Peristaltic Transport of a Jeffrey Fluid with Variable Viscosity through a Porous Medium in an Asymmetric Channel

The peristaltic flow of a Jeffrey fluid with variable viscosity through a porous medium in an asymmetric channel is investigated. The channel asymmetric is produced by choosing the peristaltic wave train on the wall of different amplitude and phase. The governing nonlinear partial differential equations for the Jeffrey fluid model are derived in Cartesian coordinates system. Analytic solutions for stream function, velocity, pressure gradient, and pressure rise are first developed by regular perturbation method, and then the role of pertinent parameters is illustrated graphically

An Investigation of a Latent Heat Storage Porous Bed and Condensing Flow Through it,”

In this work the transient analysis of the behavior of a packed bed of encapsulated phase change material (PCM) and the condensing flow through it is Introduction Packed bed heat storage units have been used extensively in a wide variety of applications. Packed beds as storage media are attractive, for they offer a compact structure due to their relatively greater heat storage capacity as compared to systems that utilize energy transporting fluid as the storage medium. Also due to the large surface area offered by packed beds for heat transfer between the energy transporting fluid and the bed particles, the process of energy transfer and storage becomes very efficient. The earlier forms of packed bed energy storage units relied solely on the sensible heat capacity of solid bed particles for storing thermal energy. This form has been satisfactorily employed for various applications. However, certain applications may impose a limitation on the size and weight of the packed bed system utilized. For instance, in the case of a heat rejection system in pulsed space power supplies that incorporates packed beds, the reduction of mass and volume is of utmost importance. In such cases utilization of only the sensible heat capacity of a certain material for energy storage may not be efficient. The remedy to this can be found in the utilization of latent heat in the process of energy storage. Recently, encapsulated phase-change materials (PCM) have received considerable attention as energy storage materials. The use of an encapsulated PCM is very appealing since it makes the utilization of latent heat storage capacity possible. This is achieved by using a PCM that has a melting temperature within the temperature range of operation of the system incorporating the packed bed. The principal advantage of PCMs in packed beds is that the energy storage density of the bed is increased significantly and thus, the size and mass of the storage system required for a particular application are reduced proportionally. Different PCMs have been considered for use in packed bed energy storage units in different applications. For applications over 450°C, significant consideration has been given to salt

Simultaneous Heat and Mass Transfer Accompanied by Phase Change in Porous

Introduction Transport processes in porous media have been the subject of extensive investigations due to the applicability of such studies in a variety of problems, such as geothermal operations, soil hydrology, nuclear waste disposal, drying technology, and energy conservation. A very important area in the field of energy conservation is the effect of condensation on the performance of high-porosity insulation materials. A typical insulation material consists of a solid matrix, a gas phase which itself consists of air and water vapor, and a very small amount of adsorbed liquid water. When the insulation matrix is exposed to environments of different temperature and humidity, diffusion and bulk convection of the air, vapor, and liquid occur. In addition, air infiltration due to small differences in total pressure across the insulation matrix augments this transport process. Condensation occurs at any point in the insulation where the water vapor concentration becomes greater than the saturation concentration corresponding to the temperature at that point. As the condensation takes place the latent heat of vaporization is released which acts as a heat source for the heat transfer process. The condensation also creates a liquid phase which may be pendular or mobile due to the capillary action and gravity. In summary, the complete problem is a combined mass, momentum, and energy transfer in a porous medium containing a multiphase mixture of air, vapor, and water in the void space. The general aspects of combined transport in porous media It is crucial to gain a fundamental understanding of the conditions which promote condensation, as condensation will significantly affect energy transfer across the insulation matrix. This in turn greatly influences the R value of the insulation. Furthermore, condensation directly affects the physical integrity of the insulation and its deterioration. A more thorough knowledge of the condensation process in an insulation material will allow better predictions of the condensation rates and the qualitative effects of the controlling parameters. In addition, an understanding of the condensation process will ultimately help in establishing the design locations for the vapor barriers

Nanoflows through disordered media: a joint Lattice Boltzmann and Molecular Dynamics investigation

We investigate nanoflows through dilute disordered media by means of joint lattice Boltzmann (LB) and molecular dynamics (MD) simulations -- when the size of the obstacles is comparable to the size of the flowing particles -- for randomly located spheres and for a correlated particle-gel. In both cases at sufficiently low solid fraction, $\Phi<0.01$, LB and MD provide similar values of the permeability. However, for $\Phi > 0.01$, MD shows that molecular size effects lead to a decrease of the permeability, as compared to the Navier-Stokes predictions. For gels, the simulations highlights a surplus of permeability, which can be accommodated within a rescaling of the effective radius of the gel monomers.Comment: 4 pages, 4 figure

Heatline visualization of natural convection in a porous cavity occupied by a fluid with temperature-dependent viscosity

Temperature dependent viscosity effect in buoyancy driven flow, of a gas or a liquid, in an enclosure filled with a porous medium is studied numerically, based on the general model of momentum transfer in a porous medium. The Arrhenius model, which proposes an exponential form of viscosity-temperature relation, is applied to examine three cases of viscosity-temperature relation: constant, decreasing and increasing. Application of arithmetic and harmonic mean values of the viscosity is also investigated for their ability to represent the Nusselt number versus the effective Rayleigh number. Heatlines are illustrated for a more comprehensive investigation of the problem

Effects of viscous dissipation and boundary conditions on forced convection in a channel occupied by a saturated porous medium

Forced convection with viscous dissipation in a parallel plate channel filled by a saturated porous medium is investigated numerically. Three different viscous dissipation models are examined. Two different sets of wall conditions are considered: isothermal and isoflux. Analytical expressions are also presented for the asymptotic temperature profile and the asymptotic Nusselt number. With isothermal walls, the Brinkman number significantly influences the developing Nusselt number but not the asymptotic one. At constant wall heat flux, both the developing and the asymptotic Nusselt numbers are affected by the value of the Brinkman number. The Nusselt number is sensitive to the porous medium shape factor under all conditions considered

Effects of viscous dissipation and boundary conditions on forced convection in a channel occupied by a saturated porous medium

Forced convection with viscous dissipation in a parallel plate channel filled by a saturated porous medium is investigated numerically. Three different viscous dissipation models are examined. Two different sets of wall conditions are considered: isothermal and isoflux. Analytical expressions are also presented for the asymptotic temperature profile and the asymptotic Nusselt number. With isothermal walls, the Brinkman number significantly influences the developing Nusselt number but not the asymptotic one. At constant wall heat flux, both the developing and the asymptotic Nusselt numbers are affected by the value of the Brinkman number. The Nusselt number is sensitive to the porous medium shape factor under all conditions considered

Effects of temperature dependent viscosity on Bénard convection in a porous medium using a non-Darcy model

Temperature-dependent viscosity variation effect on Benard convection, of a gas or a liquid, in an enclosure filled with a porous medium is studied numerically, based on the general model of momentum transfer in a porous medium. The exponential form of viscosity-temperature relation is applied to examine three cases of viscosity-temperature relation: constant (mu = mu(C)), decreasing (down to 0.13 mu C) and increasing (up to 7.39 mu(C)). Effects of fluid viscosity variation on isotherms, streamlines, and the Nusselt number are studied. Application of the effective and average Rayleigh number is examined. Defining a reference temperature, which does not change with the Rayleigh number but increases with the Darcy number, is found to be a viable option to account for temperature-dependent viscosity variation. (C) 2007 Published by Elsevier Ltd