Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
18
4
2015
THE ONSET OF TRANSIENT SORET-DRIVEN BUOYANCY CONVECTION IN NANOPARTICLE SUSPENSIONS WITH PARTICLE-CONCENTRATION-DEPENDENT VISCOSITY IN A POROUS MEDIUM
The onset of transient Soret-driven convection in a horizontal layer of a porous medium saturated by a fluid with nanoparticles suspensions, which is heated from above, is studied where the viscosity depends on the local concentration of nanoparticles of practical importance. For the case of high solutal Darcy-Rayleigh number RsD with a large negative Soret coefficient DT, the applied even small temperature on the upper boundary creates Soret diffusion and then the convective motion occurs during the transient diffusion stage. In conjunction with the Soret diffusion, the nanoparticle concentration becomes stratified as given by Eq. (22), and hence the viscosity is stratified. The nanofluid is considered to be dilute, i.e., the volume concentrations of nanoparticles is very small 0.01%−2.0%, and this permits the porous medium to be taken as a weakly heterogeneous medium with variation in the vertical direction of viscosity. In turn this allows an approximate analytical solution to be obtained using a spectral method. The critical times of the onset of this Soret-driven convection are obtained as a function of the modified solute Rayleigh-Darcy number Rs*D for different values of viscosity variation parameter Q. Decreasing Q can enhanced these times Q. The results from theory are also compared with the experimental results. We show that the results from the theoretical predictions are too close to explain the experimental work.
Dhananjay
Yadav
School of Mechanical Engineering, Yonsei University Seoul, South Korea
MinChan
Kim
jeju national university
369-378
SURFACE AFFINITY AND INTERDIFFUSIVITY OF CARBON DIOXIDE INSIDE HYDROTALCITE−SILICA MICROPORES: CO2 INTERDIFFUSION INSIDE HT−Si MICROPORES
The different level of carbon dioxide diffusion in microporous hydrotalcite-silica membrane can be explained by the attractive forces between the molecules and the affinitive medium between molecules of different gas species and the molecular weight of the gases. For a molecular sieve membrane that exhibits high affinity for carbon dioxide, the gas transport in the membrane is predominantly surface adsorption. Pure carbon dioxide, despite the fact that it is heavier than hydrogen, nitrogen, and methane, is preferentially adsorbed (by losing more of its energy due to affinitive forces) onto the pore wall of hydrotalcite material in the membrane. Nitrogen gas can reduce the ability of carbon dioxide to be adsorbed and diffused into the membrane by as much as 1.9 kJ/mol at elevated pressure. The presence of the other two gases in the binary mixture can also perturb the ability of CO2 to be adsorbed and diffused into the membrane micropores.
Ahmed Daham
Wiheeb
School of Chemical Engineering, Universiti Sains Malaysia 14300 Nibong Tebal, Penang, Malaysia; Department of Chemical Engineering, College of Engineering, University of Tikrit, Salah ad Din, Iraq
Mohd Azmier
Ahmad
School of Chemical Engineering, Universiti Sains Malaysia 14300 Nibong Tebal, Penang, Malaysia
Muhamad Nazri
Murat
School of Chemical Engineering, Universiti Sains Malaysia 14300 Nibong Tebal, Penang, Malaysia
Jin-Soo
Kim
Department of Chemical Engineering, Kyung Hee University, Global Campus, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Republic of Korea
Mohd Roslee
Othman
School of Chemical Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia; Department of Chemical Engineering, Kyung Hee University, Global Campus, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Republic of Korea
379-388
BIOCONVECTIVE NON-NEWTONIAN NANOFLUID TRANSPORT OVER A VERTICAL PLATE IN A POROUS MEDIUM CONTAINING MICROORGANISMS IN A MOVING FREE STREAM
A mathematical model for natural convective flow along a vertical plate in a moving free stream in a porous medium which is filled with non-Newtonian nanofluids and gyrotactic microorganisms is presented. The effect of the viscous dissipation is taken into account in the energy equation. The governing boundary layer equations are cast into dimensionless form and then converted into a system of coupled nonlinear ordinary differential equations by using similarity transformations. The transformed equations are then solved numerically by the implicit finite difference method. The effects of the controlling parameters on the dimensionless velocity, temperature, nanoparticle volume fraction, and the motile microorganism, as well as on the local Nusselt, Sherwood, and the motile microorganism numbers are investigated, the results analyzed and then presented. The nanofluid and bioconvection parameters were found to have strong effects on the local Nusselt, Sherwood, and the motile microorganism numbers. The numerical results are compared with published data, and an excellent agreement has been found. The present study finds application in microbial fuel cells.
Waqar A.
Khan
Department of Mechanical Engineering, University of Waterloo, Waterloo, Ontario, N2L 3G1 Canada
Mohammed Jashim
Uddin
School of Mathematical Sciences, Universiti Sains Malaysia, Penang 11800, Malaysia; Department of Mathematics, American International University-Bangladesh, Banani, Dhaka 1213, Bangladesh
Ahmad I. Md.
Ismail
School of Mathematical Sciences, Universiti Sains Malaysia, Penang 11800, Malaysia
389-399
MIXED CONVECTION JET IMPINGEMENT COOLING OF A RECTANGULAR SOLID HEAT SOURCE IMMERSED IN A POROUS LAYER
The jet impingement cooling of a solid rectangular block heated from below and immersed in a fluid-saturated porous medium is considered for investigation numerically. The jet direction is considered to be perpendicular from the top to the solid rectangular block. Therefore the jet flow and the buoyancy-driven flow are in opposite directions. For a fixed block length, the governing parameters in the present Darcy flow problem are: Rayleigh number (Ra), Peclet number (Pe), solid-to-porous thermal conductivity ratio (Kr), the dimensionless thickness (or height) of the solid wall (H), in addition to the dimensionless jet width (D). The results are presented in the mixed convection regime with wide ranges of the governing parameters. At low values of Pe (natural convection cases), it is found that the effect of Pe and the jet width are negligible and the average Nusselt number (Nu) is increasing with the increase of either Rayleigh number or the thermal conductivity ratio, or decreasing the thickness of the solid wall. At high values of Pe (forced convection cases), it is found that the effect of Ra is negligible and Nu increases with either increasing Pe values, the thermal conductivity ratio or jet width, or decreasing the thickness of the solid wall. At moderate values of Pe (opposing mixed convection cases), it is observed that the values of average Nusselt number show minimum values. The value of Pe at which minimum Nu occurs depends on Ra, thermal conductivity ratio, jet width, and the thickness of the solid wall. At low values of either Ra or thermal conductivity ratio, this case where Nu shows a minimum value is not obvious. It is found that the thinner solid walls have higher values of the average Nusselt number with other parameters fixed. Therefore, for cooling applications, the numerical results indicate that the solid wall should be as thin as possible, with high thermal conductivity. The present results show that the cooling rate with the opposing missed convection mode is lower than that with the natural convention mode. The results show that the effect of the jet width D can be incorporated by plotting the average Nusselt number against Pe × D, where the results form a single curve for different values of the jet width.
Nawaf
Saeid
Mechanical Engineering Programme, Faculty of Engineering
401-413
EFFECTS OF INTERNAL HEAT GENERATION OR ABSORPTION ON HEAT TRANSFER AND FLUID FLOW WITHIN PARTIALLY HEATED SQUARE ENCLOSURE: HOMOGENEOUS FLUIDS AND POROUS MEDIA
The effects of internal heat generation or absorption on heat transfer and fluid flow within a partially heated square cavity for both homogeneous medium and porous medium are investigated in the current study. The Darcy−Brinkman and the energy transport equations are used to predict the heat transfer process in the porous medium when it is generated by heating at the bottom walls of the cavity. Numerical results are presented and analyzed in terms of fluid flow, thermal field structures, as well as average Nusselt number profiles over a wide range of dimensionless quantities [internal Rayleigh number (RaI) varied between −106 and 106, heat source length, porosity coefficient values, and Darcy number in the range 10−5 to 10−2]. The effect of heat generation and absorption in the homogenous medium and porous medium is also discussed. It was seen that an optimal heat transfer rate is obtained for both high internal Rayleigh number and high porosity coefficient (ε = 0.8 and RaI = 106, whereas a lower thermal rate was found in the first computations for (ε = 0.4 and RaI = 105). The correlations of heat transfer rates in both homogenous and porous medium cases are established in the current investigation.
Najib
Hdhiri
University of Tunis El Manar, Faculty of Sciences of Tunis, Laboratory of Fluid Mechanics, Department of Physics, 2092 Tunis, Tunisia
Brahim
Ben-Beya
University of Tunis El Manar, Faculty of Sciences of Tunis, Laboratory of Fluid Mechanics, Department of Physics, 2092 Tunis, Tunisia
Taieb
Lili
University of Tunis El Manar, Faculty of Sciences of Tunis, Laboratory of Fluid Mechanics, Department of Physics, 2092 Tunis, Tunisia
415-435
LAMINAR FORCED CONVECTION OF FERROFLUID IN A HORIZONTAL TUBE PARTIALLY FILLED WITH POROUS MEDIA IN THE PRESENCE OF A MAGNETIC FIELD
The effect of magnetic field on laminar forced convection of ferrofluid in a horizontal tube partially filled with porous media is investigated. Governing equations are solved numerically using the finite volume method and the SIMPLE algorithm, to obtain thermohydrodynamic characteristics and enhancement of heat transfer for different porous locations and Darcy numbers (Da). The Brinkman-Darcy model is used for simulation of homogeneous isotropic porous media that is located at the core, concentric to the tube, and local thermal equilibrium is assumed between the fluid and the solid matrix. The tube is under constant heat flux, volume fraction of the nanoparticles; Reynolds and Prandtl numbers are assumed constants. Numerical results show that using a magnetic field to reduce the pressure drop while using porous media enhances heat transfer. Also, it was found that decreasing the Darcy number from 0.1 to 0.001 results in a 56% enhancement of heat transfer. By increasing the radius ratio of porous media to the tube from 0.2 to 0.8 results in heat transfer enhancement of up to 57%. Moreover, using ferrofluid with a higher thermal conductivity than the base fluid results in a twofold heat transfer enhancement in the fully developed region and even more in the developing zone.
Yahya
Sheikhnejad
Mechanical Engineering Department, Amirkabir University of Technology, 424 Hafez Avenue, P.O. Box 15875-4413, Tehran, Iran
Reza
Hosseini
School of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), 424 Hafez Avenue, Tehran, Iran
Majid Saffar
Avval
Mechanical Engineering Department, Amirkabir University of Technology, 424 Hafez Avenue, P.O. Box 15875-4413, Tehran, Iran
437-448
NON-DARCY FLUID FLOW AND HEAT TRANSFER IN CONDUITS FITTED WITH POROUS MEDIA
Darcy's law may not he applicable for flows through highly permeable porous mediums. It is important to understand the limits of Darcy's law for flow and heat transfer through porous media. Therefore the entrance length and hydrodynamic boundary layer developing in conduits will be a function of Darcy's number and Reynolds number. In the following work, the dependence of entrance length on the Darcy and Reynolds number is correlated as a function of the controlling parameters. Also, heat transfer and thermal boundary-layer developments along the conduit are presented. The results of laminar flow in pipes are presented. Also, the effect of thermal conductivity and other controlling parameters on the rate of heat transfer are discussed for conduits filled completely or partially with porous media.
Abdulmajeed A.
Mohamad
Department of Mechanical and Manufacturing Engineering, Schulich School of Engineering, CEERE, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4
Jamel
Orfi
Department of Mechanical Engineering, King Saud University, Riyadh, Saudi Arabia
H.
Al-Ansary
Department of Mechanical Engineering, King Saud University, Riyadh, Saudi Arabia
449-453
DARCY FLOW THROUGH BUMPY TUBES
The Darcy flow in a tube with three-dimensional wall roughness is studied. Three types of bumps or roughness geometry are considered. The problem is solved by the perturbation method, assuming the amplitude of the bumps is small compared to the mean tube radius. For a given mean pressure gradient in a tube of given mean radius, the flow rate may increase or decrease depending on the roughness geometry.
C. Y.
Wang
Department of Mathematics, Michigan State University, East Lansing, MI 49924
L. H.
Yu
Department of Mathematics, National Chung Cheng University, Chiayi, Taiwan
457-461