Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
19
10
2016
ELECTRIC POWER GENERATION FROM COMBUSTION IN POROUS MEDIA
Combustion of lean air/fuel mixtures in an inert porous medium provides an efficient way to convert chemical energy of hydrocarbons into thermal energy. The porous medium effectively redistributes the heat allowing the reacting mixture to be preheated before the combustion front. For a lean propane/air mixture (equivalence ratio Φ ~ 0.6), the combustion front is steady and the combustion temperature is subadiabatic. At lower equivalence ratios the heat wave in the porous media and the combustion front can move synchronously downstream developing superadiabatic temperatures. This superadiabatic effect allows to operate at the range of ultralean mixtures (Φ ~ 0.1). Thermal energy generated by the combustion process can be converted into electricity by thermoelectric modules (TEMs). In this work, a cylindrical porous burner is designed to absorb the heat of combustion of lean propane/air mixtures. The burner is inserted in a rectangular steel block. The surface of the block is covered by a set of operating TEMs. Confining the combustion front is stabilized by using porous media with different pore sizes. Temperatures are recorded in different regions of the burner by using surface and immersion thermocouples. Adjusting the equivalence ratio, the flow rate of the gaseous mixture, the properties of the porous media, and the TEM characteristics, a quasi-static burn rate is achieved with the surrounding surface at the nominal temperatures required by the TEMs. The maximum electrical power of 9.42 W and the overall conversion efficiency of 2.93% are reached with a voltage of 5.93 V and a current of 1.59 A using a setup of four TEMs electrically connected in series.
Valeri
Bubnovich
Department of Chemical Engineering, Universidad de Santiago de Chile, 3363 B. O'Higgins, Santiago, Chile
Pedro
San Martin
Department of Chemical Engineering, Universidad de Santiago de Chile, 3363 B. O'Higgins, Santiago, Chile
Luis
Henriquez-Vargas
Department of Chemical Engineering, Universidad de Santiago de Chile, 3363 B. O'Higgins, Santiago, Chile
Nina
Orlovskaya
Department of Mechanical and Aerospace Engineering, University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816-2450
Hernan A.
Gonzaiez-Rojas
Departamento de Ingenieria Mecanica, Tecnologias de Fabricacion, Universidad Politecnica de Cataluna-ETSEIB, Av. Diagonal 647, 08028 Barcelona, Spain
841-851
IRREVERSIBILITY ANALYSIS IN MIXED CONVECTION FLOW IN A POROUS CHANNEL WITH VISCOUS DISSIPATION
Various constraints acting on a flow, such as heat transfer, viscous fluid friction, and chemical reaction, are sources of irreversibility and therefore responsible for entropy generation. In this paper, the mixed convection with viscous dissipation effect in an inclined channel filled with a saturated porous medium is investigated numerically, by using the Darcy-Brinkman model. The Navier-Stokes and energy equations are solved by classic Boussinesq approximation. First, the effect of the Darcy number on the total entropy generation in the horizontal porous channel is investigated in the absence and in the presence of viscous the dissipation term. In this case, the Prandtl number and the Brinkman number are considered as parameters. The contribution of the different irreversibility causes on the total entropy generation is analyzed by the investigation of the Bejan number versus Darcy number, with the Prandtl number as parameter. Next, the fluctuations of the transient total entropy generation were investigated when the inclination angle varies from 0 deg to 180 deg. Moreover, the effect of the channel inclination angle on both the entropy generation and the Bejan number was investigated. It was found that the total entropy generation is maximum at inclination angle close to 70 deg and minimum at 0 deg and 180 deg.
Amel
Tayari
Chemical and Process Engineering Department, Engineers National School of Gabes, Gabes University, Applied Thermodynamics Unit, Omar Ibn El Khattab St., 6029 Gabes, Tunisia
Rahma
Bouabda
Chemical and Process Engineering Department, Engineers National School of Gabes, Gabes University, Applied Thermodynamics Unit, Omar Ibn El Khattab St., 6029 Gabes, Tunisia
Mourad
Magherbi
Chemical and Process Engineering Department, Engineers National School of Gabes, Gabes University, Applied Thermodynamics Unit, Omar Ibn El Khattab St., 6029 Gabes, Tunisia
853-870
TRIPLE DIFFUSIVE CONVECTION IN A MAXWELL FLUID SATURATED POROUS LAYER: DARCY- BRINKMAN-MAXWELL MODEL
The onset of convective instability is analyzed in a triply diffusive Maxwell fluid saturated porous layer (using the Darcy-Brinkman-Maxwell model) in which density depends on three stratifying agencies (one of them is heat) having different diffusivities. Two problems have been analyzed mathematically. In the first problem, a sufficient condition is derived for the validity of the principle of the exchange of stabilities. Further, when the complement of this condition holds good, oscillatory motions of neutral or growing amplitude can exist. Thus as a second problem bounds for the complex growth rate are also obtained. The above results are uniformly valid for the quite general nature of the bounding surfaces.
Jyoti
Prakash
Department of Mathematics and Statistics, Himachal Pradesh University Summer Hill, Shimla-171005, India
Kultaran
Kumari
Department of Mathematics and Statistics, Himachal Pradesh University, Summer Hill, Shimla 171005, India
Rajeev
Kumar
Department of Mathematics, Kurukshetra University, Kurukshetra 136119, India; Department of Mathematics and Statistics, Himachal Pradesh University, Summer Hill, Shimla 171005, India
871-883
COMPARISON STUDY OF DIFFERENT VISCOUS DISSIPATION EFFECTS ON FORCED CONVECTION HEAT TRANSFER IN A POWER LAW FLUID SATURATED POROUS MEDIUM
Based on the Darcy-Brinkman-Forchheimer flow model, this study analyzed and compared the viscous dissipation effects during the process of a forced and fully developed convection heat transfer in a flat channel. The channel was filled with a kind of porous medium saturated by a power law fluid. Three different terms were considered to analyze the viscous dissipation, namely, the Darcy term, Al-Hadharami term, and Forchheimer term. In this comparative study, we have taken the Forchhemier term into consideration since some researchers thought it might have an indirect effect on the dissipation function, although others argued. The dimensionless calculation expressions of the axial velocity distribution and temperature distribution were deduced, and solved numerically by employing the classical Runge-Kutta fourth-order scheme subject to uniform heat flux. Variations of the dimensionless temperature are examined and discussed, which is the function of the Brinkman number, Darcy number, Forchheimer inertial parameter, and power law index. It is found that the temperature profiles were quite close to the velocity profiles and obviously influenced by the relative magnitude of these dimensionless parameters. The results also indicated that the rate of heat transfer was significantly affected by different viscous dissipation terms.
Xingwang
Tian
School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, China; School of Ocean and Civil Engineering, Dalian Ocean University, Dalian 116023, China
Ping
Wang
School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, China
Shiming
Xu
Dalian University of Technology, 2 Ling Gong Rd. Gan Jingzi District, Dalian 116024, China
Xi
Wu
Dalian University of Technology, 2 Ling Gong Rd. Gan Jingzi District, Dalian 116024, China
885-900
SLIP VELOCITY AND TEMPERATURE JUMP EFFECTS ON CONVECTION FROM A VERTICAL SURFACE EMBEDDED IN SATURATED POROUS MEDIA
In this, work the slip velocity and temperature jump effects on convection from a vertical plate embedded in porous media using a Darcy model has been investigated numerically. Governing equations, continuity, Darcy law, and energy were transformed into dimensionless form using a set of suitable variables and then solved numerically using a finite difference method. Results obtained were graphically drawn to illustrate the effects of slip velocity and temperature jump on the near-plate fluid velocity, temperature, shear stress, and Nusselt number. It was found that increasing of slip velocity caused decreasing in velocity and increasing heat transfer rates near the surface, while the increasing of temperature jump parameter reduced velocity and heat transfer between surface and fluid. Besides temperature jump, heat transfer is most enhanced in mixed convection compared with natural and forced convection. It was also found that the slip velocity and temperature jump do not affect the rate of forced convection heat transfer.
Hamzeh M.
Duwairi
Mechanical Engineering Department, Faculty of Engineering and Technology, The University of Jordan, 11942, Amman, Jordan
V. M.
Al-Khliefat
Jordanian Military Forces
901-912
UNSTEADY MIXED CONVECTION FLOW OVER A VERTICAL PLATE IN A POROUS MEDIUM WITH NON-UNIFORM SLOT SUCTION/INJECTION
The aim of this paper is to present the unsteady mixed convection flow over a moving vertical plate in a parallel free stream embedded in a porous medium under the effect of thermal radiation in the presence of nonuniform slot suction (injection). The unsteadiness is caused by the time-dependent free stream velocity varying arbitrarily with time. Nonsimilar solutions are obtained by solving the coupled nonlinear partial differential equations using the quasi-linearization technique in combination with an implicit finite-difference scheme. The numerical values obtained within the boundary layer for the dimensionless velocity, temperature, concentration, the local skin friction coefficient, the local Nusselt, and Sherwood numbers are presented through graphs and a table for several sets of values of the parameters. Results indicate that the local skin friction coefficient, the local Nusselt number and the Sherwood number increase with nonuniform slot suction, but the effect of nonuniform slot injection is just opposite. A comparison with previous studies available in the literature has been done and we found an excellent agreement with them.
N.
Samyuktha
Department of Mathematics, National Institute of Technology, Tiruchirappalli-620 015, Tamil Nadu, India
R.
Ravindran
Department of Mathematics, National Institute of Technology, Tiruchirappalli-620 015, Tamil Nadu, India
M.
Ganapathirao
Mathematics & Basic Science, NIIT University, Neemrana, NH-8, Delhi-Jaipur Highway, Alwar District, Rajasthan-301 705, India
913-930