. Closed-form expressions are obtained for velocity and temperature distributions and entropy generation rates. The results demonstrate that increasing values of the wall heat fluxes ratio result in greater entropy generation for positive Brinkman numbers, whereas the opposite is true for negative values of Brinkman. However, the effect of the wall heat fluxes ratio on entropy generation becomes insignificant... 

The present investigation is devoted to the second law of thermodynamics analysis of steady-state hydrodynamically and thermally fully developed laminar gasflow in a microannulus with constant but different wall heat fluxes. Slip velocity and temperature jump boundary conditions are usedtodescribe rarefaction effects. Viscous heating is also included for both the wall cooling and heating cases. Using already available velocity profile, closedform expressions are obtained for the transverse distribution of temperature and entropy generation rates. The results demonstrate that the effectof the wall heatfluxes ratioonentropy generation is negligible atlarge valuesofthe group parameter and... 

We present the rarefaction effects on diffusive mass transport in micro- and nanoscales using the results of direct simulation Monte Carlo DSMC method. Unlike the previous investigations, the momentum and heat contributions are eliminated from the computations via uniform velocity, pressure, and temperature field considerations. The effects of global Knudsen number on the diffusion phenomenon are studied for the same Peclet number and a unique mixer shape. The results indicate that there is considerable weakening in diffusion mechanism for high Knudsen number cases. As a result, the non-dimensional diffusive mass fluxes would decrease and the non-dimensional mixing length would increase as... 

Microfluidic-based concentration gradient generators (CGGs) have a number of applications in chemical, biological and pharmaceutical studies. Thus, precise design of the microfluidic system is crucial to maintaining the desired concentration gradient in microchannels. One of the design considerations is the length of microchannels in the structure of a CGG. A CGG with a short length fails to provide the complete diffusive mixing, while the size of the microchip would unfavorably increase by incorporating a long CGG. Considering a CGG as a tree-like structure consisting of T-shaped micromixers, the mixing process of the species at a straight microchannel has been solved analytically. Herein,... 

This paper deals with the modeling and simulation of binary liquid-phase adsorption of methyl mercaptan and hydrogen sulfide from a liquid butane stream by zeolite molecular sieve 13X in a fixed bed. The model equations account for the effect of axial dispersion and the inter- and intraparticle, mass-transfer resistances at isothermal operating conditions. Orthogonal collocation and Gill's fourth-order Runge-Kutta methods were used to solve the dimensionless general forms of the 4N-eoupled ordinary differential equations for simultaneous adsorption of the solutes by the adsorbent in a fixed bed. The model predictions were compared to the commercial-scale plant data of an Iranian... 

A numerical study is reported to investigate the entropy generation due to forced convection in a parallel plate channel filled by a saturated porous medium. Two different thermal boundary conditions are considered being isoflux and isothermal walls. Effects of the Poclet number, the porous medium shape factor, the dimensionless temperature difference for isothermal walls, the dimensionless heat flux for isoflux walls, and the Brinkman number on the Bejan number as well as the local and average dimensionless entropy generation rate are examined. Copyright © 2008 Inderscience Enterprises Ltd  

Results are presented from a numerical study examining the flow of a viscous, incompressible fluid through a random packing of non-overlapping spheres at moderate Reynolds numbers, spanning a wide range of flow conditions for porous media. By using a laminar model including inertial terms and assuming rough walls, numerical solutions of the Navier-Stokes equations in three-dimensional porous packed beds resulted in dimensionless pressure drops in excellent agreement with those reported in a previous study. This observation suggests that no transition to turbulence could occur in the range of the Reynolds number studied. For flows in the Forchheimer regime, numerical results are presented of... 

In the present study criterion for local thermal equilibrium assumption is studied. It concerns with the fluid flow and heat transfer between two parallel plates filled with a saturated porous medium under non-equilibrium condition. A two-equation model is utilized to represent the fluid and solid energy transport. Numerical Finite Volume Method has been developed for solving coupled energy equations and the Non-Darcian effects are considered for description of momentum equation. The effects of suitable non dimensional parameters as Peclet number and conductivity ratio has been studied thoroughly. A suitable non dimensional equation proposed in wide range of Peclet number and conductivity... 

In the present study criterion for local thermal equilibrium assumption is studied. It concerns with the fluid flow and heat transfer between two parallel plates filled with a saturated porous medium under non-equilibrium condition. A two-equation model is utilized to represent the fluid and solid energy transport. Numerical Finite Volume Method has been developed for solving coupled energy equations and the Non-Darcian effects are considered for description of momentum equation. The effects of suitable non dimensional parameters as Peclet number and conductivity ratio has been studied thoroughly. A suitable non dimensional equation proposed in wide range of Peclet number and conductivity...