Application of artificial neural network for heat transfer in porous cone

Science.gov (United States)

Athani, Abdulgaphur; Ahamad, N. Ameer; Badruddin, Irfan Anjum

2018-05-01

Heat transfer in porous medium is one of the classical areas of research that has been active for many decades. The heat transfer in porous medium is generally studied by using numerical methods such as finite element method; finite difference method etc. that solves coupled partial differential equations by converting them into simpler forms. The current work utilizes an alternate method known as artificial neural network that mimics the learning characteristics of neurons. The heat transfer in porous medium fixed in a cone is predicted using backpropagation neural network. The artificial neural network is able to predict this behavior quite accurately.

Thermal non-equilibrium in porous medium adjacent to vertical plate: ANN approach

Science.gov (United States)

Ahmed, N. J. Salman; Ahamed, K. S. Nazim; Al-Rashed, Abdullah A. A. A.; Kamangar, Sarfaraz; Athani, Abdulgaphur

2018-05-01

Thermal non-equilibrium in porous medium is a condition that refers to temperature discrepancy in solid matrix and fluid of porous medium. This type of flow is complex flow requiring complex set of partial differential equations that govern the flow behavior. The current work is undertaken to predict the thermal non-equilibrium behavior of porous medium adjacent to vertical plate using artificial neural network. A set of neurons in 3 layers are trained to predict the heat transfer characteristics. It is found that the thermal non-equilibrium heat transfer behavior in terms of Nusselt number of fluid as well as solid phase can be predicted accurately by using well-trained neural network.

Evaluation of the dependence of heat transfer coefficient on the particle diameter of a metal porous medium in a heat removal system using liquid nitrogen

International Nuclear Information System (INIS)

Sasaki, Shunsuke; Ito, Satoshi; Hashizume, Hidetoshi

2015-01-01

Cryogenic cooling system using a bronze-particle-sintered porous medium has been studied for a re mountable high-temperature superconducting magnet. This study evaluates boiling curve of subcooled liquid nitrogen as flowing in a bronze porous medium as a function of the particle diameter of the medium. We obtained Departure from Nuclear Boiling (Dnb) point from the boiling curve and discussed growth of nitrogen vapor bubble inferred from measured pressure drop. The pressure drop decreased significantly at wall superheat before reaching the DNB point whereas that slightly decreased after reaching the DNB point compared to the smallest wall superheat. This result could consider DNB rises with an increase in the particle diameter because larger particle makes vapor to move easily from the heated pore region. The influence of the particle diameter on the heat transfer performance is larger than that of coolant's degree of subcooling. (author)

Fully-developed conjugate heat transfer in porous media with uniform heating

NARCIS (Netherlands)

Lopez Penha, D.J.; Stolz, S.; Kuerten, Johannes G.M.; Nordlund, M.; Kuczaj, Arkadiusz K.; Geurts, Bernardus J.

2012-01-01

We propose a computational method for approximating the heat transfer coefficient of fully-developed flow in porous media. For a representative elementary volume of the porous medium we develop a transport model subject to periodic boundary conditions that describes incompressible fluid flow through

Numerical Simulation of Transient Free Convection Flow and Heat Transfer in a Porous Medium

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Rajesh Sharma

2013-01-01

Full Text Available The coupled momentum and heat transfer in unsteady, incompressible flow along a semi-infinite vertical porous moving plate adjacent to an isotropic porous medium with viscous dissipation effect are investigated. The Darcy-Forchheimer nonlinear drag force model which includes the effects of inertia drag forces is employed. The governing differential equations of the problem are transformed into a system of nondimensional differential equations which are solved numerically by the finite element method (FEM. The non-dimensional velocity and temperature profiles are presented for the influence of Darcy number, Forchheimer number, Grashof number, Eckert number, Prandtl number, plate velocity, and time. The Nusselt number is also evaluated and compared with finite difference method (FDM, which shows excellent agreement.

Combined effect of thermal dispersion and variable viscosity of non-darcy convection heat transfer in a fluidsaturated porous medium

KAUST Repository

El-Amin, Mohamed; Salama, Amgad; El-Amin, Ammaarah A.; Gorla, Rama Subba Reddy

2013-01-01

In this paper, the effects of thermal dispersion and variable viscosity on the non-Darcy free, mixed, and forced convection heat transfer along a vertical flat plate embedded in a fluid-saturated porous medium are investigated. Forchheimer extension

Tracer transfer in consolidated porous medium and fractured porous medium: experimentations and modelling

International Nuclear Information System (INIS)

Dalla Costa, C.

2007-07-01

We try to identify and model physical and chemical mechanisms governing the water flow and the solute transport in fractured consolidated porous medium. An original experimental device was built. The 'cube' consists of an idealized fractured medium reproduced by piling up consolidated porous cubes of 5 cm edge. Meanwhile, columns of the homogeneous consolidated porous medium are studied. The same anionic tracing technique is used in both cases. Using a system analysis approach, we inject concentration pulses in the device to obtain breakthrough curves. After identifying the mass balance and the residence time, we fit the CD and the MIM models to the experimental data. The MIM model is able to reproduce experimental curves of the homogeneous consolidated porous medium better than the CD model. The mobile water fraction is in accordance with the porous medium geometry. The study of the flow rate influence highlights an interference dispersion regime. It was not possible to highlight the observation length influence in this case. On the contrary, we highlight the effect of the observation scale on the fractured and porous medium, comparing the results obtained on a small 'cube' and a big 'cube'. The CD model is not satisfactory in this case. Even if the MIM model can fit the experimental breakthrough curves, it was not possible to obtain unique parameters for the set of experiments. (author)

Fully developed natural convection heat and mass transfer in a vertical annular porous medium with asymmetric wall temperatures and concentrations

International Nuclear Information System (INIS)

Cheng, C.-Y.

2006-01-01

This work examines the effects of the modified Darcy number, the buoyancy ratio and the inner radius-gap ratio on the fully developed natural convection heat and mass transfer in a vertical annular non-Darcy porous medium with asymmetric wall temperatures and concentrations. The exact solutions for the important characteristics of fluid flow, heat transfer, and mass transfer are derived by using a non-Darcy flow model. The modified Darcy number is related to the flow resistance of the porous matrix. For the free convection heat and mass transfer in an annular duct filled with porous media, increasing the modified Darcy number tends to increase the volume flow rate, total heat rate added to the fluid, and the total species rate added to the fluid. Moreover, an increase in the buoyancy ratio or in the inner radius-gap ratio leads to an increase in the volume flow rate, the total heat rate added to the fluid, and the total species rate added to the fluid

Experimental studies on solar parabolic dish cooker with porous medium

International Nuclear Information System (INIS)

Lokeswaran, S.; Eswaramoorthy, M.

2012-01-01

The solar cooking is the alternate method of cooking to reduce consumptions of fossil fuels. An affordable, energy efficient solar cooking technology is much need due to the fossil fuels increasing cost and it is the hottest research topic in all over the world. This paper presents an experimental analysis of the heat transfer enhancement of solar parabolic dish cookers by a porous medium made of scrap material. Using the stagnation temperature test and water boiling test are conducted on the cooking vessel with and without porous medium. Experimental results are compared for both cases in terms of thermal performance, optical efficiency, heat loss factor and cooking power. (authors)

Radiative properties effects on unsteady natural convection inside a saturated porous medium. Application for porous heat exchangers

International Nuclear Information System (INIS)

Abdesslem, Jbara; Khalifa, Slimi; Abdelaziz, Nasr; Abdallah, Mhimid

2013-01-01

The present article deals with a numerical study of coupled fluid flow and heat transfer by transient natural convection and thermal radiation in a porous bed confined between two-vertical hot plates and saturated by a homogeneous and isotropic fluid phase. The main objective is to study the effects of radiative properties on fluid flow and heat transfer behavior inside the porous material. The numerical results show that the temperature, the axial velocity, the volumetric flow rate and the convective heat flux exchanged at the channel's exit are found to be increased when the particle emissivity (ε) and/or the absorption coefficient (κ) increase or when the scattering coefficient (σ s ) and/or the single scattering albedo (ω) decrease. Furthermore, the amount of heat (Q c ) transferred to fluid and the energetic efficiency E c are found to be increased when there is a raise in the particle emissivity values. In order to improve the performance of heat exchanger, we proposed the model of a porous heat exchanger which includes a porous bed of large spherical particles with high emissivity as a practical application of the current study. - Highlights: • The temperature increases with the particle emissivity ε. • The volumetric flow rate and the convective heat flux exchanged increase with the particle emissivity ε. • The amount of heat transferred to fluid and the energetic efficiency increase with the particle emissivity ε. • A heat exchanger including a porous bed of spherical particles with high emissivity is proposed like a practical application

Homogeneous-heterogeneous reactions in curved channel with porous medium

Science.gov (United States)

Hayat, T.; Ayub, Sadia; Alsaedi, A.

2018-06-01

Purpose of the present investigation is to examine the peristaltic flow through porous medium in a curved conduit. Problem is modeled for incompressible electrically conducting Ellis fluid. Influence of porous medium is tackled via modified Darcy's law. The considered model utilizes homogeneous-heterogeneous reactions with equal diffusivities for reactant and autocatalysis. Constitutive equations are formulated in the presence of viscous dissipation. Channel walls are compliant in nature. Governing equations are modeled and simplified under the assumptions of small Reynolds number and large wavelength. Graphical results for velocity, temperature, heat transfer coefficient and homogeneous-heterogeneous reaction parameters are examined for the emerging parameters entering into the problem. Results reveal an activation in both homogenous-heterogenous reaction effect and heat transfer rate with increasing curvature of the channel.

Analysis of Cattaneo-Christov heat and mass fluxes in the squeezed flow embedded in porous medium with variable mass diffusivity

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M. Farooq

Full Text Available This research article investigates the squeezing flow of Newtonian fluid with variable viscosity over a stretchable sheet inserted in Darcy porous medium. Cattaneo-Christov double diffusion models are implemented to scrutinize the characteristics of heat and mass transfer via variable thermal conductivity and variable mass diffusivity. These models are the modification of conventional laws of Fourier’s and Fick’s via thermal and solutal relaxation times respectively. The homotopy analysis Method (HAM is being utilized to provide the solution of highly nonlinear system of coupled partial differential equations after converted into dimensionless governing equations. The behavior of flow parameters on velocity, concentration, and temperature distributions are sketched and analyzed physically. The result indicates that both concentration and temperature distributions decay for higher solutal and thermal relaxation parameters respectively. Keywords: Squeezing flow, Porous medium, Variable viscosity, Cattaneo-Christov heat and mass flux models, Variable thermal conductivity, Variable mass diffusivity

Irreversibility analysis of hydromagnetic flow of couple stress fluid with radiative heat in a channel filled with a porous medium

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A.S. Eegunjobi

Full Text Available Numerical analysis of the intrinsic irreversibility of a mixed convection hydromagnetic flow of an electrically conducting couple stress fluid through upright channel filled with a saturated porous medium and radiative heat transfer was carried out. The thermodynamics first and second laws were employed to examine the problem. We obtained the dimensionless nonlinear differential equations and solves numerically with shooting procedure joined with a fourth order Runge-Kutta-Fehlberg integration scheme. The temperature and velocity obtained, used to analyse the entropy generation rate together with some various physical parameters of the flow. Our results are presented graphically and talk over. Keywords: MHD channel flow, Couple stress fluid, Porous medium, Thermal radiation, Entropy generation, Injection/suction

Natural convection in a porous medium: External flows

International Nuclear Information System (INIS)

Cheng, P.

1985-01-01

Early theoretical work on heat transfer in porous media focussed its attention on the onset of natural convection and cellular convection in rectangular enclosures with heating from below. Recently, increased attention has been directed to the study of natural convection in a porous medium external to heated surfaces and bodies. Boundary layer approximations were introduced, and similarly solutions have been obtained for steady natural convection boundary layers adjacent to a heated flat plate, a horizontal cylinder and a sphere as well as other two-dimensional and axisymmetric bodies of arbitrary shape. Higher order boundary layer theories have been carried out to assess the accuracy of the boundary layer approximation. The effects of entrainments at the edge of the boundary layer, the inclination angle of the heated inclined plate, and the upstream geometry on the heat transfer characteristics have been investigated based on the method of matched asymptotic expansions. The conditions for the onset of vortex instability in porous layers heated from below were determined based on linear stability analyses. The effects of no-slip boundary conditions, non-Darcy and thermal dispersion, which were neglected in all of the previous theoretical investigations, have recently been re-examined. Experimental investigations on natural convection about a vertical and inclined heated plate, a horizontal cylinder, as well as plume rise from a horizontal line source of heat have been conducted. All of this work is reviewed in this paper

Analytical method for steady state heat transfer in two-dimensional porous media

Energy Technology Data Exchange (ETDEWEB)

Siegal, R.; Goldstein, M.E.

1970-07-01

A general technique has been devised for obtaining exact solutions for the heat transfer behavior of a 2- dimensional porous cooled medium. Fluid flows through the porous medium from a reservoir at constant pressure and temperature to a second reservoir at a lower pressure. For the type of flow involved, the surfaces of the porous region that are each at constant pressure are boundaries of constant velocity potential. This fact is used to map the porous region into a strip bounded by parallel potential lines in a complex potential plane. The energy equation, derived by assuming the local matrix and fluid temperatures are equal, is transformed into a separable equation when its independent variables are changed to the coordinates of the potential plane. This allows the general solution for the temperature distribution to be found in the potential plane. The solution is then mapped into the physical plane to yield the heat transfer characteristics of the porous region. An example problem of a porous wall having a step in thickness and a specified surface temperature or heat flux is worked out in detail.

Throughflow and non-uniform heating effects on double diffusive oscillatory convection in a porous medium

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Palle Kiran

2016-03-01

Full Text Available A weak nonlinear oscillatory mode of thermal instability is investigated while deriving a non autonomous complex Ginzburg–Landau equation. Darcy porous medium is considered in the presence of vertical throughflow and time periodic thermal boundaries. Only infinitesimal disturbances are considered. The disturbances in velocity, temperature and solutal fields are treated by a perturbation expansion in powers of amplitude of applied temperature field. The effect of throughflow has either to stabilize or to destabilize the system for stress free and isothermal boundary conditions. Nusselt and Sherwood numbers are obtained numerically and presented the results on heat and mass transfer. It is found that, throughflow and thermal modulation can be used alternatively to control the heat and mass transfer. Further, it is also found that oscillatory flow enhances the heat and mass transfer than stationary flow. Effect of modulation frequency and phase angle on mean Nusselt number is also discussed.

Hall effects on MHD flow of heat generating/absorbing fluid through porous medium in a rotating parallel plate channel

Science.gov (United States)

Swarnalathamma, B. V.; Krishna, M. Veera

2017-07-01

We studied heat transfer on MHD convective flow of viscous electrically conducting heat generating/absorbing fluid through porous medium in a rotating channel under uniform transverse magnetic field normal to the channel and taking Hall current. The flow is governed by the Brinkman's model. The diagnostic solutions for the velocity and temperature are obtained by perturbation technique and computationally discussed with respect to flow parameters through the graphs. The skin friction and Nusselt number are also evaluated and computationally discussed with reference to pertinent parameters in detail.

Nonlinear radiative peristaltic flow of hydromagnetic fluid through porous medium

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Q. Hussain

2018-06-01

Full Text Available The radiative heat and mass transfer in wall induced flow of hydromagnetic fluid through porous medium in an asymmetric channel is analyzed. The fluid viscosity is considered temperature dependent. In the theory of peristalsis, the radiation effects are either ignored or taken as linear approximation of radiative heat flux. Such approximation is only possible when there is sufficiently small temperature differences in the flow field; however, nonlinear radiation effects are valid for large temperature differences as well (the new feature added in the present study. Mathematical modeling of the problems include the complicated system of highly nonlinear differential equations. Semi-analytical solutions are established in the wave reference frame. Results are displayed graphically and discussed in detail for the variation of various physical parameters with the special attention to viscosity, radiation, and temperature ratio parameters. Keywords: Nonlinear thermal radiation, Variable viscosity, Porous medium, Soret and Dufour effects, Peristalsis

Non-Darcy Mixed Convection in a Doubly Stratified Porous Medium with Soret-Dufour Effects

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D. Srinivasacharya

2014-01-01

Full Text Available This paper presents the nonsimilarity solutions for mixed convection heat and mass transfer along a semi-infinite vertical plate embedded in a doubly stratified fluid saturated porous medium in the presence of Soret and Dufour effects. The flow in the porous medium is described by employing the Darcy-Forchheimer based model. The nonlinear governing equations and their associated boundary conditions are initially cast into dimensionless forms and then solved numerically. The influence of pertinent parameters on dimensionless velocity, temperature, concentration, heat, and mass transfer in terms of the local Nusselt and Sherwood numbers is discussed and presented graphically.

Effects of key factors on solar aided methane steam reforming in porous medium thermochemical reactor

International Nuclear Information System (INIS)

Wang, Fuqiang; Tan, Jianyu; Ma, Lanxin; Leng, Yu

2015-01-01

Highlights: • Effects of key factors on chemical reaction for solar methane reforming are studied. • MCRT and FVM method coupled with UDFs is used to establish numerical model. • Heat and mass transfer model coupled with thermochemical reaction is established. • LTNE model coupled with P1 approximation is used for porous matrix solar reactor. • A formula between H 2 production and conductivity of porous matrix is put forward. - Abstract: With the aid of solar energy, methane reforming process can save up to 20% of the total methane consumption. Monte Carlo Ray Tracing (MCRT) method and Finite Volume Method (FVM) combined method are developed to establish the heat and mass transfer model coupled with thermochemical reaction kinetics for porous medium solar thermochemical reactor. In order to provide more temperature information, local thermal non-equilibrium (LTNE) model coupled with P1 approximation is established to investigate the thermal performance of porous medium solar thermochemical reaction. Effects of radiative heat loss and thermal conductivity of porous matrix on temperature distribution and thermochemical reaction for solar driven steam methane reforming process are numerically studied. Besides, the relationship between hydrogen production and thermal conductivity of porous matrix are analyzed. The results illustrate that hydrogen production shows a 3 order polynomial relation with thermal conductivity of porous matrix

Computational investigation of fluid flow and heat transfer of an economizer by porous medium approach

Science.gov (United States)

Babu, C. Rajesh; Kumar, P.; Rajamohan, G.

2017-07-01

Computation of fluid flow and heat transfer in an economizer is simulated by a porous medium approach, with plain tubes having a horizontal in-line arrangement and cross flow arrangement in a coal-fired thermal power plant. The economizer is a thermal mechanical device that captures waste heat from the thermal exhaust flue gasses through heat transfer surfaces to preheat boiler feed water. In order to evaluate the fluid flow and heat transfer on tubes, a numerical analysis on heat transfer performance is carried out on an 110 t/h MCR (Maximum continuous rating) boiler unit. In this study, thermal performance is investigated using the computational fluid dynamics (CFD) simulation using ANSYS FLUENT. The fouling factor ε and the overall heat transfer coefficient ψ are employed to evaluate the fluid flow and heat transfer. The model demands significant computational details for geometric modeling, grid generation, and numerical calculations to evaluate the thermal performance of an economizer. The simulation results show that the overall heat transfer coefficient 37.76 W/(m2K) and economizer coil side pressure drop of 0.2 (kg/cm2) are found to be conformity within the tolerable limits when compared with existing industrial economizer data.

MHD effects on heat transfer over stretching sheet embedded in porous medium with variable viscosity, viscous dissipation and heat source/sink

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Hunegnaw Dessie

2014-09-01

Full Text Available In this analysis, MHD boundary layer flow and heat transfer of a fluid with variable viscosity through a porous medium towards a stretching sheet by taking in to the effects of viscous dissipation in presence of heat source/sink is considered. The symmetry groups admitted by the corresponding boundary value problem are obtained by using Lie’s scaling group of transformations. These transformations are used to convert the partial differential equations of the governing equations into self-similar non-linear ordinary differential equations. Numerical solutions of these equations are obtained by Runge-Kutta fourth order with shooting method. Numerical results obtained for different parameters such as viscosity variation parameter A, permeability parameter k1, heat source/sink parameter λ, magnetic field parameter M, Prandtl number Pr, and Eckert number Ec are drawn graphically and effects of different flow parameters on velocity and temperature profiles are discussed. The skin-friction coefficient -f″(0 and heat transfer coefficient −θ′(0 are presented in tables.

A porous medium model for predicting the duct wall temperature of sodium fast reactor fuel assembly

Energy Technology Data Exchange (ETDEWEB)

Yu, Yiqi, E-mail: yyu@anl.gov [Nuclear Engineering Division, Argonne National Laboratory, Lemont, IL 60439 (United States); Merzari, Elia; Obabko, Aleksandr [Mathematics and Computer Science Division, Argonne National Laboratory, Lemont, IL 60439 (United States); Thomas, Justin [Nuclear Engineering Division, Argonne National Laboratory, Lemont, IL 60439 (United States)

2015-12-15

Highlights: • The proposed models are 400 times less computationally expensive than CFD simulations. • The proposed models show good duct wall temperature agreement with CFD simulations. • The paper provides an efficient tool for coupled radial core expansion calculation. - Abstract: Porous medium models have been established for predicting duct wall temperature of sodium fast reactor rod bundle assembly, which is much less computationally expensive than conventional CFD simulations that explicitly represent the wire-wrap and fuel pin geometry. Three porous medium models are proposed in this paper. Porous medium model 1 takes the whole assembly as one porous medium of uniform characteristics in the conventional approach. Porous medium model 2 distinguishes the pins along the assembly's edge from those in the interior with two distinct regions, each with a distinct porosity, resistance, and volumetric heat source. This accounts for the different fuel-to-coolant volume ratio in the two regions, which is important for predicting the temperature of the assembly's exterior duct wall. In Porous medium model 3, a precise resistance distribution was employed to define the characteristic of the porous medium. The results show that both porous medium model 2 and 3 can capture the average duct wall temperature well. Furthermore, the local duct wall variations due to different sub-channel patterns in bare rod bundles are well captured by porous medium model 3, although the wire effect on the duct wall temperature in wire wrap rod bundle has not been fully reproduced yet.

Fundamental research on the gravity assisted heat pipe thermal storage unit (GAHP-TSU) with porous phase change materials (PCMs) for medium temperature applications

International Nuclear Information System (INIS)

Hu, Bo-wen; Wang, Qian; Liu, Zhen-Hua

2015-01-01

Highlights: • A novel gravity-assisted heat pipe thermal storage unit (GAHP-TSU) is presented and tested. • Composite granular solid–liquid PCM is piled up as the porous medium layer in GAHP-TSU. • GAHP-TSU avoids the major obstacle of low thermal conductivity of the PCM. • GAHP-TSU enables the thermal storage unit with outstanding heat transfer performance. - Abstract: In this study, a novel gravity-assisted heat pipe type thermal storage unit (GAHP-TSU) has been presented for the potential application in solar air conditioning and refrigeration systems, in which composite granular solid–liquid PCMs compounded by RT100 and high-density polyethylene with phase change temperature of 100 °C are piled up as a porous PCMs medium layer. Water is used as heat transfer fluid in the GAHP-TSU. The heat transfer mechanism of heat storage/release in the GAHP-TSU is similar to that of the gravity-assisted heat pipe, which is superior to traditional direct-contact or indirect-contact thermal storage units. The properties of start-up, heat transfer characteristics on the stages of heat absorption and release of the GAHP-TSU are studied in detailed, including necessary calculations based on heat transfer theory. The results show that the whole system is almost isothermal at the temperature over 70 °C and the heat transfer properties are excellent both for heat absorption and release stages. The GAHP-TSU device with low thermal conductivity of the PCMs is promising in potential industry applications

Combined natural convection and mass transfer effects on unsteady flow past an infinite vertical porous plate embedded in a porous medium with heat source

Energy Technology Data Exchange (ETDEWEB)

Das, S.S. [Department of Physics, K B D A V College, Nirakarpur, Khurda-752 019 (Orissa) (India); Tripathy, R.K. [Department of Physics, D R Nayapalli College, Bhubaneswar-751 012 (Orissa) (India); Padhy, R.K. [Department of Physics, D A V Public School, Chandrasekharpur, Bhubaneswar-751 021 (Orissa) (India); Sahu, M. [Department of Physics, Jupiter +2 Women’s Science College, IRC Village, Bhubaneswar-751 015 (Orissa) (India)

2012-07-01

This paper theoretically investigates the combined natural convection and mass transfer effects on unsteady flow of a viscous incompressible fluid past an infinite vertical porous plate embedded in a porous medium with heat source. The governing equations of the flow field are solved analytically for velocity, temperature, concentration distribution, skin friction and the rate of heat transfer using multi parameter perturbation technique and the effects of the flow parameters such as permeability parameter Kp, Grashof number for heat and mass transfer Gr, Gc; heat source parameter S, Schmidt number Sc, Prandtl number Pr etc. on the flow field are analyzed and discussed with the help of figures and tables. The permeability parameter Kp is reported to accelerate the transient velocity of the flow field at all points for small values of Kp (£1) and for higher values the effect reverses. The effect of increasing Grashof numbers for heat and mass transfer or heat source parameter is to enhance the transient velocity of the flow field at all points while a growing Schmidt number retards its effect at all points. A growing permeability parameter or heat source parameter increases the transient temperature of the flow field at all points, while a growing Prandtl number shows reverse effect. The effect of increasing Schmidt number is to decrease the concentration boundary layer thickness of the flow field at all points. Further, a growing permeability parameter enhances the skin friction at the wall and a growing Prandtl number shows reverse effect. The effect of increasing Prandtl number or permeability parameter leads to increase the magnitude of the rate of heat transfer at the wall.

Flow visualization in heat-generating porous media

International Nuclear Information System (INIS)

Lee, D.O.; Nilson, R.H.

1977-11-01

The work reported is in support of the Sandia Post-Accident Heat Removal Program, in which simulated LMFBR beds will be subjected to in-pile heating in the ACPR (Annular Core Pulsed Reactor). Flow visualization experiments were performed to gain some insight into the flow patterns and temperature distributions in a fluid-saturated heat-generating porous medium. Although much of the information presented is of a qualitative nature, it is useful in the recognition of the controlling transport process and in the formulation of analytic and numerical models

Influence of heat transfer on Poiseuille flow of MHD Jeffrey fluid through porous medium with slip boundary conditions

Science.gov (United States)

Ramesh, K.

2017-07-01

In the current article, we have discussed the Poiseuille flow of an incompressible magnetohydrodynamic Jeffrey fluid between parallel plates through homogeneous porous medium using slip boundary conditions under the effect of heat transfer. The equations governing the fluid flow are modeled in Cartesian coordinate system. The energy equation is considered under the effects viscous dissipation and heat generation. Analytical solutions for the velocity and temperature profiles are obtained. The effects of the various involved parameters on the velocity and temperature profiles are studied and the results are presented through the graphs. It is observed from our analysis that, with increase of slip parameter and pressure gradient increase the velocity. The temperature is an increasing function of heat generation parameter, Brinkman number, thermal slip parameter and non-Newtonian fluid parameter.

Heat and mass transfer effects on MHD viscoelastic fluid over a stretching sheet through porous medium in presence of chemical reaction

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Manoj Kumar Nayak

2016-03-01

Full Text Available An attempt has been made to study the heat and mass transfer effects in a boundary layer flow through porous medium of an electrically conducting viscoelastic fluid subject to transverse magnetic field in the presence of heat source/sink and chemical reaction. It has been considered the effects of radiation, viscous and Joule dissipations and internal heat generation/absorption. Closed form solutions for the boundary layer equations of viscoelastic, second-grade and Walters׳ B′ fluid models are obtained. The method of solution involves similarity transformation. The transformed equations of thermal and mass transport are solved by applying Kummer׳s function. The solutions of temperature field for both prescribed surface temperature (PST as well as prescribed surface heat flux (PHF are obtained. It is important to remark that the interaction of magnetic field is found to be counterproductive in enhancing velocity and concentration distribution whereas the presence of chemical reaction as well as porous matrix with moderate values of magnetic parameter reduces the temperature and concentration fields at all points of flow domain.

Natural convection of nanofluids over a convectively heated vertical plate embedded in a porous medium

Energy Technology Data Exchange (ETDEWEB)

Ghalambaz, M.; Noghrehabadi, A.; Ghanbarzadeh, A., E-mail: m.ghalambaz@gmail.com, E-mail: ghanbarzadeh.a@scu.ac.ir [Department of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of)

2014-04-15

In this paper, the natural convective flow of nanofluids over a convectively heated vertical plate in a saturated Darcy porous medium is studied numerically. The governing equations are transformed into a set of ordinary differential equations by using appropriate similarity variables, and they are numerically solved using the fourth-order Runge-Kutta method associated with the Gauss-Newton method. The effects of parametric variation of the Brownian motion parameter (Nb), thermophoresis parameter (Nt) and the convective heating parameter (Nc) on the boundary layer profiles are investigated. Furthermore, the variation of the reduced Nusselt number and reduced Sherwood number, as important parameters of heat and mass transfer, as a function of the Brownian motion, thermophoresis and convective heating parameters is discussed in detail. The results show that the thickness of the concentration profiles is much lower than the temperature and velocity profiles. For low values of the convective heating parameter (Nc), as the Brownian motion parameter increases, the non-dimensional wall temperature increases. However, for high values of Nc, the effect of the Brownian motion parameter on the non-dimensional wall temperature is not significant. As the Brownian motion parameter increases, the reduced Sherwood number increases and the reduced Nusselt number decreases. (author)

MHD flow of a micropolar fluid over a stretchable disk in a porous medium with heat and mass transfer

Directory of Open Access Journals (Sweden)

A. Rauf

2015-07-01

Full Text Available This article studies the simultaneous impacts of heat and mass transfer of an incompressible electrically conducting micropolar fluid generated by the stretchable disk in presence of porous medium. The thermal radiation effect is accounted via Rosseland’s approximation. The governing boundary layer equations are reduced into dimensionless form by employing the suitable similarity transformations. A finite difference base algorithm is utilized to obtain the solution expressions. The impacts of physical parameters on dimensionless axial velocity, radial velocity, micro-rotation, temperature and concentrations profiles are presented and examined carefully. Numerical computation is performed to compute shear stress, couple stress, heat and mass rate at the disk.

MHD flow of a micropolar fluid over a stretchable disk in a porous medium with heat and mass transfer

Energy Technology Data Exchange (ETDEWEB)

Rauf, A., E-mail: raufamar@ciitsahiwal.edu.pk; Meraj, M. A. [Department of Mathematics, CIIT Sahiwal 57000 (Pakistan); Ashraf, M.; Batool, K. [Department of CASPAM, Bahauddin Zakariya University, Multan 63000 (Pakistan); Hussain, M. [Department of Sciences & Humanities, National University of computer & Emerging Sciences, Islamabad 44000 (Pakistan)

2015-07-15

This article studies the simultaneous impacts of heat and mass transfer of an incompressible electrically conducting micropolar fluid generated by the stretchable disk in presence of porous medium. The thermal radiation effect is accounted via Rosseland’s approximation. The governing boundary layer equations are reduced into dimensionless form by employing the suitable similarity transformations. A finite difference base algorithm is utilized to obtain the solution expressions. The impacts of physical parameters on dimensionless axial velocity, radial velocity, micro-rotation, temperature and concentrations profiles are presented and examined carefully. Numerical computation is performed to compute shear stress, couple stress, heat and mass rate at the disk.

The effect of Coriolis force on nonlinear convection in a porous medium

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D. H. Riahi

1994-01-01

Full Text Available Nonlinear convection in a porous medium and rotating about vertical axis is studied in this paper. An upper bound to the heat flux is calculated by the method initiated first by Howard [6] for the case of infinite Prandtl number.

Heat Transfer to Pulsatile Slip Flow in a Porous Channel Filled With ...

African Journals Online (AJOL)

This paper investigate the effect of slip on the hydromagnetic pulsatile flow through a porous channel filled with saturated porous medium with time dependent boundary condition on the heated wall. Based on the pulsatile flow nature, the dimensionless flow governing equations are resolved to harmonic and non-harmonic ...

CCC, Heat Flow and Mass Flow in Liquid Saturated Porous Media

International Nuclear Information System (INIS)

Mangold, D.C.; Lippmann, M.J.; Bodvarsson, G.S.

1982-01-01

1 - Description of problem or function: The numerical model CCC (conduction-convection-consolidation) solves the heat and mass flow equations for a fully, liquid-saturated, anisotropic porous medium and computes one-dimensional (vertical) consolidation of the simulated systems. The model has been applied to problems in the fields of geothermal reservoir engineering, aquifer thermal energy storage, well testing, radioactive waste isolation, and in situ coal combustion. The code has been validated against analytic solutions for fluid and heat flow, and against a field experiment for underground storage of hot water. 2 - Method of solution: The model employs the Integrated Finite Difference Method (IFDM) in discretizing the saturated porous medium and formulating the governing equations. The sets of equations are sol- ved by an iterative solution technique. The vertical deformation of the medium is calculated using the one-dimensional consolidation theory of Terzaghi. 3 - Restrictions on the complexity of the problem: Maximum of 12 materials. It is assumed that: (a) Darcy's law adequately describes fluid movement through fractured and porous media. (b) The rock and fluid are in thermal equilibrium at any given time. (c) Energy changes due to the fluid compressibility, acceleration and viscous dissipation are neglected. (d) One-dimensional consolidation theory adequately describes the vertical deformation of the medium

Perturbation analysis of magnetohydrodynamics oscillatory flow on convective-radiative heat and mass transfer of micropolar fluid in a porous medium with chemical reaction

Directory of Open Access Journals (Sweden)

Dulal Pal

2016-03-01

Full Text Available This paper deals with the perturbation analysis of mixed convection heat and mass transfer of an oscillatory viscous electrically conducting micropolar fluid over an infinite moving permeable plate embedded in a saturated porous medium in the presence of transverse magnetic field. Analytical solutions are obtained for the governing basic equations. The effects of permeability, chemical reaction, viscous dissipation, magnetic field parameter and thermal radiation on the velocity distribution, micro-rotation, skin friction and wall couple stress coefficients are analyzed in detail. The results indicate that the effect of increasing the chemical reaction has a tendency to decrease the skin friction coefficient at the wall, while opposite trend is seen by increasing the permeability parameter of the porous medium. Also micro-rotational velocity distribution increases with an increase in the magnetic field parameter.

Conjugate heat transfer in a porous cavity filled with nano-fluids and heated by a triangular thick wall

International Nuclear Information System (INIS)

Chamkha, Ali J.; Ismael, Muneer A.

2013-01-01

The conjugate natural convection-conduction heat transfer in a square domain composed of nano-fluids filled porous cavity heated by a triangular solid wall is studied under steady-state conditions. The vertical and horizontal walls of the triangular solid wall are kept isothermal and at the same hot temperature Th. The other boundaries surrounding the porous cavity are kept adiabatic except the right vertical wall where it is kept isothermally at the lower temperature T c . Equations governing the heat transfer in the triangular wall and heat and nano-fluid flow, based on the Darcy model, in the nano-fluid-saturated porous medium together with the derived relation of the interface temperature are solved numerically using the over-successive relaxation finite-difference method. A temperature independent nano-fluids properties model is adopted. Three nano-particle types dispersed in one base fluid (water) are investigated. The investigated parameters are the nano-particles volume fraction φ (0-0.2), Rayleigh number Ra (10-1000), solid wall to base-fluid saturated porous medium thermal conductivity ratio K ro (0.44, 1, 23.8), and the triangular wall thickness D (0.1-1). The results are presented in the conventional form; contours of streamlines and isotherms and the local and average Nusselt numbers. At a very low Rayleigh number Ra = 10, a significant enhancement in heat transfer within the porous cavity with φ is observed. Otherwise, the heat transfer may be enhanced or deteriorated with φ depending on the wall thickness D and the Rayleigh number Ra. At high Rayleigh numbers and low conductivity ratios, critical values of D, regardless of 4, are observed and accounted. (authors)

On the viscous dissipation modeling of thermal fluid flow in a porous medium

KAUST Repository

Salama, Amgad

2011-02-24

The problem of viscous dissipation and thermal dispersion in saturated porous medium is numerically investigated for the case of non-Darcy flow regime. The fluid is induced to flow upward by natural convection as a result of a semi-infinite vertical wall that is immersed in the porous medium and is kept at constant higher temperature. The boundary layer approximations were used to simplify the set of the governing, nonlinear partial differential equations, which were then non-dimensionalized and solved using the finite elements method. The results for the details of the governing parameters are presented and investigated. It is found that the irreversible process of transforming the kinetic energy of the moving fluid to heat energy via the viscosity of the moving fluid (i.e.; viscous dissipation) resulted in insignificant generation of heat for the range of parameters considered in this study. On the other hand, thermal dispersion has shown to disperse heat energy normal to the wall more effectively compared with the normal diffusion mechanism. © 2011 Springer-Verlag.

Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

Science.gov (United States)

Bhadauria, B. S.; Singh, M. K.; Singh, A.; Singh, B. K.; Kiran, P.

2016-12-01

In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

Directory of Open Access Journals (Sweden)

Bhadauria B.S.

2016-12-01

Full Text Available In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

Combined effect of thermal dispersion and variable viscosity of non-darcy convection heat transfer in a fluidsaturated porous medium

KAUST Repository

El-Amin, Mohamed

2013-01-01

In this paper, the effects of thermal dispersion and variable viscosity on the non-Darcy free, mixed, and forced convection heat transfer along a vertical flat plate embedded in a fluid-saturated porous medium are investigated. Forchheimer extension is employed in the flow equation to express the non-Darcy model. The fluid viscosity varies as an inverse linear function of temperature. The coefficient of thermal diffusivity has been assumed to be the sum of the molecular diffusivity and the dynamic diffusivity due to mechanical dispersion. Similarity solutions of the governing equations, for an isothermally heated plate, are obtained. Effects of the physical parameters, which govern the problem, on the rate of heat transfer in terms of Nusselt number, the slip velocity, and the boundary layer thickness, for the two cases Darcy and non-Darcy, are shown on graphs or entered in tables. © 2013 by Begell House, Inc.

Heat and mass transfer on a MHD third grade fluid with partial slip flow past an infinite vertical insulated porous plate in a porous medium

International Nuclear Information System (INIS)

Baoku, I.G.; Olajuwon, B.I.; Mustapha, A.O.

2013-01-01

Highlights: ► We model the flow of a MHD third grade fluid, heat and mass transfer in a porous medium with partial slip flow regime. ► We examine the effects of pertinent parameters on the velocity, temperature and species concentration distributions. ► The values momentum and thermal boundary layers increase with increasing third grade parameter β. ► The consequences of increasing the permeability parameter m and partial slip parameter λ give rise to fluid velocity. ► The magnetic field parameter H decreases the momentum boundary layer and increases the concentration boundary layer. -- Abstract: The influence of third grade, partial slip and other thermophysical parameters on the steady flow, heat and mass transfer of viscoelastic third grade fluid past an infinite vertical insulated plate subject to suction across the boundary layer has been investigated. The space occupying the fluid is porous. The momentum equation is characterized by a highly nonlinear boundary value problem in which the order of the differential equation exceeds the number of available boundary conditions. An efficient numerical scheme of midpoint technique with Richardson’s extrapolation is employed to solve the governing system of coupled nonlinear equations of momentum, energy and concentration. Numerical calculations were carried out for different values of various interesting non-dimensional quantities in the slip flow regime with heat and mass transfer and were shown with the aid of figures. The values of the wall shear stress, the local rate of heat and mass transfers were obtained and tabulated. The analysis shows that as the fluid becomes more shear thickening, the momentum boundary layer decreases but the thermal boundary layer increases; the magnetic field strength is found to decrease with an increasing temperature distribution when the porous plate is insulated. The consequences of increasing the permeability parameter and Schmidt number decrease both the momentum

Experimental Study of Heat Energy Absorber with Porous Medium for Thermoelectric Conversion System

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Tzer-Ming Jeng

2013-12-01

Full Text Available The thermoelectric conversion system usually consists of the heat absorber, the thermoelectric generator (TEG and the heat sink, while the heat absorber collects the heat to increase the temperature on the hot surface of TEG and enhances the generating electricity. This study experimentally investigated the performance of the brass-beads packed-bed heat absorber for the thermoelectric conversion system. The packed-bed heat absorber is installed in a square channel with the various flow orientation systems and the small ratio of channel width to bead diameter. The flow orientation systems included the straight flow and jet flow systems. This study showed the local and average heat transfer characteristics for various parameters. The experimental results can be the base of designs for the novel porous heat absorber of the thermoelectric conversion system.

NUMERICAL STUDY OF NON-DARCIAN NATURAL CONVECTION HEAT TRANSFER IN A RECTANGULAR ENCLOSURE FILLED WITH POROUS MEDIUM SATURATED WITH VISCOUS FLUID

Directory of Open Access Journals (Sweden)

Mahmood H. Ali

2015-02-01

Full Text Available A numerical study of non-Darcian natural convection heat transfer in a rectangular enclosure filled with porous medium saturated with viscous fluid was carried out. The effects of medium Rayleigh number, porosity, particle to fluid thermal conductivity ratio, Darcy number and enclosure aspect ratio on heat transfer were examined to demonstrate the ability of using this construction in thermal insulation of buildings walls.A modified Brinkman-Forchheimer-extended Darcy flow model was used and no-slip boundary conditions were imposed for velocity at the walls and the governing equations were expressed in dimensionless stream function, vorticity, and temperature formulation. The resulting algebraic equations obtained from finite difference discritization of vorticity and temperature equations are solved using (ADI method which uses Three Diagonal Matrix Algorithm (TDMA in each direction, while that of the stream function equation solved using successive iteration method.The study was done for the range of enclosure aspect ratio ( which is in the tall layers region at medium Rayleigh number ( , Darcy number (Da=10-3, 10-4, 10-5 , porosity (e=0.35, 0.45, 0.55, particle to fluid thermal conductivity (kS/kf=5.77, 38.5, 1385.5.The results showed that the Nusselt number is direct proportional to medium Rayleigh number and porosity and reversely proportional to Darcy number, ratio of particle to fluid thermal conductivity and enclosure aspect ratio. The variables that affect the heat transfer in the above arrangement was correlated in a mathematical equation that account better for their affects on heat transfer which is represented by mean Nusselt number (Nu.

The Riemann Solution for the Injection of Steam and Nitrogen in a Porous Medium

NARCIS (Netherlands)

Lambert, W.; Marchesin, D.; Bruining, J.

2009-01-01

We solve the model for the flow of nitrogen, vapor, and water in a porous medium, neglecting compressibility, heat conductivity, and capillary effects. Our choice of injection conditions is determined by the application to clean up polluted sites. We study all mathematical structures, such as

Thermal convection around a heat source embedded in a box containing a saturated porous medium

Energy Technology Data Exchange (ETDEWEB)

Himasekhar, K.; Bau, H.H. (Univ. of Pennsylvania, Philadelphia (USA))

1988-08-01

A study of the thermal convection around a uniform flux cylinder embedded in a box containing a saturated porous medium is carried out experimentally and theoretically. The experimental work includes heat transfer and temperature field measurements. It is observed that for low Rayleigh numbers, the flow is two dimensional and time independent. Once a critical Rayleigh number is exceeded, the flow undergoes a Hopf bifurcation and becomes three dimensional and time dependent. The theoretical study involves the numerical solution of the two-dimensional Darcy-Oberbeck-Boussinesq equations. The complicated geometry is conveniently handled by mapping the physical domain onto a rectangle via the use of boundary-fitted coordinates. The numerical code can easily be extended to handle diverse geometric configurations. For low Rayleigh numbers, the theoretical results agree favorably with the experimental observations. However, the appearance of three-dimensional flow phenomena limits the range of utility of the numerical code.

Simultaneous heat and moisture transfer in porous elements: transfer function method

International Nuclear Information System (INIS)

Souza, H.A. de.

1985-01-01

The presence of moisture in a porous element may strongly affect the transfer of heat through this element due to the processes which occur associated with the phase changes at the boundary surfaces and internally in the wall body. In addition, the structural properties of the element may also be meaningfully affected. The formulation of mathematical models for the simultaneous heat and mass transfer in porous elements results in a pair of nonlinear coupled equations for the temperature and moisture content distributions, in the material. It is supposed, in this work, that the actual variation of the properties of the porous medium is small in the range of variables which describe the specific problem to be analyzed. This enables us to work with linearized equations, making possible the use of linear solution methods. In this context, the present work deals with a linear procedure for the solution of simultaneous heat and moisture transfer problems in porous elements, sujected to arbitrary boundary conditions. This results in a linear relation between the heat and mass flux densities through the boundary surfaces of the elements and their associated potentials. It is shown that the model is consistent in asymptotical limiting cases; the model is then used for analyzing the drying process of a porous element, subjected to ambient actual conditions. (Author) [pt

Numerical investigation of heat transfer in a laminar flow in a helical pipe filled with a fluid saturated porous medium: the sensitivity to parameter variations

International Nuclear Information System (INIS)

Cheng, L.; Kuznetsov, A.V.

2005-01-01

This paper presents the first attempt to investigate numerically heat transfer in a helical pipe filled with a fluid saturated porous medium; the analysis is based on the full momentum equation for porous media that accounts for the Brinkman and Forchheimer extensions of the Darcy law as well as for the flow inertia. Numerical computations are performed in an orthogonal helical coordinate system. The effects of the Darcy number, the Forchheimer coefficient as well as the Dean and Germano numbers on the axial flow velocity, secondary flow, temperature distribution, and the Nusselt number are investigated. (authors)

Numerical investigation of heat transfer in a laminar flow in a helical pipe filled with a fluid saturated porous medium: the sensitivity to parameter variations

Energy Technology Data Exchange (ETDEWEB)

Cheng, L.; Kuznetsov, A.V. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Mechanical and Aerospace Engineering

2005-07-01

This paper presents the first attempt to investigate numerically heat transfer in a helical pipe filled with a fluid saturated porous medium; the analysis is based on the full momentum equation for porous media that accounts for the Brinkman and Forchheimer extensions of the Darcy law as well as for the flow inertia. Numerical computations are performed in an orthogonal helical coordinate system. The effects of the Darcy number, the Forchheimer coefficient as well as the Dean and Germano numbers on the axial flow velocity, secondary flow, temperature distribution, and the Nusselt number are investigated. (authors)

Influence of Thermal Radiation on Unsteady Free Convection MHD Flow of Brinkman Type Fluid in a Porous Medium with Newtonian Heating

Directory of Open Access Journals (Sweden)

Farhad Ali

2013-01-01

Full Text Available The focus of this paper is to analyze the influence of thermal radiation on some unsteady magnetohydrodynamic (MHD free convection flows of an incompressible Brinkman type fluid past a vertical flat plate embedded in a porous medium with the Newtonian heating boundary condition. The fluid is considered as a gray absorbing-emitting but nonscattering medium and the Rosseland approximation in the energy equations is used to describe the radiative heat flux for optically thick fluid. For a detailed analysis of the problem, four important situations of flow due to (i impulsive motion of the plate (ii uniform acceleration of the plate (iii nonuniform acceleration of the plate, and (iv highly nonuniform acceleration of the plate are considered. The governing equations are first transformed into a system of dimensionless equations and then solved analytically using the Laplace transform technique. Numerical results for temperature and velocity are shown graphically, while skin friction and Nusselt number are computed in tables. The results show that temperature and velocity increase on increasing radiation and Newtonian heating parameters. However, the results of magnetic and porosity parameters on velocity are found quite opposite.

A novel direct-fired porous-medium boiler

Science.gov (United States)

Prasartkaew, Boonrit

2018-01-01

Nowadays, power and heat generation systems pay an important role in all economic sectors. These systems are mainly based on combustion reaction and operated under the second law of thermodynamics. A conventional boilers, a main component of heat and power generators, have thermal efficiency in the range of 70 to 85%, mainly owing to they have flue gas heat loss. This paper proposes a novel type of boiler, called a Direct-fired Porous-medium Boiler (DPB). Due to being operated without flue gas heat loss, its thermal efficiency cloud be approximately close to 100%. The steam produced from the proposed boiler; however, is not pure water steam. It is the composite gases of steam and combustion-product-gases. This paper aims at presenting the working concept and reporting the experimental results on the performance of the proposed boiler. The experiments of various operating parameters were performed and collected data were used for the performance analysis. The experimental results demonstrated that the proposed boiler can be operated as well as the conceptual design and then it is promising. It can be possibly further developed to be a high efficiency boiler by means of reducing or suppressing the surface heat loss with better insulator and/or refractory lined.

Development of flow and heat transfer in the vicinity of a vertical plate embedded in a porous medium with viscous dissipation effects

KAUST Repository

El-Amin, Mohamed; Salama, Amgad; Sun, Shuyu; Reddy Gorla, Rama Subba

2012-01-01

In this paper, the effects of viscous dissipation on unsteady free convection from an isothermal vertical flat plate in a fluidsaturated porous medium are investigated. The Darcy-Brinkman model is employed to describe the flow field. A new model of viscous dissipation is used for the Darcy-Brinkman model of porous media. The simultaneous development of the momentum and thermal boundary layers is obtained by using a finite-difference method. Boundary layer and Boussinesq approximation have been incorporated. Numerical calculations are carried out for various parameters entering into the problem. Velocity and temperature profiles as well as the local friction factor and local Nusselt number are displayed graphically. It is found that as time approaches infinity, the values of the friction factor and heat transfer coefficient approach steady state. © 2012 by Begell House, Inc.

Debris bed coolability using a 3-D two phase model in a porous medium

Energy Technology Data Exchange (ETDEWEB)

Bechaud, C.; Duval, F.; Fichot, F. [CEA Cadarache, Inst. de Protection et de Surete Nucleaire13 - Saint-Paul-lez-Durance (France); Quintard, M. [Institut de Mecanique des Fluides de Toulouse, 31 (France); Parent, M. [CEA Grenoble, Dept. de Thermohydraulique et de Physique, 38 (France)

2001-07-01

During a severe nuclear accident, a part of the molten corium resulting from the core degradation may relocate in the lower plenum of the reactor vessel. In order to predict the safety margin of the reactor under such conditions, the coolability of this porous heat-generating medium is evaluated in this study and compared with other investigations. In this work, conservation equations derived for debris beds are implemented in the three dimensional thermal-hydraulic module of the CATHARE code. The coolant flow is a two phase flow with phase change. The momentum balance equation for each fluid phase is an extension of Darcy's law. This extension takes into account the capillary effects between the two phases, the relative permeabilities and passabilities of each phase, the interfacial drag force between liquid and gas, and the porous bed configuration (porosity, particle diameter,... ). The model developed is three-dimensional which is important to better predict the flow in configuration such as counter-current flow or to emphasize preferential ways induced by porous geometry. The energy balance equations of the three phases (liquid, gas and solid phase) are obtained by a volume averaging process of the local conservation equations. In this method, the local thermal non-equilibrium between the three phases is considered and the heat exchanges, the phase change rate as well as the thermal dispersion coefficients are calculated as a function of the local geometry of the porous medium. Such a method allows the numerical estimation of these thermal properties which are very difficult to determine experimentally. This feature is a great advantage of this approach. After a brief description of the thermal-hydraulic model, one-dimensional predictions of critical dryout fluxes are presented and compared with results from the literature. Reasonable agreement is obtained. Then a two-dimensional calculation is presented and shows the influence of the porous medium

Analytical and numerical investigation of double diffusion in thermally anisotropy multilayer porous medium

Energy Technology Data Exchange (ETDEWEB)

Bennacer, R. [Neuville sur Oise, LEEVAM 5 mail Gay Lussac, Cergy-Pontoise Cedex (France); Mohamad, A.A. [CEERE University of Calgary, Department of Mechanical and Manufacturing Engineering, Calgary, Alberta (Canada); Ganaoui, M.El [Faculte des Sciences et Techniques de Limoges, Limoges (France)

2005-02-01

Double-diffusive natural convection within a multilayer anisotropic porous medium is studied numerically and analytically. The domain composed of two horizontal porous layers is subjected to a uniform horizontal heat flux and a vertical mass flux, where only the lower one is thermally anisotropic. Darcy model with classical Boussinesq approximation is used in formulating the mathematical model. The effect of thermal anisotropy and the relative width of the two layers on the flow and transfers is illustrated with characterising the transitions from the diffusive to the convective solution. Results were well compared with respect to a developed analytical approach, based on a parallel flow approximation for thermally anisotropic multilayer media. (orig.)

Mixed convection stagnation-point flow of nanofluids over a stretching/shrinking sheet in a porous medium with internal heat generation/absorption

Directory of Open Access Journals (Sweden)

Dulal Pal

2015-05-01

Full Text Available In this paper, we analyzed the buoyancy-driven radiative non-isothermal heat transfer in a nanofluid stagnation-point flow over a stretching/shrinking sheet embedded in a porous medium.The effects of thermal radiation and internal heat generation/absorption along with suction/injection at the boundary are also considered. Three different types of nanofluids, namely the Copper-water, the Alumina-water and the Titanium dioxide water are considered. The resulting coupled nonlinear differential equations are solved numerically by a fifth-order Runge-Kutta-Fehlberg integration scheme with a shooting technique. A good agreement is found between the present numerical results and the available results in the literature for some special cases. The effects of the physical parameters on the flow and temperature characteristics are presented through tables and graphs, and the salient features are discussed. The results obtained reveal many interesting behaviors that warrant further study on the heat transfer enhancement due to the nanofluids.

Analytical approach to entropy generation and heat transfer in CNT-nanofluid dynamics through a ciliated porous medium

Science.gov (United States)

Akbar, Noreen Sher; Shoaib, M.; Tripathi, Dharmendra; Bhushan, Shashi; Bég, O. Anwar

2018-03-01

The transportation of biological and industrial nanofluids by natural propulsion like cilia movement and self-generated contraction-relaxation of flexible walls has significant applications in numerous emerging technologies. Inspired by multi-disciplinary progress and innovation in this direction, a thermo-fluid mechanical model is proposed to study the entropy generation and convective heat transfer of nanofluids fabricated by the dispersion of single-wall carbon nanotubes (SWCNT) nanoparticles in water as the base fluid. The regime studied comprises heat transfer and steady, viscous, incompressible flow, induced by metachronal wave propulsion due to beating cilia, through a cylindrical tube containing a sparse (i.e., high permeability) homogenous porous medium. The flow is of the creeping type and is restricted under the low Reynolds number and long wavelength approximations. Slip effects at the wall are incorporated and the generalized Darcy drag-force model is utilized to mimic porous media effects. Cilia boundary conditions for velocity components are employed to determine analytical solutions to the resulting non-dimensionalized boundary value problem. The influence of pertinent physical parameters on temperature, axial velocity, pressure rise and pressure gradient, entropy generation function, Bejan number and stream-line distributions are computed numerically. A comparative study between SWCNT-nanofluids and pure water is also computed. The computations demonstrate that axial flow is accelerated with increasing slip parameter and Darcy number and is greater for SWCNT-nanofluids than for pure water. Furthermore the size of the bolus for SWCNT-nanofluids is larger than that of the pure water. The study is applicable in designing and fabricating nanoscale and microfluidics devices, artificial cilia and biomimetic micro-pumps.

Analytical approach to entropy generation and heat transfer in CNT-nanofluid dynamics through a ciliated porous medium

Science.gov (United States)

Akbar, Noreen Sher; Shoaib, M.; Tripathi, Dharmendra; Bhushan, Shashi; Bég, O. Anwar

2018-04-01

The transportation of biological and industrial nanofluids by natural propulsion like cilia movement and self-generated contraction-relaxation of flexible walls has significant applications in numerous emerging technologies. Inspired by multi-disciplinary progress and innovation in this direction, a thermo-fluid mechanical model is proposed to study the entropy generation and convective heat transfer of nanofluids fabricated by the dispersion of single-wall carbon nanotubes (SWCNT) nanoparticles in water as the base fluid. The regime studied comprises heat transfer and steady, viscous, incompressible flow, induced by metachronal wave propulsion due to beating cilia, through a cylindrical tube containing a sparse (i.e., high permeability) homogenous porous medium. The flow is of the creeping type and is restricted under the low Reynolds number and long wavelength approximations. Slip effects at the wall are incorporated and the generalized Darcy drag-force model is utilized to mimic porous media effects. Cilia boundary conditions for velocity components are employed to determine analytical solutions to the resulting non-dimensionalized boundary value problem. The influence of pertinent physical parameters on temperature, axial velocity, pressure rise and pressure gradient, entropy generation function, Bejan number and stream-line distributions are computed numerically. A comparative study between SWCNT-nanofluids and pure water is also computed. The computations demonstrate that axial flow is accelerated with increasing slip parameter and Darcy number and is greater for SWCNT-nanofluids than for pure water. Furthermore the size of the bolus for SWCNT-nanofluids is larger than that of the pure water. The study is applicable in designing and fabricating nanoscale and microfluidics devices, artificial cilia and biomimetic micro-pumps.

Thermal non-equilibrium heat transfer in a porous cavity in the presence of bio-chemical heat source

Directory of Open Access Journals (Sweden)

Nazari Mohsen

2015-01-01

Full Text Available This paper is concerned with thermal non-equilibrium natural convection in a square cavity filled with a porous medium in the presence of a biomass which is transported in the cavity. The biomass can consume a secondary moving substrate. The physics of the presented problem is related to the analysis of heat and mass transfer in a composting process that controlled by internal heat generation. The intensity of the bio-heat source generated in the cavity is equal to the rate of consumption of the substrate by the biomass. It is assumed that the porous medium is homogeneous and isotropic. A two-field model that represents the fluid and solid phase temperature fields separately is used for energy equation. A simplified Monod model is introduced along with the governing equations to describe the consumption of the substrate by the biomass. In other word, the transient biochemical heat source which is dependent on a solute concentration is considered in the energy equations. Investigation of the biomass activity and bio-chemical heat generation in the case of thermal non-equilibrium assumption has not been considered in the literature and they are open research topics. The effects of thermal non-equilibrium model on heat transfer, flow pattern and biomass transfer are investigated. The effective parameters which have a direct impact on the generated bio-chemical heat source are also presented. The influences of the non-dimensional parameters such as fluid-to-solid conductivity ratio on the temperature distribution are presented.

Buoyancy induced convective flow in porous media with heat source

International Nuclear Information System (INIS)

Hwang, I.T.

1978-01-01

An unbounded fluid layer in a porous medium with an internal heat source and uniformly heated from below is studied. The layer is in the gravitational field. Linear theory predicts that the disturbances of infinitesimal amplitude will start to grow when the Rayleigh number exceeds its critical value. These disturbances do not grow without limit; but by advecting heat and momentum, the disturbances alter their forms to achieve a finite amplitude. Just like infinitesimal amplitude disturbances the degeneracies of possible solutions persist for finite amplitude solutions. This study evaluates these various forms of solutions. The small parameter method of Poincare is used to treat the problem in successive order

Natural convection flow and heat transfer between a fluid layer and a porous layer inside a rectangular enclosure

International Nuclear Information System (INIS)

Beckermann, C.; Ramadhyani, S.; Viskanta, R.

1986-01-01

A numerical and experimental study is performed to analyze the steady-state natural convection fluid flow and heat transfer in a vertical rectangular enclosure that is partially filled with a vertical layer of a fluid-saturated porous medium. The flow in the porous layer is modeled utilizing the Brinkman-Forchheimer-extended Darcy equations. The numerical model is verified by conducting a number of experiments with spherical glass beads as the porous medium and water and glycerin as the fluids in rectangular test-cells. The agreement between the flow visualization results and temperature measurements and the numerical model is, in general, good. It is found that the amount of fluid penetrating from the fluid region into the porous layer depends strongly on the Darcy (Da) and Rayleigh (Ra) numbers. For a relatively low product of Ra x Da, the flow takes place primarily in the fluid layer, and heat transfer in the porous layer is by conduction only. On the other hand, fluid penetrating into a relatively highly permeable porous layer has a significant impact on the natural convection flow patterns in the entire enclosure

Theoretical and experimental investigation of thermohydrologic processes in a partially saturated, fractured porous medium

International Nuclear Information System (INIS)

Green, R.T.; Manteufel, R.D.; Dodge, F.T.; Svedeman, S.J.

1993-07-01

The performance of a geologic repository for high-level nuclear waste will be influenced to a large degree by thermohydrologic phenomena created by the emplacement of heat-generating radioactive waste. The importance of these phenomena is manifest in that they can greatly affect the movement of moisture and the resulting transport of radionuclides from the repository. Thus, these phenomena must be well understood prior to a definitive assessment of a potential repository site. An investigation has been undertaken along three separate avenues of analysis: (i) laboratory experiments, (ii) mathematical models, and (iii) similitude analysis. A summary of accomplishments to date is as follows. (1) A review of the literature on the theory of heat and mass transfer in partially saturated porous medium. (2) A development of the governing conservation and constitutive equations. (3) A development of a dimensionless form of the governing equations. (4) A numerical study of the importance and sensitivity of flow to a set of dimensionless groups. (5) A survey and evaluation of experimental measurement techniques. (6) Execution of laboratory experiments of nonisothermal flow in a porous medium with a simulated fracture

CFD prediction of mixing in a steam generator mock-up: Comparison between full geometry and porous medium approaches

International Nuclear Information System (INIS)

Dehbi, A.; Badreddine, H.

2013-01-01

Highlights: • CFD is used to simulate single phase mixing in a model steam generator. • Motive of the work is to compare porous media approach with full geometry representation of tubes. • Porous media approach is found to compare favorably with full representation in steady states. - Abstract: In CFD simulations of single phase flow mixing in a steam generator (SG) during a station blackout severe accident, one is faced with the problem of representing the thousands of SG U-tubes. Typically simplifications are made to render the problem computationally tractable. In particular, one or a number of tubes are lumped in one volume that is treated as a single porous medium which replicates the pressure loss and heat transfer characteristics of the real tube. This approach significantly reduces the computational size of the problem and hence simulation time. In this work, we endeavor to investigate the adequacy of this approach by performing a series of simulations. We first validate the porous medium approach against results of the 1/7th scale Westinghouse SG-S3 test. In a second step, we make two separate simulations of flow in the PSI SG mock-up, i.e. one in which the porous medium model is used for the tube bundle, and another in which the full geometry is represented. In all simulations, the Reynolds Stress (RSM) model of turbulence is used. We show that in steady state conditions, the porous medium treatment yields results which are comparable to those of the full geometry representation (temperature distribution, recirculation ratio, hot plume spread, etc.). Hence, the porous medium approach can be extended with a good degree of confidence to model single phase mixing in the full scale SG

Nonlinear radiative peristaltic flow of hydromagnetic fluid through porous medium

Science.gov (United States)

Hussain, Q.; Latif, T.; Alvi, N.; Asghar, S.

2018-06-01

The radiative heat and mass transfer in wall induced flow of hydromagnetic fluid through porous medium in an asymmetric channel is analyzed. The fluid viscosity is considered temperature dependent. In the theory of peristalsis, the radiation effects are either ignored or taken as linear approximation of radiative heat flux. Such approximation is only possible when there is sufficiently small temperature differences in the flow field; however, nonlinear radiation effects are valid for large temperature differences as well (the new feature added in the present study). Mathematical modeling of the problems include the complicated system of highly nonlinear differential equations. Semi-analytical solutions are established in the wave reference frame. Results are displayed graphically and discussed in detail for the variation of various physical parameters with the special attention to viscosity, radiation, and temperature ratio parameters.

A practical approach in porous medium combustion for domestic application: A review

Science.gov (United States)

Ismail, A. K.; Ibrahim, N. H.; Shamsuddin, K. A.; Abdullah, M. Z.; Zubair, M.

2018-05-01

Combustion in porous media has been widely studied. Many application involving the combustion of porous media has been reported in various way with most consider on numerical works and industrial application. Besides, recent application of porous medium combustion for domestic is the topic of interest among researchers. In this paper, a review was conducted on the combustion of porous media in term of practical application for domestic consumers. Details on the type of fuel used including bio fuel and their system have been search thoroughly. Most of the system have utilized compressed air system to provide lean combustion in domestic application. Some self-aspirating system of porous medium burner was also reported. The application of new technology such as cogeneration by using thermoelectric cells in tandem with porous medium combustion is also revised according to recent work which have already been published. Besides, the recent advances which include coating of porous material is also considered at the end of this paper.

Natural convection boundary layer with suction and mass transfer in a porous medium

International Nuclear Information System (INIS)

Bestman, A.R.

1989-03-01

The free convection boundary layer flow with simultaneous heat and mass transfer in a porous medium is studied when the boundary wall moves in its own plane with suction. The study also incorporates chemical reaction for the very simple model of a binary reaction with Arrhenius activation energy. For large suction asymptotic approximate solutions are obtained for the flow variables for various values of the activation energy. (author). 10 refs, 2 figs

Heat transfer in a Couette flow with part of the space between the plates filled with porous medium

International Nuclear Information System (INIS)

Carrocci, L.R.; Liu, C.Y.; Ismail, K.A.R.

1982-01-01

The effect of various parameters in the temperature profile is shown under boundary conditions for the Couette flow between infinite plates with part of the space filled with porous medium. The parameters observed are: pressure gradient, permeability, the non-dimensional product PE (Prandtl number x Eckert number), the relation between the thermal conductibility coefficient between porous region and pure fluid, and finally the non-dimensional product PR (Prandtl number x Reynolds number). (E.G.) [pt

Numerical investigation of premixed combustion in a porous burner with integrated heat exchanger

Energy Technology Data Exchange (ETDEWEB)

Farzaneh, Meisam; Shafiey, Mohammad; Shams, Mehrzad [K.N. Toosi University of Technology, Department of Mechanical Engineering, Tehran (Iran, Islamic Republic of); Ebrahimi, Reza [K.N. Toosi University of Technology, Department of Aerospace Engineering, Tehran (Iran, Islamic Republic of)

2012-07-15

In this paper, we perform a numerical analysis of a two-dimensional axisymmetric problem arising in premixed combustion in a porous burner with integrated heat exchanger. The physical domain consists of two zones, porous and heat exchanger zones. Two dimensional Navier-Stokes equations, gas and solid energy equations, and chemical species transport equations are solved and heat release is described by a multistep kinetics mechanism. The solid matrix is modeled as a gray medium, and the finite volume method is used to solve the radiative transfer equation to calculate the local radiation source/sink in the solid phase energy equation. Special attention is given to model heat transfer between the hot gas and the heat exchanger tube. Thus, the corresponding terms are added to the energy equations of the flow and the solid matrix. Gas and solid temperature profiles and species mole fractions on the burner centerline, predicted 2D temperature fields, species concentrations and streamlines are presented. Calculated results for temperature profiles are compared to experimental data. It is shown that there is good agreement between the numerical solutions and the experimental data and it is concluded that the developed numerical program is an excellent tool to investigate combustion in porous burner. (orig.)

Modeling approaches to natural convection in porous media

CERN Document Server

Su, Yan

2015-01-01

This book provides an overview of the field of flow and heat transfer in porous medium and focuses on presentation of a generalized approach to predict drag and convective heat transfer within porous medium of arbitrary microscopic geometry, including reticulated foams and packed beds. Practical numerical methods to solve natural convection problems in porous media will be presented with illustrative applications for filtrations, thermal storage and solar receivers.

Experimental study on convective heat transfer with thin porous bodies

International Nuclear Information System (INIS)

Nishi, Yoshihisa; Kinoshita, Izumi; Furuya, Masahiro

2001-01-01

Experimental studies are made on the convective heat transfer of three types of thin porous bodies. Heat transfer performances, flow patterns and temperature profiles near the porous bodies are compared with each other. The heat transfer performance of porous bodies with the largest pore diameter is large. It became clear that the high heat transfer performance depends on an excellent heat transportation ability inside the pore and near the surface of the porous bodies. (author)

Tracer transfer in consolidated porous medium and fractured porous medium: experimentations and modelling; Transferts d'un traceur en milieu poreux consolide et en milieu poreux fissure: experimentations et modelisations

Energy Technology Data Exchange (ETDEWEB)

Dalla Costa, C

2007-07-15

We try to identify and model physical and chemical mechanisms governing the water flow and the solute transport in fractured consolidated porous medium. An original experimental device was built. The 'cube' consists of an idealized fractured medium reproduced by piling up consolidated porous cubes of 5 cm edge. Meanwhile, columns of the homogeneous consolidated porous medium are studied. The same anionic tracing technique is used in both cases. Using a system analysis approach, we inject concentration pulses in the device to obtain breakthrough curves. After identifying the mass balance and the residence time, we fit the CD and the MIM models to the experimental data. The MIM model is able to reproduce experimental curves of the homogeneous consolidated porous medium better than the CD model. The mobile water fraction is in accordance with the porous medium geometry. The study of the flow rate influence highlights an interference dispersion regime. It was not possible to highlight the observation length influence in this case. On the contrary, we highlight the effect of the observation scale on the fractured and porous medium, comparing the results obtained on a small 'cube' and a big 'cube'. The CD model is not satisfactory in this case. Even if the MIM model can fit the experimental breakthrough curves, it was not possible to obtain unique parameters for the set of experiments. (author)

Numerical analysis of a heat-generating, truncated conical porous bed in a fluid-filled enclosure

International Nuclear Information System (INIS)

Chakravarty, Aranyak; Datta, Priyankan; Ghosh, Koushik; Sen, Swarnendu; Mukhopadhyay, Achintya

2016-01-01

Analysis of natural convection in enclosures containing heat generating porous medium has important applications related to geothermal, chemical, thermal and nuclear energy such as in-vessel cooling of debris beds in nuclear reactors, cooling of coal stockpiles etc. The objective of the present numerical study is to characterise the pattern of fluid flow and energy transfer during steady laminar natural convective flow in a cylindrical enclosure with a centrally placed heat generating porous bed. Flow through porous region is modelled using Darcy–Brinkmann–Forchheimer model and local thermal equilibrium is assumed for the porous region. Analysis is carried out for a wide range of Rayleigh number (Ra), Darcy number (Da) and thermal conductivity ratio, as well as for different bed geometries. It is observed that in addition to Ra and Da, the bed geometry also plays a very important role in determining flow field and temperature distribution within the enclosure. Interestingly, a significant change is observed in energy transfer mode from the porous bed corresponding to specific values of bed permeability and bed heat generation rate. This is characterised in terms of Ra and Da. Further, it is observed that this change in energy transfer mode is highly dependent on Ra. - Highlights: • Natural convection is analysed in an enclosure with a heat generating porous bed. • Effect of dimensionless parameters as well as bed geometry has been investigated. • Energy transfer mechanism from porous bed changes with dimensionless parameters. • Bed geometry significantly affects fluid flow and energy transfer in the enclosure.

Ultimate regime of high Rayleigh number convection in a porous medium.

Science.gov (United States)

Hewitt, Duncan R; Neufeld, Jerome A; Lister, John R

2012-06-01

Well-resolved direct numerical simulations of 2D Rayleigh-Bénard convection in a porous medium are presented for Rayleigh numbers Ra≤4×10(4) which reveal that, contrary to previous indications, the linear classical scaling for the Nusselt number, Nu~Ra, is attained asymptotically. The flow dynamics are analyzed, and the interior of the vigorously convecting system is shown to be increasingly well described as Ra→∞ by a simple columnar "heat-exchanger" model with a single horizontal wave number k and a linear background temperature field. The numerical results are approximately fitted by k~Ra(0.4).

Unsteady MHD blood flow through porous medium in a parallel plate channel

Science.gov (United States)

Latha, R.; Rushi Kumar, B.

2017-11-01

In this study, we have analyzed heat and mass transfer effects on unsteady blood flow through parallel plate channel in a saturated porous medium in the presence of a transverse magnetic field with thermal radiation. The governing higher order nonlinear PDE’S are converted to dimensionless equations using dimensionless variables. The dimensionless equations are then solved analytically using boundary conditions by choosing the axial flow transport and the fields of concentration and temperature apart from the normal velocity as a function of y and t. The effects of different pertinent parameters appeared in this model viz thermal radiation, Prandtl number, Heat source parameter, Hartmann number, Permeability parameter, Decay parameter on axial flow transport and the normal velocity are analyzed in detail.

Impact of Heat and Mass Transfer during the Transport of Nitrogen in Coal Porous Media on Coal Mine Fires

OpenAIRE

Shi, Bobo; Zhou, Fubao

2014-01-01

The application of liquid nitrogen injection is an important technique in the field of coal mine fire prevention. However, the mechanism of heat and mass transfer of cryogenic nitrogen in the goaf porous medium has not been well accessed. Hence, the implementation of fire prevention engineering of liquid nitrogen roughly relied on an empirical view. According to the research gap in this respect, an experimental study on the heat and mass transfer of liquid nitrogen in coal porous media was pr...

Non-Darcy Free Convection of Power-Law Fluids Over a Two-Dimensional Body Embedded in a Porous Medium

KAUST Repository

El-Amin, Mohamed

2010-11-27

A boundary layer analysis was presented to study the non-Darcy-free convection of a power-law fluid over a non-isothermal two-dimensional body embedded in a porous medium. The Ostwald-de Waele power-law model was used to characterize the non-Newtonian fluid behavior. Similarity solutions were obtained with variations in surface temperature or surface heat flux. In view of the fact that most of the non-Newtonian fluids have large Prandtl numbers, this study was directed toward such fluids. The effects of the porous medium parameters, k1 and k2, body shape parameter, m, and surface thermal variations parameter, p, as well as the power-law index, n, were examined. © 2010 Springer Science+Business Media B.V.

Non-Darcy Free Convection of Power-Law Fluids Over a Two-Dimensional Body Embedded in a Porous Medium

KAUST Repository

El-Amin, Mohamed; Sun, Shuyu; El-Ameen, M. A.; Jaha, Y. A.; Gorla, Rama Subba Reddy

2010-01-01

A boundary layer analysis was presented to study the non-Darcy-free convection of a power-law fluid over a non-isothermal two-dimensional body embedded in a porous medium. The Ostwald-de Waele power-law model was used to characterize the non-Newtonian fluid behavior. Similarity solutions were obtained with variations in surface temperature or surface heat flux. In view of the fact that most of the non-Newtonian fluids have large Prandtl numbers, this study was directed toward such fluids. The effects of the porous medium parameters, k1 and k2, body shape parameter, m, and surface thermal variations parameter, p, as well as the power-law index, n, were examined. © 2010 Springer Science+Business Media B.V.

A mathematical model for two-phase water, air, and heat flow around a linear heat source emplaced in a permeable medium

International Nuclear Information System (INIS)

Doughty, C.; Pruess, K.

1991-03-01

A semianalytical solution for transient two-phase water, air, and heat flow in a uniform porous medium surrounding a constant-strength linear heat source has been developed, using a similarity variable η=r/√t (r is radial distance, t is time). Although the similarity transformation requires a simplified radial geometry, all the physical mechanisms involved in two-phase fluid and heat flow may be taken into account in a rigorous way. The solution includes nonlinear thermophysical fluid and material properties, such as relative permeability and capillary pressure variations with saturation, and density and viscosity variations with temperature and pressure. The resulting governing equations form a set of coupled nonlinear ODEs, necessitating numerical integration. The solution has been applied to a partially saturated porous medium initially at a temperature well below the saturation temperature, which is the setting for the potential nuclear waste repository site at Yucca Mountain, Nevada. The resulting heat and fluid flows provide a stringent test of many of the capabilities of numerical simulation models, making the similarity solution a useful tool for model verification. Comparisons to date have shown excellent agreement between the TOUGH2 simulator and the similarity solution for a variety of conditions. 13 refs., 6 figs., 1 tab

Magnetohydrodynamic (MHD Jeffrey fluid over a stretching vertical surface in a porous medium

Directory of Open Access Journals (Sweden)

Kartini Ahmad

2017-12-01

Full Text Available This paper presents the study of steady two-dimensional mixed convection boundary layer flow and heat transfer of a Jeffrey fluid over a stretched sheet immersed in a porous medium in the presence of a transverse magnetic field. The governing partial differential equations are reduced to nonlinear ordinary differential equations with the aid of similarity transformation, which are then solved numerically using an implicit finite difference scheme. The effects of some of the embedded parameters, such as Deborah number β, magnetic parameter M, mixed convection parameter λ, porosity parameter γ and Prandtl number Pr, on the flow and heat transfer characteristics, are given in forms of tables and graphs.

Thermo-diffusion effect on free convection heat and mass transfer in a thermally linearly stratified non-darcy porous media

KAUST Repository

Murthy, P.V.S.N.

2011-12-26

Thermo-diffusion effect on free convection heat and mass transfer from a vertical surface embedded in a liquid saturated thermally stratified non - Darcy porous medium has been analyzed using a local non-similar procedure. The wall temperature and concentration are constant and the medium is linearly stratified in the vertical direction with respect to the thermal conditions. The fluid flow, temperature and concentration fields are affected by the complex interactions among the diffusion ratio Le, buoyancy ratio N, thermo-diffusion parameter Sr and stratification parameter ?. Non-linear interactions of all these parameters on the convective transport has been analyzed and variation of heat and mass transfer coefficients with thermo-diffusion parameter in the thermally stratified non-Darcy porous media is presented through computer generated plots.

Thermo-diffusion effect on free convection heat and mass transfer in a thermally linearly stratified non-darcy porous media

KAUST Repository

Murthy, P.V.S.N.; El-Amin, Mohamed

2011-01-01

Thermo-diffusion effect on free convection heat and mass transfer from a vertical surface embedded in a liquid saturated thermally stratified non - Darcy porous medium has been analyzed using a local non-similar procedure. The wall temperature and concentration are constant and the medium is linearly stratified in the vertical direction with respect to the thermal conditions. The fluid flow, temperature and concentration fields are affected by the complex interactions among the diffusion ratio Le, buoyancy ratio N, thermo-diffusion parameter Sr and stratification parameter ?. Non-linear interactions of all these parameters on the convective transport has been analyzed and variation of heat and mass transfer coefficients with thermo-diffusion parameter in the thermally stratified non-Darcy porous media is presented through computer generated plots.

Effective Heat and Mass Transport Properties of Anisotropic Porous Ceria for Solar Thermochemical Fuel Generation

Directory of Open Access Journals (Sweden)

Sophia Haussener

2012-01-01

Full Text Available High-resolution X-ray computed tomography is employed to obtain the exact 3D geometrical configuration of porous anisotropic ceria applied in solar-driven thermochemical cycles for splitting H2O and CO2. The tomography data are, in turn, used in direct pore-level numerical simulations for determining the morphological and effective heat/mass transport properties of porous ceria, namely: porosity, specific surface area, pore size distribution, extinction coefficient, thermal conductivity, convective heat transfer coefficient, permeability, Dupuit-Forchheimer coefficient, and tortuosity and residence time distributions. Tailored foam designs for enhanced transport properties are examined by means of adjusting morphologies of artificial ceria samples composed of bimodal distributed overlapping transparent spheres in an opaque medium.

Parametric study of boiling heat transfer in porous media

International Nuclear Information System (INIS)

Shi, B.; Jones, B.G.; Pan, C.

1996-01-01

Detailed numerical modeling and parametric variation studies were conducted on boiling heat transfer processes in porous deposits with emphasis on applications associated with light water nuclear power reactor systems. The processes of boiling heat transfer in the porous corrosion deposits typically involve phase changes in finite volumetric regions in the porous media. The study examined such processes in two porous media configurations, without chimneys (homogeneous porous structures) and with chimneys (heterogeneous porous structures). A 1-D model and a 2-D model were developed to simulate two-phase flows with phase changes, without dry-out, inside the porous media for both structural configurations. For closure of the governing equations, an empirical correlation of the evaporation rate for phase changes inside the porous media was introduced. In addition, numerical algorithms were developed to solve the coupled nonlinear equations of mass, momentum, energy, capillary pressure, and evaporation rate. The distributions of temperature, thermodynamic saturation, liquid pressure, vapor pressure, liquid velocity, and vapor velocity were predicted. Furthermore, the effects of heat flux, system pressure, porosity, particle diameter, chimney population density, chimney radius, and crud thickness on the all superheat, critical heat flux, and minimum saturation were examined. The predictions were found to be in good agreement with the available experimental results

Onset of convection in a porous medium with sidewall heat transfer

International Nuclear Information System (INIS)

Kassoy, D.R.; Wang, M.; Weidman, P.D.

1985-01-01

A linear stability analysis is developed for convection in a vertically oriented finite slab of saturated porous material. The large vertical sidewall surfaces admit heat transfer while the small endwalls are insulated. A vertical temperature difference is imposed between the upper and lower horizontal surfaces. Results are obtained from an asymptotic evaluation of the exact stability criteria for a rectangular parallelpiped in the limit of small gap width element of → 0, where element of = narrow horizontal dimension/height. The critical Rayleigh number R/sub c/ = 0(element of/sup -2/) when the heat transfer boundary condition is applied directly to the sidewall. The convection mode consists of tightly packed three-dimensional cells with a wave number α = 0(element of/sup -1/2/). Only when the effective Biot number is sufficiently small, 0(element of/sup 2/), are the classical results approached; R/sub c/ → 4π/sup 2/, α/sub c/ = 0(1). If the slab is sandwiched between two impermeable conducting blocks with horizontal extent similar to the slab height, then the small scale modes disappear and R/sub c/ = 0(element of/sup -1/). However, sufficiently thin conducting blocks are compatible with R/sub c/ = 0(element of/sup -2/) and α = 0(element of/sup -1/2/

Hydrodynamic instability of compressible fluid in porous medium

International Nuclear Information System (INIS)

Argal, Shraddha; Tiwari, Anita; Sharma, P K; Prajapati, R P

2014-01-01

The hydrodynamic Rayleigh -Taylor instability of two superposed compressible fluids in porous medium has been studied. The dispersion relation is derived for such a medium by using normal mode analysis. The RT instability is discussed for various simplified configuration. The effect of porosity and dynamic viscosity has been analyzed and it is observed that porosity and dynamic viscosity have stabilizing effect on the Rayleigh- Taylor instability of compressible fluids.

Fluid flow and heat transfer in rotating porous media

CERN Document Server

Vadasz, Peter

2016-01-01

This Book concentrates the available knowledge on rotating fluid flow and heat transfer in porous media in one single reference. Dr. Vadasz develops the fundamental theory of rotating flow and heat transfer in porous media and introduces systematic classification and identification of the relevant problems. An initial distinction between rotating flows in isothermal heterogeneous porous systems and natural convection in homogeneous non-­‐isothermal porous systems provides the two major classes of problems to be considered. A few examples of solutions to selected problems are presented, highlighting the significant impact of rotation on the flow in porous media.

A generalised porous medium approach to study thermo-fluid dynamics in human eyes.

Science.gov (United States)

Mauro, Alessandro; Massarotti, Nicola; Salahudeen, Mohamed; Romano, Mario R; Romano, Vito; Nithiarasu, Perumal

2018-03-22

The present work describes the application of the generalised porous medium model to study heat and fluid flow in healthy and glaucomatous eyes of different subject specimens, considering the presence of ocular cavities and porous tissues. The 2D computational model, implemented into the open-source software OpenFOAM, has been verified against benchmark data for mixed convection in domains partially filled with a porous medium. The verified model has been employed to simulate the thermo-fluid dynamic phenomena occurring in the anterior section of four patient-specific human eyes, considering the presence of anterior chamber (AC), trabecular meshwork (TM), Schlemm's canal (SC), and collector channels (CC). The computational domains of the eye are extracted from tomographic images. The dependence of TM porosity and permeability on intraocular pressure (IOP) has been analysed in detail, and the differences between healthy and glaucomatous eye conditions have been highlighted, proving that the different physiological conditions of patients have a significant influence on the thermo-fluid dynamic phenomena. The influence of different eye positions (supine and standing) on thermo-fluid dynamic variables has been also investigated: results are presented in terms of velocity, pressure, temperature, friction coefficient and local Nusselt number. The results clearly indicate that porosity and permeability of TM are two important parameters that affect eye pressure distribution. Graphical abstract Velocity contours and vectors for healthy eyes (top) and glaucomatous eyes (bottom) for standing position.

Boiling in porous media

International Nuclear Information System (INIS)

1998-01-01

This conference day of the French society of thermal engineers was devoted to the analysis of heat transfers and fluid flows during boiling phenomena in porous media. This book of proceedings comprises 8 communications entitled: 'boiling in porous medium: effect of natural convection in the liquid zone'; 'numerical modeling of boiling in porous media using a 'dual-fluid' approach: asymmetrical characteristic of the phenomenon'; 'boiling during fluid flow in an induction heated porous column'; 'cooling of corium fragment beds during a severe accident. State of the art and the SILFIDE experimental project'; 'state of knowledge about the cooling of a particulates bed during a reactor accident'; 'mass transfer analysis inside a concrete slab during fire resistance tests'; 'heat transfers and boiling in porous media. Experimental analysis and modeling'; 'concrete in accidental situation - influence of boundary conditions (thermal, hydric) - case studies'. (J.S.)

Study of stream wise transverse magnetic fluid flow with heat transfer around an obstacle embedded in a porous medium

Energy Technology Data Exchange (ETDEWEB)

Rashidi, S. [Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad 91775-1111 (Iran, Islamic Republic of); Dehghan, M. [Department of Mechanical Engineering, Semnan University, P.O. Box: 35196-45399, Semnan (Iran, Islamic Republic of); Ellahi, R., E-mail: rellahi@engr.ucr.edu [Department of Mathematics and Statistics, FBAS, IIUI, 44000 Islamabad (Pakistan); Department of Mechanical Engineering, Bourns Hall, University of California, Riverside, CA 92521 (United States); Riaz, M. [Department of QEC, National Defense University, E-9 Sector, 44000 Islamabad (Pakistan); Jamal-Abad, M.T. [Department of Mechanical Engineering, Semnan University, P.O. Box: 35196-45399, Semnan (Iran, Islamic Republic of)

2015-03-15

A mathematical model for two-dimensional fluid flow under the influence of stream wise transverse magnetic fields in laminar regime is simulated in this study. Heat transfer past a square diamond shaped porous obstacle is also taken into account. The attention is focused to investigate the effects of intensity and direction of magnetic field, Darcy and Reynolds numbers on the mechanism of convective heat transfer and flow structures. The Darcy–Brinkman–Forchheimer model along with the Maxwell equations is used. The nonlinear coupled equations using a finite volume approach (FVA) are solved numerically. The calculations are performed for different governing parameters such as Reynolds number, Nusselt number, Stuart number and Prandtl Number. The physical interpretation of velocity and isothermal contours is assigned through graphs. It is shown that the effects of a transverse magnetic field on flow behavior and heat transfer mechanism are more than that of the stream wise magnetic field. The configuration of streamlines and vorticity contours phenomena are also presented for porous diamond obstacle. Comparison of the numerical solutions with existing literature is also made. - Highlights: • This paper analyses two-dimensional fluid flow under the influence of stream wise transverse magnetic field. • Heat transfer past a square diamond shaped porous obstacle is taken into account. • The Darcy–Brinkman–Forchheimer model is used. • Finite volume approach is used to find numerical solutions. • The configuration of streamlines and vorticity contours phenomena are presented through graphs.

Evaluation of radiation heat transfer in porous medial: Application for a pebble bed modular reactor cooled by CO2 gas

Directory of Open Access Journals (Sweden)

Sidi-Ali Kamel

2013-01-01

Full Text Available This work analyses the contribution of radiation heat transfer in the cooling of a pebble bed modular reactor. The mathematical model, developed for a porous medium, is based on a set of equations applied to an annular geometry. Previous major works dealing with the subject have considered the forced convection mode and often did not take into account the radiation heat transfer. In this work, only free convection and radiation heat transfer are considered. This can occur during the removal of residual heat after shutdown or during an emergency situation. In order to derive the governing equations of radiation heat transfer, a steady-state in an isotropic and emissive porous medium (CO2 is considered. The obtained system of equations is written in a dimensionless form and then solved. In order to evaluate the effect of radiation heat transfer on the total heat removed, an analytical method for solving the system of equations is used. The results allow quantifying both radiation and free convection heat transfer. For the studied situation, they show that, in a pebble bed modular reactor, more than 70% of heat is removed by radiation heat transfer when CO2 is used as the coolant gas.

Free convective flow of a stratified fluid through a porous medium bounded by a vertical plane

Directory of Open Access Journals (Sweden)

H. K. Mondal

1994-01-01

Full Text Available Steady two-dimensional free convection flow of a thermally stratified viscous fluid through a highly porous medium bounded by a vertical plane surface of varying temperature, is considered. Analytical expressions for the velocity, temperature and the rate of heat transfer are obtained by perturbation method. Velocity distribution and rate of heat transfer for different values of parameters are shown in graphs. Velocity distribution is also obtained for certain values of the parameters by integrating the coupled differential equations by Runge-Kutta method and compared with the analytical solution. The chief concern of the paper is to study the effect of equilibrium temperature gradient on the velocity and the rate of heat transfer.

Lattice Boltzmann simulation of flow and heat transfer in random porous media constructed by simulated annealing algorithm

International Nuclear Information System (INIS)

Liu, Minghua; Shi, Yong; Yan, Jiashu; Yan, Yuying

2017-01-01

Highlights: • A numerical capability combining the lattice Boltzmann method with simulated annealing algorithm is developed. • Digitized representations of random porous media are constructed using limited but meaningful statistical descriptors. • Pore-scale flow and heat transfer information in random porous media is obtained by the lattice Boltzmann simulation. • The effective properties at the representative elementary volume scale are well specified using appropriate upscale averaging. - Abstract: In this article, the lattice Boltzmann (LB) method for transport phenomena is combined with the simulated annealing (SA) algorithm for digitized porous-medium construction to study flow and heat transfer in random porous media. Importantly, in contrast to previous studies which simplify porous media as arrays of regularly shaped objects or effective pore networks, the LB + SA method in this article can model statistically meaningful random porous structures in irregular morphology, and simulate pore-scale transport processes inside them. Pore-scale isothermal flow and heat conduction in a set of constructed random porous media characterized by statistical descriptors were then simulated through use of the LB + SA method. The corresponding averages over the computational volumes and the related effective transport properties were also computed based on these pore scale numerical results. Good agreement between the numerical results and theoretical predictions or experimental data on the representative elementary volume scale was found. The numerical simulations in this article demonstrate combination of the LB method with the SA algorithm is a viable and powerful numerical strategy for simulating transport phenomena in random porous media in complex geometries.

Effects of variable properties on MHD heat and mass transfer flow near a stagnation point towards a stretching sheet in a porous medium with thermal radiation

International Nuclear Information System (INIS)

Salem, A. M.; Fathy, Rania

2012-01-01

The effect of variable viscosity and thermal conductivity on steady magnetohydrodynamic (MHD) heat and mass transfer flow of viscous and incompressible fluid near a stagnation point towards a permeable stretching sheet embedded in a porous medium are presented, taking into account thermal radiation and internal heat genberation/absorbtion. The stretching velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing fundamental equations are first transformed into a system of ordinary differential equations using a scaling group of transformations and are solved numerically by using the fourth-order Rung—Kutta method with the shooting technique. A comparison with previously published work has been carried out and the results are found to be in good agreement. The results are analyzed for the effect of different physical parameters, such as the variable viscosity and thermal conductivity, the ratio of free stream velocity to stretching velocity, the magnetic field, the porosity, the radiation and suction/injection on the flow, and the heat and mass transfer characteristics. The results indicate that the inclusion of variable viscosity and thermal conductivity into the fluids of light and medium molecular weight is able to change the boundary-layer behavior for all values of the velocity ratio parameter λ except for λ = 1. In addition, the imposition of fluid suction increases both the rate of heat and mass transfer, whereas fluid injection shows the opposite effect. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Influence of vapor-mass flux on simultaneous heat and moisture transfer in unsaturated porous media

International Nuclear Information System (INIS)

Hartley, J.G.; Boo, J.H.

1987-01-01

This paper evaluates the validity of neglecting vapor transport by moisture content gradients (VMG) and liquid transport by temperature gradients (LTG) in coupled heat and moisture transfer in moist porous media. A review of previous work reveals discrepancies between model predictions and experimental data. The results presented here show that these discrepancies result from neglecting VMG. The governing equations which describe the coupled heat and moisture transfer are solved numerically for an infinite slab of an unsaturated porous medium, and existing experimental and empirical data for a moist sandy silt soil are used. Predicted moisture content distributions during dry-out and drying rates are found to be significantly affected by VMG. Accurate results can be obtained when VMG is neglected in the energy equation provided that it is retained in the mass conservation equation

Heat transfer in porous medium embedded with vertical plate: Non-equilibrium approach - Part B

Energy Technology Data Exchange (ETDEWEB)

Quadir, G. A., E-mail: Irfan-magami@Rediffmail.com, E-mail: gaquadir@gmail.com [School of Mechatronic Engineering, University Malaysia Perlis, Pauh Putra, 02600 Arau, Perlis (Malaysia); Badruddin, Irfan Anjum [Dept. of Mechanical Engineering, University of Malaya, Kuala Lumpur, 50603 (Malaysia)

2016-06-08

This work is continuation of the paper Part A. Due to large number of results, the paper is divided into two section with section-A (Part A) discussing the effect of various parameters such as heat transfer coefficient parameter, thermal conductivity ratio etc. on streamlines and isothermal lines. Section-B highlights the heat transfer characteristics in terms of Nusselt number The Darcy model is employed to simulate the flow inside the medium. It is assumed that the heat transfer takes place by convection and radiation. The governing partial differential equations are converted into non-dimensional form and solved numerically using finite element method.

Heat and Mass Transfer of Vacuum Cooling for Porous Foods-Parameter Sensitivity Analysis

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Zhijun Zhang

2014-01-01

Full Text Available Based on the theory of heat and mass transfer, a coupled model for the porous food vacuum cooling process is constructed. Sensitivity analyses of the process to food density, thermal conductivity, specific heat, latent heat of evaporation, diameter of pores, mass transfer coefficient, viscosity of gas, and porosity were examined. The simulation results show that the food density would affect the vacuum cooling process but not the vacuum cooling end temperature. The surface temperature of food was slightly affected and the core temperature is not affected by the changed thermal conductivity. The core temperature and surface temperature are affected by the changed specific heat. The core temperature and surface temperature are affected by the changed latent heat of evaporation. The core temperature is affected by the diameter of pores. But the surface temperature is not affected obviously. The core temperature and surface temperature are not affected by the changed gas viscosity. The parameter sensitivity of mass transfer coefficient is obvious. The core temperature and surface temperature are affected by the changed mass transfer coefficient. In all the simulations, the end temperature of core and surface is not affected. The vacuum cooling process of porous medium is a process controlled by outside process.

Analysis of fluid flow and heat transfer in a double pipe heat exchanger with porous structures

International Nuclear Information System (INIS)

Targui, N.; Kahalerras, H.

2008-01-01

A numerical study of flow and heat transfer characteristics is made in a double pipe heat exchanger with porous structures inserted in the annular gap in two configurations: on the inner cylinder (A) and on both the cylinders in a staggered fashion (B). The flow field in the porous regions is modelled by the Darcy-Brinkman-Forchheimer model and the finite volume method is used to solve the governing equations. The effects of several parameters such as Darcy number, porous structures thickness and spacing and thermal conductivity ratio are considered in order to look for the most appropriate properties of the porous structures that allow optimal heat transfer enhancement. It is found that the highest heat transfer rates are obtained when the porous structures are attached in configuration B especially at small spacing and high thicknesses

Generation of reactive oxygen species from porous silicon microparticles in cell culture medium.

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Low, Suet Peng; Williams, Keryn A; Canham, Leigh T; Voelcker, Nicolas H

2010-06-01

Nanostructured (porous) silicon is a promising biodegradable biomaterial, which is being intensively researched as a tissue engineering scaffold and drug-delivery vehicle. Here, we tested the biocompatibility of non-treated and thermally-oxidized porous silicon particles using an indirect cell viability assay. Initial direct cell culture on porous silicon determined that human lens epithelial cells only poorly adhered to non-treated porous silicon. Using an indirect cell culture assay, we found that non-treated microparticles caused complete cell death, indicating that these particles generated a toxic product in cell culture medium. In contrast, thermally-oxidized microparticles did not reduce cell viability significantly. We found evidence for the generation of reactive oxygen species (ROS) by means of the fluorescent probe 2',7'-dichlorofluorescin. Our results suggest that non-treated porous silicon microparticles produced ROS, which interacted with the components of the cell culture medium, leading to the formation of cytotoxic species. Oxidation of porous silicon microparticles not only mitigated, but also abolished the toxic effects.

Fluid-Driven Deformation of a Soft Porous Medium

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Lutz, Tyler; Wilen, Larry; Wettlaufer, John

2017-11-01

Viscous drag forces resisting the flow of fluid through a soft porous medium are maintained by restoring forces associated with deformations in the solid matrix. We describe experimental measurements of the deformation of foam under a pressure-driven flow of water along a single axis. Image analysis techniques allow tracking of the foam displacement while pressure sensors allow measurement of the fluid pressure. Experiments are performed for a series of different pressure heads ranging from 10 to 90 psi, and the results are compared to theory. This work builds on previous measurements of the fluid-induced deformation of a bed of soft hydrogel spheres. Compared to the hydrogel system, foams have the advantage that the constituents of the porous medium do not rearrange during an experiment, but they have the disadvantage of having a high friction coefficient with any boundaries. We detail strategies to characterize and mitigate the effects of friction on the observed foam deformations.

Fem Simulation of Triple Diffusive Natural Convection Along Inclined Plate in Porous Medium: Prescribed Surface Heat, Solute and Nanoparticles Flux

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Goyal M.

2017-12-01

Full Text Available In this paper, triple diffusive natural convection under Darcy flow over an inclined plate embedded in a porous medium saturated with a binary base fluid containing nanoparticles and two salts is studied. The model used for the nanofluid is the one which incorporates the effects of Brownian motion and thermophoresis. In addition, the thermal energy equations include regular diffusion and cross-diffusion terms. The vertical surface has the heat, mass and nanoparticle fluxes each prescribed as a power law function of the distance along the wall. The boundary layer equations are transformed into a set of ordinary differential equations with the help of group theory transformations. A wide range of parameter values are chosen to bring out the effect of buoyancy ratio, regular Lewis number and modified Dufour parameters of both salts and nanofluid parameters with varying angle of inclinations. The effects of parameters on the velocity, temperature, solutal and nanoparticles volume fraction profiles, as well as on the important parameters of heat and mass transfer, i.e., the reduced Nusselt, regular and nanofluid Sherwood numbers, are discussed. Such problems find application in extrusion of metals, polymers and ceramics, production of plastic films, insulation of wires and liquid packaging.

Optimization of porous microchannel heat exchanger

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Kozhukhov, N. N.; Konovalov, D. A.

2017-11-01

The technical progress in information and communication sphere leads to a sharp increase in the use of radio electronic devices. Functioning of radio electronics is accompanied by release of thermal energy, which must be diverted from the heat-stressed element. Moreover, using of electronics at negative temperatures, on the contrary, requires supply of a certain amount of heat to start the system. There arises the task of creating a system that allows both to supply and to divert the necessary amount of thermal energy. The development of complex thermostabilization systems for radio electronic equipment is due to increasing the efficiency of each of its elements separately. For more efficient operation of a heat exchanger, which directly affects the temperature of the heat-stressed element, it is necessary to calculate the mode characteristics and to take into account the effect of its design parameters. The results of optimizing the microchannel heat exchanger are presented in the article. The target optimization functions are the mass, pressure drop and temperature. The parameters of optimization are the layout of porous fins, their geometric dimensions and coolant flow. For the given conditions, the optimum variant of porous microchannel heat exchanger is selected.

Effects of variable properties on MHD heat and mass transfer flow near a stagnation point towards a stretching sheet in a porous medium with thermal radiation

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M. Salem, A.; Rania, Fathy

2012-05-01

The effect of variable viscosity and thermal conductivity on steady magnetohydrodynamic (MHD) heat and mass transfer flow of viscous and incompressible fluid near a stagnation point towards a permeable stretching sheet embedded in a porous medium are presented, taking into account thermal radiation and internal heat genberation/absorbtion. The stretching velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing fundamental equations are first transformed into a system of ordinary differential equations using a scaling group of transformations and are solved numerically by using the fourth-order Rung—Kutta method with the shooting technique. A comparison with previously published work has been carried out and the results are found to be in good agreement. The results are analyzed for the effect of different physical parameters, such as the variable viscosity and thermal conductivity, the ratio of free stream velocity to stretching velocity, the magnetic field, the porosity, the radiation and suction/injection on the flow, and the heat and mass transfer characteristics. The results indicate that the inclusion of variable viscosity and thermal conductivity into the fluids of light and medium molecular weight is able to change the boundary-layer behavior for all values of the velocity ratio parameter λ except for λ = 1. In addition, the imposition of fluid suction increases both the rate of heat and mass transfer, whereas fluid injection shows the opposite effect.

Chemical reaction effects on unsteady MHD free convective flow in a rotating porous medium with mass transfer

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Govindarajan Arunachalam

2014-01-01

Full Text Available An investigation of unsteady MHD free convective flow and mass transfer during the motion of a viscous incompressible fluid through a porous medium, bounded by an infinite vertical porous surface, in a rotating system is presented. The porous plane surface and the porous medium are assumed to rotate in a solid body rotation. The vertical surface is subjected to uniform constant suction perpendicular to it and the temperature at this surface fluctuates in time about a non-zero constant mean. Analytical expressions for the velocity, temperature and concentration fields are obtained using the perturbation technique. The effects of R (rotation parameter, k0 (permeability parameter, M (Hartmann number and w (frequency parameter on the flow characteristics are discussed. It is observed that the primary velocity component decreases with the increase in either of the rotation parameter R, the permeability parameter k0, or the Hartmann number M. It is also noted that the primary skin friction increases whenever there is an increase in the Grashof number Gr or the modified Grashof number Gm. It is clear that the heat transfer coefficient in terms of the Nusselt number decreases in the case of both air and water when there is an increase in the Hartmann number M. It is observed that the magnitude of the secondary velocity profiles increases whenever there is an increase in either of the Grashof number or the modified Grashof number for mass transfer or the permeability of the porous media. Concentration profiles decreases with an increase in the Schmidt number.

Approximation and stability of three-dimensional natural convection flows in a porous medium

International Nuclear Information System (INIS)

Janotto, Marie-Laurence

1991-01-01

The equations of the three-dimensional natural convection in a porous medium within a differentially heated horizontal walls cavity are solved by a pseudo-spectral method. First we will present the evolution of the two main modes according to two models of convection. A few asymptotic properties connected to the small and large eddies are set up and numerically validated. A new approximate inertial manifold is then proposed. The numerical scheme used is an exponential fitting algorithm the convergence of which is proved. We will present the physical mechanism at the origin of the un-stationary three-dimensional convection at high Rayleigh numbers. (author) [fr

Hall Currents and Heat Transfer Effects on Peristaltic Transport in a Vertical Asymmetric Channel through a Porous Medium

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E. Abo-Eldahab

2012-01-01

a porous medium are investigated theoretically and graphically under assumptions of low Reynolds number and long wavelength. The flow is investigated in a wave frame of reference moving with the velocity of the wave. Analytical solutions have been obtained for temperature, axial velocity, stream function, pressure gradient, and shear stresses. The trapping phenomenon is discussed. Graphical results are sketched for various embedded parameters and interpreted.

Hydromagnetic boundary layer micropolar fluid flow over a stretching surface embedded in a non-darcian porous medium with radiation

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Mostafa A. A. Mahmoud

2006-01-01

Full Text Available We have studied the effects of radiation on the boundary layer flow and heat transfer of an electrically conducting micropolar fluid over a continuously moving stretching surface embedded in a non-Darcian porous medium with a uniform magnetic field. The transformed coupled nonlinear ordinary differential equations are solved numerically. The velocity, the angular velocity, and the temperature are shown graphically. The numerical values of the skin friction coefficient, the wall couple stress, and the wall heat transfer rate are computed and discussed for various values of parameters.

Numerical simulation of porous burners and hole plate surface burners

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Nemoda Stevan

2004-01-01

Full Text Available In comparison to the free flame burners the porous medium burners, especially those with flame stabilization within the porous material, are characterized by a reduction of the combustion zone temperatures and high combustion efficiency, so that emissions of pollutants are minimized. In the paper the finite-volume numerical tool for calculations of the non-isothermal laminar steady-state flow, with chemical reactions in laminar gas flow as well as within porous media is presented. For the porous regions the momentum and energy equations have appropriate corrections. In the momentum equations for the porous region an additional pressure drop has to be considered, which depends on the properties of the porous medium. For the heat transfer within the porous matrix description a heterogeneous model is considered. It treats the solid and gas phase separately, but the phases are coupled via a convective heat exchange term. For the modeling of the reaction of the methane laminar combustion the chemical reaction scheme with 164 reactions and 20 chemical species was used. The proposed numerical tool is applied for the analyses of the combustion and heat transfer processes which take place in porous and surface burners. The numerical experiments are accomplished for different powers of the porous and surface burners, as well as for different heat conductivity character is tics of the porous regions.

Effect of Thermophysical Properties on Coupled Heat and Mass Transfer in Porous Material during Forced Convective Drying

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Wei Cai

2014-06-01

Full Text Available The convective drying kinetics of porous medium was investigated numerically. A mathematical model for forced convective drying was established to estimate the evolution of moisture content and temperature inside multilayered porous medium. The set of coupled partial differential equations with the specified boundary and initial conditions were solved numerically using a MATLAB code. An experimental setup of convective drying had been constructed and validated the theoretical model. The temperature and moisture content of the potato samples were dynamically measured and recorded during the drying process. Results indicate that thermal diffusion coefficient has significant positive impact on temperature distribution and mass diffusion coefficient might directly affect the moisture content distribution. Soret effect has a significant impact on heat flux and temperature distribution in the presence of large temperature gradient.

Heat Removal from Bipolar Transistor by Loop Heat Pipe with Nickel and Copper Porous Structures

Science.gov (United States)

Smitka, Martin; Malcho, Milan

2014-01-01

Loop heat pipes (LHPs) are used in many branches of industry, mainly for cooling of electrical elements and systems. The loop heat pipe is a vapour-liquid phase-change device that transfers heat from evaporator to condenser. One of the most important parts of the LHP is the porous wick structure. The wick structure provides capillary force to circulate the working fluid. To achieve good thermal performance of LHP, capillary wicks with high permeability and porosity and fine pore radius are expected. The aim of this work was to develop porous structures from copper and nickel powder with different grain sizes. For experiment copper powder with grain size of 50 and 100 μm and nickel powder with grain size of 10 and 25 μm were used. Analysis of these porous structures and LHP design are described in the paper. And the measurements' influences of porous structures in LHP on heat removal from the insulated gate bipolar transistor (IGBT) have been made. PMID:24959622

Development and numerical investigation of novel gradient-porous heat sinks

International Nuclear Information System (INIS)

Wang, Baicun; Hong, Yifeng; Wang, Liang; Fang, Xudong; Wang, Pengfei; Xu, Zhongbin

2015-01-01

Highlights: • A novel design of gradient-porous heat sink (GPHS) was proposed in this work. • A 3D model was constructed to study the hydraulic and thermal performances of GPHS. • GPHS is capable of improving the hydraulic and thermal performances simultaneously. • GPHS with decreasing dp by Y can effectively suppress the bottom wall temperature. - Abstract: A novel design of gradient-porous heat sink (GPHS) was proposed and numerically studied in this work. Computational simulation was carried out to analyze the effects of gradient porous material (GPM) configuration on the hydraulic and thermal performances of heat sinks in comparison of homogeneous-porous heat sink (HPHS) serving as the control. Both gradient pore-size (dp) in the flow direction and the direction normal to flow direction were studied. It was found that, compared with conventional HPHS, GPHS can effectively improve the hydraulic and thermal performances simultaneously. Both the friction factor and overall thermal resistance of heat sinks with GPM configurations are considerably lowered. The Nusselt numbers of GPHS with gradient in flow direction are larger than those of homogeneous porous material (HPM) configurations. GPHS is also featured with the capabilities of effectively suppressing the bottom wall temperature and enhancing the convection performance.

Impact of heat and mass transfer during the transport of nitrogen in coal porous media on coal mine fires.

Science.gov (United States)

Shi, Bobo; Zhou, Fubao

2014-01-01

The application of liquid nitrogen injection is an important technique in the field of coal mine fire prevention. However, the mechanism of heat and mass transfer of cryogenic nitrogen in the goaf porous medium has not been well accessed. Hence, the implementation of fire prevention engineering of liquid nitrogen roughly relied on an empirical view. According to the research gap in this respect, an experimental study on the heat and mass transfer of liquid nitrogen in coal porous media was proposed. Overall, the main mechanism of liquid nitrogen fire prevention technology in the coal mine is the creation of an inert and cryogenic atmosphere. Cryogenic nitrogen gas vapor cloud, heavier than the air, would cause the phenomenon of "gravity settling" in porous media firstly. The cryogen could be applicable to diverse types of fires, both in the openings and in the enclosures. Implementation of liquid nitrogen open-injection technique in Yangchangwan colliery achieved the goals of fire prevention and air-cooling. Meanwhile, this study can also provide an essential reference for the research on heat and mass transfer in porous media in the field of thermal physics and engineering.

Impact of Heat and Mass Transfer during the Transport of Nitrogen in Coal Porous Media on Coal Mine Fires

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Bobo Shi

2014-01-01

Full Text Available The application of liquid nitrogen injection is an important technique in the field of coal mine fire prevention. However, the mechanism of heat and mass transfer of cryogenic nitrogen in the goaf porous medium has not been well accessed. Hence, the implementation of fire prevention engineering of liquid nitrogen roughly relied on an empirical view. According to the research gap in this respect, an experimental study on the heat and mass transfer of liquid nitrogen in coal porous media was proposed. Overall, the main mechanism of liquid nitrogen fire prevention technology in the coal mine is the creation of an inert and cryogenic atmosphere. Cryogenic nitrogen gas vapor cloud, heavier than the air, would cause the phenomenon of “gravity settling” in porous media firstly. The cryogen could be applicable to diverse types of fires, both in the openings and in the enclosures. Implementation of liquid nitrogen open-injection technique in Yangchangwan colliery achieved the goals of fire prevention and air-cooling. Meanwhile, this study can also provide an essential reference for the research on heat and mass transfer in porous media in the field of thermal physics and engineering.

Boiling phenomenon and heat transfer in bead-packed porous structure

International Nuclear Information System (INIS)

Zhang Xiaojie; ZHu Yanlei; Bai Bofeng; Yan Xiao; Xiao Zejun

2009-01-01

A visual study on pool boiling behavior and phase distribution was conducted on the porous structures made of staggered glass beads at atmospheric pressure. The bead-packed structure was heated on the bottom. The investigations were carried out respectively at different glass bead diameters which were 4 mm, 6 mm and 8 mm. The results show that during subcooled boiling, small isolated bubbles are formed on the heated surface and combine into main-bubbles, the dispersion frequency of the main-bubbles is low and the small bubbles scatter in the bead-packed porous structures. At the initial stage of saturated boiling, the bubble growth rate, the volume of main-bubbles and the range of continuous vapor phase increase. The dispersion frequency of main-bubbles increases with the increasing of heat flux. During film boiling, the heated surface is absolutely covered with vapor film and the porous structure is full of liquid. The larger the diameter of beads is, the higher heat flux is needed for the same phenomenon, and the higher maximum value of heat transfer coefficient will be. During the whole saturated boiling, and the heat transfer enhanced firstly and then weakened. Being opposite to that of the diameters of 4 mm and 8 mm, the heat transfer coefficient in the 6 mm-bead-packed porous structure decreases with the increasing of the heat flux. (authors)

A frame work for heat generation/absorption and modified homogeneous–heterogeneous reaction in flow based on non-Darcy–Forchheimer medium

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Tasawar Hayat

2018-04-01

Full Text Available The present work aims to report the consequences of Darcy–Forchheimer medium in flow of Cross fluid model toward a stretched surface. Flow in porous space is categorized by Darcy–Forchheimer medium. Further heat transfer characteristics are examined via thermal radiation and heat generation/absorption. Transformation procedure is used. The arising system of nonlinear ordinary differential equations is solved numerically by means of shooting method. The effects of different flow variables on velocity, temperature, concentration, skin friction, and heat transfer rate are discussed. The obtained outcomes show that velocity was enhanced with the increase in the Weissenberg number but decays with increase in the porosity parameter and Hartman number. Temperature field is boosted by thermal radiation and heat generation; however, it decays with the increase in the Prandtl number. Keywords: Cross Fluid, Heat Generation/Absorption, Homogeneous–Heterogeneous Reactions, Non-Darcy–Forchheimer Medium, Thermal Radiation

Numerical Modelling Of Humid Air Flow Around A Porous Body

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Bohojło-Wiśniewska Aneta

2015-09-01

Full Text Available This paper presents an example of humid air flow around a single head of Chinese cabbage under conditions of complex heat transfer. This kind of numerical simulation allows us to create a heat and humidity transfer model between the Chinese cabbage and the flowing humid air. The calculations utilize the heat transfer model in porous medium, which includes the temperature difference between the solid (vegetable tissue and fluid (air phases of the porous medium. Modelling and calculations were performed in ANSYS Fluent 14.5 software.

Mixed convection boundary layer flow over a vertical surface embedded in a thermally stratified porous medium

International Nuclear Information System (INIS)

Ishak, Anuar; Nazar, Roslinda; Pop, Ioan

2008-01-01

The mixed convection boundary layer flow through a stable stratified porous medium bounded by a vertical surface is investigated. The external velocity and the surface temperature are assumed to vary as x m , where x is measured from the leading edge of the vertical surface and m is a constant. Numerical solutions for the governing Darcy and energy equations are obtained. The results indicate that the thermal stratification significantly affects the surface shear stress as well as the surface heat transfer, besides delays the boundary layer separation

MHD heat and mass diffusion flow by natural convection past a surface embedded in a porous medium

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Chaudhary R.C.

2009-01-01

Full Text Available This paper presents an analytical study of the transient hydromagnetic natural convection flow past a vertical plate embedded in a porous medium, taking account of the presence of mass diffusion and fluctuating temperature about time at the plate. The governing equations are solved in closed form by the Laplace-transform technique. The results are obtained for temperature, velocity, penetration distance, Nusselt number and skin-friction. The effects of various parameters are discussed on the flow variables and presented by graphs.

Effective medium approximation for elastic constants of porous solids with microscopic heterogeneity

International Nuclear Information System (INIS)

Berryman, J.G.

1986-01-01

Formulas for the scattering from an inhomogeneous sphere in a fluid-saturated porous medium are used to construct a self-consistent effective medium approximation for the coefficients in Biot's equations of poroelasticity [J. Acoust. Soc. Am. 28, 168 (1956)] when the material constituting the porous solid frame is not homogeneous on the microscopic scale. The discussion is restricted to porous materials exhibiting both macroscopic and microscopic isotropy. Brown and Korringa [Geophysics 40, 608 (1975)] have previously found the general form of these coefficients. The present results give explicit estimates of all the coefficients in terms of the moduli of the solid constituents. The results are also shown to be completely consistent with the well-known results of Gassmann and of Biot and Willis, as well as those of Brown and Korringa

Energy dissipation during an explosion in a porous elasto-plastic medium

Energy Technology Data Exchange (ETDEWEB)

Lovetskii, E.E.; Maslennikov, A.M.; Fetisov, V.S.

1979-01-01

A study is made of the redistribution of energy from camouflage blasting in a saturated porous medium. The study is undertaken with the aid of a numerical solution to a system of hydrodynamic equations, that account for shear strength of the substance under investigation. A study is made of the energy characteristics of explosion, their dynamic development, the influence of strength parameters of the medium, and porosity on these characteristics. A mechanism that is associated with the impact compression of matter is identified as the basic mechanism of energy dissipation for dry porous media. Water saturation of pores brings the energy characteristics of the explosion close to the explosion in a monolith. 12 references, 5 figures, 1 table.

Heat Removal from Bipolar Transistor by Loop Heat Pipe with Nickel and Copper Porous Structures

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Patrik Nemec

2014-01-01

Full Text Available Loop heat pipes (LHPs are used in many branches of industry, mainly for cooling of electrical elements and systems. The loop heat pipe is a vapour-liquid phase-change device that transfers heat from evaporator to condenser. One of the most important parts of the LHP is the porous wick structure. The wick structure provides capillary force to circulate the working fluid. To achieve good thermal performance of LHP, capillary wicks with high permeability and porosity and fine pore radius are expected. The aim of this work was to develop porous structures from copper and nickel powder with different grain sizes. For experiment copper powder with grain size of 50 and 100 μm and nickel powder with grain size of 10 and 25 μm were used. Analysis of these porous structures and LHP design are described in the paper. And the measurements’ influences of porous structures in LHP on heat removal from the insulated gate bipolar transistor (IGBT have been made.

Opposing flow in square porous annulus: Influence of Dufour effect

International Nuclear Information System (INIS)

Athani, Abdulgaphur; Al-Rashed, Abdullah A. A. A.; Khaleed, H. M. T.

2016-01-01

Heat and mass transfer in porous medium is very important area of research which is also termed as double diffusive convection or thermo-solutal convection. The buoyancy ratio which is the ratio of thermal to concentration buoyancy can have negative values thus leading to opposing flow. This article is aimed to study the influence of Dufour effect on the opposing flow in a square porous annulus. The partial differential equations that govern the heat and mass transfer behavior inside porous medium are solved using finite element method. A three node triangular element is used to divide the porous domain into smaller elements. Results are presented with respect to geometric and physical parameters such as duct diameter ratio, Rayleigh number, radiation parameter etc. It is found that the heat transfer increase with increase in Rayleigh number and radiation parameter. It is observed that Dufour coefficient has more influence on velocity profile.

Opposing flow in square porous annulus: Influence of Dufour effect

Energy Technology Data Exchange (ETDEWEB)

Athani, Abdulgaphur, E-mail: abbu.bec@gmail.com [Dept. of Mechanical Engineering, Anjuman Institute of Technology & Management, Bhatkal (India); Al-Rashed, Abdullah A. A. A., E-mail: aa.alrashed@paaet.edu.kw [Dept. of Automotive and Marine Engineering Technology, College of Technological Studies, The Public Authority for Applied Education and Training (Kuwait); Khaleed, H. M. T., E-mail: khalid-tan@yahoo.com [Dept of Mechanical Engineering, Faculty of Engineering, Islamic University, Madinah Munawwarra (Saudi Arabia)

2016-06-21

Heat and mass transfer in porous medium is very important area of research which is also termed as double diffusive convection or thermo-solutal convection. The buoyancy ratio which is the ratio of thermal to concentration buoyancy can have negative values thus leading to opposing flow. This article is aimed to study the influence of Dufour effect on the opposing flow in a square porous annulus. The partial differential equations that govern the heat and mass transfer behavior inside porous medium are solved using finite element method. A three node triangular element is used to divide the porous domain into smaller elements. Results are presented with respect to geometric and physical parameters such as duct diameter ratio, Rayleigh number, radiation parameter etc. It is found that the heat transfer increase with increase in Rayleigh number and radiation parameter. It is observed that Dufour coefficient has more influence on velocity profile.

Experimental Investigation of Natural Convection into a Horizontal Annular Tube with Porous Medium Effects

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Saad Najeeb Shehab

2018-12-01

Full Text Available In this work, an experimental investigation has been done for heat transfer by natural-convection through a horizontal concentric annulus with porous media effects. The porous structure in gap spacing consists of a glass balls and replaced by plastic (PVC balls with different sizes. The outer surface of outer tube is isothermally cooled while the outer surface of inner tube is heated with constant heat flux condition. The inner tube is heated with different supplied electrical power levels. Four different radius ratios of annulus are used. The effects of porous media material, particles size and annulus radius ratio on heat dissipation in terms of average Nusselt number have been analyzed. The experimental results show that the average Nusselt number increases with increasing annulus radius ratio and particle diameter for same porous media material. Furthermore, two empirical correlations of average Nusselt number with average Rayleigh number for glass and PVC particles are developed. The present experimental results are compared with previously works and good correspondence is showed.

Unsteady flow of an incompressible fluid in a horizontal porous medium with suction

International Nuclear Information System (INIS)

Bestman, A.R.

1988-04-01

A theoretical analysis of two-dimensional unsteady flow in a porous medium bounded by a horizontal wall is presented as a perturbation on a basic flow. It is assumed that the perturbation is occasioned by a sudden suction at the wall. Even for a highly permeable medium the characteristic Reynolds number in porous media flow is usually small and asymptotic solutions are developed by the Laplace transform technique. It is observed that the perturbed shear stress at the wall decays exponentially with time. (author). 5 refs

Chemical reaction effect on MHD free convective surface over a moving vertical plate through porous medium

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R.S. Tripathy

2015-09-01

Full Text Available An attempt has been made to study the heat and mass transfer effect in a boundary layer flow of an electrically conducting viscous fluid subject to transverse magnetic field past over a moving vertical plate through porous medium in the presence of heat source and chemical reaction. The governing non-linear partial differential equations have been transformed into a two-point boundary value problem using similarity variables and then solved numerically by fourth order Runge–Kutta fourth order method with shooting technique. Graphical results are discussed for non-dimensional velocity, temperature and concentration profiles while numerical values of the skin friction, Nusselt number and Sherwood number are presented in tabular form for various values of parameters controlling the flow system.

A numerical study of EGS heat extraction process based on a thermal non-equilibrium model for heat transfer in subsurface porous heat reservoir

Science.gov (United States)

Chen, Jiliang; Jiang, Fangming

2016-02-01

With a previously developed numerical model, we perform a detailed study of the heat extraction process in enhanced or engineered geothermal system (EGS). This model takes the EGS subsurface heat reservoir as an equivalent porous medium while it considers local thermal non-equilibrium between the rock matrix and the fluid flowing in the fractured rock mass. The application of local thermal non-equilibrium model highlights the temperature-difference heat exchange process occurring in EGS reservoirs, enabling a better understanding of the involved heat extraction process. The simulation results unravel the mechanism of preferential flow or short-circuit flow forming in homogeneously fractured reservoirs of different permeability values. EGS performance, e.g. production temperature and lifetime, is found to be tightly related to the flow pattern in the reservoir. Thermal compensation from rocks surrounding the reservoir contributes little heat to the heat transmission fluid if the operation time of an EGS is shorter than 15 years. We find as well the local thermal equilibrium model generally overestimates EGS performance and for an EGS with better heat exchange conditions in the heat reservoir, the heat extraction process acts more like the local thermal equilibrium process.

SCDAP/RELAP5 Modeling of Heat Transfer and Flow Losses in Lower Head Porous Debris

International Nuclear Information System (INIS)

Coryell, E.W.; Siefken, L.J.; Paik, S.

1998-01-01

Designs are described for implementing models for calculating the heat transfer and flow losses in porous debris in the lower head of a reactor vessel. The COUPLE model in SCDAP/RELAP5 represents both the porous and non-porous debris that results from core material slumping into the lower head. Currently, the COUPLE model has the capability to model convective and radiative heat transfer from the surfaces of non-porous debris in a detailed manner and to model only in a simplistic manner the heat transfer from porous debris. In order to advance beyond the simplistic modeling for porous debris, designs are developed for detailed calculations of heat transfer and flow losses in porous debris. Correlations are identified for convective heat transfer in porous debris for the following modes of heat transfer; (1) forced convection to liquid, (2) forced convection to gas, (3) nucleate boiling, (4) transition boiling, and (5) film boiling. Interphase heat transfer is modeled in an approximate manner. A design is also described for implementing a model of heat transfer by radiation from debris to the interstitial fluid. A design is described for implementation of models for flow losses and interphase drag in porous debris. Since the models for heat transfer and flow losses in porous debris in the lower head are designed for general application, a design is also described for implementation of these models to the analysis of porous debris in the core region. A test matrix is proposed for assessing the capability of the implemented models to calculate the heat transfer and flow losses in porous debris. The implementation of the models described in this report is expected to improve the COUPLE code calculation of the temperature distribution in porous debris and in the lower head that supports the debris. The implementation of these models is also expected to improve the calculation of the temperature and flow distribution in porous debris in the core region

Thermal convection and nonlinear effects of a superfluid 3He-4He mixture in a porous medium

International Nuclear Information System (INIS)

Chien, L.C.L.

1986-01-01

The convective instability of one-component classical fluids in a porous medium confined between two unbounded slabs was studied. This system behaves like a high Prandtl number bulk fluid. It has boundary conditions similar to the stress-free boundary conditions of bulk one-component classical fluids. Both the amplitude expansion method and the Galerkin method were used to investigate the nonlinear steady convection. Two dimensional rolls are the only stable motion at the onset of convection. Beyond threshold, the steady convection rolls become unstable to formation of cross-roll and zigzag instabilities. Applying the phase-dynamics approach for the zigzag instability, the author obtained the diffusion coefficient D, which can signal the onset of instability. Also investigated was the convective instability of superfluid 3 He- 4 He mixtures in porous media. Assuming no interaction between the average superflow and the porous medium and treating the normal flow in the equation of motion like a classical fluid in a porous medium, it was found that the superfluid mixtures in a porous medium. To investigate the effects of a lateral boundary, the convective instability of classical one-component fluids in porous media inside a box was studied. The zigzag instability does not exist because of the boundary conditions at the side of the box

Similarity Solution for Combined Free-Forced Convection Past a Vertical Porous Plate in a Porous Medium with a Convective Surface Boundary Condition

Directory of Open Access Journals (Sweden)

Garg P.

2016-12-01

Full Text Available This paper studies the mathematical implications of the two dimensional viscous steady laminar combined free-forced convective flow of an incompressible fluid over a semi infinite fixed vertical porous plate embedded in a porous medium. It is assumed that the left surface of the plate is heated by convection from a hot fluid which is at a temperature higher than the temperature of the fluid on the right surface of the vertical plate. To achieve numerical consistency for the problem under consideration, the governing non linear partial differential equations are first transformed into a system of ordinary differential equations using a similarity variable and then solved numerically under conditions admitting similarity solutions. The effects of the physical parameters of both the incompressible fluid and the vertical plate on the dimensionless velocity and temperature profiles are studied and analysed and the results are depicted both graphically and in a tabular form. Finally, algebraic expressions and the numerical values are obtained for the local skin-friction coefficient and the local Nusselt number.

Convection heat transfer in the double pass solar collector with porous media

International Nuclear Information System (INIS)

Md Yusof Theeran; Mohd Yusof Othman; Baharuddin Yatim; Kamaruzzaman Sopian; Mohd Hafidz Roslan

2006-01-01

This paper describes about heat transfer characteristics in the double pass solar heater with porous media. Nusselt and Stanton number had been used to shown the heat transfer. Nusselt number had been measured and compared with several theories. Stanton number in the double pass solar heater with porous media and without porous media had been compared. Predicted value of Stanton number will be shown in this paper

Double diffusive conjugate heat transfer: Part I

Science.gov (United States)

Azeem, Soudagar, Manzoor Elahi M.

2018-05-01

The present work is undertaken to investigate the effect of solid wall being placed at left of square cavity filled with porous medium. The presence of a solid wall in the porous medium turns the situation into a conjugate heat transfer problem. The boundary conditions are such that the left vertical surface is maintained at highest temperature and concentration whereas right vertical surface at lowest temperature and concentration in the medium. The top and bottom surfaces are adiabatic. The additional conduction equation along with the regular momentum and energy equations of porous medium are solved in an iterative manner with the help of finite element method. It is seen that the heat and mass transfer rate is lesser due to smaller thermal and concentration gradients.

Effect of porous material heating on the drag force of a cylinder with gas-permeable porous inserts in a supersonic flow

Science.gov (United States)

Mironov, S. G.; Poplavskaya, T. V.; Kirilovskiy, S. V.

2017-10-01

The paper presents the results of an experimental investigation of supersonic flow around a solid cylinder with a gas-permeable porous insert on its front end and of supersonic flow around a hollow cylinder with internal porous inserts in the presence of heating of the porous material. The experiments were performed in a supersonic wind tunnel with Mach number 4.85 and 7 with porous inserts of cellular-porous nickel. The results of measurements on the filtration stand of the air filtration rate through the cellular-porous nickel when it is heated are also shown. For a number of experiments, numerical modeling based on the skeletal model of a cellular-porous material was carried out.

Uzawa smoother in multigrid for the coupleD porous medium and stokes flow system

NARCIS (Netherlands)

P. Luo (Peiyao); C. Rodrigo (Carmen); F.J. Gaspar Lorenz (Franscisco); C.W. Oosterlee (Kees)

2017-01-01

textabstractThe multigrid solution of coupled porous media and Stokes flow problems is considered. The Darcy equation as the saturated porous medium model is coupled to the Stokes equations by means of appropriate interface conditions. We focus on an efficient multigrid solution technique for the

Free Convection over a Permeable Horizontal Flat Plate Embedded in a Porous Medium with Radiation Effects and Mixed Thermal Boundary Conditions

OpenAIRE

Najiyah S. Khasi'ie; Roziena Khairuddin; Najihah Mohamed; Mohd Zuki Salleh; Roslinda Nazar; Ioan Pop

2012-01-01

Problem statement: In this study, the mathematical modeling of free convection boundary layer flow over a permeable horizontal flat plate embedded in a porous medium under mixed thermal boundary conditions and radiation effects is considered. Approach: The transformed boundary layer equations are solved numerically using the shooting method. Results: Numerical solutions are obtained for the wall temperature, the heat transfer coefficient, as well as the velocity and temperature profiles. The ...

SCDAP/RELAP5 Modeling of Heat Transfer and Flow Losses in Lower Head Porous Debris

International Nuclear Information System (INIS)

Siefken, Larry James; Coryell, Eric Wesley; Paik, Seungho; Kuo, Han Hsiung

1999-01-01

Designs are described for implementing models for calculating the heat transfer and flow losses in porous debris in the lower head of a reactor vessel. The COUPLE model in SCDAP/RELAP5 represents both the porous and nonporous debris that results from core material slumping into the lower head. Currently, the COUPLE model has the capability to model convective and radiative heat transfer from the surfaces of nonporous debris in a detailed manner and to model only in a simplistic manner the heat transfer from porous debris. In order to advance beyond the simplistic modeling for porous debris, designs are developed for detailed calculations of heat transfer and flow losses in porous debris. Correlations are identified for convective heat transfer in porous debris for the following modes of heat transfer; (1) forced convection to liquid, (2) forced convection to gas, (3) nucleate boiling, (4) transition boiling, and (5) film boiling. Interphase heat transfer is modeled in an approximate manner. Designs are described for models to calculate the flow losses and interphase drag of fluid flowing through the interstices of the porous debris, and to apply these variables in the momentum equations in the RELAP5 part of the code. Since the models for heat transfer and flow losses in porous debris in the lower head are designed for general application, a design is also described for implementation of these models to the analysis of porous debris in the core region. A test matrix is proposed for assessing the capability of the implemented models to calculate the heat transfer and flow losses in porous debris. The implementation of the models described in this report is expected to improve the COUPLE code calculation of the temperature distribution in porous debris and in the lower head that supports the debris. The implementation of these models is also expected to improve the calculation of the temperature and flow distribution in porous debris in the core region

MAGNUM-2D, Heat Transport and Groundwater Flow in Fractured Porous Media

International Nuclear Information System (INIS)

Langford, D.W.; Baca, R.G.

2001-01-01

1 - Description of program or function: MAGNUM2D was developed to analyze thermally driven fluid motion in the deep basalts below the Paco Basin at the Westinghouse Hanford Site. Has been used in the Basalt Waste Isolation Project to simulate nonisothermal groundwater flow in a heterogeneous anisotropic medium and heat transport in a water-rock system near a high level nuclear waste repository. Allows three representations of the hydrogeologic system: an equivalent porous continuum, a system of discrete, unfilled, and inter- connecting fractures separated by impervious rock mass, and a low permeability porous continuum with several discrete, unfilled fractures traversing the medium. The calculations assume local thermodynamic equilibrium between the rock and groundwater, non- isothermal Darcy flow in the continuum portions of the rock, and nonisothermal Poiseuille flow in discrete unfilled fractures. In addition, the code accounts for thermal loading within the elements, zero normal gradient and fixed boundary conditions for both temperature and hydraulic head, and simulation of the temperature and flow independently. The Q2DGEOM preprocessor was developed to generate, modify, plot and verify quadratic two dimensional finite element geometries. The BCGEN preprocessor generates the boundary conditions for head and temperature and ICGEN generates the initial conditions. The GRIDDER post-processor interpolates non-regularly spaced nodal flow and temperature data onto a regular rectangular grid. CONTOUR plots and labels contour lines for a function of two variables and PARAM plots cross sections and time histories for a function of time and one or two spatial variables. NPRINT generates data tables that display the data along horizontal or vertical cross sections. VELPLT differentiates the hydraulic head and buoyancy data and plots the velocity vectors. The PATH post-processor plots flow paths and computes the corresponding travel times. 2 - Method of solution: MAGNUM2

A numerical model for self-compacting concrete flow through reinforced sections. A porous medium analogy

International Nuclear Information System (INIS)

Vasilic, Ksenija

2016-01-01

This thesis addresses numerical simulations of self-compacting concrete (SCC) castings and suggests a novel modelling approach that treats reinforcement zones in a formwork as porous media. As a relatively new field in concrete technology, numerical simulations of fresh concrete flow can be a promising aid to optimise casting processes and to avoid on-site casting incidents by predicting the flow behaviour of concrete during the casting process. The simulations of fresh concrete flow generally involve complex mathematical modelling and time-consuming computations. In case of a casting prediction, the simulation time is additionally significantly increased because each reinforcement bar occurring in succession has to be considered one by one. This is particularly problematic when simulating SCC casting, since this type of concrete is typically used for heavily reinforced structural members. However, the wide use of numerical tools for casting prediction in practice is possible only if the tools are user-friendly and simulations are time-saving. In order to shorten simulation time and to come closer to a practical tool for casting prediction, instead to model steel bars one by one, this thesis suggests to model zones with arrays of steel bars as porous media. Consequently, one models the flow of SCC through a reinforcement zone as a free-surface flow of a non-Newtonian fluid, propagating through the medium. By defining characteristic parameters of the porous medium, the influence on the flow and the changed (apparent) behaviour of concrete in the porous matrix can be predicted. This enables modelling of any reinforcement network as a porous zone and thus significantly simplifies and fastens simulations of reinforced components' castings. Within the thesis, a computational model for SCC flow through reinforced sections was developed. This model couples a fluid dynamics model for fresh concrete and the macroscopic approach for the influence of the porous medium

A numerical model for self-compacting concrete flow through reinforced sections. A porous medium analogy

Energy Technology Data Exchange (ETDEWEB)

Vasilic, Ksenija

2016-05-01

This thesis addresses numerical simulations of self-compacting concrete (SCC) castings and suggests a novel modelling approach that treats reinforcement zones in a formwork as porous media. As a relatively new field in concrete technology, numerical simulations of fresh concrete flow can be a promising aid to optimise casting processes and to avoid on-site casting incidents by predicting the flow behaviour of concrete during the casting process. The simulations of fresh concrete flow generally involve complex mathematical modelling and time-consuming computations. In case of a casting prediction, the simulation time is additionally significantly increased because each reinforcement bar occurring in succession has to be considered one by one. This is particularly problematic when simulating SCC casting, since this type of concrete is typically used for heavily reinforced structural members. However, the wide use of numerical tools for casting prediction in practice is possible only if the tools are user-friendly and simulations are time-saving. In order to shorten simulation time and to come closer to a practical tool for casting prediction, instead to model steel bars one by one, this thesis suggests to model zones with arrays of steel bars as porous media. Consequently, one models the flow of SCC through a reinforcement zone as a free-surface flow of a non-Newtonian fluid, propagating through the medium. By defining characteristic parameters of the porous medium, the influence on the flow and the changed (apparent) behaviour of concrete in the porous matrix can be predicted. This enables modelling of any reinforcement network as a porous zone and thus significantly simplifies and fastens simulations of reinforced components' castings. Within the thesis, a computational model for SCC flow through reinforced sections was developed. This model couples a fluid dynamics model for fresh concrete and the macroscopic approach for the influence of the porous medium

Transient response of a cylindrical cavity in viscoelastic saturated porous medium

Directory of Open Access Journals (Sweden)

LIU Tao

2016-10-01

Full Text Available The study on dynamic characteristics for fluid-solid coupling system in saturated porous medium is of significant academic value and potential application foreground.In this paper,the transient response of a cylindrical cavity in infinite viscoelastic saturated porous medium with the circular lining is studied,and the corresponding results can be used in the design of foundation engineering,such as the tunnel analyses in saturated soil,the nuclear waste disposal engineering,and the exploitation and utilization of geothermal reservoirs and so on.Firstly,based on the porous media theory,the governing equations of coupled system are presented,and the corresponding boundary conditions,initial conditions as well as the joint conditions are derived.Then,the differential quadrature element method and the second-order backward difference scheme are applied to discretize the governing differential equations of the coupled system on the spatial and temporal domains,respectively.Finally,the Newton-Raphson method is adopted to solve the discretization equations with the initial conditions,the transient responses of the coupled system are analyzed,the effects of the parameters are considered,and the validity of the numerical method is verified.

Numerical study of heat transfer and combustion in IC engine with a porous media piston region

International Nuclear Information System (INIS)

Zhou, Lei; Xie, Mao-Zhao; Luo, Kai Hong

2014-01-01

Based on superadiabatic combustion in porous medium (PM), the porous medium engine as a new combustion concept is proposed to achieve high combustion efficiency and low emissions. In this paper, an axisymmetric model with detailed chemistry and two-temperature treatment is implemented into a variant of the KIVA-3V code to simulate the working process of the PM engine. Comparisons with the same engine but without PM are conducted. Temperature evolution of the PM and its effects are discussed in detail. Key factors affecting heat transfer, combustion and emissions of the PM engine, such as porosity, the initial PM temperature and equivalence ratio, are analyzed. The results show that the characteristics of heat transfer, emissions and combustion of the PM engine are superior to the engine without PM, providing valuable support for the PM engine concept. In particular, the PM engine is shown to sustain ultra lean combustion. - Graphical abstract: In the PM engine, a PM reactor is mounted on the piston head as shown in Fig. 1 which shows the schematic diagram of the computational domain. The heat exchange process between PM material and compressed air increases with upward motion of piston at compression stroke. At the TDC, almost all the air is compressed and closed to PM volume, meanwhile, the fuel is injected into PM chamber to achieve homogenization combustion. - Highlights: •Two-temperature treatment studies the working process of the PM engine. •Self-balancing temperature of the PM determines the continued and stable work. •Stronger heat exchange occurs between gas and PM with smaller porosity. •The PM engine can have lower levels of NO x , unburnt HC and CO emissions

Pengaruh Rasio Step pada Sudden Enlargement Channel terhadap Heat Flux Kondensasi di Porous Media

Directory of Open Access Journals (Sweden)

Djoko Hari Praswanto

2017-08-01

Full Text Available One of the most significant parameter in air conditioning problems is air humidity. A porous media can be used as a heat exchanger component in order to increase the heat transfer performance which is significantly depends on the heat flux values inside of them. To determine the heat flux value, a following test section was modeled in this research. A vapor passed through a channel whereas a particular porous media made of active carbon acted as its heat exchanger media. However, the sudden enlargement at the inlet of channel could affect the homogeneity of temperature distributions and also caused some several turbulencies. The research method is vapor flowed over the porous media for 60 minute with temperature of 300oC.The vapor velocity is varied from 1 m/s to 3 m/s and the step ratio also varied between 0 until 1.66. From the experiment shows the bigger step ratio and vapor velocity results the bigger heat flux and air humidity after passed through the low porous media. Heat transfer was occured in porous media including convection heat transfer with the value of Gr/Re2 smaller than 1.

Modeling of heat transfer within porous multi-constituent materials

International Nuclear Information System (INIS)

Niezgoda, M.

2012-01-01

The CEA works a great deal with porous materials - carbon composites, ceramics - and aims to optimize their properties for specific uses. These materials can be composed of several constituents and generally has a complex structure with pore size of several tens of micrometers. It is used in large-scale systems that are bigger than its own characteristic scale in which they are considered as equivalent to a homogeneous medium for the simulation of its behavior in its using environment without taking into account its local morphology. We are especially interested in the effective thermal diffusivity of heterogeneous materials that we estimate as a function of temperature with the help of an inverse method by considering they are homogeneous. The identification of the diffusivity of porous and/or semi-transparent materials is made difficult because of the strong conducto-radiative coupling can quickly occur when the temperature increases. We have thus modeled the coupled conductive and radiative heat transfer as a function of the temperature within porous multi-constituent materials from their morphology discretized into a set of homogeneous voxels. We have developed a methodology that consists in starting from a 3D-microstructure of the studied materials obtained by tomography. The microstructures constitute the numerical support to this modeling that renders it possible, on the one hand, to simulate any kind of numerical thermal experiments, especially the flash method whose the results render it possible to estimate the thermal diffusivity, and on the other hand, to reproduce the thermal behavior of our materials in their using conditions. (author) [fr

Effect of Initial Hydraulic Conditions on Capillary Rise in a Porous Medium: Pore-Network Modeling

KAUST Repository

Joekar-Niasar, V.; Hassanizadeh, S. M.

2012-01-01

The dynamics of capillary rise in a porous medium have been mostly studied in initially dry systems. As initial saturation and initial hydraulic conditions in many natural and industrial porous media can be variable, it is important to investigate

Experimental Study on Water Sensitivity Difference Based on Oiliness of Porous Medium Rock

Directory of Open Access Journals (Sweden)

Jie Li

2017-01-01

Full Text Available This study presents the differences of water sensitivity experiment of porous medium rock between conventional dry core samples and oil-bearing core. The comparison was made to analyze the impact of single-phase fluid and multiphase fluid on the actual sensitivity of rock. The nuclear magnetic resonance (NMR test was carried out to reveal the distribution of oil in porous medium and the microscopic influence mechanism of oil phase. The study shows that the initial oil in place could isolate the clay from water, and then the expansion and the migration of the clay were prevented to reduce the decrease of degree of damage.

Experimental study on local heat transfer characteristics of porous media with internal heat source

International Nuclear Information System (INIS)

Zan Yuanfeng; Wang Taotao; Xiao Zejun; Wang Fei; Huang Yanping

2008-01-01

Model of porous media with internal heat source is established. The model uses water as flowing media, and the stainless steel test section is packed with steel spheres in manner of regular triangle, respectively. The armoured resistance wire is inserted inside the steel sphere. On the basis of the experimental model, many parameters of the local heat transfer characteristics including current velocity and wall temperature of steel sphere are measured. The experimental results show that the coefficient of heat transfer scarcely changes with pressure. The coefficient of heat transfer increases with the surface heat flux of steel sphere. When raising the inlet temperature of the cooling water, the coefficient of heat transfer presents the descending trend. In addition, the influence of entrance effect on heat transfer is discovered in the experiment, which is much less than the liquid flow in the light tube. After experiment data are analyzed and processed, the relation model of heat transfer on local heat transfer characteristic of porous media with internal heat source was described with a power-law-equation. The deviations between calculation and experimental values are within ±10%. (authors)

Hydrocarbons biodegradation in unsaturated porous medium

International Nuclear Information System (INIS)

Gautier, C.

2007-12-01

Biological processes are expected to play an important role in the degradation of petroleum hydrocarbons in contaminated soils. However, factors influencing the kinetics of biodegradation are still not well known, especially in the unsaturated zone. To address these biodegradation questions in the unsaturated zone an innovative experimental set up based on a physical column model was developed. This experimental set up appeared to be an excellent tool for elaboration of a structured porous medium, with well defined porous network and adjusted water/oil saturations. Homogeneous repartition of both liquid phases (i.e., aqueous and non aqueous) in the soil pores, which also contain air, was achieved using ceramic membranes placed at the bottom of the soil column. Reproducible interfaces (and connectivity) are developed between gas, and both non mobile water and NAPL phases, depending on the above-defined characteristics of the porous media and on the partial saturations of these three phases (NAPL, water and gas). A respirometric apparatus was coupled to the column. Such experimental set up have been validated with hexadecane in dilution in an HMN phase. This approach allowed detailed information concerning n-hexadecane biodegradation, in aerobic condition, through the profile of the oxygen consumption rate. We have taken benefit of this technique, varying experimental conditions, to determine the main parameters influencing the biodegradation kinetics and compositional evolution of hydrocarbons, under steady state unsaturated conditions and with respect to aerobic metabolism. Impacts of the nitrogen quantity and of three different grain sizes have been examined. Biodegradation of petroleum cut, as diesel cut and middle distillate without aromatic fraction, were, also studied. (author)

Simulation of water flow in fractured porous medium by using discretized virtual internal bond

Science.gov (United States)

Peng, Shujun; Zhang, Zhennan; Li, Chunfang; He, Guofu; Miao, Guoqing

2017-12-01

The discretized virtual internal bond (DVIB) is adopted to simulate the water flow in fractured porous medium. The intact porous medium is permeable because it contains numerous micro cracks and pores. These micro discontinuities construct a fluid channel network. The representative volume of this fluid channel network is modeled as a lattice bond cell with finite number of bonds in statistical sense. Each bond serves as a fluid channel. In fractured porous medium, many bond cells are cut by macro fractures. The conductivity of the fracture facet in a bond cell is taken over by the bonds parallel to the flow direction. The equivalent permeability and volumetric storage coefficient of a micro bond are calibrated based on the ideal bond cell conception, which makes it unnecessary to consider the detailed geometry of a specific element. Such parameter calibration method is flexible and applicable to any type of element. The accuracy check results suggest this method has a satisfying accuracy in both the steady and transient flow simulation. To simulate the massive fractures in rockmass, the bond cells intersected by fracture are assigned aperture values, which are assumed random numbers following a certain distribution law. By this method, any number of fractures can be implicitly incorporated into the background mesh, avoiding the setup of fracture element and mesh modification. The fracture aperture heterogeneity is well represented by this means. The simulation examples suggest that the present method is a feasible, simple and efficient approach to the numerical simulation of water flow in fractured porous medium.

Analytical solution for the transient response of a fluid/saturated porous medium halfspace system subjected to an impulsive line source

Science.gov (United States)

Shan, Zhendong; Ling, Daosheng; Jing, Liping; Li, Yongqiang

2018-05-01

In this paper, transient wave propagation is investigated within a fluid/saturated porous medium halfspace system with a planar interface that is subjected to a cylindrical P-wave line source. Assuming the permeability coefficient is sufficiently large, analytical solutions for the transient response of the fluid/saturated porous medium halfspace system are developed. Moreover, the analytical solutions are presented in simple closed forms wherein each term represents a transient physical wave, especially the expressions for head waves. The methodology utilised to determine where the head wave can emerge within the system is also given. The wave fields within the fluid and porous medium are first defined considering the behaviour of two compressional waves and one tangential wave in the saturated porous medium and one compressional wave in the fluid. Substituting these wave fields into the interface continuity conditions, the analytical solutions in the Laplace domain are then derived. To transform the solutions into the time domain, a suitable distortion of the contour is provided to change the integration path of the solution, after which the analytical solutions in the Laplace domain are transformed into the time domain by employing Cagniard's method. Numerical examples are provided to illustrate some interesting features of the fluid/saturated porous medium halfspace system. In particular, the interface wave and head waves that propagate along the interface between the fluid and saturated porous medium can be observed.

MHD convective flow through porous medium in a horizontal channel with insulated and impermeable bottom wall in the presence of viscous dissipation and Joule heating

Directory of Open Access Journals (Sweden)

K.V.S. Raju

2014-06-01

Full Text Available This paper deals with a steady MHD forced convective flow of a viscous fluid of finite depth in a saturated porous medium over a fixed horizontal channel with thermally insulated and impermeable bottom wall in the presence of viscous dissipation and joule heating. The governing equations are solved in the closed form and the exact solutions are obtained for velocity and temperature distributions when the temperatures on the fixed bottom and on the free surface are prescribed. The expressions for flow rate, mean velocity, temperature, mean temperature, mean mixed temperature in the flow region and the Nusselt number on the free surface have been obtained. The cases of large and small values of porosity coefficients have been obtained as limiting cases. Further, the cases of small depth (shallow fluid and large depth (deep fluid are also discussed. The results are presented and discussed with the help of graphs.

Numerical simulation of the transport phenomena due to sudden heating in porous media

Energy Technology Data Exchange (ETDEWEB)

Lei, S.Y.; Zheng, G.Y.; Wang, B.X.; Yang, R.G.; Xia, C.M.

1997-07-01

Such process as wet porous media suddenly heated by hot fluids frequently occurs in nature and in industrial applications. The three-variable simulation model was developed to predict violent transport phenomena due to sudden heating in porous media. Two sets of independent variables were applied to different regions in porous media in the simulation. For the wet zone, temperature, wet saturation and air pressure were used as the independent variables. For the dry zone, the independent variables were temperature, vapor pressure and air pressure. The model simulated two complicated transport processes in wet unsaturated porous media which is suddenly heated by melting metal or boiling water. The effect of the gas pressure is also investigated on the overall transport phenomena.

Analytical Solutions of Ionic Diffusion and Heat Conduction in Multilayered Porous Media

Directory of Open Access Journals (Sweden)

Yu Bai

2015-01-01

Full Text Available Ionic diffusion and heat conduction in a multiple layered porous medium have many important engineering applications. One of the examples is the chloride ions from deicers penetrating into concrete structures such as bridge decks. Different overlays can be placed on top of concrete surface to slowdown the chloride penetration. In this paper, the chloride ion diffusion equations were established for concrete structures with multiple layers of protective system. By using Laplace transformation, an analytical solution was developed first for chloride concentration profiles in two-layered system and then extended to multiple layered systems with nonconstant boundary conditions, including the constant boundary and linear boundary conditions. Because ionic diffusion in saturated media and heat conduction are governed by the same form of partial differential equations with different materials parameters, the analytical solution was further extended to handle heat conduction in a multiple layered system under nonconstant boundary conditions. The numerical results were compared with available test data. The basic trends of the analytical solution and the test data agreed quite well.

Lattice Boltzmann simulation for temperature-sensitive magnetic fluids in a porous square cavity

International Nuclear Information System (INIS)

Jin Licong; Zhang Xinrong; Niu Xiaodong

2012-01-01

A lattice Boltzmann method is developed to simulate temperature-sensitive magnetic fluids in a porous cavity. In the simulation, the magnetic force, efficient gravity, viscous loss term and geometric loss term in porous medium are imported to the momentum equation. To test the reliability of the method, a validation with water in porous cavity is carried out. Good agreements with the previous results verify that the present lattice Boltzmann method is promising for simulation of magnetic fluids in porous medium. In this study, we investigate the change of magnetization with external magnetic field, and we present numerical results for the streamlines, isotherms, and magnetization at vertical or horizontal mid-profiles for different values of Ram. In addition, Nusselt numbers changing with magnetic Rayleigh numbers are also investigated. - Highlights: → Developed a lattice Boltzmann method for magnetic nano-fluids in porous cavity. → Clarified flow and heat transfer for different values of (magnetic) Rayleigh numbers. → Heat transfer enhancement for magnetic fluid in porous cavity.

Effect of Variable Viscosity on Vortex Instability of Non-Darcy Mixed Convection Boundary Layer Flow Adjacent to a Nonisothermal Horizontal Surface in a Porous Medium

Directory of Open Access Journals (Sweden)

A. M. Elaiw

2012-01-01

Full Text Available We study the effect of variable viscosity on the flow and vortex instability for non-Darcy mixed convection boundary layer flow on a nonisothermal horizontal plat surface in a saturated porous medium. The variation of viscosity is expressed as an exponential function of temperature. The analysis of the disturbance flow is based on linear stability theory. The base flow equations and the resulting eigenvalue problem are solved using finite difference schemes. It is found that the variable viscosity effect enhances the heat transfer rate and destabilizes the flow for liquid heating, while the opposite trend is true for gas heating.

A porous media calculation for the isolation condenser heat transfer and circulation

International Nuclear Information System (INIS)

Jaakko, Miettinen; Ismo, Karppinen

2003-01-01

In the development of advanced light water reactors, thermohydraulic phenomena are versatile in comparison with the present concepts. The new features include, for example, passive safety systems, where energy transport takes place by natural circulation instead of forced flow. In the isolation condenser, the steam generated in the reactor vessel is conduced into the heat transfer tubes. The tube bundle has been submerged into a large water pool, where the heat flux through the tube wall initially is heating the subcooled water, but rather soon boiling take place. The temperature differences and void fraction in the pool create large two-phase circulation. For modeling of the entire condenser a combined application of two types of simulation models has been selected. For the whole geometry, a porous media solution has been developed, where the existence of the heat transfer tubes in the water pool and their heat generation is described by the porous media approach. The 3-dimensional solution of two-phase equations is based on the drift-flux formalism. The condensation and liquid film generation inside the heat transfer tube is modelled using a 1-dimensional model considering the steam core, liquid film and heat transfer tube. The heat flux through the tube wall defines the boundary conditions for the water pool. Parallel to the porous media development for the entire process facility, the phase change models have been improved for Fluent 6 mixture model, and the code is used for analysing in detail the heat transfer around the tubing. The purpose in the analyses is to obtain more detailed information of the flow field and vapour distribution around the tube bundle. By combining the porous media model for the entire facility, with the CFD models for the two-phase flow details around the heat transfer tubes and experimental studies the most important mechanisms around the condensation pool can be gathered. In this context the porous media model is considered. (author)

Experimental investigation of clogging dynamics in homogeneous porous medium

Science.gov (United States)

Shen, Jikang; Ni, Rui

2017-03-01

A 3-D refractive-index matching Lagrangian particle tracking (3D-RIM-LPT) system was developed to study the filtration and the clogging process inside a homogeneous porous medium. A small subset of particles flowing through the porous medium was dyed and tracked. As this subset was randomly chosen, its dynamics is representative of all the rest. The statistics of particle locations, number, and velocity were obtained as functions of different volumetric concentrations. It is found that in our system the clogging time decays with the particle concentration following a power law relationship. As the concentration increases, there is a transition from depth filtration to cake filtration. At high concentration, more clogged pores lead to frequent flow redirections and more transverse migrations of particles. In addition, the velocity distribution in the transverse direction is symmetrical around zero, and it is slightly more intermittent than the random Gaussian curve due to particle-particle and particle-grain interactions. In contrast, as clogging develops, the longitudinal velocity of particles along the mean flow direction peaks near zero because of many trapped particles. But at the same time, the remaining open pores will experience larger pressure and, as a result, particles through those pores tend to have larger longitudinal velocities.

Numerical investigation of vapor–liquid heat and mass transfer in porous media

International Nuclear Information System (INIS)

Xin, Chengyun; Rao, Zhonghao; You, Xinyu; Song, Zhengchang; Han, Dongtai

2014-01-01

Highlights: • The heat and mass transfer behaviors in porous media was investigated. • A modified separate flow model (MSFM) was developed. • The influence of heat flux direction on heat and fluid flow behaviors is great. • The saturation profile is weakly discontinuous on the phase interface. • A countercurrent flow exists in two-phase region. - Abstract: A modified separate flow model (MSFM) is developed to numerically investigate the heat and mass transfer behaviors in porous media in this paper. In the MSFM, the effects of capillarity, liquid phase change, nonisothermal two-phase region and the local thermal non-equilibrium (LTNE) are considered. The vapor and liquid velocities are both converted into intermediate variables in the simulations and conveniently convergent solutions are obtained because a special upwind scheme for the convection or boiling heat transfer source and variable convergence factors are simultaneously employed. Two typical numerical examples with a one-dimension model of porous media are studied that the high heat fluxes are vertical and parallel to the fluid flow direction, respectively. And the results indicated that the influence of heat flux direction on heat and fluid flow behaviors in porous media is great. The nonisothermal phenomenon in the two-phase region is obvious for the former while the LTNE phenomenon is remarkable in the two-phase region for the latter. The results also showed several similar behaviors that the saturation profile is weakly discontinuous on the phase interface and a countercurrent flow exists in two-phase region

Natural convection heat and mass transfer in MHD fluid flow past a moving vertical plate with variable surface temperature and concentration in a porous medium

Directory of Open Access Journals (Sweden)

K. Javaherdeh

2015-09-01

Full Text Available A numerical investigation of two-dimensional steady laminar free convection flow with heat and mass transfer past a moving vertical plate in a porous medium subjected to a transverse magnetic field is carried out. The temperature and concentration level at the plate surface are assumed to follow a power-law type of distribution. The governing non-linear set of equations is solved numerically employing a fully implicit finite difference method. Results are presented to illustrate the influence of different parameters such as Grashof number (Gr, porosity parameter (Kp, magnetic field parameter (Mn and exponents in the power law variation of the surface temperature and concentration, m and n. The dimensionless velocity, temperature and concentration profiles are analyzed and numerical data for the local Nusselt number and Sherwood number are presented. The study accentuates the significance of the relevant parameters.

SCDAP/RELAP5 modeling of heat transfer and flow losses in lower head porous debris. Rev. 1

International Nuclear Information System (INIS)

Siefken, L.J.; Coryell, E.W.; Paik, S.; Kuo, H.

1999-01-01

Designs are described for implementing models for calculating the heat transfer and flow losses in porous debris in the lower head of a reactor vessel. The COUPLE model in SCDAP/RELAP5 represents both the porous and nonporous debris that results from core material slumping into the lower head. Currently, the COUPLE model has the capability to model convective and radiative heat transfer from the surfaces of nonporous debris in a detailed manner and to model only in a simplistic manner the heat transfer from porous debris. In order to advance beyond the simplistic modeling for porous debris, designs are developed for detailed calculations of heat transfer and flow losses in porous debris. Correlations are identified for convective heat transfer in porous debris for the following modes of heat transfer; (1) forced convection to liquid, (2) forced convection to gas, (3) nucleate boiling, (4) transition boiling, and (5) film boiling. Interphase heat transfer is modeled in an approximate ma nner. Designs are described for models to calculate the flow losses and interphase drag of fluid flowing through the interstices of the porous debris, and to apply these variables in the momentum equations in the RELAP5 part of the code. Since the models for heat transfer and flow losses in porous debris in the lower head are designed for general application, a design is also described for implementation of these models to the analysis of porous debris in the core region. A test matrix is proposed for assessing the capability of the implemented models to calculate the heat transfer and flow losses in porous debris. The implementation of the models described in this report is expected to improve the COUPLE code calculation of the temperature distribution in porous debris and in the lower head that supports the debris. The implementation of these models is also expected to improve the calculation of the temperature and flow distribution in porous debris in the core region

Control of optical transport parameters of 'porous medium – supercritical fluid' systems

Energy Technology Data Exchange (ETDEWEB)

Zimnyakov, D A; Ushakova, O V; Yuvchenko, S A [Yuri Gagarin State Technical University of Saratov, Saratov (Russian Federation); Bagratashvili, V N [M. V. Lomonosov Moscow State University, Moscow (Russian Federation)

2015-11-30

The possibility of controlling optical transport parameters (in particular, transport scattering coefficient) of porous systems based on polymer fibres, saturated with carbon dioxide in different phase states (gaseous, liquid and supercritical) has been experimentally studied. An increase in the pressure of the saturating medium leads to a rise of its refractive index and, correspondingly, the diffuse-transmission coefficient of the system due to the decrease in the transport scattering coefficient. It is shown that, in the case of subcritical saturating carbon dioxide, the small-angle diffuse transmission of probed porous layers at pressures close to the saturated vapour pressure is determined by the effect of capillary condensation in pores. The immersion effect in 'porous medium – supercritical fluid' systems, where the fluid pressure is used as a control parameter, is considered. The results of reconstructing the values of transport scattering coefficient of probed layers for different refractive indices of a saturating fluid are presented. (radiation scattering)

Description of regional blow-up in a porous-medium equation

Directory of Open Access Journals (Sweden)

Carmen Cortazar

2002-10-01

Full Text Available We describe the (finite-time blow-up phenomenon for a non-negative solution of a porous medium equation of the form $$ u_t = Delta u^m + u^m $$ in the entire space. Here $m>1$ and the initial condition is assumed compactly supported. Blow-up takes place exactly inside a finite number of balls with same radii and exhibiting the same self-similar profile.

Ice-water convection in an inclined rectangular cavity filled with a porous medium

Energy Technology Data Exchange (ETDEWEB)

Zhang, X. (Dept. of Mechanical Engineering, Ecole Polytechnique de Montreal (Canada)); Kahawita, R. (Dept. of Civil Engineering, Ecole Polytechnique de Montreal (Canada))

1994-10-01

This paper reports on the results of a numerical study on the equilibrium state of the convection of water in the presence of ice in an inclined rectangular cavity filled with a porous medium. One side of the cavity is maintained at a temperature higher than the fusion temperature while the opposite side is cooled to a temperature lower than the fusion temperature. The two remaining sides are insulated. Results are analysed in terms of the density inversion parameter, the tilt angle, and the cooling temperature. It appears that the phenomenon of density inversion plays an important role in the equilibrium of an ice-water system when the heating temperature is below 20 . In a vertical cavity, the density inversion causes the formation of two counter-rotating vortices leading to a water volume which is wider at the bottom than at the top. When the cavity is inclined, there exist two branches of solutions which exhibit the bottom heating and the side heating characteristics, respectively (the Benard and side heating branches). Due to the inversion of density, the solution on the Benard branch may fail to converge to a steady state at small tilt angles and exhibits an oscillating behavior. On the side heating branch, a maximum heat transfer rate is obtained at a tilt angle of about 70 but the water volume was found to depend very weakly on the inclination of the cavity. Under the effect of subcooling, the interplay between conduction in the solid phase and convection in the liquid leads to an equilibrium ice-water interface which is most distorted at some intermediate cooling temperature. (orig.)

Natural convection in porous media with heat generation

International Nuclear Information System (INIS)

Hardee, H.C. Jr.; Nilson, R.H.

1976-12-01

Heat transfer characteristics of a fluid saturated porous media are investigated for the case of uniform internal heat generation with cooling from above. Analytical models of conduction and single phase cellular convection show good agreement with previous Rayleigh number correlations and with experimental data obtained by Joule heating of salt water in a sand bed. An approximate dryout criterion is also derived for two phase boiling heat transfer in a fixed bed which is neither channeled nor fluidized. Correlation of dryout data using this criterion is encouraging, especially considering the analytical rather than correlational basis of the criterion

On the viscous dissipation modeling of thermal fluid flow in a porous medium

KAUST Repository

Salama, Amgad; El-Amin, Mohamed; Abbas, Ibrahim A A; Sun, Shuyu

2011-01-01

wall that is immersed in the porous medium and is kept at constant higher temperature. The boundary layer approximations were used to simplify the set of the governing, nonlinear partial differential equations, which were then non

The Effects of Variable Viscosity, Viscous Dissipation and Chemical Reaction on Heat and Mass Transfer Flow of MHD Micropolar Fluid along a Permeable Stretching Sheet in a Non-Darcian Porous Medium

Directory of Open Access Journals (Sweden)

A. M. Salem

2013-01-01

Full Text Available A numerical model is developed to study the effects of temperature-dependent viscosity on heat and mass transfer flow of magnetohydrodynamic(MHD micropolar fluids with medium molecular weight along a permeable stretching surface embedded in a non-Darcian porous medium in the presence of viscous dissipation and chemical reaction. The governing boundary equations for momentum, angular momentum (microrotation, and energy and mass transfer are transformed to a set of nonlinear ordinary differential equations by using similarity solutions which are then solved numerically by shooting technique. A comparison between the analytical and the numerical solutions has been included. The effects of the various physical parameters entering into the problem on velocity, microrotation, temperature and concentration profiles are presented graphically. Finally, the effects of pertinent parameters on local skin-friction coefficient, local Nusselt number and local Sherwood number are also presented graphically. One important observation is that for some kinds of mixtures (e.g., H2, air with light and medium molecular weight, the magnetic field and temperature-dependent viscosity effects play a significant role and should be taken into consideration as well.

A note on similarity in single-phase and porous-medium natural convection

International Nuclear Information System (INIS)

Lyall, H.G.

1981-03-01

The similarity laws for single-phase and porous-medium natural convection are developed. For single-phase flow Nu = Nu(Ra) implies that inertial effects are negligible, while Nu = Nu(Ra.Pr) implies that viscous effects are. The first correlation is adequate for Pr>10, while the second applies for Pr<0.01. For intermediate values of Pr, a more general correlation, Nu = Nu(Ra,Pr) is necessary. For a porous-medium, if inertial effects and dispersion are negligible, Nu* = Nu*(Ra*). However dispersion will only be negligible if the ratio of grain size d to the width of the region L is very small (d/L<< l). If this condition does not hold it is necessary to model d/L. If inertial effects are significant, i.e. the Reynolds number is too large for Darcy's law to apply, a group containing the effective Prandtl number, Pr*, also needs to be modelled for similarity. (author)

Effect of Darcy, fluid Rayleigh and heat generation parameters on natural convection in a porous square enclosure: A Brinkman-extended Darcy model

International Nuclear Information System (INIS)

Das, S.; Sahoo, R.K.

1999-01-01

Analysis of flow and convective heat transfer in volumetrically heated porous layer has become a separate topic for research in the last twenty five years in view of its importance in various engineering applications, such as heat removal from nuclear fuel debris, heat transfer associated with storage of nuclear waste, exothermic reaction in packed-bed reactors, heat recovery from geothermal systems and particularly in the field of large storage systems of agricultural products. Here, a pressure-velocity solution for natural convection for fluid saturated heat generating porous medium in a square enclosure is analyzed by finite element method. The numerical solutions obtained for wide range of fluid Rayleigh number, Ra f , Darcy number, Da, and heat generating number, Q d . The justification for taking these non-dimensional parameters independently is to establish the effect of individual parameters on flow patterns. It has been observed that peak temperature occurs at the top central part and weaker velocity prevails near the vertical walls of the enclosure due to the heat generation parameter alone. On comparison, the modified Rayleigh number used by the earlier investigators, can not explain explicitly the effect of heat generation parameter on natural convection within an enclosure having differentially heated vertical walls. At higher Darcy number, the peak temperature and peak velocity are comparatively more, resulting in better enhancement of heat transfer rate

Numerical study of natural convection in porous media (metals) using Lattice Boltzmann Method (LBM)

Energy Technology Data Exchange (ETDEWEB)

Zhao, C.Y., E-mail: c.y.zhao@warwick.ac.u [School of Engineering, University of Warwick, Coventry CV4 7AL (United Kingdom); School of Energy and Power Engineering, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Dai, L.N.; Tang, G.H.; Qu, Z.G.; Li, Z.Y. [School of Energy and Power Engineering, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China)

2010-10-15

A thermal lattice BGK model with doubled populations is proposed to simulate the two-dimensional natural convection flow in porous media (porous metals). The accuracy of this method is validated by the benchmark solutions. The detailed flow and heat transfer at the pore level are revealed. The effects of pore density (cell size) and porosity on the natural convection are examined. Also the effect of porous media configuration (shape) on natural convection is investigated. The results showed that the overall heat transfer will be enhanced by lowering the porosity and cell size. The square porous medium can have a higher heat transfer performance than spheres due to the strong flow mixing and more surface area.

Conceptual Design of a Condensing Heat Exchanger for Space Systems Using Porous Media

Science.gov (United States)

Hasan, Mohammad M.; Khan, Lutful I.; Nayagam, Vedha; Balasubramaniam, Ramaswamy

2006-01-01

Condensing heat exchangers are used in many space applications in the thermal and humidity control systems. In the International Space Station (ISS), humidity control is achieved by using a water cooled fin surface over which the moist air condenses, followed by "slurper bars" that take in both the condensate and air into a rotary separator and separates the water from air. The use of a cooled porous substrate as the condensing surface provides and attractive alternative that combines both heat removal as well as liquid/gas separation into a single unit. By selecting the pore sizes of the porous substrate a gravity independent operation may also be possible with this concept. Condensation of vapor into and on the porous surface from the flowing air and the removal of condensate from the porous substrate are the critical processes involved in the proposed concept. This paper describes some preliminary results of the proposed condensate withdrawal process and discusses the on-going design and development work of a porous media based condensing heat exchanger at the NASA Glenn Research Center in collaboration with NASA Johnson Space Center.

Heat transfer through natural convection in a porous saturated medium between two vertical cylinders

Energy Technology Data Exchange (ETDEWEB)

Hasnaoui, M. [Faculte des Sciences Semlalia, Marrakech (Morocco); Vasseur, P.; Bilgen, E.; Robillard, L. [Ecole Polytechnique, Montreal, PQ (Canada)

1993-12-31

A numerical and analytical study of two dimensional, laminar and near steady convection in a vertical porous annular region. The mathematical model was established, basing on Darcy-Oberbeck-Boussinesq equations. The analytical resolution is in the limit where the width of the porous layer is small compared to the cylinders height and it is based on the hypothesis of the parallel flow. (Authors). 4 refs., 4 figs.

Pool boiling with high heat flux enabled by a porous artery structure

Science.gov (United States)

Bai, Lizhan; Zhang, Lianpei; Lin, Guiping; Peterson, G. P.

2016-06-01

A porous artery structure utilizing the concept of "phase separation and modulation" is proposed to enhance the critical heat flux of pool boiling. A series of experiments were conducted on a range of test articles in which multiple rectangular arteries were machined directly into the top surface of a 10.0 mm diameter copper rod. The arteries were then covered by a 2.0 mm thickness microporous copper plate through silver brazing. The pool wall was fabricated from transparent Pyrex glass to allow a visualization study, and water was used as the working fluid. Experimental results confirmed that the porous artery structure provided individual flow paths for the liquid supply and vapor venting, and avoided the detrimental effects of the liquid/vapor counter flow. As a result, a maximum heat flux of 610 W/cm2 over a heating area of 0.78 cm2 was achieved with no indication of dryout, prior to reaching the heater design temperature limit. Following the experimental tests, the mechanisms responsible for the boiling critical heat flux and performance enhancement of the porous artery structure were analyzed.

Test results from a helium gas-cooled porous metal heat exchanger

International Nuclear Information System (INIS)

North, M.T.; Rosenfeld, J.H.; Youchison, D.L.

1996-01-01

A helium-cooled porous metal heat exchanger was built and tested, which successfully absorbed heat fluxes exceeding all previously tested gas-cooled designs. Helium-cooled plasma-facing components are being evaluated for fusion applications. Helium is a favorable coolant for fusion devices because it is not a plasma contaminant, it is not easily activated, and it is easily removed from the device in the event of a leak. The main drawback of gas coolants is their relatively poor thermal transport properties. This limitation can be removed through use of a highly efficient heat exchanger design. A low flow resistance porous metal heat exchanger design was developed, based on the requirements for the Faraday shield for the International Thermonuclear Experimental Reactor (ITER) device. High heat flux tests were conducted on two representative test articles at the Plasma Materials Test Facility (PMTF) at Sandia National Laboratories. Absorbed heat fluxes as high as 40 MW/m 2 were successfully removed during these tests without failure of the devices. Commercial applications for electronics cooling and other high heat flux applications are being identified

Effect of Initial Hydraulic Conditions on Capillary Rise in a Porous Medium: Pore-Network Modeling

KAUST Repository

Joekar-Niasar, V.

2012-01-01

The dynamics of capillary rise in a porous medium have been mostly studied in initially dry systems. As initial saturation and initial hydraulic conditions in many natural and industrial porous media can be variable, it is important to investigate the influence of initial conditions on the dynamics of the process. In this study, using dynamic pore-network modeling, we simulated capillary rise in a porous medium for different initial saturations (and consequently initial capillary pressures). Furthermore, the effect of hydraulic connectivity of the wetting phase in corners on the height and velocity of the wetting front was studied. Our simulation results show that there is a trade-off between capillary forces and trapping due to snap-off, which leads to a nonlinear dependence of wetting front velocity on initial saturation at the pore scale. This analysis may provide a possible answer to the experimental observations in the literature showing a non-monotonic dependency between initial saturation and the macroscopic front velocity. © Soil Science Society of America.

Nanofluid MHD natural convection through a porous complex shaped cavity considering thermal radiation

Science.gov (United States)

Sheikholeslami, M.; Li, Zhixiong; Shamlooei, M.

2018-06-01

Control volume based finite element method (CVFEM) is applied to simulate H2O based nanofluid radiative and convective heat transfer inside a porous medium. Non-Darcy model is employed for porous media. Influences of Hartmann number, nanofluid volume fraction, radiation parameter, Darcy number, number of undulations and Rayleigh number on nanofluid behavior were demonstrated. Thermal conductivity of nanofluid is estimated by means of previous experimental correlation. Results show that Nusselt number enhances with augment of permeability of porous media. Effect of Hartmann number on rate of heat transfer is opposite of radiation parameter.

Enhancement of heat transfer from a continuously moving porous fin exposed in convective–radiative environment

International Nuclear Information System (INIS)

Bhanja, Dipankar; Kundu, Balaram; Aziz, Abdul

2014-01-01

Highlights: • Analytical model for thermal analysis of moving porous fins. • Heat transfer from the fin surface due to convection and radiation. • For practical design aspects, optimization analysis was carried out. • Comparative study was made between the solid and porous moving fins. • Porous moving fin has more heat transfer ability than the stationary fin. - Abstract: In the present article, an exercise has been devoted to establish an analytical model for the determination of temperature distribution, fin efficiency and optimum design parameters of a porous moving fin which is losing heat by simultaneous convection and radiation to its surroundings. For the adaptation of this consideration, the governing equation becomes highly nonlinear. An analytical technique called Adomian decomposition method (ADM) is proposed for the solution methodology. The accuracy of the analytic solution is validated by using a numeric scheme called finite difference method. The results indicate that the numerical data and analytical approach are in agreement with each other. As the present study is an analytic, it is extended to the analysis for determination of optimum dimensions of said fin by satisfying either the maximization of rate of heat transfer for a given fin volume or by the minimization of fin volume for a desired heat transfer rate. The study is further extended to the porous fin in stationary condition and it is found that porous fin in moving condition transfers more heat than stationary condition. Investigation has also been made on solid moving fin to compare the outcomes of these parameters

Numerical heat transfer analysis of transcritical hydrocarbon fuel flow in a tube partially filled with porous media

Directory of Open Access Journals (Sweden)

Jiang Yuguang

2016-01-01

Full Text Available Hydrocarbon fuel has been widely used in air-breathing scramjets and liquid rocket engines as coolant and propellant. However, possible heat transfer deterioration and threats from local high heat flux area in scramjet make heat transfer enhancement essential. In this work, 2-D steady numerical simulation was carried out to study different schemes of heat transfer enhancement based on a partially filled porous media in a tube. Both boundary and central layouts were analyzed and effects of gradient porous media were also compared. The results show that heat transfer in the transcritical area is enhanced at least 3 times with the current configuration compared to the clear tube. Besides, the proper use of gradient porous media also enhances the heat transfer compared to homogenous porous media, which could help to avoid possible over-temperature in the thermal protection.

Freezing heat transfer within water-saturated porous media

International Nuclear Information System (INIS)

Sasaki, Akira; Aiba, Shinya; Fukusako, Shoichiro.

1990-01-01

In the present study, analytical and experimental investigations were performed so as to clarify the characteristics of freezing heat transfer in porous media saturated with water in a vertical rectangular cavity. In order to establish the momentum equation, the law of conservation of momentum was applied to the fluid in our control volume, and the equation took into account Forchheimer's extension as the resistance to flow in the porous media. Three different sizes of glass, iron and copper beads were used as the porous media in this study. The temperature of the cold wall was kept at -10degC, while that of the hot wall was varied from 2degC to 22 degC. Comparisons between the analytical results and the experimental ones show good agreement with the exception of the copper bead results. (author)

Numerical Simulation for Magneto Nanofluid Flow Through a Porous Space with Melting Heat Transfer

Science.gov (United States)

Hayat, T.; Shah, Faisal; Alsaedi, A.; Waqas, M.

2018-02-01

Melting heat transfer and non-Darcy porous medium effects in MHD stagnation point flow toward a stretching surface of variable thickness are addressed. Brownian motion and thermophoresis in nanofluid modeling are retained. Zero mass flux condition for concentration at surface is imposed. The problem of ordinary differential system are analyzed numerically through shooting technique. Graphically results of various physical variables on the velocity, temperature and concentration are studied. Skin friction coefficient local Nusselt number and Sherwood number are also addressed through tabulated values. The results described here illustrate that the velocity field is higher via larger melting parameter. However reverse situation is examined for Hartman number. Moreover the influence of thermophoresis parameter on temperature and concentration is noted similar.

Numerical Simulation for Magneto Nanofluid Flow Through a Porous Space with Melting Heat Transfer

Science.gov (United States)

Hayat, T.; Shah, Faisal; Alsaedi, A.; Waqas, M.

2018-05-01

Melting heat transfer and non-Darcy porous medium effects in MHD stagnation point flow toward a stretching surface of variable thickness are addressed. Brownian motion and thermophoresis in nanofluid modeling are retained. Zero mass flux condition for concentration at surface is imposed. The problem of ordinary differential system are analyzed numerically through shooting technique. Graphically results of various physical variables on the velocity, temperature and concentration are studied. Skin friction coefficient local Nusselt number and Sherwood number are also addressed through tabulated values. The results described here illustrate that the velocity field is higher via larger melting parameter. However reverse situation is examined for Hartman number. Moreover the influence of thermophoresis parameter on temperature and concentration is noted similar.

Heat-pipe effect on the transport of gaseous radionuclides released from a nuclear waste container

International Nuclear Information System (INIS)

Zhou, W.; Chambre, P.L.; Pigford, T.H.; Lee, W.W.L.

1990-11-01

When an unsaturated porous medium is subjected to a temperature gradient and the temperature is sufficiently high, vadose water is heated and vaporizes. Vapor flows under its pressure gradient towards colder regions where it condenses. Vaporization and condensation produce a liquid saturation gradient, creating a capillary pressure gradient inside the porous medium. Condensate flows towards the hot end under the influence of a capillary pressure gradient. This is a heat pipe in an unsaturated porous medium. We study analytically the transport of gaseous species released from a spent-fuel waste package, as affected by a time-dependent heat pipe in an unsaturated rock. For parameter values typical of a potential repository in partially saturated fractured tuff at Yucca Mountain, we found that a heat pipe develops shortly after waste is buried, and the heat-pipe's spatial extent is time-dependent. Water vapor movements produced by the heat pipe can significantly affect the migration of gaseous radionuclides. 12 refs., 6 figs., 1 tab

Transient, compressible heat and mass transfer in porous media using the strongly implicit iteration procedure.

Science.gov (United States)

Curry, D. M.; Cox, J. E.

1972-01-01

Coupled nonlinear partial differential equations describing heat and mass transfer in a porous matrix are solved in finite difference form with the aid of a new iterative technique (the strongly implicit procedure). Example numerical results demonstrate the characteristics of heat and mass transport in a porous matrix such as a charring ablator. It is emphasized that multidimensional flow must be considered when predicting the thermal response of a porous material subjected to nonuniform boundary conditions.

Natural convection in square cavity filled with ferrofluid saturated porous medium in the presence of uniform magnetic field

Energy Technology Data Exchange (ETDEWEB)

Javed, Tariq [Department of Mathematics and Statistics, FBAS, International Islamic University, Islamabad 44000 (Pakistan); Mehmood, Z., E-mail: rajaziafat@yahoo.com [Department of Mathematics and Statistics, FBAS, International Islamic University, Islamabad 44000 (Pakistan); Abbas, Z. [Department of Mathematics, The Islamia University, Bahawalpur (Pakistan)

2017-02-01

This article contains numerical results for free convection through square enclosure enclosing ferrofluid saturated porous medium when uniform magnetic field is applied upon the flow along x-axis. Heat is provided through bottom wall and a square blockage placed near left or right bottom corner of enclosure as a heat source. Left and right vertical boundaries of the cavity are considered insulated while upper wall is taken cold. The problem is modelled in terms of system of nonlinear partial differential equations. Finite element method has been adopted to compute numerical simulations of mathematical problem for wide range of pertinent flow parameters including Rayleigh number, Hartman number, Darcy number and Prandtl number. Analysis of results reveals that the strength of streamline circulation is an increasing function of Darcy and Prandtl number where convection heat transfer is dominant for large values of these parameters whereas increase in Hartman number has opposite effects on isotherms and streamline circulations. Thermal conductivity and hence local heat transfer rate of fluid gets increased when ferroparticles are introduced in the fluid. Average Nusselt number increases with increase in Darcy and Rayleigh numbers while it is decreases when Hartman number is increased.

Natural convection in square cavity filled with ferrofluid saturated porous medium in the presence of uniform magnetic field

International Nuclear Information System (INIS)

Javed, Tariq; Mehmood, Z.; Abbas, Z.

2017-01-01

This article contains numerical results for free convection through square enclosure enclosing ferrofluid saturated porous medium when uniform magnetic field is applied upon the flow along x-axis. Heat is provided through bottom wall and a square blockage placed near left or right bottom corner of enclosure as a heat source. Left and right vertical boundaries of the cavity are considered insulated while upper wall is taken cold. The problem is modelled in terms of system of nonlinear partial differential equations. Finite element method has been adopted to compute numerical simulations of mathematical problem for wide range of pertinent flow parameters including Rayleigh number, Hartman number, Darcy number and Prandtl number. Analysis of results reveals that the strength of streamline circulation is an increasing function of Darcy and Prandtl number where convection heat transfer is dominant for large values of these parameters whereas increase in Hartman number has opposite effects on isotherms and streamline circulations. Thermal conductivity and hence local heat transfer rate of fluid gets increased when ferroparticles are introduced in the fluid. Average Nusselt number increases with increase in Darcy and Rayleigh numbers while it is decreases when Hartman number is increased.

Investigation of the pressure drop inside a rectangular channel with a built-in U-shaped tube bundle heat exchanger

Directory of Open Access Journals (Sweden)

Xi-yue Liu

2017-01-01

Full Text Available A simplified approach which utilizes an isotropic porous medium model has been widely adopted for modeling the flow through a compact heat exchanger. With respect to situations where the compact heat exchangers are partially installed inside a channel, such as the application of recuperators in an intercooled recuperative engine, the use of an isotropic porous medium model needs to be carefully assessed because the flow passing through the heat exchanger is very complicated. For this purpose, in this study the isotropic porous medium model is assessed together with specific pressure–velocity relationships for flow field modeling inside a rectangular channel with a built-in double-U-shaped tube bundle heat exchanger. Firstly, experiments were conducted using models to investigate the relationship between the pressure drop and the inlet velocity for a specific heat exchanger with different installation angles inside a rectangular channel. Secondly, a series of numerical computations were carried out using the isotropic porous medium model and the pressure–velocity relationship was then modified by introducing correction coefficients empirically. Finally, a three-dimensional (3-D direct computation was made using a computational fluid dynamics (CFD method for the comparison of detailed flow fields. The results suggest that the isotropic porous medium model is capable of making precise pressure drop predictions given the reasonable pressure–velocity relationship but is unable to precisely simulate the detailed flow features.

Steam injection into water-saturated porous rock

NARCIS (Netherlands)

Bruining, J.; Marchesin, D.; Duijn, van C.J.

2003-01-01

We formulate conservation laws governing steam injection in a linear porous medium containing water. Heat losses to the outside are neglected. We find a complete and systematic description of all solutions of the Riemann problem for the injection of a mixture of steam and water into a

Heat and mass transfer of liquid nitrogen in coal porous media

Science.gov (United States)

Lang, Lu; Chengyun, Xin; Xinyu, Liu

2018-04-01

Liquid nitrogen has been working as an important medium in fire extinguishing and prevention, due to its efficiency in oxygen exclusion and heat removal. Such a technique is especially crucial for coal industry in China. We built a tunnel model with a temperature monitor system (with 36 thermocouples installed) to experimentally study heat and mass transfer of liquid nitrogen in non-homogeneous coal porous media (CPM), and expected to optimize parameters of liquid nitrogen injection in engineering applications. Results indicate that injection location and amount of liquid nitrogen, together with air leakage, significantly affect temperature distribution in CPM, and non-equilibrium heat inside and outside of coal particles. The injection position of liquid nitrogen determines locations of the lowest CPM temperature and liquid nitrogen residual. In the deeper coal bed, coal particles take longer time to reach thermal equilibrium between their surface and inside. Air leakage accelerates temperature increase at the bottom of the coal bed, which is a major reason leading to fire prevention inefficiency. Measurement fluctuation of CPM temperature may be caused by incomplete contact of coal particles with liquid nitrogen flowing in the coal bed. Moreover, the secondary temperature drop (STD) happens and grows with the more injection of liquid nitrogen, and the STD phenomenon is explained through temperature distributions at different locations.

Monolithic multigrid method for the coupled Stokes flow and deformable porous medium system

NARCIS (Netherlands)

P. Luo (Peiyao); C. Rodrigo (Carmen); F.J. Gaspar Lorenz (Franscisco); C.W. Oosterlee (Cornelis)

2018-01-01

textabstractThe interaction between fluid flow and a deformable porous medium is a complicated multi-physics problem, which can be described by a coupled model based on the Stokes and poroelastic equations. A monolithic multigrid method together with either a coupled Vanka smoother or a decoupled

Crystal precipitation and dissolution in a porous medium: Effective equations and numerical experiments

NARCIS (Netherlands)

Noorden, van T.L.

2009-01-01

We investigate a two-dimensional microscale model for crystal dissolution and precipitation in a porous medium. The model contains a free boundary and allows for changes in the pore volume. Using a level set formulation of the free boundary, we apply a formal homogenization procedure to obtain

Intermittent Lagrangian velocities and accelerations in three-dimensional porous medium flow.

Science.gov (United States)

Holzner, M; Morales, V L; Willmann, M; Dentz, M

2015-07-01

Intermittency of Lagrangian velocity and acceleration is a key to understanding transport in complex systems ranging from fluid turbulence to flow in porous media. High-resolution optical particle tracking in a three-dimensional (3D) porous medium provides detailed 3D information on Lagrangian velocities and accelerations. We find sharp transitions close to pore throats, and low flow variability in the pore bodies, which gives rise to stretched exponential Lagrangian velocity and acceleration distributions characterized by a sharp peak at low velocity, superlinear evolution of particle dispersion, and double-peak behavior in the propagators. The velocity distribution is quantified in terms of pore geometry and flow connectivity, which forms the basis for a continuous-time random-walk model that sheds light on the observed Lagrangian flow and transport behaviors.

Heat transfer analysis of porous media receiver with different transport and thermophysical models using mixture as feeding gas

International Nuclear Information System (INIS)

Wang, Fuqiang; Tan, Jianyu; Wang, Zhiqiang

2014-01-01

Highlights: • Using local thermal non-equilibrium model to solve heat transfer of porous media. • CH 4 /H 2 O mixture is adopted as feeding gas of porous media receiver. • Radiative transfer equation between porous strut is solved by Rosseland approximation. • Transport and thermophysical models not included in Fluent are programmed by UDFs. • Variations of model on thermal performance of porous media receiver are studied. - Abstract: The local thermal non-equilibrium model is adopted to solve the steady state heat and mass transfer problems of porous media solar receiver. The fluid entrance surface is subjected to concentrated solar radiation, and CH 4 /H 2 O mixture is adopted as feeding gas. The radiative heat transfer equation between porous strut is solved by Rosseland approximation. The impacts of variation in transport and thermophysical characteristics model of gas mixture on thermal performance of porous media receiver are investigated. The transport and thermophysical characteristics models which are not included in software Fluent are programmed by user defined functions (UDFs). The numerical results indicate that models of momentum source term for porous media receiver have significant impact on pressure drop and static pressure distribution, and the radiative heat transfer cannot be omitted during the thermal performance analysis of porous media receiver

Entropy generation of viscous dissipative flow in thermal non-equilibrium porous media with thermal asymmetries

International Nuclear Information System (INIS)

Chee, Yi Shen; Ting, Tiew Wei; Hung, Yew Mun

2015-01-01

The effect of thermal asymmetrical boundaries on entropy generation of viscous dissipative flow of forced convection in thermal non-equilibrium porous media is analytically studied. The two-dimensional temperature, Nusselt number and entropy generation contours are analysed comprehensively to provide insights into the underlying physical significance of the effect on entropy generation. By incorporating the effects of viscous dissipation and thermal non-equilibrium, the first-law and second-law characteristics of porous-medium flow are investigated via various pertinent parameters, i.e. heat flux ratio, effective thermal conductivity ratio, Darcy number, Biot number and averaged fluid velocity. For the case of symmetrical wall heat flux, an optimum condition with a high Nusselt number and a low entropy generation is identified at a Darcy number of 10 −4 , providing an ideal operating condition from the second-law aspect. This type of heat and fluid transport in porous media covers a wide range of engineering applications, involving porous insulation, packed-bed catalytic process in nuclear reactors, filtration transpiration cooling, and modelling of transport phenomena of microchannel heat sinks. - Highlights: • Effects of thermal asymmetries on convection in porous-medium are studied. • Exergetic effectiveness of porous media with thermal asymmetries is investigated. • 2-D temperature, Nusselt number and entropy generation contours are analyzed. • Significance of viscous dissipation in entropy generation is scrutinized. • Significance of thermal non-equilibrium in entropy generation is studied

Numerical simulation for a two-phase porous medium flow problem with rate independent hysteresis

KAUST Repository

Brokate, M.; Botkin, N.D.; Pykhteev, O.A.

2012-01-01

The paper is devoted to the numerical simulation of a multiphase flow in porous medium with a hysteretic relation between the capillary pressures and the saturations of the phases. The flow model we use is based on Darcys law. The hysteretic

Analytical solution to the diffusion, sorption and decay chain equation in a saturated porous medium between two reservoirs

International Nuclear Information System (INIS)

Guzman, Juan; Maximov, Serguei; Escarela-Perez, Rafael; López-García, Irvin; Moranchel, Mario

2015-01-01

The diffusion and distribution coefficients are important parameters in the design of barrier systems used in radioactive repositories. These coefficients can be determined using a two-reservoir configuration, where a saturated porous medium is allocated between two reservoirs filled by stagnant water. One of the reservoirs contains a high concentration of radioisotopes. The goal of this work is to obtain an analytical solution for the concentration of all radioisotopes in the decay chain of a two-reservoir configuration. The analytical solution must be obtained by taking into account the diffusion and sorption processes. Concepts such as overvalued concentration, diffusion and decay factors are employed to this end. It is analytically proven that a factor of the solution is identical for all chains (considering a time scaling factor), if certain parameters do not change. In addition, it is proven that the concentration sensitivity, due to the distribution coefficient variation, depends of the porous medium thickness, which is practically insensitive for small porous medium thicknesses. The analytical solution for the radioisotope concentration is compared with experimental and numerical results available in literature. - Highlights: • Saturated porous media allocated between two reservoirs. • Analytical solution of the isotope transport equation. • Transport considers diffusion, sorption and decay chain

Heat and mass transfer by free convection in a porous medium along a surface of arbitrary shape

International Nuclear Information System (INIS)

Hossain, M.A.; Nakayama, A.

1993-06-01

Free convection flow of a viscous incompressible fluid in the presence of species concentration along a surface of arbitrary shape embedded in a saturated porous medium is investigated with non-uniform surface temperature and surface concentration distributions. The equations governing the flow, derived in the form of local similarity and nonsimilarity equations, are integrated numerically using the implicit finite difference approximation together with the Keller box method. Exact solutions of the local similarity equations are also obtained and compared with the finite difference solutions. All the solutions are shown graphically in terms of local Nusselt number, Nu χ , and local Sherwood number, Sh χ , against the physical parameter ξ (which characterizes the streamwise distance along the surface from the leading edge) taking the value of the Lewis number, Le, equals 1 0, 5, and 10 while N (which defines the ratio between the buoyancy forces arise due to thermal and mass diffusion) is unity. (author). Refs, 5 figs, 1 tab

Effect of thermal radiation and Hall current on heat and mass transfer of unsteady MHD flow of a viscoelastic micropolar fluid through a porous medium

Directory of Open Access Journals (Sweden)

B.I. Olajuwon

2014-12-01

Full Text Available Heat and mass transfer effects on unsteady flow of a viscoelastic micropolar fluid over an infinite moving permeable plate in a saturated porous medium in the presence of a transverse magnetic field with Hall effect and thermal radiation are studied. The governing system of partial differential equations is transformed to dimensionless equations using dimensionless variables. The dimensionless equations are then solved analytically using perturbation technique to obtain the expressions for velocity, microrotation, temperature and concentration. With the help of graphs, the effects of magnetic field parameter M, thermal radiation parameter Nr, Hall current parameter m, K, viscoelastic parameter a, and slip parameter h on the velocity, microrotation, temperature and concentration fields within the boundary layer are discussed. The result showed that increase in Nr and m increases translational velocity across the boundary layer while (a decreases translational velocity in the vicinity of the plate but the reverse happens when away from the plate. As h increases the translational velocity across the boundary layer increases. The higher the values of Nr, the higher the micro-rotational velocity effect while m lowers it. Also the effects n, a, m, Nr, Pr and Sc on the skin friction coefficient, Nusselt number and Sherwood numbers are presented numerically in tabular form. The result also revealed that increase in n reduces the skin friction coefficient. Pr enhances the rate of heat transfer while Sc enhances the rate of mass transfer.

Heat and Mass Transfer with Free Convection MHD Flow Past a Vertical Plate Embedded in a Porous Medium

Directory of Open Access Journals (Sweden)

Farhad Ali

2013-01-01

on free convection unsteady magnetohydrodynamic (MHD flow of viscous fluid embedded in a porous medium is presented. The flow in the fluid is induced due to uniform motion of the plate. The dimensionless coupled linear partial differential equations are solved by using Laplace transform method. The solutions that have been obtained are expressed in simple forms in terms of elementary function exp(· and complementary error function erfc(·. They satisfy the governing equations; all imposed initial and boundary conditions and can immediately be reduced to their limiting solutions. The influence of various embedded flow parameters such as the Hartmann number, permeability parameter, Grashof number, dimensionless time, Prandtl number, chemical reaction parameter, Schmidt number, and Soret number is analyzed graphically. Numerical solutions for skin friction, Nusselt number, and Sherwood number are also obtained in tabular forms.

Super-adiabatic combustion in Al2O3 and SiC coated porous media for thermoelectric power conversion

International Nuclear Information System (INIS)

Mueller, Kyle T.; Waters, Oliver; Bubnovich, Valeri; Orlovskaya, Nina; Chen, Ruey-Hung

2013-01-01

The combustion of ultra-lean fuel/air mixtures provides an efficient way to convert the chemical energy of hydrocarbons and low-calorific fuels into useful power. Matrix-stabilized porous medium combustion is an advanced technique in which a solid porous medium within the combustion chamber conducts heat from the hot gaseous products in the upstream direction to preheat incoming reactants. This heat recirculation extends the standard flammability limits, allowing the burning of ultra-lean and low-calorific fuel mixtures and resulting a combustion temperature higher than the thermodynamic equilibrium temperature of the mixture (i.e., super-adiabatic combustion). The heat generated by this combustion process can be converted into electricity with thermoelectric generators, which is the goal of this study. The design of a porous media burner coupled with a thermoelectric generator and its testing are presented. The combustion zone media was a highly-porous alumina matrix interposed between upstream and downstream honeycomb structures with pore sizes smaller than the flame quenching distance, preventing the flame from propagating outside of the central section. Experimental results include temperature distributions inside the combustion chamber and across a thermoelectric generator; along with associated current, voltage and power output values. Measurements were obtained for a catalytically inert Al 2 O 3 medium and a SiC coated medium, which was tested for the ability to catalyze the super-adiabatic combustion. The combustion efficiency was obtained for stoichiometric and ultra-lean (near the lean flammability limit) mixtures of CH 4 and air. - Highlights: • Design of a porous burner coupled with a thermoelectric module. • Super-adiabatic combustion in a highly-porous ceramic matrix was investigated. • Both alumina and silicon carbide ceramic surfaces were used as porous media. • Catalytic properties of Al 2 O 3 and SiC ceramic surfaces were studied

Osteoinduction on acid and heat treated porous Ti metal samples in canine muscle.

Directory of Open Access Journals (Sweden)

Toshiyuki Kawai

Full Text Available Samples of porous Ti metal were subjected to different acid and heat treatments. Ectopic bone formation on specimens embedded in dog muscle was compared with the surface characteristics of the specimen. Treatment of the specimens by H2SO4/HCl and heating at 600 °C produced micrometer-scale roughness with surface layers composed of rutile phase of titanium dioxide. The acid- and heat-treated specimens induced ectopic bone formation within 6 months of implantation. A specimen treated using NaOH followed by HCl acid and then heat treatment produced nanometer-scale surface roughness with a surface layer composed of both rutile and anatase phases of titanium dioxide. These specimens also induced bone formation after 6 months of implantation. Both these specimens featured positive surface charge and good apatite-forming abilities in a simulated body fluid. The amount of the bone induced in the porous structure increased with apatite-forming ability and higher positive surface charge. Untreated porous Ti metal samples showed no bone formation even after 12 months. Specimens that were only heat treated featured a smooth surface composed of rutile. A mixed acid treatment produced specimens with micrometer-scale rough surfaces composed of titanium hydride. Both of them also showed no bone formation after 12 months. The specimens that showed no bone formation also featured almost zero surface charge and no apatite-forming ability. These results indicate that osteoinduction of these porous Ti metal samples is directly related to positive surface charge that facilitates formation of apatite on the metal surfaces in vitro.

Modeling of strongly heat-driven flow in partially saturated fractured porous media

International Nuclear Information System (INIS)

Pruess, K.; Tsang, Y.W.; Wang, J.S.Y.

1985-01-01

The authors have performed modeling studies on the simultaneous transport of heat, liquid water, vapor, and air in partially saturated fractured porous media, with particular emphasis on strongly heat-driven flow. The presence of fractures makes the transport problem very complex, both in terms of flow geometry and physics. The numerical simulator used for their flow calculations takes into account most of the physical effects which are important in multi-phase fluid and heat flow. It has provisions to handle the extreme non-linearities which arise in phase transitions, component disappearances, and capillary discontinuities at fracture faces. They model a region around an infinite linear string of nuclear waste canisters, taking into account both the discrete fractures and the porous matrix. From an analysis of the results obtained with explicit fractures, they develop equivalent continuum models which can reproduce the temperature, saturation, and pressure variation, and gas and liquid flow rates of the discrete fracture-porous matrix calculations. The equivalent continuum approach makes use of a generalized relative permeability concept to take into account the fracture effects. This results in a substantial simplification of the flow problem which makes larger scale modeling of complicated unsaturated fractured porous systems feasible. Potential applications for regional scale simulations and limitations of the continuum approach are discussed. 27 references, 13 figures, 2 tables

Modeling of strongly heat-driven flow in partially saturated fractured porous media

International Nuclear Information System (INIS)

Pruess, K.; Tsang, Y.W.; Wang, J.S.Y.

1984-10-01

We have performed modeling studies on the simultaneous transport of heat, liquid water, vapor, and air in partially saturated fractured porous media, with particular emphasis on strongly heat-driven flow. The presence of fractures makes the transport problem very complex, both in terms of flow geometry and physics. The numerical simulator used for our flow calculations takes into account most of the physical effects which are important in multi-phase fluid and heat flow. It has provisions to handle the extreme non-linearities which arise in phase transitions, component disappearances, and capillary discontinuities at fracture faces. We model a region around an infinite linear string of nuclear waste canisters, taking into account both the discrete fractures and the porous matrix. From an analysis of the results obtained with explicit fractures, we develop equivalent continuum models which can reproduce the temperature, saturation, and pressure variation, and gas and liquid flow rates of the discrete fracture-porous matrix calculations. The equivalent continuum approach makes use of a generalized relative permeability concept to take into account for fracture effects. This results in a substantial simplification of the flow problem which makes larger scale modeling of complicated unsaturated fractured porous systems feasible. Potential applications for regional scale simulations and limitations of the continuum approach are discussed. 27 references, 13 figures, 2 tables

Natural convection in a composite fluid-porous cavity by the boundary element method

International Nuclear Information System (INIS)

Jecl, R.; Skerget, L.

2005-01-01

The main purpose of this work is to present the use of the boundary element method (BEM) for analyzing the convective fluid flow and heat transfer in composite fluid-porous media domain when the fluid is compressible. In our case the flow is modeled by utilizing the Brinkman extended Darcy momentum equation (Brinkman model) which is commonly used when it is important to satisfy the no-slip boundary condition and when one wishes to compare flows in porous medium with those in pure fluids. The Brinkman equation reduce to the classical Navier Stokes equation for clear fluid when the permeability tends to infinity (porosity is equal to unity), i.e. when the solid matrix in the porous medium disappears and, when the permeability is finite the equation is valid for porous medium. Therefore it is possible to handle porous medium free fluid interface problems by changing the properties of the medium in the computational domain appropriately. Our goal is to widen the applicability of the computational model based on the boundary domain integral method (BDIM) which is an extension of the classical BEM. The governing equations are transformed by using the velocity-vorticity variables formulation and therefore the computation scheme is partitioned into kinematic and kinetic part. (authors)

Two-demensional analysis of heat and mass transfer in porous media using the strongly implicit procedure

Science.gov (United States)

Curry, D. M.

1974-01-01

Numerical results of the heat and mass transfer in a porous matrix are presented. The coupled, nonlinear partial differential equations describing this physical phenomenon are solved in finite difference form for two dimensions, using a new iterative technique (the strongly implicit procedure). The influence of the external environment conditions (heating and pressure) is shown to produce two-dimensional flow in the porous matrix. Typical fluid and solid temperature distributions in the porous matrix and internal pressure distributions are presented.

Superfluid density and heat capacity measurements of 4He in porous gold

International Nuclear Information System (INIS)

Yoon, J.; Chan, M.

1995-01-01

Superfluid density of full pore 4 He as well as thin film 4 He confined in porous gold were measured as a function of temperature. The superfluid transition temperature of full pore was found to be 2.156 K. In both cases power law dependence on reduced temperature was found and the exponent was found to be the same as that of bulk 4 He. Porous gold is made by electrochemically leaching out silver from silver-gold alloy. The porous gold sample the authors fabricated has porosity of 55 with a diameter of 250 angstrom. Electron microscope picture shows that the structure of porous gold is exceedingly similar to that of Vycor. Heat capacity measurement of full pore 4 He in porous gold is in progress

An Interface Tracking Algorithm for the Porous Medium Equation.

Science.gov (United States)

1983-03-01

equation (1.11). N [v n n 2(2) = n . AV k + wk---IY" 2] +l~ x A t K Ax E E 2+ VeTA i;- 2k1 n- o (nr+l) <k-<.(n+l) N [Av] [ n+l <Ax Z m(v ) I~+lIAxAt...RD-R127 685 AN INTERFACE TRACKING ALGORITHM FOR THE POROUS MEDIUM / EQURTION(U) WISCONSIN UNIV-MRDISON MATHEMATICS RESEARCH CENTER E DIBENEDETTO ET...RL. MAR 83 NRC-TSR-249 UNCLASSIFIED DAG29-88-C-8041 F/G 12/1i N E -EEonshhhhI EhhhMhhhhhhhhE mhhhhhhhhhhhhE mhhhhhhhhhhhhI IMhhhhhhhMhhhE

Permeability of model porous medium formed by random discs

Science.gov (United States)

Gubaidullin, A. A.; Gubkin, A. S.; Igoshin, D. E.; Ignatev, P. A.

2018-03-01

Two-dimension model of the porous medium with skeleton of randomly located overlapping discs is proposed. The geometry and computational grid are built in open package Salome. Flow of Newtonian liquid in longitudinal and transverse directions is calculated and its flow rate is defined. The numerical solution of the Navier-Stokes equations for a given pressure drop at the boundaries of the area is realized in the open package OpenFOAM. Calculated value of flow rate is used for defining of permeability coefficient on the base of Darcy law. For evaluating of representativeness of computational domain the permeability coefficients in longitudinal and transverse directions are compered.

Mathematical modeling of deformation of a porous medium, considering its strengthening due to pore collapse

Energy Technology Data Exchange (ETDEWEB)

Sadovskii, V. M., E-mail: sadov@icm.krasn.ru; Sadovskaya, O. V., E-mail: o-sadov@icm.krasn.ru [Institute of Computational Modeling, SB RAS, Akademgorodok 50/44, 660036 Krasnoyarsk (Russian Federation)

2015-10-28

Based on the generalized rheological method, the mathematical model describing small deformations of a single-phase porous medium without regard to the effects of a fluid or gas in pores is constructed. The change in resistance of a material to the external mechanical impacts at the moment of pore collapse is taken into account by means of the von Mises–Schleicher strength condition. In order to consider irreversible deformations, alongside with the classical yield conditions by von Mises and Tresca– Saint-Venant, the special condition modeling the plastic loss of stability of a porous skeleton is used. The random nature of the pore size distribution is taken into account. It is shown that the proposed mathematical model satisfies the principles of thermodynamics of irreversible processes. Phenomenological parameters of the model are determined on the basis of the approximate calculation of the problem on quasi-static loading of a cubic periodicity cell with spherical voids. In the framework of the obtained model, the process of propagation of plane longitudinal waves of the compression in a homogenous porous medium, accompanied by the plastic deformation of a skeleton and the collapse of pores, is analyzed.

Mixed convective heat transfer from a vertical plate embedded in a ...

Indian Academy of Sciences (India)

Melting effect with heat and mass transfer in porous media has much ... convection boundary layer flow about a vertical surface embedded in a porous medium, ..... Salama A 2008 Combined effect of thermal dispersion and radiation on free.

Temperature dependency of the thermal conductivity of porous heat storage media

Science.gov (United States)

Hailemariam, Henok; Wuttke, Frank

2018-04-01

Analyzing the variation of thermal conductivity with temperature is vital in the design and assessment of the efficiency of sensible heat storage systems. In this study, the temperature variation of the thermal conductivity of a commercial cement-based porous heat storage material named - Füllbinder L is analyzed in saturated condition in the temperature range between 20 to 70°C (water based storage) with a steady state thermal conductivity and diffusivity meter. A considerable decrease in the thermal conductivity of the saturated sensible heat storage material upon increase in temperature is obtained, resulting in a significant loss of system efficiency and slower loading/un-loading rates, which when unaccounted for can lead to the under-designing of such systems. Furthermore, a new empirical prediction model for the estimation of thermal conductivity of cement-based porous sensible heat storage materials and naturally occurring crystalline rock formations as a function of temperature is proposed. The results of the model prediction are compared with the experimental results with satisfactory results.

Natural Convection Heat Transfer in Concentric Horizontal Annuli Containing a Saturated Porous Medi

Directory of Open Access Journals (Sweden)

Ahmed F. Alfahaid, R.Y. Sakr

2012-10-01

Full Text Available Natural convection in horizontal annular porous media has become a subject receiving increasing attention due to its practical importance in the problem of insulators, such as ducting system in high temperature gas-cooled reactors, heating systems, thermal energy storage systems, under ground cable systems, etc. This paper presents a numerical study for steady state thermal convection in a fully saturated porous media bounded by two horizontal concentric cylinders, the cylinders are impermeable to fluid motion and maintained at different, uniform temperatures.  The solution scheme is based on two-dimensional model, which is governed by Darcy-Oberbeck-Boussinesq equations. The finite element method using Galerkin technique is developed and employed to solve the present problem. A numerical simulation is carried out to examine the parametric effects of Rayleigh number and radius ratio on the role played by natural convection heat transfer in the porous annuli. The numerical results obtained from the present model were compared with the available published results and good agreement is observed. The average Nusselt number at the heating surface of the inner cylinder is correlated to Rayleigh number and radius ratio.Keywords: Natural convection, numerical investigation, saturated porous media, finite element method, concentric horizontal annuli.

Analysis of a double pipe heat exchanger performance by use of porous baffles and pulsating flow

International Nuclear Information System (INIS)

Targui, N.; Kahalerras, H.

2013-01-01

Highlights: • A double pipe heat exchanger performance is numerically studied. • Use of porous baffles and pulsating flow to enhance heat exchanger efficiency. • The governing equations are solved by the control volume method. • The efficiency increases with the amplitude and frequency of pulsation. • The highest values of are obtained when only hot fluid is pulsating (Case3). - Abstract: A numerical investigation is carried out to analyze the effect of porous baffles and flow pulsation on a double pipe heat exchanger performance. The hot fluid flows in the inner cylinder, whereas the cold fluid circulates in the annular gap. The Darcy–Brinkman–Forchheimer model is adopted to describe the flow in the porous regions and the finite volume method is used to solve the governing equations with the appropriate boundary conditions. The effects of the amplitude and frequency of pulsation, as well as the porous baffles permeability on the flow structure and the heat exchanger efficiency are analyzed. The results reveal that the addition of an oscillating component to the mean flow affects the flow structure, and enhances the heat transfer in comparison to the steady non pulsating flow. The highest heat exchanger performance is obtained when only the flow of the hot fluid is pulsating

Estimation of Knudsen diffusion coefficients from tracer experiments conducted with a binary gas system and a porous medium

Science.gov (United States)

Hibi, Yoshihiko; Kashihara, Ayumi

2018-03-01

A previous study has reported that Knudsen diffusion coefficients obtained by tracer experiments conducted with a binary gas system and a porous medium are consistently smaller than those obtained by permeability experiments conducted with a single-gas system and a porous medium. To date, however, that study is the only one in which tracer experiments have been conducted with a binary gas system. Therefore, to confirm this difference in Knudsen diffusion coefficients, we used a method we had developed previously to conduct tracer experiments with a binary carbon dioxide-nitrogen gas system and five porous media with permeability coefficients ranging from 10-13 to 10-11 m2. The results showed that the Knudsen diffusion coefficient of N2 (DN2) (cm2/s) was related to the effective permeability coefficient ke (m2) as DN2 = 7.39 × 107ke0.767. Thus, the Knudsen diffusion coefficients of N2 obtained by our tracer experiments were consistently 1/27 of those obtained by permeability experiments conducted with many porous media and air by other researchers. By using an inversion simulation to fit the advection-diffusion equation to the distribution of concentrations at observation points calculated by mathematically solving the equation, we confirmed that the method used to obtain the Knudsen diffusion coefficient in this study yielded accurate values. Moreover, because the Knudsen diffusion coefficient did not differ when columns with two different lengths, 900 and 1500 mm, were used, this column property did not influence the flow of gas in the column. The equation of the dusty gas model already includes obstruction factors for Knudsen diffusion and molecular diffusion, which relate to medium heterogeneity and tortuosity and depend only on the structure of the porous medium. Furthermore, there is no need to take account of any additional correction factor for molecular diffusion except the obstruction factor because molecular diffusion is only treated in a multicomponent

Analysis of heat transfer regulation and modification employing intermittently emplaced porous cavities

International Nuclear Information System (INIS)

Vafai, K.; Huang, P.C.

1994-01-01

The present work forms a fundamental investigation on the effects of using intermittently porous cavities for regulating and modifying the flow and temperature fields and therefore changing the skin friction and heat transfer characteristics of an external surface. A general flow model that accounts for the effects of the impermeable boundary and inertial effects is used to describe the flow inside the porous region. Solutions of the problem have been carried out using a finite-difference method through the use of a stream function-vorticity transformation. Various interesting characteristics of the flow and temperature fields in the composite layer are analyzed and discussed in detail. The effects of various governing dimensionless parameters, such as the Darcy number, Reynolds number, Prandtl number, the inertia parameter as well as the effects of pertinent geometric parameters are thoroughly explored. Furthermore, the interactive effects of the embedded porous substrates on skin friction and heat transfer characteristics of an external surface are analyzed. The configuration analyzed in this work provides an innovative approach in altering the frictional and heat transfer characteristics of an external surface. 27 refs., 12 figs., 1 tab

Pore-scale study on flow and heat transfer in 3D reconstructed porous media using micro-tomography images

International Nuclear Information System (INIS)

Liu, Zhenyu; Wu, Huiying

2016-01-01

Highlights: • The complex porous domain has been reconstructed with the micro CT scan images. • Pore-scale numerical model based on LB method has been established. • The correlations for flow and heat transfer were derived from the predictions. • The numerical approach developed in this work is suitable for complex porous media. - Abstract: This paper presents the numerical study on fluid flow and heat transfer in reconstructed porous media at the pore-scale with the double-population thermal lattice Boltzmann (LB) method. The porous geometry was reconstructed using micro-tomography images from micro-CT scanner. The thermal LB model was numerically tested before simulation and a good agreement was achieved by compared with the existing results. The detailed distributions of velocity and temperature in complex pore spaces were obtained from the pore-scale simulation. The correlations for flow and heat transfer in the specific porous media sample were derived based on the numerical results. The numerical method established in this work provides a promising approach to predict pore-scale flow and heat transfer characteristics in reconstructed porous domain with real geometrical effect, which can be extended for the continuum modeling of the transport process in porous media at macro-scale.

Film condensation on a porous vertical surface in a porous media

International Nuclear Information System (INIS)

Ebinuma, C.D.; Liu, C.Y.; Ismail, K.A.R.

1983-01-01

The problem of dry saturated steam film condensation by natural convection on a porous surface in a porous medium is presented. Through the classical Darcy law for flow in porous medium and the approximations considered in the Boundary layer theory, it is shown that the analytical solution exists only when the normal velocity to the porous wall is inversly proportional to the square root of the distance along the plate. (E.G.) [pt

Effects of anisotropy in permeability on the two-phase flow and heat transfer in a porous cavity

Energy Technology Data Exchange (ETDEWEB)

Zhang, X.L. [Dept. de Genie Mecanique, Univ. de Montreal, PQ (Canada); Hung Nguyen, T. [Dept. de Genie Mecanique, Univ. de Montreal, PQ (Canada); Kahawita, R. [Ecole Polytechnique de Montreal, PQ (Canada)

1997-02-01

This paper reports on the results of a numerical study of convection flow and heat transfer in a rectangular porous cavity filled with a phase change material under steady state conditions. The two vertical walls of the cavity are subject respectively to temperatures below and above the melting point of the PCM while adiabatic conditions are imposed on the horizontal walls. The porous medium is characterized by an anisotropic permeability tensor with the principal axes arbitrarily oriented with respect to the gravity vector. The problem is governed by the aspect ratioA, the Rayleigh numberRa, the anisotropy ratioR and the orientation angle {theta} of the permeability tensor. The method of solution is based on the control volume approach in conjunction with the Landau-transformation to map the irregular flow domain into a rectangular one. (orig.AKF) (orig.). With 10 figs. [Deutsch] In der Arbeit wird ueber die Ergebnisse einer numerischen Studie, betreffend die stationaere Konvektionsstroemung und den stationaeren Waermeuebergang in einer rechteckigen, mit einem poroesen, phasenveraenderlichen Medium (PCM) verfuellten Kavitaet, berichtet. Den zwei vertikalen Berandungen der Kavitaet sind zwei, den Schmelzpunkt des PCM einschliessende Temperaturen aufgepraegt, waehrend die beiden horizontalen Berandungen adiabat gehalten werden. Das poroese Medium ist durch einen anisotropen Permeabilitaetstensor charakterisiert, dessen Hauptachsen bezueglich des Gravitationsvektors beliebig orientiert sein koennen. Das Problem ist durch das Seitenverhaeltnis A, die Rayleigh-Zahl Ra, das Anisotropienverhaeltnis R und den Orientierungswinkel {Theta} des Permeabilitaetstensor bestimmt. Die Loesungsmethode basiert auf dem Kontrollvolumenprinzip in Verbindung mit der Landau-Transformation ueber welche das irregulaere Stroemungsgebiet in ein rechteckiges abgebildet wird. (orig./AKF) (orig.)

Experimental study on heat transfer enhancement of laminar ferrofluid flow in horizontal tube partially filled porous media under fixed parallel magnet bars

Energy Technology Data Exchange (ETDEWEB)

Sheikhnejad, Yahya; Hosseini, Reza, E-mail: hoseinir@aut.ac.ir; Saffar Avval, Majid

2017-02-15

In this study, steady state laminar ferroconvection through circular horizontal tube partially filled with porous media under constant heat flux is experimentally investigated. Transverse magnetic fields were applied on ferrofluid flow by two fixed parallel magnet bar positioned on a certain distance from beginning of the test section. The results show promising notable enhancement in heat transfer as a consequence of partially filled porous media and magnetic field, up to 2.2 and 1.4 fold enhancement were observed in heat transfer coefficient respectively. It was found that presence of both porous media and magnetic field simultaneously can highly improve heat transfer up to 2.4 fold. Porous media of course plays a major role in this configuration. Virtually, application of Magnetic field and porous media also insert higher pressure loss along the pipe which again porous media contribution is higher that magnetic field. - Highlights: • Porous media can improve the coefficient of heat transfer up to 2.2 fold. • Both porous media and Nano particles have undesired pressure drop effect. • Application of both porous media and magnetic field in ferrofluid flow will result in significant enhancement in heat transfer up to 2.4 fold. • Magnet bar effect is mainly restricted to approximately one fourth of the test section. • Diluted Ferrofluids 2%, results in over 1.4 fold enhancement in heat transfer coefficient.

Effect of deformability on fluid flow through a fractured-porous medium

International Nuclear Information System (INIS)

Tsang, C.F.; Noorishad, J.; Witherspoon, P.A.

1985-01-01

A permeable geologic medium containing interstitial fluids generally undergoes deformation as the fluid pressure changes. Depending on the nature of the medium, the strain ranges from infinitesimal to finite quantities. This response is the result of a coupled hydraulic-mechanical phenomenon which can basically be formulated in the generalized three-dimensional theory of consolidation. Dealing mainly with media of little deformability, traditional hydrogeology accounts for medium deformability as far as it affects the volume of pore spaces, through the introduction of a coefficient of specific storage in the fluid flow equation. This treatment can be justified on the basis of a one-dimensional effective stress law and the assumption of homogeneity of the total stress field throughout the medium. The present paper uses a numerical model called ROCMAS (Noorishad et al., 1982; Noorishad e al., 1984) which was developed to calculate fluid flow through a deformable fractured-porous medium. The code employs the Finite Element Method based on a variational approach. It has been verified against a number of simple analytic solutions. In this work, the code is used to address the role of medium deformability in continuous and pulse testing techniques. The errors that may result because of application of traditional fluid flow methods are discussed. It is found that low pressure continuous well testing or pulse testing procedures can reduce such errors. 16 references, 9 figures, 1 table

A Conditionally Stable Scheme for a Transient Flow of a Non-Newtonian Fluid Saturating a Porous Medium

KAUST Repository

El-Amin, Mohamed

2012-06-02

The problem of thermal dispersion effects on unsteady free convection from an isothermal horizontal circular cylinder to a non-Newtonian fluid saturating a porous medium is examined numerically. The Darcy-Brinkman-Forchheimer model is employed to describe the flow field. The thermal diffusivity coefficient has been assumed to be the sum of the molecular diffusivity and the dynamic diffusivity due to mechanical dispersion. The simultaneous development of the momentum and thermal boundary layers are obtained by using finite difference method. The stability conditions are determined for each difference equation. Using an explicit finite difference scheme, solutions at each time-step have been found and then stepped forward in time until reaching steady state solution. Velocity and temperature profiles are shown graphically. It is found that as time approaches infinity, the values of friction factor and heat transfer coefficient approach the steady state values.

A Conditionally Stable Scheme for a Transient Flow of a Non-Newtonian Fluid Saturating a Porous Medium

KAUST Repository

El-Amin, Mohamed; Salama, Amgad; Sun, Shuyu

2012-01-01

The problem of thermal dispersion effects on unsteady free convection from an isothermal horizontal circular cylinder to a non-Newtonian fluid saturating a porous medium is examined numerically. The Darcy-Brinkman-Forchheimer model is employed to describe the flow field. The thermal diffusivity coefficient has been assumed to be the sum of the molecular diffusivity and the dynamic diffusivity due to mechanical dispersion. The simultaneous development of the momentum and thermal boundary layers are obtained by using finite difference method. The stability conditions are determined for each difference equation. Using an explicit finite difference scheme, solutions at each time-step have been found and then stepped forward in time until reaching steady state solution. Velocity and temperature profiles are shown graphically. It is found that as time approaches infinity, the values of friction factor and heat transfer coefficient approach the steady state values.

Aligned Magnetic Field, Radiation, and Rotation Effects on Unsteady Hydromagnetic Free Convection Flow Past an Impulsively Moving Vertical Plate in a Porous Medium

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Sandeep Naramgari

2014-01-01

Full Text Available We analyse the effects of aligned magnetic field, radiation, and rotation on unsteady hydromagnetic free convection flow of a viscous incompressible electrically conducting fluid past an impulsively moving vertical plate in a porous medium in presence of heat source. An exact solution of the governing equations in dimensionless form is obtained by Laplace transform technique in ramped temperature case. To compare the results obtained in this case with that of isothermal plate, the exact solution of the governing equations is also obtained for isothermal plate and results are discussed graphically in both ramped temperature and isothermal cases.

Fluid flow in a porous medium with transverse permeability discontinuity

Science.gov (United States)

Pavlovskaya, Galina E.; Meersmann, Thomas; Jin, Chunyu; Rigby, Sean P.

2018-04-01

Magnetic resonance imaging (MRI) velocimetry methods are used to study fully developed axially symmetric fluid flow in a model porous medium of cylindrical symmetry with a transverse permeability discontinuity. Spatial mapping of fluid flow results in radial velocity profiles. High spatial resolution of these profiles allows estimating the slip in velocities at the boundary with a permeability discontinuity zone in a sample. The profiles are compared to theoretical velocity fields for a fully developed axially symmetric flow in a cylinder derived from the Beavers-Joseph [G. S. Beavers and D. D. Joseph, J. Fluid Mech. 30, 197 (1967), 10.1017/S0022112067001375] and Brinkman [H. C. Brinkman, Appl. Sci. Res. A 1, 27 (1947), 10.1007/BF02120313] models. Velocity fields are also computed using pore-scale lattice Boltzmann modeling (LBM) where the assumption about the boundary could be omitted. Both approaches give good agreement between theory and experiment, though LBM velocity fields follow the experiment more closely. This work shows great promise for MRI velocimetry methods in addressing the boundary behavior of fluids in opaque heterogeneous porous media.

New Non-Stationary Gradient Model of Heat-Mass-Electric Charge Transfer in Thin Porous Media

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V. Rogankov

2017-10-01

Full Text Available The well-known complicated system of non-equilibrium balance equations for a continuous fluid (f medium needs the new non-Gibbsian model of f-phase to be applicable for description of the heterogeneous porous media (PMs. It should be supplemented by the respective coupled thermal and caloric equations of state (EOS developed specially for PMs to become adequate and solvable for the irreversible transport f-processes. The set of standard assumptions adopted by the linear (or quasi-linear non-equilibrium thermodynamics are based on the empirical gradient-caused correlations between flows and forces. It leads, in particular, to the oversimplified stationary solutions for PMs. The most questionable but typical modeling suppositions of the stationary gradient (SG theory are: 1 the assumption of incompressibility accepted, as a rule, for f-flows; 2 the ignorance of distinctions between the hydrophilic and hydrophobic influence of a porous matrix on the properties; 3 the omission of effects arising due to the concomitant phase intra-porous transitions between the neighboring f-fragments with the sharp differences in densities; 4 the use of exclusively Gibbsian (i.e. homogeneous and everywhere differentiable description of any f-phase in PM; 5 the very restrictive reduction of the mechanical velocity field to its specific potential form in the balance equation of f-motion as well as of the heat velocity field in the balance equation of internal energy; 6 the neglect of the new specific peculiarities arising due to the study of any non-equilibrium PM in the meso- and nano-scales of a finite-size macroscopic (N,V-system of discrete particles. This work is an attempt to develop the alternative non-stationary gradient (NSG model of real irreversible processes in PM. Another aim is to apply it without the above restrictions 1-6 to the description of f-flows through the obviously non-Gibbsian thin porous medium (TPM. We will suppose that it is composed by two

The heat and moisture transport properties of wet porous media

International Nuclear Information System (INIS)

Wang, B.X.; Fang, Z.H.; Yu, W.P.

1989-01-01

Existing methods for determining heat and moisture transport properties in porous media are briefly reviewed, and their merits and deficiencies are discussed. Emphasis is placed on research in developing new transient methods undertaken in China during the recent years. An attempt has been made to relate the coefficients in the heat and mass transfer equations with inherent properties of the liquid and matrix and then to predict these coefficients based on limited measurements

INVESTIGATION OF HEAT CONDUCTION AND SPECIFIC ELECTRIC IMPEDANCE OF POROUS MATERIALS

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E. S. Golubtsova

2004-01-01

Full Text Available In this article there was investigated the influence of porosity and temperature change on heat condition and electrical resistance of porous iron (PZh4M nickel and steel 14X17H2. There are received the adequate equations of regression, establishing connection between heat conduction and electrical resistance of the investigated materials with their porosity and temperature.

Three-dimensional Rayleigh-Taylor convection of miscible fluids in a porous medium

Science.gov (United States)

Suekane, Tetsuya; Nakanishi, Yuji; Wang, Lei

2017-11-01

Natural convection of miscible fluids in a porous medium is relevant for fields, such as geoscience and geoengineering, and for the geological storage of CO2. In this study, we use X-ray computer tomography to visualize 3D fingering structures associated with the Rayleigh-Taylor instability between miscible fluids in a porous medium. In the early stages of the onset of the Rayleigh-Taylor instability, a fine crinkling pattern gradually appears at the interface. As the wavelength and amplitude increase, descending fingers form on the interface and extend vertically downward; moreover, ascending and highly symmetric fingers form. The adjacent fingers are cylindrical in shape and coalesce to form large fingers. Fingers appearing on the interface tend to become finer with increasing Rayleigh number, which is consistent with linear perturbation theory. If the Péclet number exceeds 10, the transverse dispersion increases the finger diameter and enhances finger coalescence, strongly impacting the decay in finger number density. When mechanical dispersion is negligible, the finger-extension velocity, the mass-transfer rate, and the onset time scale with Rayleigh number. Mechanical dispersion not only reduces the onset time but also enhances mass transport, which indicates that mechanical dispersion influences the long-term dissolution process of CO2 injected into aquifers.

A linear analytical study of Soret-driven ferrothermohaline convection in an anisotropic porous medium

International Nuclear Information System (INIS)

Sekar, R.; Raju, K.; Vasanthakumari, R.

2013-01-01

The Soret-driven ferrothermoconvective instability of multi- component fluid in an anisotropic porous medium heated from below and salted from above has been analyzed using Brinkman model for various values of anisotropic parameter. The salinity effect is contained in magnetization and density of the ferrofluid and the system is assumed to have anisotropy in the vertical direction and isotropy in the horizontal direction. A small perturbation imparted on the basic state and a linear stability analysis is used for this model for which the normal mode technique is applied. The present analysis has been carried out through both stationary as well as oscillatory modes. The vertical anisotropy tends to destabilize the system. -- Highlights: ► We examine the effect of anisotropy and magnetization of convection in Soret effect. ► The system loses its stability for critical Rayleigh number for various parameters like R s and K 1 . ► The larger temperature difference is needed to guarantee the occurring of convection. ► The Soret effect plays a dominant role for the stability of the system

Boundary Layer Flows in Porous Media with Lateral Mass Flux

DEFF Research Database (Denmark)

Nemati, H; H, Bararnia; Noori, F

2015-01-01

Solutions for free convection boundary layers on a heated vertical plate with lateral mass flux embedded in a saturated porous medium are presented using the Homotopy Analysis Method and Shooting Numerical Method. Homotopy Analysis Method yields an analytic solution in the form of a rapidly...

On the description of the properties of fractured rock using the concept of a porous medium

International Nuclear Information System (INIS)

Stokes, J.

1980-05-01

In order to describe the flow of groundwater through fractured rock, water is either assumed to flow through a pervious continuum of through descrete fractures between impervious blocks of rock. The latter approach being the one demanding more information on the rock, problems on groundwater flow are usually discussed using the porous medium approach. It is often a question of debate wether the continuum approach is applicable to the fractured rock under consideration. Therefore, it is essential that after assuming that a certain flow region acts as a porous medium, we use a procedure for measuring the properties that at the same time gives a test of this assumption. When giving a description of groundwater flow, the goal is often a presentation of pathlines and flowtimes between points of interest and the ground surface. Using a porous medium approach, this means that hydraulic conductivity and porosity must be known through the medium. In order to cope with transient flow, we must also know the time constant governing the development of the flow. The pathlines depend to a great extent on the variation of conductivity through space. A conductivity decreasing with depth will force the pathlines to the surface giving local flow. If instead the conductivity is constant, the flow is regional. It is therefore important to know the gradient of hydraulic conductivity. Finally, as we know that the flow takes place through a geological structure, the anisotropic behaviour of the rock must be known in order to describe the flow. In this report a procedure to measure the properties listed above is developed. (author)

A model to analyse the flow of an incompressible Newtonian fluid through a rigid, homogeneous, isotropic and infinite porous medium

International Nuclear Information System (INIS)

Gama, R.M.S. da; Sampaio, R.

1985-01-01

The flow of an incompressible Newtonian fluid through a rigid, homogeneous, isotropic and infinite porous medium which has a given inicial distribuition of the mentioned fluid, is analyzed. It is proposed a model that assumes that the motion is caused by concentration gradient, but it does not consider the friction between the porous medium and the fluid. We solve an onedimensional case where the mathematical problem is reduced to the solution of a non-linear hyperbolic system of differential equations, subjected to an inicial condition given by a step function, called 'Riemann Problem'. (Author) [pt

Effects of chemical reaction in thermal and mass diffusion of micropolar fluid saturated in porous regime with radiation and ohmic heating

Directory of Open Access Journals (Sweden)

Kumar Hitesh

2016-01-01

Full Text Available The present paper analyzes the chemically reacting free convection MHD micropolar flow, heat and mass transfer in porous medium past an infinite vertical plate with radiation and viscous dissipation. The non-linear coupled partial differential equations are solved numerically using an implicit finite difference scheme known as Keller-box method. The results for concentration, transverse velocity, angular velocity and temperature are obtained and effects of various parameters on these functions are presented graphically. The numerical discussion with physical interpretations for the influence of various parameters also presented.

Computed tomography for the quantitative characterization of flow through a porous medium

International Nuclear Information System (INIS)

Auzerais, F.M.; Dussan, E.B.; Reischer, A.J.

1991-01-01

X-ray computer tomography (CT) has become an increasingly popular research tool in petroleum engineering for characterizing porous media. Its highly detailed images have been used to construct maps of porosity, saturation and atomic composition, and to visualize the displacement of fluids. However, extracting data necessary to characterize flow through porous media is both time consuming and dependent on the availability of extensive computational resources - - a consequence of the large size of the image files. The authors of this paper applied to known technique, based upon the ability to recognize regions with similar features, which avoids these difficulties. It allows the authors to substitute for the image, the pixel location of the boundaries of the recognized regions, reducing considerably the computer storage requirements. The authors this technique to study the dynamics of two miscible liquids of different densities flowing through a porous medium where buoyancy plays an important role. The authors' specific concern is the movement of mud filtrate as it penetrates a permeable formation in the vicinity of a recently drilled wellbore. The authors quantify the manner in which impermeable horizontal barriers influence the movement of the filtrate

Experimental study on method for heat transfer enhancement using a porous material

International Nuclear Information System (INIS)

Shimura, Takuya; Takeda, Tetsuaki

2011-01-01

There are several methods for enhancement of heat transfer; for example, there are attaching various fins on the heat transfer surface, processing the surface roughly, and so on. When cooling high temperature circular or rectangular channels by forced convection of gas, there are several methods for enhancement of heat transfer such as attaching radial or spiral fins on the channel surface or inserting twisted tape in the channel. In the case of the gas heating type steam reformer, disk type fins are attached on the outside surface of the reformer tube, and the tube is inserted into the guide tube to increase an amount of heat transferred from the high temperature gas. However, it has to take into consideration the deterioration of the structure strength by attaching the fins on the tube surface with the design of the steam reformer. The objective of this study is to clarify performances of a method for heat transfer enhancement using porous material with high porosity. The experiment has been performed using an apparatus which simulated the passage structure of the steam reformer to obtain characteristics of heat transfer and pressure drop. From the results obtained in this experiment, the heat transfer rate by this method showed a good performance in the laminar flow region. It was also found that the method for heat transfer enhancement using porous material with high porosity is further improved under the high temperature condition as compared with the other methods for heat transfer enhancement. (author)

Study on Spheroidization and Related Heat Treatments of Medium Carbon Alloy Steels

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Harisha S. R.

2018-01-01

Full Text Available The importance of medium carbon steels as engineering materials is reflected by the fact that out of the vast majority of engineering grade ferrous alloys available and used in the market today, a large proportion of them are from the family of medium carbon steels. Typically medium carbon steels have a carbon range of 0.25 to 0.65% by weight, and a manganese content ranging from 0.060 to 1.65% by weight. Medium carbon steels are more resistive to cutting, welding and forming as compared to low carbon steels. From the last two decades a number of research scholars reported the use of verity of heat treatments to tailor the properties of medium carbon steels. Spheroidizing is the novel industrial heat treatment employed to improve formability and machinability of medium/high carbon low alloy steels. This exclusive study covers procedure, the effects and possible outcomes of various heat treatments on medium carbon steels. In the present work, other related heat treatments like annealing and special treatments for property alterations which serve as pretreatments for spheroidizing are also reviewed. Medium carbon steels with property alterations by various heat treatment processes are finding increased responsiveness in transportation, aerospace, space, underwater along with other variegated fields. Improved tribological and mechanical properties consisting of impact resistance, stiffness, abrasion and strength are the main reasons for the increased attention of these steels in various industries. In the present scenario for the consolidation of important aspects of various heat treatments and effects on mechanical properties of medium carbons steel, a review of different research papers has been attempted. This review may be used as a guide to provide practical data for heat treatment industry, especially as a tool to enhance workability and tool life.

MODELING OF HEAT TRANSFER IN A POROUS TURBINE BEARING COOLING SYSTEM

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A. A. Genbach

2017-01-01

Full Text Available A new porous cooling system in which the coolant supply is produced by the combined action of capillary and gravitational forces is proposed and studied for various technical devices and systems developed by the authors. The cooling surface is made of stainless steel, brass, copper, bronze, nickel, glass and alundum. The wall thickness is (0.05–2.00 ∙ 10⁻³m. Visual observations were carried out by using high-speed camera filming with the use of SCS-1M. Experiments were carried out with water at pressures ranging between 0.01–10.00 MPa, under-heating to 0–20 K, excess liquid of 1–14 of steam flow, thermal load of (1–60 ∙ 104  W/m², temperature pressure of 1–60 K and the system orientation of ±(0–90 degrees. Studies carried out on a model plant has identified two areas of the process of vaporization of the liquid and an influence of operating and design characteristics. The optimal coolant flow and the most effective form of reticulated porous structure are identified. Visual observations have made it possible to describe the physical picture of the processes and to generalize experimental data on the removed heat flows with an accuracy of ±20 % depending on the thermophysical properties of the fluid, wall, temperature difference, excess fluid, porous structures and heat exchange interface.

Cumulative effects of using pin fin heat sink and porous metal foam on thermal management of lithium-ion batteries

International Nuclear Information System (INIS)

Mohammadian, Shahabeddin K.; Zhang, Yuwen

2017-01-01

Highlights: • 3D transient thermal analysis of a pouch Li-ion cell has been carried out. • Using pin fin heat sink improves the temperature reduction at low pumping powers. • Using pin fin heat sink enhances the temperature uniformity at low air flow rates. • Porous aluminum foam insertion with pin fins improves temperature reduction. • Porous aluminum foam insertion with pin fins enhances temperature uniformity. - Abstract: Three-dimensional transient thermal analysis of an air-cooled module was carried out to investigate cumulative effects of using pin fin heat sink and porous metal foam on thermal management of a Li-ion (lithium-ion) battery pack. Five different cases were designed as Case 1: flow channel without any pin fin or porous metal foam insertion, Case 2: flow channel with aluminum pin fins, Case 3: flow channel with porous aluminum foam pin fins, Case 4: fully inserted flow channel with porous aluminum foam, and Case 5: fully inserted flow channel with porous aluminum foam and aluminum pin fins. The effects of porous aluminum insertions, pin fin types, air flow inlet temperature, and air flow inlet velocity on the temperature uniformity and maximum temperature inside the battery pack were systematically investigated. The results showed that using pin fin heat sink (Case 2) is appropriate only for low air flow velocities. In addition, the use of porous aluminum pin fins or embedding porous aluminum foam inside the air flow channel (Cases 3 and 4) are not beneficial for thermal management improvement. The combination of aluminum pin fins and porous aluminum foam insertion inside the air flow channel (Case 5) is a proper option that improves both temperature reduction and temperature uniformity inside the battery cell.

Effects of anodizing parameters and heat treatment on nanotopographical features, bioactivity, and cell culture response of additively manufactured porous titanium.

Science.gov (United States)

Amin Yavari, S; Chai, Y C; Böttger, A J; Wauthle, R; Schrooten, J; Weinans, H; Zadpoor, A A

2015-06-01

Anodizing could be used for bio-functionalization of the surfaces of titanium alloys. In this study, we use anodizing for creating nanotubes on the surface of porous titanium alloy bone substitutes manufactured using selective laser melting. Different sets of anodizing parameters (voltage: 10 or 20V anodizing time: 30min to 3h) are used for anodizing porous titanium structures that were later heat treated at 500°C. The nanotopographical features are examined using electron microscopy while the bioactivity of anodized surfaces is measured using immersion tests in the simulated body fluid (SBF). Moreover, the effects of anodizing and heat treatment on the performance of one representative anodized porous titanium structures are evaluated using in vitro cell culture assays using human periosteum-derived cells (hPDCs). It has been shown that while anodizing with different anodizing parameters results in very different nanotopographical features, i.e. nanotubes in the range of 20 to 55nm, anodized surfaces have limited apatite-forming ability regardless of the applied anodizing parameters. The results of in vitro cell culture show that both anodizing, and thus generation of regular nanotopographical feature, and heat treatment improve the cell culture response of porous titanium. In particular, cell proliferation measured using metabolic activity and DNA content was improved for anodized and heat treated as well as for anodized but not heat-treated specimens. Heat treatment additionally improved the cell attachment of porous titanium surfaces and upregulated expression of osteogenic markers. Anodized but not heat-treated specimens showed some limited signs of upregulated expression of osteogenic markers. In conclusion, while varying the anodizing parameters creates different nanotube structure, it does not improve apatite-forming ability of porous titanium. However, both anodizing and heat treatment at 500°C improve the cell culture response of porous titanium

PORFLO - a continuum model for fluid flow, heat transfer, and mass transport in porous media. Model theory, numerical methods, and computational tests

International Nuclear Information System (INIS)

Runchal, A.K.; Sagar, B.; Baca, R.G.; Kline, N.W.

1985-09-01

Postclosure performance assessment of the proposed high-level nuclear waste repository in flood basalts at Hanford requires that the processes of fluid flow, heat transfer, and mass transport be numerically modeled at appropriate space and time scales. A suite of computer models has been developed to meet this objective. The theory of one of these models, named PORFLO, is described in this report. Also presented are a discussion of the numerical techniques in the PORFLO computer code and a few computational test cases. Three two-dimensional equations, one each for fluid flow, heat transfer, and mass transport, are numerically solved in PORFLO. The governing equations are derived from the principle of conservation of mass, momentum, and energy in a stationary control volume that is assumed to contain a heterogeneous, anisotropic porous medium. Broad discrete features can be accommodated by specifying zones with distinct properties, or these can be included by defining an equivalent porous medium. The governing equations are parabolic differential equations that are coupled through time-varying parameters. Computational tests of the model are done by comparisons of simulation results with analytic solutions, with results from other independently developed numerical models, and with available laboratory and/or field data. In this report, in addition to the theory of the model, results from three test cases are discussed. A users' manual for the computer code resulting from this model has been prepared and is available as a separate document. 37 refs., 20 figs., 15 tabs

Heat and mass transfer in porous cavity: Assisting flow

Energy Technology Data Exchange (ETDEWEB)

Badruddin, Irfan Anjum [Dept. of Mechanical Engineering, University of Malaya, Kuala Lumpur, 50603 (Malaysia); Quadir, G. A. [School of Mechatronic Engineering, University Malaysia Perlis, Pauh Putra, 02600 Arau, Perlis (Malaysia)

2016-06-08

In this paper, investigation of heat and mass transfer in a porous cavity is carried out. The governing partial differential equations are non-dimensionalised and solved using finite element method. The left vertical surface of the cavity is maintained at constant temperature and concentration which are higher than the ambient temperature and concentration applied at right vertical surface. The top and bottom walls of the cavity are adiabatic. Heat transfer is assumed to take place by natural convection and radiation. The investigation is carried out for assisting flow when buoyancy and gravity force act in same direction.

Simultaneous Contact Sensing and Characterizing of Mechanical and Dynamic Heat Transfer Properties of Porous Polymeric Materials

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Bao-guo Yao

2017-10-01

Full Text Available Porous polymeric materials, such as textile fabrics, are elastic and widely used in our daily life for garment and household products. The mechanical and dynamic heat transfer properties of porous polymeric materials, which describe the sensations during the contact process between porous polymeric materials and parts of the human body, such as the hand, primarily influence comfort sensations and aesthetic qualities of clothing. A multi-sensory measurement system and a new method were proposed to simultaneously sense the contact and characterize the mechanical and dynamic heat transfer properties of porous polymeric materials, such as textile fabrics in one instrument, with consideration of the interactions between different aspects of contact feels. The multi-sensory measurement system was developed for simulating the dynamic contact and psychological judgment processes during human hand contact with porous polymeric materials, and measuring the surface smoothness, compression resilience, bending and twisting, and dynamic heat transfer signals simultaneously. The contact sensing principle and the evaluation methods were presented. Twelve typical sample materials with different structural parameters were measured. The results of the experiments and the interpretation of the test results were described. An analysis of the variance and a capacity study were investigated to determine the significance of differences among the test materials and to assess the gage repeatability and reproducibility. A correlation analysis was conducted by comparing the test results of this measurement system with the results of Kawabata Evaluation System (KES in separate instruments. This multi-sensory measurement system provides a new method for simultaneous contact sensing and characterizing of mechanical and dynamic heat transfer properties of porous polymeric materials.

Magnetic power conversion with machines containing full or porous wheel heat exchangers

Science.gov (United States)

Egolf, Peter W.; Kitanovski, Andrej; Diebold, Marc; Gonin, Cyrill; Vuarnoz, Didier

2009-04-01

A first part of the article contains a thermodynamic theory describing the temperature distribution in a Curie wheel. The occurring nonlinear ordinary differential equation has an analytical solution. If a Curie wheel is stabilized by levitation, it is named Palmy wheel. These wheels show a full structure, and because of this reason, their uptake of heat from a flame (Curie wheel) or by (solar) light absorption (Palmy wheel) only on the periphery of a cylinder is very limited. To improve the method, a modification of the principle by introducing a convective heat transport into a porous wheel is discussed. By this the power conversion rate from a heat flux to mechanical and electric power is very much increased. The second part of the article presents results of a theoretical/numerical study on the efficiencies of magnetic power conversion plants operating with porous wheels. Furthermore, these efficiencies—which are promising—are compared with those of existing power conversion plants, as e.g. geothermal binary cycle power plants.

Magnetic power conversion with machines containing full or porous wheel heat exchangers

International Nuclear Information System (INIS)

Egolf, Peter W.; Kitanovski, Andrej; Diebold, Marc; Gonin, Cyrill; Vuarnoz, Didier

2009-01-01

A first part of the article contains a thermodynamic theory describing the temperature distribution in a Curie wheel. The occurring nonlinear ordinary differential equation has an analytical solution. If a Curie wheel is stabilized by levitation, it is named Palmy wheel. These wheels show a full structure, and because of this reason, their uptake of heat from a flame (Curie wheel) or by (solar) light absorption (Palmy wheel) only on the periphery of a cylinder is very limited. To improve the method, a modification of the principle by introducing a convective heat transport into a porous wheel is discussed. By this the power conversion rate from a heat flux to mechanical and electric power is very much increased. The second part of the article presents results of a theoretical/numerical study on the efficiencies of magnetic power conversion plants operating with porous wheels. Furthermore, these efficiencies-which are promising-are compared with those of existing power conversion plants, as e.g. geothermal binary cycle power plants

Modeling of heat transfer in a vascular tissue-like medium during an interstitial hyperthermia process.

Science.gov (United States)

Hassanpour, Saeid; Saboonchi, Ahmad

2016-12-01

This paper aims to evaluate the role of small vessels in heat transfer mechanisms of a tissue-like medium during local intensive heating processes, for example, an interstitial hyperthermia treatment. To this purpose, a cylindrical tissue with two co- and counter-current vascular networks and a central heat source is introduced. Next, the energy equations of tissue, supply fluid (arterial blood), and return fluid (venous blood) are derived using porous media approach. Then, a 2D computer code is developed to predict the temperature of blood (fluid phase) and tissue (solid phase) by conventional volume averaging method and a more realistic solution method. In latter method, despite the volume averaging the blood of interconnect capillaries is separated from the arterial and venous blood phases. It is found that in addition to blood perfusion rate, the arrangement of vascular network has considerable effects on the pattern and amount of the achieved temperature. In contrast to counter-current network, the co-current network of vessels leads to considerable asymmetric pattern of temperature contours and relocation of heat affected zone along the blood flow direction. However this relocation can be prevented by changing the site of hyperthermia heat source. The results show that the cooling effect of co-current blood vessels during of interstitial heating is more efficient. Despite much anatomical dissimilarities, these findings can be useful in designing of protocols for hyperthermia cancer treatment of living tissue. Copyright © 2016 Elsevier Ltd. All rights reserved.

Periodic mixed convection in horizontal porous layer heated from below by isoflux heater

International Nuclear Information System (INIS)

Saeid, Nawaf H.; Pop, I.

2006-01-01

Numerical study for transient mixed convection in a two-dimensional horizontal porous layer heated from below by a constant heat flux source is carried out in the present paper. The transient thermal field, flow field and average Nusselt number are presented for a wide range of the Peclet number, Pe, for the particular case of Rayleigh number Ra=10x2 and the ratio of heater length to the porous layer thickness A=1, 3 and 5. It is found that for A=3 and A=5 with small values of the Peclet number, the free convection mode is dominated, while for large values, of the Peclet number, the forced convection mode is dominated. However, for moderate values the oscillatory mixed convection is observed and a periodic variation of the average Nusselt number is obtained. When the heater length is equal to the porous layer thickness (A=1) the steady-state results are obtained for the range of Pe=0.01-10. (author)

On the Onset of Thermal Convection in a Layer of Oldroydian Visco-Elastic Fluid Saturated by Brinkman–Darcy Porous Medium

Directory of Open Access Journals (Sweden)

Chand Ramesh

2015-12-01

Full Text Available Thermal instability in a horizontal layer of Oldroydian visco-elastic fluid in a porous medium is investigated. For porous medium the Brinkman–Darcy model is considered. A linear stability analysis based upon perturbation method and normal mode technique is used to find solution of the fluid layer confined between two free-free boundaries. The onset criterion for stationary and oscillatory convection is derived analytically. The influence of the Brinkman–Darcy, Prandtl–Darcy number, stress relaxation parameter on the stationary and oscillatory convection is studied both analytically and graphically. The sufficient condition for the validity of PES has also been derived.

A numerical and experimental study of two-phase flow and heat transfer in a porous formation with localized heating from below

International Nuclear Information System (INIS)

Easterday, O.T.; Wang, C.Y.; Cheng, P.

1995-01-01

Understanding and predicting two-phase flow and heat transfer in porous media is of fundamental interest for a number of engineering applications. Examples include thermal technologies for remediation of contaminated subsurfaces, the extraction of geothermal energy from vapor-dominated reservoirs, and the assessment of high-level nuclear waste repositories. A numerical and experimental study is reported for two-phase flow and heat transfer in a horizontal porous formation with water through flow and partial heating from below. Based on a newly developed two-phase mixture model, numerical results of the temperature distribution, liquid saturation, liquid and vapor phase velocity fields are presented for three representative cases with varying inlet velocities. It is found that the resulting two-phase structure and flow patterns are strongly dependent upon the water inlet velocity and the bottom heat flux. The former parameter measures the flow along the horizontal direction, while the latter creates a relative motion between the phases in the vertical direction. Experiments are also performed to measure temperature distributions and to visualize the two-phase flow patterns. Qualitative agreement between experiments and numerical predictions is achieved. Overall, this combined experimental and numerical study has provided new insight into conjugate single- and two-phase flow and heat transfer in porous media, although future research is required if accurate modeling of these complex problems is to be accomplished

Two-phase jet impingement cooling for high heat flux wide band-gap devices using multi-scale porous surfaces

International Nuclear Information System (INIS)

Joshi, Shailesh N.; Dede, Ercan M.

2017-01-01

Highlights: • Jet impingement with phase change on multi-scale porous surfaces is investigated. • Porous coated flat, pin-fin, open tunnel, and closed tunnel structures are studied. • Boiling curve, heat transfer coefficient, and pressure drop metrics are reported. • Flow visualization shows vapor removal from the surface is a key aspect of design. • The porous coated pin-fin surface exhibits superior two-phase cooling performance. - Abstract: In the future, wide band-gap (WBG) devices such as silicon carbide and gallium nitride will be widely used in automotive power electronics due to performance advantages over silicon-based devices. The high heat fluxes dissipated by WBG devices pose extreme cooling challenges that demand the use of advanced thermal management technologies such as two-phase cooling. In this light, we describe the performance of a submerged two-phase jet impingement cooler in combination with porous coated heat spreaders and multi-jet orifices. The cooling performance of four different porous coated structures was evaluated using R-245fa as the coolant at sub-cooling of 5 K. The results show that the boiling performance of a pin-fin heat spreader is the highest followed by that for an open tunnel (OPT), closed tunnel (CLT), and flat heat spreader. Furthermore, the flat heat spreader demonstrated the lowest critical heat flux (CHF), while the pin-fin surface sustained a heat flux of 218 W/cm 2 without reaching CHF. The CHF values of the OPT and CLT surfaces were 202 W/cm 2 and 194 W/cm 2 , respectively. The pin-fin heat spreader has the highest two-phase heat transfer coefficient of 97,800 W/m 2 K, while the CLT surface has the lowest heat transfer coefficient of 69,300 W/m 2 K, both at a heat flux of 165 W/cm 2 . The variation of the pressure drop of all surfaces is similar for the entire range of heat fluxes tested. The flat heat spreader exhibited the least pressure drop, 1.73 kPa, while the CLT surface had the highest, 2.17 kPa at a

Free convection boundary layer flow past a horizontal flat plate embedded in porous medium filled by nano-fluid containing gyro-tactic microorganisms

Energy Technology Data Exchange (ETDEWEB)

Aziz, A. [Department of Mechanical Engineering, School of Engineering and Applied Science, Gonzaga University, Spokane, WA 99258 (United States); Khan, W.A. [Department of Engineering Sciences, National University of Sciences and Technology, Karachi 75350 (Pakistan); Pop, I. [Department of Applied Mathematics, Babes-Bolyai University, Cluj-Napoca (Romania)

2012-06-15

The steady boundary layer free convection flow past a horizontal flat plate embedded in a porous medium filled by a water-based nano-fluid containing gyro-tactic microorganisms is investigated. The Oberbeck-Boussinesq approximation is assumed in the analysis. The effects of bio-convection parameters on the dimensionless velocity, temperature, nano-particle concentration and density of motile microorganisms as well as on the local Nusselt, Sherwood and motile microorganism numbers are investigated and presented graphically. In the absence of bio-convection, the results are compared with the existing data in the open literature and found to be in good agreement. The bio-convection parameters strongly influence the heat, mass, and motile microorganism transport rates. (authors)

Lubrication and thermal characteristics of mechanical seal with porous surface based on cavitation

Science.gov (United States)

Huilong, Chen; Muzi, Zuo; Tong, Liu; Yu, Wang; Cheng, Xu; Qiangbo, Wu

2014-04-01

The theory model of mechanical seals with laser-textured porous surface (LST-MS) was established. The liquid film of LST-MS was simulated by the Fluent software, using full cavitation model and non-cavitation model separately. Dynamic mesh technique and relationship between viscosity and temperature were applied to simulate the internal flow field and heat characteristics of LST-MS, based on the more accurate cavitation model. Influence of porous depth ratio porous diameter ɛ and porous density SP on lubrication performance and the variation of lubrication and thermal properties with shaft speed and sealing pressure were analyzed. The results indicate that the strongest hydrodynamic pressure effect and the biggest thickness of liquid film are obtained when ɛ and SP are respectively about 0.025 and 0.5 which were thought to be the optimum value. The frictional heat leads to the increase of liquid film temperature and the decrease of medium viscosity with the shaft speed increasing. The hydrodynamic pressure effect increases as shaft speed increasing, however it decreases as the impact of frictional heat.

Transport of radionuclides by concentrated brine in a porous medium with micropore-macropore structure

International Nuclear Information System (INIS)

Hassanizadeh, S.M.

1987-01-01

This work concerns itself with the study of effects of soil aggregation and high salt concentrations on the transport of radionuclides by concentrated brine flowing through an aggregated porous medium. The medium is considered to be composed of porous rock aggregates separated by macropores through which the brine flows and transport of salt and radionuclides takes place. The aggregates contain dead-end pores, cracks, and stationary pockets collectively called micropores. The micropore space does not contribute to the flow, but it serves as a storage for salt and radionuclides. Adsorption of radionuclides takes place at internal surfaces of aggregates where they assume that a linear equilibrium isotherm describes the process. A one-dimensional numerical model is developed which is based on two sets of equations: one set for the flow and transport of salt and another set for transport of radionuclides. Results of numerical experiments clearly indicate that the existence of high salt concentrations markedly reduces the peak of nuclides concentration and slows down their movement. Also, it is found that diffusive mass exchange between macropores and aggregates results in a pronounced lowering of the radionuclides concentration peaks. 9 references, 7 figures

'Butterfly effect' in porous Bénard convection heated from below

Energy Technology Data Exchange (ETDEWEB)

Siri, Z.; Liew, K. Y. [Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ibrahim, R. I. [Faculty of Science and Technology, Universiti Sains Islam Malaysia, 71800 Bandar Baru Nilai, Negeri Sembilan Darul Khusus (Malaysia)

2014-07-10

Transition from steady to chaos for the onset of Bénard convection in porous medium was analyzed. The governing equation is reduced to ordinary differential equation and solved using built in MATLAB ODE45. The transition from steady to chaos take over from a limit cycle followed by homoclinic explosion.

Transfers in porous medium, drying; Transferts en milieu poreux, sechage

Energy Technology Data Exchange (ETDEWEB)

Ferrasse, J.H.; Arlabosse, P.; Puaux, J.P. [Ecole des Mines d' Albi-Carnaux, Centre Energetique Environnement, 81 - Albi (France)] (and others)

2000-07-01

This congress, on thermology, took place at Lyon in France, the 15-17 may 2000 with a presentation of 143 papers on the recent researches and specialized discussions. The talks published in this book are sorted out in ten thema. One of the thema concerns the transfers in porous medium and the drying, with seven talks presented. They can be applied to many natural domains as the residual waters filtering, the hydrocarbons extraction, the soil utilization for energy source or reserve, the thermal insulation improvement. In the drying domain, two papers are presented, one on the development of the drying of sewage sludges, the other on a drying process for superheated steam. (A.L.B.)

Mixed convection flow and heat transfer in a vertical wavy channel ...

African Journals Online (AJOL)

Mixed convection flow and heat transfer in a vertical wavy channel filled with porous and fluid layers is studied analytically. The flow in the porous medium is modeled using Darcy-Brinkman equation. The coupled non-linear partial differential equations describing the conservation of mass, momentum and energy are solved ...

Particles and solutes migration in porous medium : radionuclides and clayey particles simultaneous transport under the effect of a salinity gradient

International Nuclear Information System (INIS)

Faure, M.H.

1994-01-01

This work deals with the radiation protection of high-level and long-life radioactive waste storages. The colloids presence in ground waters can accelerate the radionuclides migration in natural geological deposits. The aim of this thesis is then to control particularly the particles motion in porous medium in order to anticipate quantitatively their migration. Liquid chromatography columns are filled with a clayey sand and fed with a decreasing concentration sodium chloride solution in order to study the particles outlet under a salinity gradient. When the porous medium undergoes a decrease of salinity it deteriorates. The adsorption of the cations : sodium 22, calcium 45, cesium 137 and neptunium 237 is then studied by the ions exchange method. The radionuclide solution is injected before the decrease of the feed solution salinity. The decrease of the sodium chloride concentration leads to the decrease of the radionuclides concentration because the adsorption competition between the sodium ion and the injected cation is lower. The particles transport, without fouling of the porous medium, is carried out in particular physical and chemical conditions which are described. (O.L.). 71 refs., 105 figs., 26 tabs

The thermal non-equilibrium porous media modelling for CFD study of woven wire matrix of a Stirling regenerator

International Nuclear Information System (INIS)

Costa, S.C.; Barreno, I.; Tutar, M.; Esnaola, J.A.; Barrutia, H.

2015-01-01

Highlights: • A numerical procedure to derive porous media’s coefficients is proposed. • The local thermal non-equilibrium porous media model is more suitable for regenerators. • The regenerator temperature profiles can be better fitted to a logarithmic curve. • The wound woven wire matrix provides lower performance compared to stacked. • The numerical characterization methodology is useful for the multi-D Stirling engine models. - Abstract: Different numerical methods can be applied to the analysis of the flow through the Stirling engine regenerator. One growing approach is to model the regenerator as porous medium to simulate and design the full Stirling engine in three-dimensional (3-D) manner. In general, the friction resistance coefficients and heat transfer coefficient are experimentally obtained to describe the flow and thermal non-equilibrium through a porous medium. A finite volume method (FVM) based non-thermal equilibrium porous media modelling approach characterizing the fluid flow and heat transfer in a representative small detailed flow domain of the woven wire matrix is proposed here to obtain the porous media coefficients without further requirement of experimental studies. The results are considered to be equivalent to those obtained from the detailed woven wire matrix for the pressure drop and heat transfer. Once the equivalence between the models is verified, this approach is extended to model oscillating regeneration cycles through a full size regenerator porous media for two different woven wire matrix configurations of stacked and wound types. The results suggest that the numerical modelling approach proposed here can be applied with confidence to model the regenerator as a porous media in the multi-dimensional (multi-D) simulations of Stirling engines

Influence of gas hydrates crystals or ice crystals on the permeability of a porous medium; Influence de cristaux d'hydrates de gaz ou de glace sur la permeabilite d'un milieu poreux

Energy Technology Data Exchange (ETDEWEB)

Bonnefoy, O

2005-03-15

The first part is a bibliographic study. We study the conditions for thermodynamic equilibrium of the hydrates as a bulk medium and the composition of the liquid and solid phases. We then describe the basics of fluid dynamics in a porous medium. Eventually, we merge the two approaches and study the influence of the porous medium on the hydrate stability. An off-shore hydrate field (Blake Ridge) and an on-shore field (Mallik) are precisely described. The latter will be used as a reference case for subsequent numerical simulations. The second part is devoted to the experiments. Their goal is to measure the permeability of a sediment containing crystals. To get closer to natural geologic conditions, crystals are synthesized in absence of free gas. It turns out that hydrates form in a very heterogeneous way in the porous medium, which makes the measurements non representative. We believe that this result has a general character and that, at the laboratory time-scale, it is difficult, to say the least to achieve a uniform distribution of gas hydrates grown from dissolved gas. To circumvent this difficulty, we show, with a theoretical approach, that ice crystals behave much the same way as the hydrate crystals, concerning the Van der Waals forces that govern the agglomeration. This allows us to calculate the Hamaker constant of the hydrates. The second series of experiments focuses on the permeability of a non consolidated porous medium under mechanical stress, where the pores are filled with ice crystals. Two silica beads populations are used to form a porous medium: 3 mm and 0.2 mm. With the large grains, results show two thresholds: for saturations below the lower threshold, the presence of crystals does not modify the permeability. For saturations above the upper threshold, the permeability vanishes almost completely (percolation phenomenon). Between these two limits, the permeability decreases exponentially with the saturation. With the fine grains, the permeability

Effects of anodizing parameters and heat treatment on nanotopographical features, bioactivity, and cell culture response of additively manufactured porous titanium

Energy Technology Data Exchange (ETDEWEB)

Amin Yavari, S., E-mail: s.aminyavari@tudelft.nl [Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands); Chai, Y.C. [Prometheus, Division of Skeletal Tissue Engineering, Bus 813, O& N1, Herestraat 49, KU Leuven, 3000 Leuven (Belgium); Tissue Engineering Laboratory, Skeletal Biology and Engineering Research Center, Bus 813, O& N1, Herestraat 49, KU Leuven, 3000 Leuven (Belgium); Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia); Böttger, A.J. [Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands); Wauthle, R. [KU Leuven, Department of Mechanical Engineering, Section Production Engineering, Machine Design and Automation (PMA), Celestijnenlaan 300B, 3001 Leuven (Belgium); 3D Systems — LayerWise NV, Grauwmeer 14, 3001 Leuven (Belgium); Schrooten, J. [Department of Metallurgy and Materials Engineering, KU Leuven, Kasteelpark Arenberg 44 — PB2450, B-3001 Heverlee (Belgium); Weinans, H. [Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands); Department of Orthopedics and Dept. Rheumatology, UMC Utrecht, Heidelberglaan100, 3584CX Utrecht (Netherlands); Zadpoor, A.A. [Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands)

2015-06-01

Anodizing could be used for bio-functionalization of the surfaces of titanium alloys. In this study, we use anodizing for creating nanotubes on the surface of porous titanium alloy bone substitutes manufactured using selective laser melting. Different sets of anodizing parameters (voltage: 10 or 20 V anodizing time: 30 min to 3 h) are used for anodizing porous titanium structures that were later heat treated at 500 °C. The nanotopographical features are examined using electron microscopy while the bioactivity of anodized surfaces is measured using immersion tests in the simulated body fluid (SBF). Moreover, the effects of anodizing and heat treatment on the performance of one representative anodized porous titanium structures are evaluated using in vitro cell culture assays using human periosteum-derived cells (hPDCs). It has been shown that while anodizing with different anodizing parameters results in very different nanotopographical features, i.e. nanotubes in the range of 20 to 55 nm, anodized surfaces have limited apatite-forming ability regardless of the applied anodizing parameters. The results of in vitro cell culture show that both anodizing, and thus generation of regular nanotopographical feature, and heat treatment improve the cell culture response of porous titanium. In particular, cell proliferation measured using metabolic activity and DNA content was improved for anodized and heat treated as well as for anodized but not heat-treated specimens. Heat treatment additionally improved the cell attachment of porous titanium surfaces and upregulated expression of osteogenic markers. Anodized but not heat-treated specimens showed some limited signs of upregulated expression of osteogenic markers. In conclusion, while varying the anodizing parameters creates different nanotube structure, it does not improve apatite-forming ability of porous titanium. However, both anodizing and heat treatment at 500 °C improve the cell culture response of porous titanium

Exact Analysis of the Flow and Heat Transfer of the SA-TiO2 Non-Newtonian Nanofluid Between Two Coaxial Cylinders Through a Porous Medium

Science.gov (United States)

Almazmumy, Mariam; Ebaid, Abdelhalim

2017-08-01

In this article, the flow and heat transfer of a non-Newtonian nanofluid between two coaxial cylinders through a porous medium has been investigated. The velocity, temperature, and nanoparticles concentration of the present mathematical model are governed by a system of nonlinear ordinary differential equations. The objective of this article is to obtain new exact solutions for the temperature and the nanoparticles concentration and, therefore, compare them with the previous approximate results in the literature. Moreover, the velocity equation has been numerically solved. The effects of the pressure gradient, thermophoresis, third-grade, Brownian motion, and porosity parameters on the included phenomena have been discussed through several tables and plots. It is found that the velocity profile is increased by increasing the pressure gradient parameter, thermophoresis parameter (slightly), third-grade parameter, and Brownian motion parameter (slightly); however, it decreases with an increase in the porosity parameter and viscosity power index. In addition, the temperature and the nanoparticles concentration reduce with the strengthen of the Brownian motion parameter, while they increase by increasing the thermophoresis parameter. Furthermore, the numerical solution and the physical interpretation in the literature for the same problem have been validated with the current exact analysis, where many remarkable differences and errors have been concluded. Therefore, the suggested analysis may be recommended with high trust for similar problems.

Autonomous Sensors for Measuring Continuously the Moisture and Salinity of a Porous Medium

Science.gov (United States)

Chavanne, Xavier; Frangi, Jean-Pierre

2017-01-01

The article describes a new field sensor to monitor continuously in situ moisture and salinity of a porous medium via measurements of its dielectric permittivity, conductivity and temperature. It intends to overcome difficulties and biases encountered with sensors based on the same sensitivity principle. Permittivity and conductivity are determined simultaneously by a self-balanced bridge, which measures directly the admittance of sensor electrodes in medium. All electric biases are reduced and their residuals taken into account by a physical model of the instrument, calibrated against reference fluids. Geometry electrode is optimized to obtain a well representative sample of the medium. The sensor also permits acquiring a large amount of data at high frequency (six points every hour, and even more) and to access it rapidly, even in real time, owing to autonomy capabilities and wireless communication. Ongoing developments intend to simplify and standardize present sensors. Results of field trials of prototypes in different environments are presented. PMID:28492471

Autonomous Sensors for Measuring Continuously the Moisture and Salinity of a Porous Medium.

Science.gov (United States)

Chavanne, Xavier; Frangi, Jean-Pierre

2017-05-11

The article describes a new field sensor to monitor continuously in situ moisture and salinity of a porous medium via measurements of its dielectric permittivity, conductivity and temperature. It intends to overcome difficulties and biases encountered with sensors based on the same sensitivity principle. Permittivity and conductivity are determined simultaneously by a self-balanced bridge, which measures directly the admittance of sensor electrodes in medium. All electric biases are reduced and their residuals taken into account by a physical model of the instrument, calibrated against reference fluids. Geometry electrode is optimized to obtain a well representative sample of the medium. The sensor also permits acquiring a large amount of data at high frequency (six points every hour, and even more) and to access it rapidly, even in real time, owing to autonomy capabilities and wireless communication. Ongoing developments intend to simplify and standardize present sensors. Results of field trials of prototypes in different environments are presented.

Magnetogravitational stability of resistive plasma through porous medium with thermal conduction and FLR corrections

International Nuclear Information System (INIS)

Vaghela, D.S.; Chhajlani, R.K.

1989-01-01

The problem of stability of self gravitating magnetized plasma in porous medium is studied incorporating electrical resistivity, thermal conduction and FLR corrections. Normal mode analysis is applied to derive the dispersion relation. Wave propagation is discussed for parallel and perpendicular directions to the magnetic field. Applying Routh Hurwitz Criterion the stability of the medium is discussed and it is found that Jeans' criterion determines the stability of the medium. Magnetic field, porosity and resistivity of the medium have no effect on Jeans' Criterion in longitudinal direction. For perpendicular direction, in case of resistive medium Jeans' expression remains unaffected by magnetic field but for perfectly conducting medium magnetic field modifies the Jeans' expression to show the stabilizing effect. Thermal conductivity affects the sonic mode by making the process isothermal instead of adiabatic. Porosity of the medium is effective only in case of perpendicular direction to magnetic field for perfectly conducting plasma as it reduces the stabilizing effect of magnetic field. For longitudinal wave propagation, though Finite Larmor Radius (FLR) corrections have no effect on sonic mode but it changes the growth rate for Alfven mode. For transverse wave propagation FLR corrections and porosity affect the Jeans' expression in case of non-viscous medium but viscosity of the medium removes the effect of FLR and porosity on Jeans' condition. (author)

Finite medium Green's function solutions to nuclide transport in porous media

International Nuclear Information System (INIS)

Oston, S.G.

1979-01-01

Current analytical techniques for predicting the transport of nuclides in porous materials center on the Green's function approach - i.e., determining the response characteristics of a geologic pathway to an impulse function input. To data, the analyses all have set the boundary conditions needed to solve the 1-D transport equation as though each pathway were infinite in length. The purpose of this work is to critically examine the effect that this infinite pathway assumption has on Green's function models of nuclide transport in porous media. The work described herein has directly attacked the more difficult problem of obtaining suitable Green's functions for finite pathways whose dimensions, in fact, may not be much greater than the diffusion length. Two different finite media Green's functions describing the nuclide mass flux have been determined, depending on whether the pathway is terminated by a high or a low flow resistance at the outlet end. Pulse shapes and peak amplitudes have been computed for each Green's function over a wide range of geohydrologic parameters. These results have been compared to both infinite and semi-infinite medium solutions. It was found that predicted pulse shapes are quite sensitive to selection of a Green's function model for short pathways only. For long pathways all models tend toward a symmetric Gaussian flux-time history at the outlet. Thus, the results of our previous waste transport studies using the infinite pathway assumption are still generally valid because they always included at least one long pathway. It was also found that finite medium models offer some unique computational advantages for evaluating nuclide transport in a series of connecting pathways

Coupled processes in single fractures, double fractures and fractured porous media

International Nuclear Information System (INIS)

Tsang, C.F.

1986-12-01

The emplacement of a nuclear waste repository in a fractured porous medium provides a heat source of large dimensions over an extended period of time. It also creates a large cavity in the rock mass, changing significantly the stress field. Such major changes induce various coupled thermohydraulic, hydromechanic and hydrochemical transport processes in the environment around a nuclear waste repository. The present paper gives, first, a general overview of the coupled processes involving thermal, mechanical, hydrological and chemical effects. Then investigations of a number of specific coupled processes are described in the context of fluid flow and transport in a single fracture, two intersecting fractures and a fractured porous medium near a nuclear waste repository. The results are presented and discussed

Heating of Porous Icy Dust Aggregates

Energy Technology Data Exchange (ETDEWEB)

Sirono, Sin-iti [Earth and Environmental Sciences, Nagoya University, Tikusa-ku, Furo-cho, Nagoya 464-8601 (Japan)

2017-06-10

At the beginning of planetary formation, highly porous dust aggregates are formed through coagulation of dust grains. Outside the snowline, the main component of an aggregate is H{sub 2}O ice. Because H{sub 2}O ice is formed in amorphous form, its thermal conductivity is extremely small. Therefore, the thermal conductivity of an icy dust aggregate is low. There is a possibility of heating inside an aggregate owing to the decay of radionuclides. It is shown that the temperature increases substantially inside an aggregate, leading to crystallization of amorphous ice. During the crystallization, the temperature further increases sufficiently to continue sintering. The mechanical properties of icy dust aggregates change, and the collisional evolution of dust aggregates is affected by the sintering.

Evaluation of Heat Losses Behind the Front of the Detonation Moving Along the Metallic Porous Surface

Directory of Open Access Journals (Sweden)

S. V. Golovastov

2016-01-01

Full Text Available The paper considers a computational technique of the heat flow from the hot products of detonation combustion into the porous coating and estimates the efficiency of the coating layer that results in slowing the flame front down with disregard the transverse displacement of the combustion products weight of a hydrogen-air mixture.Initial thermodynamic parameters of combustion products on the porous coating surface have been estimated. A drag (stagnation temperature of flow was determined.The statement of task was to calculate the heat flow into the long cylindrical metal fiber with radius of 15 μm. The reference values of heat capacity and heat diffusivity were used to estimate a thermal diffusivity in a wide range of temperatures. An approximation of the parameters is given for a wide range of temperatures.The calculation algorithm using an explicit four-point scheme is presented. The convergence and accuracy of the results were confirmed. The theoretical estimation using cylindrical Bessel functions was made to prove the accuracy of the results.Total heat loss was estimated using the photos of moving detonation front and hot combustion gases.Comparison of the total heat loss and the amount of energy absorbed by a single fiber allowed us to find that the porous coating thickness, resulting in attenuation of detonation wave, is efficient.

Heat and Mass Transfer Model in Freeze-Dried Medium

Science.gov (United States)

Alfat, Sayahdin; Purqon, Acep

2017-07-01

There are big problems in agriculture sector every year. One of the major problems is abundance of agricultural product during the peak of harvest season that is not matched by an increase in demand of agricultural product by consumers, this causes a wasted agricultural products. Alternative way was food preservation by freeze dried method. This method was already using heat transfer through conduction and convection to reduce water quality in the food. The main objective of this research was to design a model heat and mass transfer in freeze-dried medium. We had two steps in this research, the first step was design of medium as the heat injection site and the second was simulate heat and mass transfer of the product. During simulation process, we use physical property of some agriculture product. The result will show how temperature and moisture distribution every second. The method of research use finite element method (FEM) and will be illustrated in three dimensional.

Effect of magnetic field on Rayleigh-Taylor instability of quantum and stratified plasma in porous medium

International Nuclear Information System (INIS)

Sharma, P.K.; Tiwari, Anita; Argal, Shraddha; Chhajlani, R.K.

2013-01-01

This paper is devoted to an investigation of Quantum effects and magnetic field effects on the Rayleigh Taylor instability of two superposed incompressible fluids in bounded porous medium. The Quantum magneto hydrodynamic equations are solved by using normal mode method and a dispersion relation is obtained. The dispersion relation is derived for the case where plasma is bounded by two rigid planes z = 0 and z = h. The Rayleigh Taylor instability growth rate and stability condition of the medium is discussed in the presence of quantum effect, magnetic field, porosity and permeability. It is found that the magnetic field and medium porosity have stabilizing influence while permeability has destabilizing influence on the Rayleigh Taylor instability. (author)

A Finite Difference Scheme for Double-Diffusive Unsteady Free Convection from a Curved Surface to a Saturated Porous Medium with a Non-Newtonian Fluid

KAUST Repository

El-Amin, Mohamed

2011-05-14

In this paper, a finite difference scheme is developed to solve the unsteady problem of combined heat and mass transfer from an isothermal curved surface to a porous medium saturated by a non-Newtonian fluid. The curved surface is kept at constant temperature and the power-law model is used to model the non-Newtonian fluid. The explicit finite difference method is used to solve simultaneously the equations of momentum, energy and concentration. The consistency of the explicit scheme is examined and the stability conditions are determined for each equation. Boundary layer and Boussinesq approximations have been incorporated. Numerical calculations are carried out for the various parameters entering into the problem. Velocity, temperature and concentration profiles are shown graphically. It is found that as time approaches infinity, the values of wall shear, heat transfer coefficient and concentration gradient at the wall, which are entered in tables, approach the steady state values.

Radiation and mass transfer effects on an unsteady MHD free convection flow past a heated vertical plate in a porous medium with viscous dissipation

Directory of Open Access Journals (Sweden)

Prasad Ramachandra V.

2007-01-01

Full Text Available An unsteady, two-dimensional, hydromagnetic, laminar free convective boundary-layer flow of an incompressible, Newtonian, electrically-conducting and radiating fluid past an infinite heated vertical porous plate with heat and mass transfer is analyzed, by taking into account the effect of viscous dissipation. The dimensionless governing equations for this investigation are solved analytically using two-term harmonic and non-harmonic functions. Numerical evaluation of the analytical results is performed and graphical results for velocity, temperature and concentration profiles within the boundary layer and tabulated results for the skin-friction coefficient, Nusselt number and Sherwood number are presented and discussed. It is observed that, when the radiation parameter increases, the velocity and temperature decrease in the boundary layer, whereas when thermal and solutal Grashof increases the velocity increases.

Analysis of the processes defining radionuclide migration from deep geological repositories in porous medium

International Nuclear Information System (INIS)

Brazauskaite, A.; Poskas, P.

2004-01-01

Due to the danger of exposure arising from long-lived radionuclides to humans and environment, spent nuclear fuel (SNF) and high level waste (HLW) are not allowed to be disposed of in near surface repositories. There exists an international consensus that such high level and long-lived radioactive wastes are best disposed of in geological repositories using a system of engineered and natural barriers. At present, the geological repository of SNF and HLW has not been realized yet in any country but there is a lot of experience in the assessment of radionuclide migration from deep repositories, investigations of different processes related to the safety of a disposal system. The aim of this study was to analyze the processes related to the radionuclide migration from deep geological repositories in porous medium such as SNF matrix dissolution, release mechanism of radionuclides from SNF matrix, radionuclide solubility, sorption, diffusive, advective transport of radionuclides from the canister and through the engineered and natural barriers. It has been indicated that SNF matrix dissolution, radionuclide solubility and sorption are sensitive to ambient conditions prevailing in the repository. The approaches that could be used for modeling the radionuclide migration from deep repositories in porous medium are also presented. (author)

Carbofuran biodegradation in brackish groundwater and its effect on the hydraulic properties of the porous medium

Science.gov (United States)

Amiaz, Yanai; Ronen, Zeev; Adar, Eilon; Weisbrod, Noam

2015-04-01

A chalk fractured aquitard beneath an industrial site is subjected to intense contamination due to percolation of contaminants from the different facilities operating at the site. In order to reduce further contamination, draining trenches were excavated and filled with coarse gravel (3-4 cm in diameter) forming a porous medium, to which the contaminated groundwater discharges from the fractures surrounding the trenches. This research is aimed at establishing a biodegrading process of high efficiency and performance within the draining trenches. The research includes both field and laboratory experiments. An experimental setup of five columns (50 cm length and 4.5 cm in diameter) was constructed under highly controlled conditions. Over the course of the experiments, the columns were filled with different particle sizes and placed in a temperature controlled chamber. Filtered groundwater (0.2 µm) from the site groundwater, enriched by a model contaminant carbofuran (CRF), was injected to the columns; as two of the columns were inoculated by CRF degrading microorganisms native in the site's groundwater, two columns were inoculated by CRF degrading bacteria from the external environment, and one column was used as a control. During the experiment, measurements were taken from different locations along each column. These include: (a) CRF concentration and (b) hydraulic pressure and solution viscosity (in order to obtain the changes in permeability). A tracer test using uranine was carried out in parallel, in order to obtain the changes in hydraulic parameters. Correlating CRF concentration variations to changes of hydraulic parameters enable the deduction due to the effect that biological activity (under different temperature regimes) has on the hydraulic properties of the porous medium and its effect on the process of contaminant groundwater bodies' remediation. Preliminary results suggest that although biodegradation occurs, microbial activity has minor effect on

Influence of gas hydrates crystals or ice crystals on the permeability of a porous medium; Influence de cristaux d'hydrates de gaz ou de glace sur la permeabilite d'un milieu poreux

Energy Technology Data Exchange (ETDEWEB)

Bonnefoy, O.

2005-03-15

The first part is a bibliographic study. We study the conditions for thermodynamic equilibrium of the hydrates as a bulk medium and the composition of the liquid and solid phases. We then describe the basics of fluid dynamics in a porous medium. Eventually, we merge the two approaches and study the influence of the porous medium on the hydrate stability. An off-shore hydrate field (Blake Ridge) and an on-shore field (Mallik) are precisely described. The latter will be used as a reference case for subsequent numerical simulations. The second part is devoted to the experiments. Their goal is to measure the permeability of a sediment containing crystals. To get closer to natural geologic conditions, crystals are synthesized in absence of free gas. It turns out that hydrates form in a very heterogeneous way in the porous medium, which makes the measurements non representative. We believe that this result has a general character and that, at the laboratory time-scale, it is difficult, to say the least to achieve a uniform distribution of gas hydrates grown from dissolved gas. To circumvent this difficulty, we show, with a theoretical approach, that ice crystals behave much the same way as the hydrate crystals, concerning the Van der Waals forces that govern the agglomeration. This allows us to calculate the Hamaker constant of the hydrates. The second series of experiments focuses on the permeability of a non consolidated porous medium under mechanical stress, where the pores are filled with ice crystals. Two silica beads populations are used to form a porous medium: 3 mm and 0.2 mm. With the large grains, results show two thresholds: for saturations below the lower threshold, the presence of crystals does not modify the permeability. For saturations above the upper threshold, the permeability vanishes almost completely (percolation phenomenon). Between these two limits, the permeability decreases exponentially with the saturation. With the fine grains, the permeability

Interface model conditions for a non-equilibrium heat transfer model for conjugate fluid/porous/solid domains

International Nuclear Information System (INIS)

Betchen, L.J.; Straatman, A.G.

2005-01-01

A mathematical and numerical model for the treatment of conjugate fluid flow and heat transfer problems in domains containing pure fluid, porous, and pure solid regions has been developed. The model is general and physically reasoned, and allows for local thermal non-equilibrium in the porous region. The model is developed for implementation on a simple collocated finite volume grid. Of particular novelty are the conditions implemented at the interfaces between porous regions, and those containing a pure solid or pure fluid. The model is validated by simulation of a three-dimensional porous plug problem for which experimental results are available. (author)

Modeling of filtration of 2-types particles suspension in a porous medium

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Galaguz Yuri

2017-01-01

Full Text Available The filtration problem describes the process of concreting loose soil with a liquefied concrete solution. The filtration of 2-types particles suspension in a homogeneous porous medium with a size-exclusion particles retention mechanism is considered. The difference in the filtration coefficients of 2-types particles leads to the separation of the filtration domain into two zones, in one of which two types of particles are deposited and in another – only particles of one type are deposited. In this paper, the mobile boundary of two zones is calculated, and numerical solution of the problem is calculated.

Investigation of Boiling Heat Transfer of Binary Mixture from Vertical Tube Embedded in porous Media

Institute of Scientific and Technical Information of China (English)

HailongMo; TongzeMa; 等

1996-01-01

Ethanol-water binary mixtures with 7 different mole fractions of ethanol ranging from 0 to 1 were adopted as testing liquids in the experiment.The vertical heating tube was inserted in porous matrix composed of five well sorted glass beads whise diameters range from 0.5 to 4.3mm.Due to the effect of composition,the trend of combination of vapor bubbles was reduced.resulting in the increase of peak heat flux of binary mixture,With the increase of ethanol mole fraction,0.5mm diameter bead of peak heat flux of binary mixture.with the increase of ethanol mole fraction.0.5mm diameter bead had lower value of peak heat flux,while for pure liquid the critical state is difficult to appear,with given diameter of glass bead,there existed an optimum value of mole fraction of ethanol,which was decreased with the increase of bead diameter,A dimensionless heat transfer coefficient was predicted through the introduction of a dimensionless parameter of porous matrix which agreed with the experimental results satisfactorily.

Medium Deep High Temperature Heat Storage

Science.gov (United States)

Bär, Kristian; Rühaak, Wolfram; Schulte, Daniel; Welsch, Bastian; Chauhan, Swarup; Homuth, Sebastian; Sass, Ingo

2015-04-01

Heating of buildings requires more than 25 % of the total end energy consumption in Germany. Shallow geothermal systems for indirect use as well as shallow geothermal heat storage systems like aquifer thermal energy storage (ATES) or borehole thermal energy storage (BTES) typically provide low exergy heat. The temperature levels and ranges typically require a coupling with heat pumps. By storing hot water from solar panels or thermal power stations with temperatures of up to 110 °C a medium deep high temperature heat storage (MDHTS) can be operated on relatively high temperature levels of more than 45 °C. Storage depths of 500 m to 1,500 m below surface avoid conflicts with groundwater use for drinking water or other purposes. Permeability is typically also decreasing with greater depth; especially in the crystalline basement therefore conduction becomes the dominant heat transport process. Solar-thermal charging of a MDHTS is a very beneficial option for supplying heat in urban and rural systems. Feasibility and design criteria of different system configurations (depth, distance and number of BHE) are discussed. One system is designed to store and supply heat (300 kW) for an office building. The required boreholes are located in granodioritic bedrock. Resulting from this setup several challenges have to be addressed. The drilling and completion has to be planned carefully under consideration of the geological and tectonical situation at the specific site.

One-dimensional scanning of moisture in heated porous building materials with NMR.

Science.gov (United States)

van der Heijden, G H A; Huinink, H P; Pel, L; Kopinga, K

2011-02-01

In this paper we present a new dedicated NMR setup which is capable of measuring one-dimensional moisture profiles in heated porous materials. The setup, which is placed in the bore of a 1.5 T whole-body scanner, is capable of reaching temperatures up to 500 °C. Moisture and temperature profiles can be measured quasi simultaneously with a typical time resolution of 2-5 min. A methodology is introduced for correcting temperature effects on NMR measurements at these elevated temperatures. The corrections are based on the Curie law for paramagnetism and the observed temperature dependence of the relaxation mechanisms occurring in porous materials. Both these corrections are used to obtain a moisture content profile from the raw NMR signal profile. To illustrate the methodology, a one-sided heating experiment of concrete with a moisture content in equilibrium with 97% RH is presented. This kind of heating experiment is of particular interest in the research on fire spalling of concrete, since it directly reveals the moisture and heat transport occurring inside the concrete. The obtained moisture profiles reveal a moisture peak building up behind the boiling front, resulting in a saturated layer. To our knowledge the direct proof of the formation of a moisture peak and subsequent moisture clogging has not been reported before. Copyright © 2010 Elsevier Inc. All rights reserved.

On natural convection in enclosures filled with fluid-saturated porous media including viscous dissipation

Energy Technology Data Exchange (ETDEWEB)

Costa, V.A.F. [Departamento de Engenharia Mecanica, Universidade de Aveiro, Campus Universitario de Santiago, 3810-193 Aveiro (Portugal)

2006-07-15

Care needs to be taken when considering the viscous dissipation in the energy conservation formulation of the natural convection problem in fluid-saturated porous media. The unique energy formulation compatible with the First Law of Thermodynamics informs us that if the viscous dissipation term is taken into account, also the work of pressure forces term needs to be taken into account. In integral terms, the work of pressure forces must equal the energy dissipated by viscous effects, and the net energy generation in the overall domain must be zero. If only the (positive) viscous dissipation term is considered in the energy conservation equation, the domain behaves as a heat multiplier, with an heat output greater than the heat input. Only the energy formulation consistent with the First Law of Thermodynamics leads to the correct flow and temperature fields, as well as of the heat transfer parameters characterizing the involved porous device. Attention is given to the natural convection problem in a square enclosure filled with a fluid-saturated porous medium, using the Darcy Law to describe the fluid flow, but the main ideas and conclusions apply equally for any general natural or mixed convection heat transfer problem. It is also analyzed the validity of the Oberbeck-Boussinesq approximation when applied to natural convection problems in fluid-saturated porous media. (author)

Peristaltic Flow of Carreau Fluid in a Rectangular Duct through a Porous Medium

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R. Ellahi

2012-01-01

Full Text Available We have examined the peristaltic flow of Carreau fluid in a rectangular channel through a porous medium. The governing equations of motion are simplified by applying the long wavelength and low Reynolds number approximations. The reduced highly nonlinear partial differential equations are solved jointly by homotopy perturbation and Eigen function expansion methods. The expression for pressure rise is computed numerically by evaluating the numerical integration. The physical features of pertinent parameters have been discussed by plotting graphs of velocity, pressure rise, pressure gradient, and stream functions.

Development of small and medium reactors for power and heat production

International Nuclear Information System (INIS)

Becka, J.

1978-01-01

Data are given on the current state of development of small and medium-power reactors designed mainly for electric power production in small power grids, for heat production for small- and medium-power desalination plants with possible electric power generation, for process steam production and heat development for district heating systems, again combined with electric power generation, and for propelling big and fast passenger ships. A diagram is shown of the primary system of an integrated PWR derived from the Otto Hahn reactor. The family is listed of the standard sizes of the integral INTERATOM company pressurized water reactors. Also listed are the specifications and design of CAS 2CG and AS 3G type reactors used mainly for long-distance heating systems. (J.B.)

Unsteady MHD Mixed Convection Slip Flow of Casson Fluid over Nonlinearly Stretching Sheet Embedded in a Porous Medium with Chemical Reaction, Thermal Radiation, Heat Generation/Absorption and Convective Boundary Conditions.

Science.gov (United States)

Ullah, Imran; Bhattacharyya, Krishnendu; Shafie, Sharidan; Khan, Ilyas

2016-01-01

Numerical results are presented for the effect of first order chemical reaction and thermal radiation on mixed convection flow of Casson fluid in the presence of magnetic field. The flow is generated due to unsteady nonlinearly stretching sheet placed inside a porous medium. Convective conditions on wall temperature and wall concentration are also employed in the investigation. The governing partial differential equations are converted to ordinary differential equations using suitable transformations and then solved numerically via Keller-box method. It is noticed that fluid velocity rises with increase in radiation parameter in the case of assisting flow and is opposite in the case of opposing fluid while radiation parameter has no effect on fluid velocity in the forced convection. It is also seen that fluid velocity and concentration enhances in the case of generative chemical reaction whereas both profiles reduces in the case of destructive chemical reaction. Further, increase in local unsteadiness parameter reduces fluid velocity, temperature and concentration. Over all the effects of physical parameters on fluid velocity, temperature and concentration distribution as well as on the wall shear stress, heat and mass transfer rates are discussed in detail.

Natural convection heat transfer from a horizontal wavy surface in a porous enclosure

International Nuclear Information System (INIS)

Murthy, P.V.S.N.; Kumar, B.V.R.; Singh, P.

1997-01-01

The effect of surface undulations on the natural convection heat transfer from an isothermal surface in a Darcian fluid-saturated porous enclosure has been numerically analyzed using the finite element method on a graded nonuniform mesh system. The flow-driving Rayleigh number Ra together with the geometrical parameters of wave amplitude a, wave phase φ, and the number of waves N considered in the horizontal dimension of the cavity are found to influence the flow and heat transfer process in the enclosure. For Ra around 50 and above, the phenomenon of flow separation and reattachment is noticed on the walls of the enclosure. A periodic shift in the reattachment point from the bottom wall to the adjacent walls in the clockwise direction, leading to the manifestation of cycles of unicellular and bicellular clockwise and counterclockwise flows, is observed, with the phase varying between 0 degree and 350 degree. The counterflow in the secondary circulation zone is intensified with the increase in the value of Ra. The counterflow on the wavy wall hinders the heat transfer into the system. An increase in either wave amplitude or the number of waves considered per unit length decreases the global heat flux into the system. Only marginal changes in global heat flux are noticed with increasing Ra. On the whole, the comparison of global heat flux results in the wavy wall case with those of the horizontal flat wall case shows that, in a porous enclosure, the wavy wall reduces the heat transfer into the system

MHD flow of a dusty viscoelastic liquid through a porous medium between two inclined parallel plates

International Nuclear Information System (INIS)

Singh, A.K.; Singh, N.P.

1996-01-01

Magnetohydrodynamic flow of a dusty viscoelastic liquid (Oldroyd B-liquid) through a porous medium between two parallel plates inclined to the horizon has been studied. The liquid velocity, dust particle velocity and flux of flow have been obtained. Earlier results have been deduced as particular cases of the present investigation. The physical situation of the motion has been discussed graphically. (author)

Large-scale model of flow in heterogeneous and hierarchical porous media

Science.gov (United States)

Chabanon, Morgan; Valdés-Parada, Francisco J.; Ochoa-Tapia, J. Alberto; Goyeau, Benoît

2017-11-01

Heterogeneous porous structures are very often encountered in natural environments, bioremediation processes among many others. Reliable models for momentum transport are crucial whenever mass transport or convective heat occurs in these systems. In this work, we derive a large-scale average model for incompressible single-phase flow in heterogeneous and hierarchical soil porous media composed of two distinct porous regions embedding a solid impermeable structure. The model, based on the local mechanical equilibrium assumption between the porous regions, results in a unique momentum transport equation where the global effective permeability naturally depends on the permeabilities at the intermediate mesoscopic scales and therefore includes the complex hierarchical structure of the soil. The associated closure problem is numerically solved for various configurations and properties of the heterogeneous medium. The results clearly show that the effective permeability increases with the volume fraction of the most permeable porous region. It is also shown that the effective permeability is sensitive to the dimensionality spatial arrangement of the porous regions and in particular depends on the contact between the impermeable solid and the two porous regions.

Heat transfer studies in waste repository design

International Nuclear Information System (INIS)

Boehm, R.F.; Chen, Y.T.; Izzeldin, A.; Kuharic, W.; Sudan, N.

1994-01-01

The main task of this project is the development of visualization methods in heat transfer through porous media. Experiments have been performed related to the determination of the wavelength that gives equality of the refractive indices of the porous material and the liquid. The work has been accomplished using the calibration setup consisting of a 2-in. long test cell filled with 2-mm diameter soda-lime glass beads. A supplemental task is an unsaturated flow experiment with heat transfer in porous media. For this work the medium of interest in quartz beads. Essentially two-dimensional flows of admitted water are able to be examined. During this quarter, the setup and calibration of the experimental instrumentation was done. Also the modification of the main experimental tank and the inflow system was carried out. Initial testing was done

Numerical simulation on coolant flow and heat transfer in core

International Nuclear Information System (INIS)

Yao Zhaohui; Wang Xuefang; Shen Mengyu

1997-01-01

To simulate the coolant flow and the heat transfer characteristics of a core, a computer code, THAPMA (Thermal Hydraulic Analysis Porous Medium Analysis) has been developed. In THAPMA code, conservation equations are based on a porous-medium formulation, which uses four parameters, i.e, volume porosity, directional surface porosity, distributed resistance, and distributed heat source (sink), to model the effects of fuel rods and other internal solid structures on flow and heat transfer. Because the scheme and the solution are very important in accuracy and speed of calculation, a new difference scheme (WSUC) has been used in the energy equation, and a modified PISO solution method have been employed to simulate the steady/transient states. The code has been proved reliable and can effectively solve the transient state problem by several numerical tests. According to the design of Qinshan NPP-II, the flow and heat transfer phenomena in reactor core have been numerically simulated. The distributions of the velocity and the temperature can provide a theoretical basis for core design and safety analysis

Mixed convection in fluid superposed porous layers

CERN Document Server

Dixon, John M

2017-01-01

This Brief describes and analyzes flow and heat transport over a liquid-saturated porous bed. The porous bed is saturated by a liquid layer and heating takes place from a section of the bottom. The effect on flow patterns of heating from the bottom is shown by calculation, and when the heating is sufficiently strong, the flow is affected through the porous and upper liquid layers. Measurements of the heat transfer rate from the heated section confirm calculations. General heat transfer laws are developed for varying porous bed depths for applications to process industry needs, environmental sciences, and materials processing. Addressing a topic of considerable interest to the research community, the brief features an up-to-date literature review of mixed convection energy transport in fluid superposed porous layers.

Porosity effects in flame length of the porous burners

Directory of Open Access Journals (Sweden)

Fatemeh Bahadori

2014-10-01

Full Text Available Furnaces are the devices for providing heat to the industrial systems like boilers, gas turbines and etc. The main challenge of furnaces is emission of huge air pollutants. However, porous burners produce less contaminant compared to others. The quality of the combustion process in the porous burners depends on the length of flame in the porous medium. In this paper, the computational fluid dynamic (CFD is used to investigate the porosity effects on the flame length of the combustion process in porous burner. The simulation results demonstrate that increasing the porosity increases the flame length and the combustion zone extends forward. So, combustion quality increases and production of carbon monoxide decrease. It is possible to conclude that temperature distribution in low porosity burner is lower and more uniform than high porosity one. Therefore, by increasing the porosity of the burner, the production of nitrogen oxides increases. So, using an intermediate porosity in the burner appears to be reasonable.

Numerical simulation for a two-phase porous medium flow problem with rate independent hysteresis

International Nuclear Information System (INIS)

Brokate, M.; Botkin, N.D.; Pykhteev, O.A.

2012-01-01

The paper is devoted to the numerical simulation of a multiphase flow in porous medium with a hysteretic relation between the capillary pressures and the saturations of the phases. The flow model we use is based on Darcy's law. The hysteretic relation between the capillary pressures and the saturations is described by a play-type hysteresis operator. We propose a numerical algorithm for treating the arising system of equations, discuss finite element schemes and present simulation results for the case of two phases.

Experimental research on thermal characteristics of a hybrid thermocline heat storage system

International Nuclear Information System (INIS)

Yin, Huibin; Ding, Jing; Yang, Xiaoxi

2014-01-01

Considering the high-temperature thermal utilization of solar energy as the research background in this paper and focussing on the heat storage process, a kind of hybrid thermocline heat storage method in multi-scale structure and relevant experimental systems are designed by using the mixed molten nitrate salt as the heat storage medium and two representative porous materials, i.e. zirconium ball and silicon carbide (SiC) foam, as the heat storage fillers. The fluid flow and heat storage performance of molten salt in multi-scale structure are experimentally investigated. The results show that the theoretical heat storage efficiencies amongst the three experimental heat storage manners are less than 80% because of the existence of thermocline layers. Comparing to the single-phase molten salt heat storage, the two hybrid thermocline heat storage manners with porous fillers lead to a certain decrease in the effective heat storage capacity. The presence of porous fillers can also help to maintain the molten salt fluid as ideal gravity flow or piston flow and partially replace expensive molten salt. Therefore, it requires a combination of heat storage capacity and economical consideration for optimization design when similar spherical particles or foam ceramics are employed as the porous fillers. -- Highlights: • A hybrid thermocline heat storage method in multi-scale structure is developed. • The fluid flow and heat storage performance are experimentally investigated. • Stable thermocline can form in single tank for the experimental cases. • The hybrid thermocline heat storage with porous filler is promising

Numerical artifacts in the Generalized Porous Medium Equation: Why harmonic averaging itself is not to blame

Science.gov (United States)

Maddix, Danielle C.; Sampaio, Luiz; Gerritsen, Margot

2018-05-01

The degenerate parabolic Generalized Porous Medium Equation (GPME) poses numerical challenges due to self-sharpening and its sharp corner solutions. For these problems, we show results for two subclasses of the GPME with differentiable k (p) with respect to p, namely the Porous Medium Equation (PME) and the superslow diffusion equation. Spurious temporal oscillations, and nonphysical locking and lagging have been reported in the literature. These issues have been attributed to harmonic averaging of the coefficient k (p) for small p, and arithmetic averaging has been suggested as an alternative. We show that harmonic averaging is not solely responsible and that an improved discretization can mitigate these issues. Here, we investigate the causes of these numerical artifacts using modified equation analysis. The modified equation framework can be used for any type of discretization. We show results for the second order finite volume method. The observed problems with harmonic averaging can be traced to two leading error terms in its modified equation. This is also illustrated numerically through a Modified Harmonic Method (MHM) that can locally modify the critical terms to remove the aforementioned numerical artifacts.

Numerical study of steady/unsteady flow and heat transfer in porous media using a characteristics-based matrix-free implicit FV method on unstructured grids

International Nuclear Information System (INIS)

Chiem, Kok Siong; Zhao Yong

2004-01-01

In this study, a high-resolution characteristic-based finite-volume (FV) method on unstructured grids [Int. J. Numer. Method Eng. 50 (2001) 11; Int. J. Heat Fluid Flow 21 (2000) 432] is extended by a matrix-free implicit dual-time stepping scheme for the numerical simulation of steady and unsteady flow and heat transfer with porous media. The method has been used to study the characteristics of a complex problem: flow and heat transfer in a channel with multiple discrete porous blocks, which was originally proposed by Huang and Vafai [J. Thermophys. Heat Transfer 8 (3) (1994) 563]. In addition, flow and heat transfer in a channel partially or fully filled with porous layers and containing solid protruding blocks with constant heat flux on its lower surface are also investigated in details. Hydrodynamic and heat transfer results are reported for both steady and transient flow cases. In particular, the effects of Darcy and Reynolds numbers on heat transfer augmentation and pressure loss are studied. An in-depth discussion of the formation and variation of recirculation is presented and the existence of optimum porous insert is demonstrated. At high Reynolds numbers the flow in the porous channel exhibits a cyclic characteristics although unlike the non-porous channel flow, the cyclic vortex development is only restricted to a small area behind the last solid block, while temperature changes more slowly and does not exhibit cyclic variations over a long period of time. It is shown that for all the cases studied altering some parametric values can have significant and interesting effects on both flow pattern as well as heat transfer characteristics

Direct measurements of adsorption heats of hydrogen on nano-porous carbons

International Nuclear Information System (INIS)

Akihiko Matsumoto; Kazumasa Yamamoto; Tomoyuki Miyata

2005-01-01

Since a exciting report of hydrogen storage in single-walled carbon nano-tubes by Dillon and his colleagues, nano-porous carbon materials, such as carbon nano-tubes, carbon nano-horns and micro-porous activated carbon, have attracted considerable attention as hydrogen storage materials. Adsorption plays a predominating role in the hydrogen storage process on solid surfaces. The adsorption is a spontaneous process, which is caused by interaction between gas molecules and surface, hence, it is always exothermic process and observed as adsorption heats. For this reason, direct measurement of the adsorption heats by adsorption micro-calorimetry would provide quantitative information on the strength of adsorption interaction and the adsorption mechanism. However, the adsorption amounts of hydrogen on carbon materials are far less than those of condensable vapors near room temperature due to low critical temperature of hydrogen (33.2 K), therefore, the adsorption heats can not be determined accurately at conventional measurement conditions near room temperature and the atmospheric pressure. This contribution reports the calorimetric characterization of hydrogen adsorption on nano-porous carbon materials at low temperature and high-pressure conditions. The high-pressure adsorption apparatus consists of a volumetric adsorption line connected to a twin-conduction type microcalorimeter. Activated carbon fibers (ACF, Ad'all Co.) of different micro-pore sizes (Table 1) were used as model adsorbents. Each ACF has slit-shaped micropores of uniform size. The adsorption isotherms and differential heats of adsorption at high-pressure region from 0 to 10 MPa were simultaneously measured at isothermal condition from 203 to 298 K. The adsorption isotherms on ACF were of Henry type regardless of adsorption temperature and pore width; the uptakes increased linearly with equilibrium pressure. The adsorption isotherm at lower sorption temperature tended to show higher sorptivity. The

Porous debris behavior modeling of QUENCH-02, QUENCH-03 and QUENCH-09 experiments

International Nuclear Information System (INIS)

Kisselev, A.E.; Kobelev, G.V.; Strizhov, V.F.; Vasiliev, A.D.

2006-01-01

The heat-up, melting, relocation, hydrogen generation phenomena, relevant for high-temperature stages both in a reactor case and small-scale integral tests like QUENCH, are governed in particular by heat and mass transfer in porous debris and molten pools which are formed in the core region. Porous debris formation and behavior in QUENCH experiments (QUENCH-02, QUENCH-03, QUENCH-09) plays a considerable role and its adequate modeling is important for thermal analysis. In particular, the analysis of QUENCH experiments shows that the major hydrogen release takes place in debris and melt regions formed in the upper part of the fuel assembly. The porous debris model was implemented in the Russian best estimate numerical code RATEG/SVECHA/HEFEST developed for modelling thermal hydraulics and severe accident phenomena in a reactor. The original approach for debris evolution is developed in the model from classical principles using a set of parameters including debris porosity; average particle diameter; temperatures and mass fractions of solid, liquid and gas phases; specific interface areas between different phases; effective thermal conductivity of each phase, including radiative heat conductivity; mass and energy fluxes through the interfaces. The debris model is based on the system of continuity, momentum and energy conservation equations, which consider the dynamics of volume-averaged velocities and temperatures of fluid, solid and gaseous phases of porous debris. The model is used for calculation of QUENCH experiments. The results obtained by the model are compared to experimental data concerning different aspects of thermal behavior: thermal hydraulics of porous debris, radiative heat transfer in a porous medium, the generalized melting and refreezing behavior of materials, hydrogen production. (author)

Coupled heat and groundwater flow in porous rock

International Nuclear Information System (INIS)

Rae, J.; Robinson, P.C.; Wickens, L.M.

1983-01-01

There are a number of technical areas where coupled heat and flow problems occur for water in porous rock. The area of most interest to the authors has been the possible disposal underground of high-level radioactive waste. High-level waste can emit enough heat to drive significant flows by buoyancy effects and groundwater flow is expected to be the chief transport process for solute leached from such a repository. The possible disposal of radioactive waste under the seabed raises many similar questions and needs similar techniques to find answers. Other areas where related questions arise are the storage and retrieval of hot water in underground reservoirs, the attempts to extract useful geothermal energy by pumping water into fracture systems in hot rock and in certain thermal techniques for persuading oil to flow in tight reservoirs. The authors address questions in a rather general way and give examples which lie more in the area of waste disposal

Using a quasi-heat-pulse method to determine heat and moisture transfer properties for porous orthotropic wood products or cellular solid materials

Science.gov (United States)

M. A. Dietenberger

2006-01-01

Understanding heat and moisture transfer in a wood specimen as used in the K-tester has led to an unconventional numerical solution arid intriguing protocol to deriving the transfer properties. Laplace transform solutions of Luikov’s differential equations are derived for one-dimensional heat and moisture transfer in porous hygroscopic orthotropic materials and for a...

The effects of radiogenic heat on groundwater flow

International Nuclear Information System (INIS)

Beddoes, R.J.; Tammemagi, H.Y.

1986-03-01

The effects of radiogenic heat released by a nuclear waste repository on the groundwater flow in the neighbouring rock mass is reviewed. The report presents an overview of the hydrogeologic properties of crystalline rocks in the Canadian Shield and also describes the mathematical theory of groundwater flow and heat transfer in both porous media and fractured rock. Numerical methods for the solution of the governing equations are described. A number of case histories are described where analyses of flow systems have been performed both with and without radiogenic heat sources. A number of relevant topics are reviewed such as the role of the porous medium model, boundary conditions and, most importantly, the role of complex coupled processes where the effects of heat and water flow are intertwined with geochemical and mechanical processes. The implications to radioactive waste disposal are discussed

Integrated compartmental model for describing the transport of solute in a fractured porous medium. [FRACPORT

Energy Technology Data Exchange (ETDEWEB)

DeAngelis, D.L.; Yeh, G.T.; Huff, D.D.

1984-10-01

This report documents a model, FRACPORT, that simulates the transport of a solute through a fractured porous matrix. The model should be useful in analyzing the possible transport of radionuclides from shallow-land burial sites in humid environments. The use of the model is restricted to transport through saturated zones. The report first discusses the general modeling approach used, which is based on the Integrated Compartmental Method. The basic equations of solute transport are then presented. The model, which assumes a known water velocity field, solves these equations on two different time scales; one related to rapid transport of solute along fractures and the other related to slower transport through the porous matrix. FRACPORT is validated by application to a simple example of fractured porous medium transport that has previously been analyzed by other methods. Then its utility is demonstrated in analyzing more complex cases of pulses of solute into a fractured matrix. The report serves as a user's guide to FRACPORT. A detailed description of data input, along with a listing of input for a sample problem, is provided. 16 references, 18 figures, 3 tables.

METAL CHIP HEATING PROCESS INVESTIGATION (Part I

Directory of Open Access Journals (Sweden)

O. M. Dyakonov

2007-01-01

Full Text Available The main calculation methods for heat- and mass transfer in porous heterogeneous medium have been considered. The paper gives an evaluation of the possibility to apply them for calculation of metal chip heating process. It has been shown that a description of transfer processes in a chip has its own specific character that is attributed to difference between thermal and physical properties of chip material and lubricant-coolant components on chip surfaces. It has been determined that the known expressions for effective heat transfer coefficients can be used as basic ones while approaching mutually penetrating continuums. A mathematical description of heat- and mass transfer in chip medium can be considered as a basis of mathematical modeling, numerical solution and parameter optimization of the mentioned processes.

Entropy generation analysis of the revised Cheng-Minkowycz problem for natural convective boundary layer flow of nanofluid in a porous medium

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Rashidi Mohammad Mehdi

2015-01-01

Full Text Available The similar solution on the equations of the revised Cheng-Minkowycz problem for natural convective boundary layer flow of nanofluid through a porous medium gives (using an analytical method, a system of non-linear partial differential equations which are solved by optimal homotopy analysis method. Effects of various drastic parameters on the fluid and heat transfer characteristics have been analyzed. A very good agreement is observed between the obtained results and the numerical ones. The entropy generation has been derived and a comprehensive parametric analysis on that has been done. Each component of the entropy generation has been analyzed separately and the contribution of each one on the total value of entropy generation has been determined. It is found that the entropy generation as an important aspect of the industrial applications has been affected by various parameters which should be controlled to minimize the entropy generation.

Finite element computation of multi-physical micropolar transport phenomena from an inclined moving plate in porous media

Science.gov (United States)

Shamshuddin, MD.; Anwar Bég, O.; Sunder Ram, M.; Kadir, A.

2018-02-01

Non-Newtonian flows arise in numerous industrial transport processes including materials fabrication systems. Micropolar theory offers an excellent mechanism for exploring the fluid dynamics of new non-Newtonian materials which possess internal microstructure. Magnetic fields may also be used for controlling electrically-conducting polymeric flows. To explore numerical simulation of transport in rheological materials processing, in the current paper, a finite element computational solution is presented for magnetohydrodynamic, incompressible, dissipative, radiative and chemically-reacting micropolar fluid flow, heat and mass transfer adjacent to an inclined porous plate embedded in a saturated homogenous porous medium. Heat generation/absorption effects are included. Rosseland's diffusion approximation is used to describe the radiative heat flux in the energy equation. A Darcy model is employed to simulate drag effects in the porous medium. The governing transport equations are rendered into non-dimensional form under the assumption of low Reynolds number and also low magnetic Reynolds number. Using a Galerkin formulation with a weighted residual scheme, finite element solutions are presented to the boundary value problem. The influence of plate inclination, Eringen coupling number, radiation-conduction number, heat absorption/generation parameter, chemical reaction parameter, plate moving velocity parameter, magnetic parameter, thermal Grashof number, species (solutal) Grashof number, permeability parameter, Eckert number on linear velocity, micro-rotation, temperature and concentration profiles. Furthermore, the influence of selected thermo-physical parameters on friction factor, surface heat transfer and mass transfer rate is also tabulated. The finite element solutions are verified with solutions from several limiting cases in the literature. Interesting features in the flow are identified and interpreted.

A mathematical theorem on the onset of Couple-Stress fluid permeated with suspended dust particles saturating a porous medium

Directory of Open Access Journals (Sweden)

G Rana

2016-09-01

Full Text Available In this paper, the effect of suspended particles on thermal convection in Couple-Stress fluid saturating a porous medium is considered. By applying linear stability theory and normal mode analysis method, a mathematical theorem is derived which states that the viscoelastic thermal convection at marginal state, cannot manifest as stationary convection if the thermal Rayleigh number R, the medium permeability parameter Pl, the couple-stress parameter F and suspended particles parameter B, satisfy the inequality

A generalized power-law scaling law for a two-phase imbibition in a porous medium

KAUST Repository

El-Amin, Mohamed

2013-11-01

Dimensionless time is a universal parameter that may be used to predict real field behavior from scaled laboratory experiments in relation to imbibition processes in porous media. Researchers work to nondimensionalize the time has been through the use of parameters that are inherited to the properties of the moving fluids and the porous matrix, which may be applicable to spontaneous imbibition. However, in forced imbibition, the dynamics of the process depends, in addition, on injection velocity. Therefore, we propose the use of scaling velocity in the form of a combination of two velocities, the first of which (the characteristic velocity) is defined by the fluid and the porous medium parameters and the second is the injection velocity, which is a characteristic of the process. A power-law formula is suggested for the scaling velocity such that it may be used as a parameter to nondimensionalize time. This may reduce the complexities in characterizing two-phase imbibition through porous media and works well in both the cases of spontaneous and forced imbibition. The proposed scaling-law is tested against some oil recovery experimental data from the literature. In addition, the governing partial differential equations are nondimensionalized so that the governing dimensionless groups are manifested. An example of a one-dimensional countercurrent imbibition is considered numerically. The calculations are carried out for a wide range of Ca and Da to illustrate their influences on water saturation as well as relative water/oil permeabilities. © 2013 Elsevier B.V.

A generalized power-law scaling law for a two-phase imbibition in a porous medium

KAUST Repository

El-Amin, Mohamed; Salama, Amgad; Sun, Shuyu

2013-01-01

Dimensionless time is a universal parameter that may be used to predict real field behavior from scaled laboratory experiments in relation to imbibition processes in porous media. Researchers work to nondimensionalize the time has been through the use of parameters that are inherited to the properties of the moving fluids and the porous matrix, which may be applicable to spontaneous imbibition. However, in forced imbibition, the dynamics of the process depends, in addition, on injection velocity. Therefore, we propose the use of scaling velocity in the form of a combination of two velocities, the first of which (the characteristic velocity) is defined by the fluid and the porous medium parameters and the second is the injection velocity, which is a characteristic of the process. A power-law formula is suggested for the scaling velocity such that it may be used as a parameter to nondimensionalize time. This may reduce the complexities in characterizing two-phase imbibition through porous media and works well in both the cases of spontaneous and forced imbibition. The proposed scaling-law is tested against some oil recovery experimental data from the literature. In addition, the governing partial differential equations are nondimensionalized so that the governing dimensionless groups are manifested. An example of a one-dimensional countercurrent imbibition is considered numerically. The calculations are carried out for a wide range of Ca and Da to illustrate their influences on water saturation as well as relative water/oil permeabilities. © 2013 Elsevier B.V.

Numerical simulation for a two-phase porous medium flow problem with rate independent hysteresis

KAUST Repository

Brokate, M.

2012-05-01

The paper is devoted to the numerical simulation of a multiphase flow in porous medium with a hysteretic relation between the capillary pressures and the saturations of the phases. The flow model we use is based on Darcys law. The hysteretic relation between the capillary pressures and the saturations is described by a play-type hysteresis operator. We propose a numerical algorithm for treating the arising system of equations, discuss finite element schemes and present simulation results for the case of two phases. © 2011 Elsevier B.V. All rights reserved.

Heat and Water Transport in Soils and Across the Soil-Atmosphere Interface: Comparison of Model Concepts

DEFF Research Database (Denmark)

Vanderborght, Jan; Smits, Kathleen; Mosthaf, Klaus

Evaporation from the soil surface represents a water flow and transport process in a porous medium that is coupled with free air flow and with heat fluxes in the system. We give an overview of different model concepts that are used to describe this process. These range from non-isothermal two......-phase flow two-component transport in the porous medium that is coupled with one-phase flow two-component transport in the free air to isothermal water flow in the porous with upper boundary conditions defined by a potential evaporation flux when available energy and transfer to the free air flow...... models were found. The effect of vapor flow in the porous medium on cumulative evaporation could be evaluated using the desorptivity, Sevap, which represents a weighted average of liquid and vapor diffusivity over the range of soil water contents between the soil surface water content and the initial...

Heat and Mass Transfer in a High-Porous Low-Temperature Thermal Insulation in Real Operating Conditions

Directory of Open Access Journals (Sweden)

Polovnikov Vyacheslav Yu.

2015-01-01

Full Text Available The results of numerical simulation of heat and mass transfer in a high-porous low-temperature insulation in conditions of insulation freezing, a moisture migration to the front of phase transition and a condensation forming on an outer contour of interaction were obtained. Values of heat leakage were established.

CALCULATION OF LONG-TERM FILTRATION IN A POROUS MEDIUM

Directory of Open Access Journals (Sweden)

Ludmila I. Kuzmina

2018-03-01

Full Text Available he filtration problem in a porous medium is an important part of underground hydromechanics. Filtration of suspensions and colloids determines the processes of strengthening the soil and creating waterproof walls in the ground while building the foundations of buildings and underground structures. It is assumed that the formation of a deposit is dominated by the size-exclusion mechanism of pore blocking: solid particles pass freely through large pores and get stuck at the inlet of pores smaller than the diameter of the particles. A one-dimensional mathematical model for the filtration of a monodisperse suspension includes the equation for the mass balance of suspended and retained particles and the kinetic equation for the growth of the deposit. For the blocking filtration coefficient with a double root, the exact solution is given implicitly. The asymptotics of the filtration problem is constructed for large time. The numerical calculation of the problem is carried out by the finite differences method. It is shown that asymptotic approximations rapidly converge to a solution with the increase of the expansion order.

The Influence of Uniform Suction/Injection on Heat Transfer of MHD Hiemenz Flow in Porous Media

DEFF Research Database (Denmark)

Ghsemi, E; Soleimani, S; Barari, Amin

2012-01-01

The steady two-dimensional laminar forced magneto-hydrodynamic (MHD) Hiemenz flow against a flat plate with variable wall temperature in a porous medium is analyzed. The transformed nonlinear boundary-layer equations are solved analytically by homotopy analysis method (HAM). Results for the veloc...

Effects of heat treatment on microstructure and mechanical behaviour of additive manufactured porous Ti6Al4V

Science.gov (United States)

Ahmadi, S. M.; Jain, R. K. Ashok Kumar; Zadpoor, A. A.; Ayas, C.; Popovich, V. A.

2017-12-01

Titanium and its alloys such as Ti6Al4V play a major role in the medical industry as bone implants. Nowadays, by the aid of additive manufacturing (AM), it is possible to manufacture porous complex structures which mimic human bone. However, AM parts are near net shape and post processing may be needed to improve their mechanical properties. For instance, AM Ti6Al4V samples may be brittle and incapable of withstanding dynamic mechanical loads due to their martensitic microstructure. The aim of this study was to apply two different heat treatment regimes (below and above β-transus) to investigate their effects on the microstructure and mechanical properties of porous Ti6Al4V specimens. After heat treatment, fine acicular α‧ martensitic microstructure was transformed to a mixture of α and β phases. The ductility of the heat-treated specimens, as well as some mechanical properties such as hardness, plateau stress, and first maximum stress changed while the density and elastic gradient of the porous structure remained unchanged.

Gravity-driven flow and heat transfer in a spent nuclear fuel storage pool

International Nuclear Information System (INIS)

Gay, R.R.

1983-01-01

The GFLOW code analyzes a three-dimensional rectangular porous medium by dividing the porous medium into a number of nodes or cells specified by the user. The finite difference form of the fluid conservation equations is solved for each node by application of a modified ''marker and cell'' numerical technique. The existence of spent nuclear fuel in any node is modeled by using a porosity value less than unity in that node and by including a surface heat transfer term in the fluid energy equation. In addition, local pressure losses due to grid spaces or other planar flow obstructions can be modeled by local loss coefficients. Heat conduction in the fuel is simulated by a fast running implicit finite difference model of the fuel, gap, and clad regions of the fuel rod

Biogenic Cracks in Porous Rock

Science.gov (United States)

Hemmerle, A.; Hartung, J.; Hallatschek, O.; Goehring, L.; Herminghaus, S.

2014-12-01

Microorganisms growing on and inside porous rock may fracture it by various processes. Some of the mechanisms of biofouling and bioweathering are today identified and partially understood but most emphasis is on chemical weathering, while mechanical contributions have been neglected. However, as demonstrated by the perseverance of a seed germinating and cracking up a concrete block, the turgor pressure of living organisms can be very significant. Here, we present results of a systematic study of the effects of the mechanical forces of growing microbial populations on the weathering of porous media. We designed a model porous medium made of glass beads held together by polydimethylsiloxane (PDMS), a curable polymer. The rheological properties of the porous medium, whose shape and size are tunable, can be controlled by the ratio of crosslinker to base used in the PDMS (see Fig. 1). Glass and PDMS being inert to most chemicals, we are able to focus on the mechanical processes of biodeterioration, excluding any chemical weathering. Inspired by recent measurements of the high pressure (~0.5 Mpa) exerted by a growing population of yeasts trapped in a microfluidic device, we show that yeast cells can be cultured homogeneously within porous medium until saturation of the porous space. We investigate then the effects of such an inner pressure on the mechanical properties of the sample. Using the same model system, we study also the complex interplay between biofilms and porous media. We focus in particular on the effects of pore size on the penetration of the biofilm within the porous sample, and on the resulting deformations of the matrix, opening new perspectives into the understanding of life in complex geometry. Figure 1. Left : cell culture growing in a model porous medium. The white spheres represent the grains, bonds are displayed in grey, and microbes in green. Right: microscopy picture of glass beads linked by PDMS bridges, scale bar: 100 μm.

Investigation of permeability effect on slip velocity and temperature jump boundary conditions for FMWNT/Water nanofluid flow and heat transfer inside a microchannel filled by a porous media

Science.gov (United States)

Nojoomizadeh, Mehdi; D'Orazio, Annunziata; Karimipour, Arash; Afrand, Masoud; Goodarzi, Marjan

2018-03-01

The fluid flow and heat transfer of a nanofluid is numerically examined in a two dimensional microchannel filled by a porous media. Present nanofluid consists of the functionalized multi-walled carbon nanotubes suspended in water which are enough stable through the base fluid. The homogenous mixture is in the thermal equilibrium which means provide a single phase substance. The porous media is considered as a Darcy- Forchheimer model. Moreover the slip velocity and temperature jump boundary conditions are assumed on the microchannel horizontal sides which mean the influences of permeability and porosity values on theses boundary conditions are presented for the first time at present work. To do this, the wide range of thermo physical parameters are examined as like Da = 0.1 to 0.001, Re = 10,100, dimensionless slip coefficient from 0.001 to 0.1 at different mass fraction of nanoparticles. It is observed that less Darcy number leads to more local Nusselt number and also applying the porous medium corresponds to higher slip velocity.

Scaled particle theory for a hard spherocylinder fluid in a disordered porous medium: Carnahan-Starling and Parsons-Lee corrections

Directory of Open Access Journals (Sweden)

M.F. Holovko

2018-03-01

Full Text Available The scaled particle theory (SPT approximation is applied for the study of the influence of a porous medium on the isotropic-nematic transition in a hard spherocylinder fluid. Two new approaches are developed in order to improve the description in the case of small lengths of spherocylinders. In one of them, the so-called SPT-CS-PL approach, the Carnahan-Starling (CS correction is introduced to improve the description of thermodynamic properties of the fluid, while the Parsons-Lee (PL correction is introduced to improve the orientational ordering. The second approach, the so-called SPT-PL approach, is connected with generalization of the PL theory to anisotropic fluids in disordered porous media. The phase diagram is obtained from the bifurcation analysis of a nonlinear integral equation for the singlet distribution function and from the thermodynamic equilibrium conditions. The results obtained are compared with computer simulation data. Both ways and both approaches considerably improve the description in the case of spherocylinder fluids with smaller spherocylinder lengths. We did not find any significant differences between the results of the two developed approaches. We found that the bifurcation analysis slightly overestimates and the thermodynamical analysis underestimates the predictions of the computer simulation data. A porous medium shifts the phase diagram to smaller densities of the fluid and does not change the type of the transition.

Porous structure evolution of cellulose carbon fibres during heating in the initial activation stage

Energy Technology Data Exchange (ETDEWEB)

Babel, Krzysztof [Institute of Chemical Wood Technology, Agricultural Academy of Poznan, Ul. Wojska Polskiego 38/42, 60-637 Poznan (Poland)

2004-01-15

This paper is focused on the description of changes in the porous structure during fast heating to the activation temperature of the viscose fibres, pyrolysed to different final temperatures. Standard regenerated cellulose fibre structures were tested. Fabrics were subjected to pyrolysis, the samples being heated to final temperatures of 400, 600 and 850 C. Carbon fibres were subsequently heated to activation temperature (850 C) at a rate of 100 C/min, and then the samples were cooled down. The characteristics of obtained carbon preparations were examined. We have defined a level of restructuring and internal ordering of fibres which originated during slow pyrolysis as well as the range of temperature differences of pyrolysis and activation where fast increase of carbon fibre temperature before activation is advantageous for the development of porous structure. It allows for partial release of pores and fast rebuilding of structure accompanied by a considerable number of defects in the carbon matrix with higher reactivity to oxidiser which, in turn, promotes the development of pores in active carbon during oxidation. Temperature difference for viscose carbon fibres is approximately 150-300 C at pyrolysis temperature of 550-700 C.

Low-Reynolds number flow of a viscous fluid in a channel partially filled with a porous medium

International Nuclear Information System (INIS)

Deng, C.; Martinez, D.M.

2003-01-01

Steady flow inside a rectangular channel with wall suction and partially filled with a porous material is examined. We solve the Navier-Stokes equations in the clear fluid region of the channel and the Brinkman extended Darcy's law in the porous material. The stress jump conditions outlined by Ochoa-Tapia and Whitaker are employed at the interface between these two regions. Ochoa-Tapia and Whitaker's conditions contain an empirical constant β which is unknown a priori. In this work we propose a method to estimate β. To do so, we solve for the flow field using two different approaches. In the first approach, the flow is assumed to be of similarity form and a new asymmetric solution is reported; β is retained in this formulation. In the second approach, we re-pose the equations of motion over the entire domain by considering the porous medium as a sink-term (which can be turned on and off); β is not required in this formulation. We estimate the value of β by comparing the resulting flow fields. (author)

FEFLOW finite element modeling of flow, mass and heat transport in porous and fractured media

CERN Document Server

Diersch, Hans-Jörg G

2013-01-01

Placing advanced theoretical and numerical methods in the hands of modeling practitioners and scientists, this book explores the FEFLOW system for solving flow, mass and heat transport processes in porous and fractured media. Offers applications and exercises.

On the propagation of a quasi-static disturbance in a heterogeneous, deformable, and porous medium with pressure-dependent properties

Energy Technology Data Exchange (ETDEWEB)

Vasco, D.W.

2011-10-01

Using an asymptotic technique, valid when the medium properties are smoothly-varying, I derive a semi-analytic expression for the propagation velocity of a quasi-static disturbance traveling within a nonlinear-elastic porous medium. The phase, a function related to the propagation time, depends upon the properties of the medium, including the pressure-sensitivities of the medium parameters, and on pressure and displacement amplitude changes. Thus, the propagation velocity of a disturbance depends upon its amplitude, as might be expected for a nonlinear process. As a check, the expression for the phase function is evaluated for a poroelastic medium, when the material properties do not depend upon the fluid pressure. In that case, the travel time estimates agree with conventional analytic estimates, and with values calculated using a numerical simulator. For a medium with pressure-dependent permeability I find general agreement between the semi-analytic estimates and estimates from a numerical simulation. In this case the pressure amplitude changes are obtained from the numerical simulator.

Trial production of ceramic heat storage unit and study on thermal properties and thermal characteristics of the heat storage unit. Mixed salts of Na2CO3, MgCl2 and CaCl2 as heat storage medium

International Nuclear Information System (INIS)

Shiina, Yasuaki

1998-12-01

Heat storage technique of high temperature and high density latent heat can be applied to an accumulator of heat generated by nuclear power plant in the night and to a thermal load absorber. For the practical use of the heat storage technique, it is important to improve heat exchange characteristics between heat storage medium, such as molten salts, and heat transfer fluid because of low thermal conductivity of the molten salts, to improve durability among molten salt and structure materials and to develop the molten salt with stable thermal properties for a long period. Considering the possibility for the improvement of heat exchange characteristics of phase change heat storage system by absorbing molten salt in porous ceramics with high thermal conductivity, high temperature proof and high resistance to corrosion, several samples of the ceramics heat storage unit were made. Basic characteristics of the samples (strength, thermal properties, temperature characteristics during phase change) were measured experimentally and analytically to study the utility and applicability of the samples for the heat storage system. The results show that the heat storage unit should be used in inactive gas condition because water in the air absorbed in the molten salts would yield degeneration of properties and deterioration of strength and that operation temperature should be confined near fusion temperature because some molten salts would be vaporized and mass would be decreased in considerable high temperature. The results also show that when atmospheric temperature changes around the melting temperature, change in ceramic temperature becomes small. This result suggests the possibility that ceramic heat storage unit could be used as thermal load absorber. (J.P.N.)

Long-term flow/chemistry feedback in a porous medium with heterogenous permeability: Kinetic control of dissolution and precipitation

International Nuclear Information System (INIS)

Bolton, E.W.; Lasaga, A.C.; Rye, D.M.

1999-01-01

The kinetics of dissolution and precipitation is of central importance to understanding the long-term evolution of fluid flows in crustal environments, with implications for problems as diverse as nuclear waste disposal and crustal evolution. The authors examine the dynamics of such evolution for several geologically relevant permeability distributions (models for en-echelon cracks, an isolated sloping fractured zone, and two sloping high-permeability zones that are close enough together to interact). Although the focus is on a simple quartz matrix system, generic features emerge from this study that can aid in the broader goal of understanding the long-term feedback between flow and chemistry, where dissolution and precipitation is under kinetic control. Examples of thermal convection in a porous medium with spatially variable permeability reveal features of central importance to water-rock interaction. After a transient phase, an accelerated rate of change of porosity may be used with care to decrease computational time, as an alternative to the quasi-stationary state approximation (Lichtner, 1988). Kinetic effects produce features not expected by traditional assumptions made on the basis of equilibrium, for example, that cooling fluids are oversaturated and heating fluids are undersaturated with respect to silicic acid equilibrium. Indeed, the authors observe regions of downwelling oversaturated fluid experiencing heating and regions of upwelling, yet cooling, undersaturated fluid. When oscillatory convection is present, the amplitudes of oscillation generally increase with time in near-surface environments, whereas amplitudes tend to decrease over long times near the heated lower boundary. The authors examine the scaling behavior of characteristic length scales, of terms in the solute equation, and of the typical deviation from equilibrium, each as a function of the kinetic rate parameters

Nusselt correlation to predict heat transfer from an oscillated vertical annular fluid column through a porous domain

Science.gov (United States)

Sayar, Ersin; Sari, Ugurcan

2017-04-01

Experimental evaluation of the heat transfer in oscillating flow under the constant heat flux and constant amplitude fluid displacement conditions is presented for a vertical annular flow through a stainless steel wool porous media. The analysis is carried out for two different heat fluxes and for five different frequencies. The data is acquired from the measurements both in the initial transient period and in the pseudo-steady (cyclic) period by the system. The physical and mathematical behavior of the resulting Nusselt numbers are analyzed, according to data acquired from the experiments and in accordance with the results of the Buckingham Pi theorem. A cycle and space averaged Nusselt number correlation is suggested as a function of kinetic Reynolds number for oscillating flows. The suggested correlation is useful in predicting heat transfer from oscillating flows through highly porous and permeable solid media at low actuation frequencies and at low heat fluxes applied in the wall. The validity of the Nusselt numbers acquired by correlation is discussed using experimental Nusselt numbers for the selected kinetic Reynolds number interval. The present investigation has possible applications in moderate sized wicked heat pipes, solid matrix compact heat exchangers compromising of metallic foams, filtration equipment, and steam generators.

SIMSOL, Multiphase Fluid and Heat Flow in Porous Media

International Nuclear Information System (INIS)

Doughty, C.

2001-01-01

1 - Description of program or function: SIMSOL calculates transient fluid and heat flow for a uniform geologic medium containing water (in both liquid and vapor phases) and air, surrounding a constant- strength linear heat source. 2 - Method of solution: SIMSOL simplifies the partial differential governing equations involving time and a radial spatial coordinate to ordinary differential equations via a similarity transformation. The resulting coupled ordinary differential equations form a two- point boundary problem which is numerically integrated using an iterative Newton-Raphson scheme. 3 - Restrictions on the complexity of the problem: SIMSOL is limited to problems with highly idealized geometry: radial symmetry, uniform material properties and initial conditions, infinite radial extent, constant-strength heat source

Numerical/Laplace transform analysis for MHD radiating heat/mass transport in a Darcian porous regime bounded by an oscillating vertical surfac

Directory of Open Access Journals (Sweden)

Sahin Ahmed

2015-03-01

Full Text Available Analytical and numerical solutions of a non-linear MHD flow with heat and mass transfer characteristics of an incompressible, viscous, electrically conducting and Boussinesq’s fluid over a vertical oscillating plate embedded in a Darcian porous medium in the presence of thermal radiation effect have been presented. The fluid considered here is gray, absorbing/emitting radiating, but non-scattering medium. At time t > 0, the plate temperature and concentration near the plate raised linearly with time t. The dimensionless governing coupled, non-linear boundary layer partial differential equations are solved by an efficient, accurate, extensively validated and unconditionally stable finite difference scheme of the Crank–Nicolson type as well as by the Laplace Transform technique. An increase in porosity parameter (K is found to depress fluid velocities and shear stress in the regime. Also it has been found that, when the conduction-radiation (R increased, the fluid velocity and the temperature profiles decreased. Applications of the study arise in materials processing and solar energy collector systems.

1 D Additive correction strategy for solving tow dimensional problem of heat and mas transfer in porous media with non-rectangular domain

International Nuclear Information System (INIS)

Al Mers, A.; Mimet, A.

2006-01-01

We propose a new procedure using 1 D additive correction strategy (AC), for resolution of tow dimensional problem of heat and mass transfer in field reactor of adsorption cooling machine. The reactor contains a porous medium constituted of activated carbon reacting by adsorption with ammonia. The present paper demonstrated how the new procedure of the (AC) propose here can be used, in the case of non-rectangular domain and strongly anisotropic coefficients, to improve the convergence rate of different iterative solvers currently used: Point Gauss-Seidel (GS), the line Gauss-Seidel (LGS), strongly implicit procedure (SIP) and the strongly implicit solver (SIS). Results shows that for different solvers, the performance of the additive correction strategy is efficiently improved by using the new procedure.(Author)

Direct measurements of adsorption heats of hydrogen on nano-porous carbons

International Nuclear Information System (INIS)

Akihiko, Matsumoto; Kazumasa, Yamamoto; Tomoyuki, Miyata

2005-01-01

Since a exciting report of hydrogen storage in single-walled carbon nano-tubes by Dillon and his colleagues [1], nano-porous carbon materials, such as carbon nano-tubes, carbon nano-horns and micro-porous activated carbon, have attracted considerable attention as hydrogen storage materials. Adsorption plays a predominating role in the hydrogen storage process on solid surfaces. The adsorption is a spontaneous process, which is caused by interaction between gas molecules and surface, hence, it is always exothermic process and observed as adsorption heats. For this reason, direct measurement of the adsorption heats by adsorption microcalorimetry would provide quantitative information on the strength of adsorption interaction and the adsorption mechanism. However, the adsorption amounts of hydrogen on carbon materials are far less than those of condensable vapors near room temperature due to low critical temperature of hydrogen (33.2 K), therefore, the adsorption heats can not be determined accurately at conventional measurement conditions near room temperature and the atmospheric pressure. This contribution reports the calorimetric characterization of hydrogen adsorption on nano-porous carbon materials at low temperature and high-pressure conditions. The high-pressure adsorption apparatus consists of a volumetric adsorption line connected to a twin-conduction type microcalorimeter. Activated carbon fibers (ACF, Ad'all Co.) of different micropore sizes (Table 1) were used as model adsorbents. Each ACF has slit-shaped micropores of uniform size [2]. The adsorption isotherms and differential heats of adsorption at high-pressure region from 0 to 10 MPa were simultaneously measured at isothermal condition from 203 to 298 K. The adsorption isotherms on ACF were of Henry type regardless of adsorption temperature and pore width; the uptakes increased linearly with equilibrium pressure. The adsorption isotherm at lower sorption temperature tended to show higher sorptivity

Analysis of heat transfer for unsteady MHD free convection flow of rotating Jeffrey nanofluid saturated in a porous medium

Directory of Open Access Journals (Sweden)

Nor Athirah Mohd Zin

Full Text Available In this article, the influence of thermal radiation on unsteady magnetohydrodynamics (MHD free convection flow of rotating Jeffrey nanofluid passing through a porous medium is studied. The silver nanoparticles (AgNPs are dispersed in the Kerosene Oil (KO which is chosen as conventional base fluid. Appropriate dimensionless variables are used and the system of equations is transformed into dimensionless form. The resulting problem is solved using the Laplace transform technique. The impact of pertinent parameters including volume fraction φ, material parameters of Jeffrey fluid λ1, λ, rotation parameter r, Hartmann number Ha, permeability parameter K, Grashof number Gr, Prandtl number Pr, radiation parameter Rd and dimensionless time t on velocity and temperature profiles are presented graphically with comprehensive discussions. It is observed that, the rotation parameter, due to the Coriolis force, tends to decrease the primary velocity but reverse effect is observed in the secondary velocity. It is also observed that, the Lorentz force retards the fluid flow for both primary and secondary velocities. The expressions for skin friction and Nusselt number are also evaluated for different values of emerging parameters. A comparative study with the existing published work is provided in order to verify the present results. An excellent agreement is found. Keywords: Jeffrey nanofluid, AgNPs, MHD and Porosity, Rotating flow, Laplace transform technique

Macroscopic numerical simulation model of multi-constituent fluid flows in porous medium; Modele macroscopique de simulation numerique d'ecoulements de fluides multiconstituants en milieu poreux

Energy Technology Data Exchange (ETDEWEB)

Wilbois, B.

2003-07-01

In this work, a new model is built which allows to take into consideration the overall mass transfer phenomena (in particular convection) taking place inside a mixture of n{sub c} constituents in a porous medium. This model should allow to foresee the quantitative composition of fluids in oil fields and also to improve the knowledge of the flow of different species inside mixtures. The overall physical phenomena taking place at oil fields is explained in the first chapter. Chapter 2 recalls some thermodynamical notions at the equilibrium and outside equilibrium. These notions, necessary to understand the forecasting methods used by petroleum geologists, are described in chapter 3. This chapter includes also a bibliographic study about the methods of simulation of mass and heat transfers in porous media. In chapter 4, using the thermodynamical relations of irreversible processes described in chapter 2, a new type of macroscopic model allowing to describe the overall phenomena analyzed is developed. The numerical method used to solve this new system of equations is precised. Finally, chapter 5 proposes a set of cases for the validation of the uncoupled phenomena and some qualitative examples of modeling of coupled phenomena. (J.S.)

Heat Transfer and Flows of Thermal Convection in a Fluid-Saturated Rotating Porous Medium

Directory of Open Access Journals (Sweden)

Jianhong Kang

2015-01-01

Full Text Available Thermal convection at the steady state for high Rayleigh number in a rotating porous half space is investigated. Taking into account the effect of rotation, Darcy equation is extended to incorporate the Coriolis force term in a rotating reference frame. The velocity and temperature fields of thermal convection are obtained by using the homotopy analysis method. The influences of Taylor number and Rayleigh number on the Nusselt number, velocity profile, and temperature distribution are discussed in detail. It is found that the Nusselt number decreases rapidly with the increase of Taylor number but tends to have an asymptotic value. Besides, the rotation can give rise to downward flow in contrast with the upward thermal convection.

Influence of radiation on double conjugate diffusion in a porous cavity

International Nuclear Information System (INIS)

Azeem,; Idris, Mohd Yamani Idna; Khan, T. M. Yunus; Badruddin, Irfan Anjum; Nik-Ghazali, N.

2016-01-01

The current work highlights the effect of radiation on the conjugate heat and mass transfer in a square porous cavity having a solid wall. The solid wall is placed at the center of cavity. The left surface of cavity is maintained at higher temperature T_w and concentration C_w whereas the right surface is maintained at T_c and C_c such that T_w>T_c and Cw>Cc. The top and bottom surfaces are adiabatic. The governing equations are solved with the help of finite element method by making use of triangular elements. The results are discussed with respect to two different heights of solid wall inside the porous medium along with the radiation parameter.

Scattering by a spherical inhomogeneity in a fluid-saturated porous medium

International Nuclear Information System (INIS)

Berryman, J.G.

1985-01-01

A fast compressional wave incident on an inhomogeneity in a fluid-saturated porous medium will produce three scattered elastic waves: a fast compressional wave, a slow compressional wave, and a shear wave. This problem is formulated as a multipole expansion using Biot's equations of poroelasticity. The solution for the first term (n = 0) in the multipole series involves a 4 x 4 system which is solved analytically in the long-wavelength limit. All higher-order terms (n > or = 1) require the solution of a 6 x 6 system. A procedure for solving these equations by splitting the problem into a 4 x 4 system and a 2 x 2 system and then iterating is introduced. The first iterate is just the solution of the elastic wave scattering problem in the absence of fluid effects. Higher iterates include the successive perturbation effects of fluid/solid interaction

Chaotic dynamics of large-scale double-diffusive convection in a porous medium

Science.gov (United States)

Kondo, Shutaro; Gotoda, Hiroshi; Miyano, Takaya; Tokuda, Isao T.

2018-02-01

We have studied chaotic dynamics of large-scale double-diffusive convection of a viscoelastic fluid in a porous medium from the viewpoint of dynamical systems theory. A fifth-order nonlinear dynamical system modeling the double-diffusive convection is theoretically obtained by incorporating the Darcy-Brinkman equation into transport equations through a physical dimensionless parameter representing porosity. We clearly show that the chaotic convective motion becomes much more complicated with increasing porosity. The degree of dynamic instability during chaotic convective motion is quantified by two important measures: the network entropy of the degree distribution in the horizontal visibility graph and the Kaplan-Yorke dimension in terms of Lyapunov exponents. We also present an interesting on-off intermittent phenomenon in the probability distribution of time intervals exhibiting nearly complete synchronization.

Examination of thermophotovoltaic GaSb cell technology in low and medium temperatures waste heat

Science.gov (United States)

Utlu, Z.; Önal, B. S.

2018-02-01

In this study, waste heat was evaluated and examined by means of thermophotovoltaic systems with the application of energy production potential GaSb cells. The aim of our study is to examine GaSb cell technology at low and medium temperature waste heat. The evaluation of the waste heat to be used in the system is designed to be used in the electricity, industry and iron and steel industry. Our work is research. Graphic analysis is done with Matlab program. The low and medium temperature waste heat graphs applied on the GaSb cell are in the results section. Our study aims to provide a source for future studies.

Experimental investigation on the evaporation of a wet porous layer inside a vertical channel with resolution of the heat equation by inverse method

International Nuclear Information System (INIS)

Terzi, A.; Foudhil, W.; Harmand, S.; Ben Jabrallah, S.

2016-01-01

Highlights: • Experimental study of the evaporation of a wet porous layer inside a vertical channel. • Resolution of the heat equation by inverse method. • The use of the porous layer is more efficient for high heating flux and low liquid inlet flow. • To improve the evaporation, the system must operate at low water inlet flow. - Abstract: In this paper, we realize an Experimental study of the evaporation of a wet porous layer inside a vertical channel. To develop this study, an experimental dispositive was realised. We measure the temperature along the plate and the evaporated flow rate using the test bed. From these measurements we note that the profiles of the temperature are divided into two areas: the heating and the evaporation zone. We also note that the use of the porous layer is more efficient for high heating flux and low liquid inlet flow. In addition, we studied different dimensionless numbers by solving the energy equation by inverse method. We note that the latent Nusselt number is more important than the sensible Nusselt Number, which proves that the flow dissipated by evaporation is greater than the one used by the film to increase its temperature.

PATCHY BLAZAR HEATING: DIVERSIFYING THE THERMAL HISTORY OF THE INTERGALACTIC MEDIUM

International Nuclear Information System (INIS)

Lamberts, Astrid; Chang, Philip; Pfrommer, Christoph; Puchwein, Ewald; Broderick, Avery E.; Shalaby, Mohamad

2015-01-01

TeV-blazars potentially heat the intergalactic medium (IGM) as their gamma rays interact with photons of the extragalactic background light to produce electron–positron pairs, which lose their kinetic energy to the surrounding medium through plasma instabilities. This results in a heating mechanism that is only weakly sensitive to the local density, and therefore approximately spatially uniform, naturally producing an inverted temperature–density relation in underdense regions. In this paper we go beyond the approximation of uniform heating and quantify the heating rate fluctuations due to the clustered distribution of blazars and how this impacts the thermal history of the IGM. We analytically compute a filtering function that relates the heating rate fluctuations to the underlying dark matter density field. We implement it in the cosmological code GADGET-3 and perform large-scale simulations to determine the impact of inhomogeneous heating. We show that because of blazar clustering, blazar heating is inhomogeneous for z ≳ 2. At high redshift, the temperature–density relation shows an important scatter and presents a low temperature envelope of unheated regions, in particular at low densities and within voids. However, the median temperature of the IGM is close to that in the uniform case, albeit slightly lower at low redshift. We find that blazar heating is more complex than initially assumed and that the temperature–density relation is not unique. Our analytic model for the heating rate fluctuations couples well with large-scale simulations and provides a cost-effective alternative to subgrid models

Hydrocarbons biodegradation in unsaturated porous medium; Biodegradation des hydrocarbures en milieu poreux insature

Energy Technology Data Exchange (ETDEWEB)

Gautier, C

2007-12-15

Biological processes are expected to play an important role in the degradation of petroleum hydrocarbons in contaminated soils. However, factors influencing the kinetics of biodegradation are still not well known, especially in the unsaturated zone. To address these biodegradation questions in the unsaturated zone an innovative experimental set up based on a physical column model was developed. This experimental set up appeared to be an excellent tool for elaboration of a structured porous medium, with well defined porous network and adjusted water/oil saturations. Homogeneous repartition of both liquid phases (i.e., aqueous and non aqueous) in the soil pores, which also contain air, was achieved using ceramic membranes placed at the bottom of the soil column. Reproducible interfaces (and connectivity) are developed between gas, and both non mobile water and NAPL phases, depending on the above-defined characteristics of the porous media and on the partial saturations of these three phases (NAPL, water and gas). A respirometric apparatus was coupled to the column. Such experimental set up have been validated with hexadecane in dilution in an HMN phase. This approach allowed detailed information concerning n-hexadecane biodegradation, in aerobic condition, through the profile of the oxygen consumption rate. We have taken benefit of this technique, varying experimental conditions, to determine the main parameters influencing the biodegradation kinetics and compositional evolution of hydrocarbons, under steady state unsaturated conditions and with respect to aerobic metabolism. Impacts of the nitrogen quantity and of three different grain sizes have been examined. Biodegradation of petroleum cut, as diesel cut and middle distillate without aromatic fraction, were, also studied. (author)

Effect of constant and uniform heat generation on the thermal behaviour of porous solids with asymmetric boundary conditions

International Nuclear Information System (INIS)

Heggs, P.J.; Dare, J.

2007-01-01

The generation of heat due to chemical reaction will have a significant effect on the temperature profile and heat transfer within a porous body. Most forms of analysis only consider the symmetric situation or else make use of various assumptions that greatly simplify the analysis, for example: the Semenov or the Frak-kamenetskii models. The objective of this paper is to develop an improved understanding of the thermal behaviour of a porous body with uniform internal heat generation, which is in contact with two fluids at different temperatures and with different heat transfer coefficients. The mathematical representation is a one dimensional Poisson equation with asymmetric boundary conditions. The analytical solution reveals four regimes for heat flow: (a) purely conduction at zero heat generation, (b) a combination of heat flow by conduction through the body between the hot and cold fluids and all heat generated passing to the colder fluid, (c) no heat flow by conduction between the two fluids and all heat generated passing the cold flow - the so-called critical heat generation, and (d) the heat generated passes to both the cold and hot fluids and there is a maximum temperature within the body greater than that of the hot fluid, the so-called supercritical region. Expressions are developed to allow predictions of the conditions pertaining to each regime. This new representation covers the Semenov and Frank-Kamenetskii models and all possible solutions intermediate of the them. (authors)

Porous (Swiss-Cheese Graphite

Directory of Open Access Journals (Sweden)

Joseph P. Abrahamson

2018-05-01

Full Text Available Porous graphite was prepared without the use of template by rapidly heating the carbonization products from mixtures of anthracene, fluorene, and pyrene with a CO2 laser. Rapid CO2 laser heating at a rate of 1.8 × 106 °C/s vaporizes out the fluorene-pyrene derived pitch while annealing the anthracene coke. The resulting structure is that of graphite with 100 nm spherical pores. The graphitizablity of the porous material is the same as pure anthracene coke. Transmission electron microscopy revealed that the interfaces between graphitic layers and the pore walls are unimpeded. Traditional furnace annealing does not result in the porous structure as the heating rates are too slow to vaporize out the pitch, thereby illustrating the advantage of fast thermal processing. The resultant porous graphite was prelithiated and used as an anode in lithium ion capacitors. The porous graphite when lithiated had a specific capacity of 200 mAh/g at 100 mA/g. The assembled lithium ion capacitor demonstrated an energy density as high as 75 Wh/kg when cycled between 2.2 V and 4.2 V.

Application of infrared thermography for temperature distributions in fluid-saturated porous media

DEFF Research Database (Denmark)

Imran, Muhammad; Nick, Hamid; Schotting, Ruud J.

2016-01-01

is achieved with a combination of invasive sensors which are inserted into the medium and non-invasive thermal sensors in which sensors are not inserted to measure temperatures but it works through the detection of infrared radiation emitted from the surface. Thermocouples of relatively thin diameter are used......Infrared thermography has increasingly gained importance because of environmental and technological advancements of this method and is applied in a variety of disciplines related to non-isothermal flow. However, it has not been used so far for quantitative thermal analysis in saturated porous media....... This article suggests infrared thermographic approach to obtain the entire surface temperature distribution(s) in water-saturated porous media. For this purpose, infrared thermal analysis is applied with in situ calibration for a better understanding of the heat transfer processes in porous media. Calibration...

A medium-independent variational macroscopic theory of two-phase porous media – Part I: Derivation of governing equations and stress partitioning laws

OpenAIRE

Serpieri , Roberto; Travascio , Francesco

2016-01-01

A macroscopic continuum theory of two-phase saturated porous media is derived by a purely variational deduction based on the least Action principle. The proposed theory proceeds from the consideration of a minimal set of kinematic descriptors and keeps a specific focus on the derivation of most general medium-independent governing equations, which have a form independent from the particular constitutive relations and thermodynamic constraints characterizing a specific medium. The kinematics o...

Non-equilibrium thermochemical heat storage in porous media: Part 1 – Conceptual model

International Nuclear Information System (INIS)

Nagel, T.; Shao, H.; Singh, A.K.; Watanabe, N.; Roßkopf, C.; Linder, M.; Wörner, A.; Kolditz, O.

2013-01-01

Thermochemical energy storage can play an important role in the establishment of a reliable renewable energy supply and can increase the efficiency of industrial processes. The application of directly permeated reactive beds leads to strongly coupled mass and heat transport processes that also determine reaction kinetics. To advance this technology beyond the laboratory stage requires a thorough theoretical understanding of the multiphysics phenomena and their quantification on a scale relevant to engineering analyses. Here, the theoretical derivation of a macroscopic model for multicomponent compressible gas flow through a porous solid is presented along with its finite element implementation where solid–gas reactions occur and both phases have individual temperature fields. The model is embedded in the Theory of Porous Media and the derivation is based on the evaluation of the Clausius–Duhem inequality. Special emphasis is placed on the interphase coupling via mass, momentum and energy interaction terms and their effects are partially illustrated using numerical examples. Novel features of the implementation of the described model are verified via comparisons to analytical solutions. The specification, validation and application of the full model to a calcium hydroxide/calcium oxide based thermochemical storage system are the subject of part 2 of this study. - Highlights: • Rigorous application of the Theory of Porous Media and the 2nd law of thermodynamics. • Thermodynamically consistent model for thermochemical heat storage systems. • Multicomponent gas; modified Fick's and Darcy's law; thermal non-equilibrium; solid–gas reactions. • Clear distinction between source and production terms. • Open source finite element implementation and benchmarks

Densification of porous bodies in a granular pressure-transmitting medium

International Nuclear Information System (INIS)

Olevsky, E.A.; Ma, J.; LaSalvia, J.C.; Meyers, M.A.

2007-01-01

Densification is a critical step in the manufacture of near-net-shaped components via powder processing. A non-isostatic stress state will in general result in shape distortion in addition to densification. In the quasi-isostatic pressing (QIP) process the green body is placed into a granular pressure-transmitting medium (i.e. PTM), which is itself contained in a rigid die. Upon the application of a uniaxial load, the PTM redistributes the tractions on the green body, thereby creating a stress state that is quasi-isostatic. The character of the deformation of the PTM is studied using model experiments on pressing of the PTM in a rigid die and a scanning electron microscopy analysis of the PTM powder. An important problem of the optimization of the PTM chemical composition enabling the maximum densification of a porous specimen with the minimum possible shape distortion is solved. The results of modeling agree satisfactorily with the experimental data on cold QIPing Ti and Ni powder samples and hot QIPing TiC-TiNi cermet composites

Heat and water transport in soils and across the soil-atmosphere interface: 1. Theory and different model concepts

DEFF Research Database (Denmark)

Vanderborght, Jan; Fetzer, Thomas; Mosthaf, Klaus

2017-01-01

on a theoretical level by identifying the underlying simplifications that are made for the different compartments of the system: porous medium, free flow and their interface, and by discussing how processes not explicitly considered are parameterized. Simplifications can be grouped into three sets depending......Evaporation is an important component of the soil water balance. It is composed of water flow and transport processes in a porous medium that are coupled with heat fluxes and free air flow. This work provides a comprehensive review of model concepts used in different research fields to describe...

An artificial compressibility CBS method for modelling heat transfer and fluid flow in heterogeneous porous materials

CSIR Research Space (South Africa)

Malan, AG

2011-08-01

Full Text Available to modelling both forced convection as well as heat transfer and fluid flow through heterogeneous saturated porous materials via an edge-based finite volume discretization scheme. A volume-averaged set of local thermal disequilibrium governing equations...

SCDAP/RELAP5 modeling of fluid heat transfer and flow losses through porous debris in a light water reactor

International Nuclear Information System (INIS)

Harvego, E. A.; Siefken, L. J.

2000-01-01

The SCDAP/RELAP5 code is being developed at the Idaho National Engineering and Environmental Laboratory under the primary sponsorship of the U.S. Nuclear Regulatory Commission (NRC) to provide best-estimate transient simulations of light water reactor coolant systems during severe accidents. This paper describes the modeling approach used in the SCDAP/RELAP5 code to calculate fluid heat transfer and flow losses through porous debris that has accumulated in the vessel lower head and core regions during the latter stages of a severe accident. The implementation of heat transfer and flow loss correlations into the code is discussed, and calculations performed to assess the validity of the modeling approach are described. The different modes of heat transfer in porous debris include: (1) forced convection to liquid, (2) forced convection to gas, (3) nucleate boiling, (4) transition boiling, (5) film boiling, and (6) transition from film boiling to convection to vapor. The correlations for flow losses in porous debris include frictional and form losses. The correlations for flow losses were integrated into the momentum equations in the RELAP5 part of the code. Since RELAP5 is a very general non-homogeneous non-equilibrium thermal-hydraulics code, the resulting modeling methodology is applicable to a wide range of debris thermal-hydraulic conditions. Assessment of the SCDAP/RELAP5 debris bed thermal-hydraulic models included comparisons with experimental measurements and other models available in the open literature. The assessment calculations, described in the paper, showed that SCDAP/RELAP5 is capable of calculating the heat transfer and flow losses occurring in porous debris regions that may develop in a light water reactor during a severe accident

HAM solutions on MHD squeezing axisymmetric flow of water nanofluid through saturated porous medium between two parallel disks

Science.gov (United States)

Reddy, B. Siva Kumar; Rao, K. V. Surya Narayana; Vijaya, R. Bhuvana

2017-07-01

In this paper, we have considered the unsteady magnetohydrodynamic squeezing axi-symmetric flow of water-nanofluid through saturated porous medium between two parallel disks. The equations for the governing flow are solved by Galerkin optimal Homotopy asymptotic method. The effects of non-dimensional parameters on velocity, temperature and concentration have been discussed with the help of graphs. Also we obtained local Nusselt number and computationally discussed with reference to flow parameters.

Radiative mixed convection over an isothermal cone embedded in a porous medium with variable permeability

KAUST Repository

El-Amin, Mohamed; Ebrahiem, N.A.; Salama, Amgad; Sun, S.

2011-01-01

The interaction of mixed convection with thermal radiation of an optical dense viscous fluid adjacent to an isothermal cone imbedded in a porous medium with Rosseland diffusion approximation incorporating the variation of permeability and thermal conductivity is numerically investigated. The transformed conservation laws are solved numerically for the case of variable surface temperature conditions. Numerical results are given for the dimensionless temperature profiles and the local Nusselt number for various values of the mixed convection parameter , the cone angle parameter ?, the radiation-conduction parameter R d, and the surface temperature parameter H. Copyright 2011 M. F. El-Amin et al.

Interfacial energies of aqueous mixtures and porous coverings for enhancing pool boiling heat transfer

Energy Technology Data Exchange (ETDEWEB)

Melendez, Elva [CIICAp, Universidad Autonoma del Estado de Morelos, 62210 (Mexico); Reyes, Rene [Departamento de Ingenieria Quimica y Alimentos, Universidad de las Americas Puebla, Santa Catarina Martir Cholula, Puebla 72820 (Mexico)

2006-08-15

The interfacial energies effects on pool boiling were measured for combinations of aqueous ethanol mixtures and cationic surfactants. The mixture with 16% ethanol by weight had the lowest contact angle (associated to the highest wettability) and produced the highest convective heat transfer coefficient, h, among the aqueous ethanol mixtures. The surfactant sodium-lauryl-sulfate added at 100 ppm (its calculated critical micelle concentration CMC) to the 16% ethanol aqueous mixture produced an additional increment of the wettability of the mixture and of the h values; other concentrations of the surfactant reduced de contact angle and h values. The effect of these interfacial energies represents a mass-transfer contribution to pool boiling and the proposal of mixture effects both as increased spreadability and as micelle states. Several randomly constructed porous coverings, contributing to the breakage of vapor slugs around the heater, were tested; produced the highest h values for average pore diameters of 0.5 mm, and covering thickness of 0.972 mm. The synergistic effect on h of the interfacial energies of mixtures at their critical micelle concentration, and porous coverings was measured. Therefore, the independent driving forces combined in this study for increasing pool boiling heat transfer are (a) spreadability of the liquid on the solid; (b) the bubble's size reduction, achieved by micelle states; and (c) the bubble's breakage, induced by the porous coverings, for vapor flow not under pressure drop control. (author)

Effects of Liquid Transpiration Cooling on Heat Transfer to the Diverging Region of a Porous-Walled Nozzle

National Research Council Canada - National Science Library

Schieb, Daniel

1997-01-01

This research effort investigated the effects of evaporation of water on the heat transferred to the wall of the diverging portion of a porous walled nozzle The AFIT High Pressure Shock Tube was used...

Sensitivity and inversion of full seismic waveforms in stratified porous medium

International Nuclear Information System (INIS)

Barros, L. de

2007-12-01

Characterization of porous media parameters, and particularly the porosity, permeability and fluid properties are very useful in many applications (hydrologic, natural hazards or oil industry). The aim of my research is to evaluate the possibility to determine these properties from the full seismic wave fields. First, I am interested in the useful parameters and the specific properties of the seismic waves in the poro-elastic theory, often called Biot (1956) theory. I then compute seismic waves propagation in fluid saturated stratified porous media with a reflectivity method coupled with the discrete wavenumber integration method. I first used this modeling to study the possibilities to determine the carbon dioxide concentration and localization thanks to the reflected P-waves in the case of the deep geological storage of Sleipner (North Sea). The sensitivity of the seismic response to the poro-elastic parameters are then generalized by the analytical computation of the Frechet derivatives which are expressed in terms of the Green's functions of the unperturbed medium. The numerical tests show that the porosity and the consolidation are the main parameters to invert. The sensitivity operators are then introduced in a inversion algorithm based on iterative modeling of the full waveform. The classical algorithm of generalized least-square inverse problem is solved by the quasi-Newton technique (Tarantola, 1984). The inversion of synthetic data show that we can invert for the porosity and the fluid and solid parameters (densities and mechanical modulus, or volume rate of fluid and mineral) can be correctly rebuilt if the other parameters are well known. However, the strong seismic coupling of the porous parameters leads to difficulties to invert simultaneously for several parameters. One way to get round these difficulties is to use additional information and invert for one single parameter for the fluid properties (saturating rate) or for the lithology. An other way

Monolithic multigrid method for the coupled Stokes flow and deformable porous medium system

Science.gov (United States)

Luo, P.; Rodrigo, C.; Gaspar, F. J.; Oosterlee, C. W.

2018-01-01

The interaction between fluid flow and a deformable porous medium is a complicated multi-physics problem, which can be described by a coupled model based on the Stokes and poroelastic equations. A monolithic multigrid method together with either a coupled Vanka smoother or a decoupled Uzawa smoother is employed as an efficient numerical technique for the linear discrete system obtained by finite volumes on staggered grids. A specialty in our modeling approach is that at the interface of the fluid and poroelastic medium, two unknowns from the different subsystems are defined at the same grid point. We propose a special discretization at and near the points on the interface, which combines the approximation of the governing equations and the considered interface conditions. In the decoupled Uzawa smoother, Local Fourier Analysis (LFA) helps us to select optimal values of the relaxation parameter appearing. To implement the monolithic multigrid method, grid partitioning is used to deal with the interface updates when communication is required between two subdomains. Numerical experiments show that the proposed numerical method has an excellent convergence rate. The efficiency and robustness of the method are confirmed in numerical experiments with typically small realistic values of the physical coefficients.

Influence of radiation on double conjugate diffusion in a porous cavity

Energy Technology Data Exchange (ETDEWEB)

Azeem,; Idris, Mohd Yamani Idna [Dept. of Computer System & Technology, University of Malaya, Kuala Lumpur (Malaysia); Khan, T. M. Yunus, E-mail: yunus.tatagar@gmail.com [Dept. of Mechanical Engineering, University of Malaya, Kuala Lumpur, 50603 (Malaysia); Dept. of Mechanical Engineering, BVB College of Engineering & Technology, Hubli (India); Badruddin, Irfan Anjum, E-mail: irfan-magami@Rediffmail.com; Nik-Ghazali, N. [Dept. of Mechanical Engineering, University of Malaya, Kuala Lumpur, 50603 (Malaysia)

2016-05-06

The current work highlights the effect of radiation on the conjugate heat and mass transfer in a square porous cavity having a solid wall. The solid wall is placed at the center of cavity. The left surface of cavity is maintained at higher temperature T{sub w} and concentration C{sub w} whereas the right surface is maintained at T{sub c} and C{sub c} such that T{sub w}>T{sub c} and Cw>Cc. The top and bottom surfaces are adiabatic. The governing equations are solved with the help of finite element method by making use of triangular elements. The results are discussed with respect to two different heights of solid wall inside the porous medium along with the radiation parameter.

Influence of yield stress on free convective boundary-layer flow of a non-Newtonian nanofluid past a vertical plate in a porous medium

International Nuclear Information System (INIS)

Hady, F. M.; Ibrahim, F. S.; Abdel-Gaied, S. M.; Eid, M. R.

2011-01-01

The effect of yield stress on the free convective heat transfer of dilute liquid suspensions of nanofluids flowing on a vertical plate saturated in porous medium under laminar conditions is investigated considering the nanofluid obeys the mathematical model of power-law. The model used for non-Newtonian nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing boundary- layer equations are cast into dimensionless system which is solved numerically using a deferred correction technique and Newton iteration. This solution depends on yield stress parameter Ω, a power-law index n, Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. Analyses of the results found that the reduced Nusselt and Sherwood numbers are decreasing functions of the higher yield stress parameter for each dimensionless numbers, n and Le, except the reduced Sherwood number is an increasing function of higher Nb for different values of yield stress parameter

Crystal structure and nanotopographical features on the surface of heat-treated and anodized porous titanium biomaterials produced using selective laser melting

Energy Technology Data Exchange (ETDEWEB)

Amin Yavari, S., E-mail: s.aminyavari@tudelft.nl [Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands); FT Innovations BV, Braamsluiper 1, 5831 PW Boxmeer (Netherlands); Wauthle, R. [KU Leuven, Department of Mechanical Engineering, Section Production Engineering, Machine Design and Automation (PMA), Celestijnenlaan 300B, 3001 Leuven (Belgium); LayerWise NV, Kapeldreef 60, Leuven (Belgium); Böttger, A.J. [Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands); Schrooten, J. [Department of Metallurgy and Materials Engineering, KU Leuven, Kasteelpark Arenberg 44 PB 2450, 3001 Heverlee (Belgium); Weinans, H. [Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands); Department of Orthopedics and Department of Rheumatology, UMC Utrecht, Heidelberglaan 100, 3584 CX Utrecht (Netherlands); Zadpoor, A.A. [Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands)

2014-01-30

Porous titanium biomaterials manufactured using additive manufacturing techniques such as selective laser melting are considered promising materials for orthopedic applications where the biomaterial needs to mimic the properties of bone. Despite their appropriate mechanical properties and the ample pore space they provide for bone ingrowth and osseointegration, porous titanium structures have an intrinsically bioinert surface and need to be subjected to surface bio-functionalizing procedures to enhance their in vivo performance. In this study, we used a specific anodizing process to build a hierarchical oxide layer on the surface of porous titanium structures made by selective laser melting of Ti6Al4V ELI powder. The hierarchical structure included both nanotopographical features (nanotubes) and micro-features (micropits). After anodizing, the biomaterial was heat treated in Argon at different temperatures ranging between 400 and 600 °C for either 1 or 2 h to improve its bioactivity. The effects of applied heat treatment on the crystal structure of TiO{sub 2} nanotubes and the nanotopographical features of the surface were studied using scanning electron microscopy and X-ray diffraction. It was shown that the transition from the initial crystal structure, i.e. anatase, to rutile occurs between 500 and 600 °C and that after 2 h of heat treatment at 600 °C the crystal structure is predominantly rutile. The nanotopographical features of the surface were found to be largely unchanged for heat treatments carried out at 500 °C or below, whereas they were partially or largely disrupted after heat treatment at 600 °C. The possible implications of these findings for the bioactivity of porous titanium structures are discussed.

Diffusion Driven Combustion Waves in Porous Media

Science.gov (United States)

Aldushin, A. P.; Matkowsky, B. J.

2000-01-01

Filtration of gas containing oxidizer, to the reaction zone in a porous medium, due, e.g., to a buoyancy force or to an external pressure gradient, leads to the propagation of Filtration combustion (FC) waves. The exothermic reaction occurs between the fuel component of the solid matrix and the oxidizer. In this paper, we analyze the ability of a reaction wave to propagate in a porous medium without the aid of filtration. We find that one possible mechanism of propagation is that the wave is driven by diffusion of oxidizer from the environment. The solution of the combustion problem describing diffusion driven waves is similar to the solution of the Stefan problem describing the propagation of phase transition waves, in that the temperature on the interface between the burned and unburned regions is constant, the combustion wave is described by a similarity solution which is a function of the similarity variable x/square root of(t) and the wave velocity decays as 1/square root of(t). The difference between the two problems is that in the combustion problem the temperature is not prescribed, but rather, is determined as part of the solution. We will show that the length of samples in which such self-sustained combustion waves can occur, must exceed a critical value which strongly depends on the combustion temperature T(sub b). Smaller values of T(sub b) require longer sample lengths for diffusion driven combustion waves to exist. Because of their relatively small velocity, diffusion driven waves are considered to be relevant for the case of low heat losses, which occur for large diameter samples or in microgravity conditions, Another possible mechanism of porous medium combustion describes waves which propagate by consuming the oxidizer initially stored in the pores of the sample. This occurs for abnormally high pressure and gas density. In this case, uniformly propagating planar waves, which are kinetically controlled, can propagate, Diffusion of oxidizer decreases

Ukrainian brown-coal tars recovered at low-temperature carbonization with solid heating medium

Energy Technology Data Exchange (ETDEWEB)

Kuznetsov, V I; Govorova, R P; Fadeicheva, A G; Kigel, T B; Chernykh, M K

1955-01-01

Three samples of tar were recovered in the laboratory from brown coals carbonized at 375/sup 0/ to 456/sup 0/ +- 25/sup 0/ in a retort with inner heating by solid circulating medium, namely, semicoke (ratio: 4 or 3:1) first heated to 700/sup 0/. One comparative (parallel) experiment was carried out in a retort with inner heating by inert gases entering the retort at 580/sup 0/ to 600/sup 0/ and leaving it at 115/sup 0/ to 120/sup 0/. The tars that were recovered from the retort with the solid heating medium contained a high percentage of coal dust and moisture, which were separated from the tars in supercentrifuges (15,000 rpm). Four samples of cleaned tars were fractionated in a Cu flask with a 2-ball fractional column. The tars from the retort with the solid-heating medium are characterized by increased yield of the petroleum-ether fraction (16.3 or 19.3%) and decreased yield of the paraffin fraction (15.1 to 21.2%) in comparison with those of tar from the retort with gas heating (5.9% of the petroleum ether fraction and 36.5% of paraffin fraction). The yield of paraffin from the paraffin fraction also decreased from 90.6% to 62.6-74.3%. This result shows that in the first case the carbonized products were cracked to a higher degree than those from the retort with gas heating. In raw phenols recovered from fractions of investigated tars, the yield of the phenol-cresol fraction (182/sup 0/ to 204/sup 0/) decreased from 25.9% to 13.0-18.9%.

Transient heat characteristics of water-saturated porous media with freezing; Toketsu wo tomonau gansui takoshitsu sonai no hiteijo netsu tokusei

Energy Technology Data Exchange (ETDEWEB)

Sasaki, A [Akita National College of Technology, Akita (Japan)

1998-02-25

Analytical and experimental investigations were performed to examine the transient heat characteristics of water-saturated porous media with freezing. As a physical model, a two-dimensional vertical cavity was considered. One vertical wall was abruptly cooled below the fusion temperature. Other three walls were thermally insulated. Three different sizes of glass, and iron, alumina and copper beads were used as the porous media in this study. The cold energy stored up in the porous media and the average thickness of frozen layer were measured in the experiments. Comparisons of the analytical results with the experimental ones were made, and the effects of Darcy number, Stefan number and modified Prandtl number on the transient heat characteristics were discussed. The dimensionless equations for predicting the averaged frozen layer thickness and the stored cold energy were obtained as a function of various dimensionless parameters. 8 refs., 16 figs., 1 tab.

Gravity modulation of thermal instability in a viscoelastic fluid saturated anisotropic porous medium

Energy Technology Data Exchange (ETDEWEB)

Bhadauria, Beer S. [Babasaheb Bhimrao Ambedkar Univ., Lucknow (India). Dept. of Applied Mathematics and Statistics; Banaras Hindu Univ., Varanasi (India). Dept. of Mathematics; Srivastava, Atul K. [Banaras Hindu Univ., Varanasi (India). Dept. of Mathematics; Sacheti, Nirmal C.; Chandran, Pallath [Sultan Qaboos Univ., Muscat (Oman). Dept. of Mathematics

2012-01-15

The present paper deals with a thermal instability problem in a viscoelastic fluid saturating an anisotropic porous medium under gravity modulation. To find the gravity modulation effect, the gravity field is considered in two parts: a constant part and an externally imposed time-dependent periodic part. The time-dependent part of the gravity field, which can be realized by shaking the fluid, has been represented by a sinusoidal function. Using Hill's equation and the Floquet theory, the convective threshold has been obtained. It is found that gravity modulation can significantly affect the stability limits of the system. Further, we find that there is a competition between the synchronous and subharmonic modes of convection at the onset of instability. Effects of various parameters on the onset of instability have also been discussed. (orig.)

Experimental procedure for determination of dispersion coefficient in a column of porous medium using radiotracer; Procedimento experimental para determinacao do coeficiente de dispersao num meio poroso em coluna utilizando radiotracador

Energy Technology Data Exchange (ETDEWEB)

Souza, Roberto de [Universidade Federal, Rio de Janeiro, RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia; Heilbron Filho, Paulo Fernando Lavalle [Comissao Nacional de Energia Nuclear (CNEN), Rio de Janeiro, RJ (Brazil)

1997-12-31

The experimental procedures used for determination of parameters such as the molecular diffusion and the diffusion by mechanical convection, responsible for the dispersion in the porous medium, are presented. The experiments were conduct in a column, based on the theory of hydrodynamic dispersion. The radiotracer technique was employed to monitor the dispersion of the radioactive cloud through the porous medium. The radionuclide employed was the bromide 82 (Br{sup 82}), in the KBr chemical form 11 refs., 5 figs., 4 tabs.; e-mail: rs at serv.com.ufrj.br; paulo at cnen.gov.br

Fiscal 1980 Sunshine Project research report. Development of hydrothermal power plant. Development of binary cycle power plant (Research on heat cycle, heat medium, material and heat medium turbine); 1980 nendo nessui riyo hatsuden plant no kaihatsu seika hokokusho. Binary cycle hatsuden plant no kaihatsu (netsu cycle oyobi netsubaitai no kenkyu, zairyo no kenkyu narabini netsubaitai turbine no kenkyu)

Energy Technology Data Exchange (ETDEWEB)

NONE

1981-03-01

This report summarizes the fiscal 1980 research result on each element of the next 10MW class geothermal binary cycle power plant, following last year. In the research on heat cycle and heat medium, measurement was made on the liquid density, vapor density, liquid specific heat, vapor specific heat and thermal conductivity of 8 heat media to prepare the precise pressure enthalpy chart. The thermal stability of each medium was also measured under a flow condition. The heat cycle of each medium was calculated in a hydrothermal temperature range of 120-160 degrees C for evaluation of its output. In the research on material, field corrosion test and laboratory simulation were made on 3 kinds of heat exchanger martials for acidic hot water to study the corrosion behavior of welding members. In the research on heat medium turbine, study was made on sealing characteristics such as differential pressure, flow rate and friction of sealing oil for oil film seal and mechanical seal as shaft seal devices of heat medium turbines for the 10MW class geothermal plant. (NEDO)

Natural convection heat transfer in an anisotropic porous cavity heated from the side. 1st Report. Theory; Tosuiritsu ni ihosei wo yusuru howa takoshitsu sonai no sokuho kanetsu ni yoru shizen tairyu netsu dentatsu. 1. Riron kaiseki

Energy Technology Data Exchange (ETDEWEB)

Kimura, S [Kanazawa University, Ishikawa (Japan). Faculty of Engineering; Okajima, A [Kanazawa University, Ishikawa (Japan)

1998-02-25

Natural convection heat transfer and flow structure in an anisotropic porous medium of square cavity saturated with Boussinesq fluid has been studied analytically and numerically. Based on asymptotic analysis three distinctive regimes are found depending upon the magnitude of permeability ratio K. In the vicinity of K=1 the average Nusselt number and fluid velocity are scaled with (KRa){sup 1/2} when either K or the Rayleigh number Ra is varied. In the limit of K {yields} 0 the heat transfer across the cavity approaches to the conductive state, and the convecting velocity, which is primarily in the vertical direction, is scaled with KRa. In the other end of spectrum, namely K {yields} {infinity}, the average Nusselt number and the convecting velocity are scaled with Ra and independent of K. The asymptotic results are verified with two-dimensional numerical calculations. The ranges of K of the respective regimes are also determined based on the numerical results. 12 refs., 12 figs.

Energetic and Exergetic Analysis of Low and Medium Temperature District Heating Network Integration

DEFF Research Database (Denmark)

Li, Hongwei; Svendsen, Svend

In this paper, energetic and exergetic approaches were applied to an exemplary low temperature district heating (LTDH) network with supply/return water temperature at 55oC/25 oC. The small LTDH network is annexed to a large medium temperature district heating (MTDH) network. The LTDH network can ...... will reduce the amount of water supply from the MTDH network and improve the system energy conversion efficiency. Through the simulation, the system energetic and exergetic efficiencies based on the two network integration approaches were calculated and evaluated.......In this paper, energetic and exergetic approaches were applied to an exemplary low temperature district heating (LTDH) network with supply/return water temperature at 55oC/25 oC. The small LTDH network is annexed to a large medium temperature district heating (MTDH) network. The LTDH network can...... be supplied through upgrading the return water from the MTDH network with a small centralized heat pump. Alternatively, the supply and return water from the MTDH network can be mixed with a shunt at the junction point to supply the LTDH network. Comparing with the second approach, the heat pump system...

Map of fluid flow in fractal porous medium into fractal continuum flow.

Science.gov (United States)

Balankin, Alexander S; Elizarraraz, Benjamin Espinoza

2012-05-01

This paper is devoted to fractal continuum hydrodynamics and its application to model fluid flows in fractally permeable reservoirs. Hydrodynamics of fractal continuum flow is developed on the basis of a self-consistent model of fractal continuum employing vector local fractional differential operators allied with the Hausdorff derivative. The generalized forms of Green-Gauss and Kelvin-Stokes theorems for fractional calculus are proved. The Hausdorff material derivative is defined and the form of Reynolds transport theorem for fractal continuum flow is obtained. The fundamental conservation laws for a fractal continuum flow are established. The Stokes law and the analog of Darcy's law for fractal continuum flow are suggested. The pressure-transient equation accounting the fractal metric of fractal continuum flow is derived. The generalization of the pressure-transient equation accounting the fractal topology of fractal continuum flow is proposed. The mapping of fluid flow in a fractally permeable medium into a fractal continuum flow is discussed. It is stated that the spectral dimension of the fractal continuum flow d(s) is equal to its mass fractal dimension D, even when the spectral dimension of the fractally porous or fissured medium is less than D. A comparison of the fractal continuum flow approach with other models of fluid flow in fractally permeable media and the experimental field data for reservoir tests are provided.

Rotation and Radiation Effects on MHD Flow through Porous Medium Past a Vertical Plate with Heat and Mass Transfer

Directory of Open Access Journals (Sweden)

Uday Singh Rajput

2017-11-01

Full Text Available Effects of rotation and radiation on unsteady MHD flow past a vertical plate with variable wall temperature and mass diffusion in the presence of Hall current is studied here. Earlier we studied chemical reaction effect on unsteady MHD flow past an exponentially accelerated inclined plate with variable temperature and mass diffusion in the presence of Hall current. We had obtained the results which were in agreement with the desired flow phenomenon. To study further, we are changing the model by considering radiation effect on fluid, and changing the geometry of the model. Here in this paper we are taking the plate positioned vertically upward and rotating with velocity Ω . Further, medium of the flow is taken as porous. The plate temperature and the concentration level near the plate increase linearly with time. The governing system of partial differential equations is transformed to dimensionless equations using dimensionless variables. The dimensionless equations under consideration have been solved by Laplace transform technique. The model contains equations of motion, diffusion equation and equation of energy. To analyze the solution of the model, desirable sets of the values of the parameters have been considered. The governing equations involved in the flow model are solved by the Laplace-transform technique. The results obtained have been analyzed with the help of graphs drawn for different parameters. The numerical values obtained for the drag at boundary and Nusselt number have been tabulated. We found that the values obtained for velocity, concentration and temperature are in concurrence with the actual flow of the fluid

Heat and mass transfer in a contaminated porous concrete slab with variable dielectric properties

International Nuclear Information System (INIS)

Li, W.; Ebadian, M.A.

1994-01-01

The effect of temperature dependent dielectric properties on concrete decontamination and decommissioning using microwave technology is investigated theoretically in this paper. The concrete is treated as a porous material, which has residual water and air within the pores. A one-dimensional model of unsteady heat and mass transport in the porous concrete with temperature dependent dielectric properties is developed. Based on this model, temperature and pressure with different microwave frequencies are predicted, the effects of the temperature dependent dielectric properties on microwave power dissipation, the temperature and pressure distributions for different microwave frequencies, and the different microwave power intensities are analyzed in detail. Four available industrial microwave frequencies of 0.896, 2.45, 10.6 and 18.0 GHz are used in the analysis. As a result of the dielectric properties varying with temperature, the power dissipation also varies with the heating times. Comparing the results for both temperature dependent and constant dielectric properties reveals that the variation of dielectric permittivity with temperature must be considered in a theoretical model of the concrete decontamination and decommissioning process for a low microwave frequency (f <2.45 GHz). (Author)

Impact of Heat and Mass Transfer on MHD Oscillatory Flow of Jeffery ...

African Journals Online (AJOL)

The objective of this paper is to study Dufour, Soret and thermal conductivity on unsteady heat and mass transfer of magneto hydrodynamic (MHD) oscillatory flow of Jeffery fluid through a porous medium in a channel. The partial differential equations governing the flow have been solved numerically using semi-implicit ...

Modelling and simulation of a natural convection flow in a saturated porous cavity

International Nuclear Information System (INIS)

Costa, M.L.M.; Sampaio, R.; Gama, R.M.S. da.

1991-09-01

The natural convection flow in a two-dimensional fluid-saturated porous cavity is modelled by means of a Theory of Mixtures viewpoint in which fluid and porous medium are regarded as continuous constituents of a binary mixture, coexisting superposed. A local description, that allows distinct temperature profiles for both fluid and solid constituents is obtained. The model, simplified by the Boussinesq approximation, is simulated with the help of the Control Volumes Method. The effect of some usual parameters like Rayleigh, Darcy and Prandtl numbers and of a new dimensionless number, relating coefficients associated to the heat exchange between fluid and solid constituents (due to its temperature difference) and coefficients of heat conduction for each constituent, is considered. Stream lines for the fluid constituent and isotherms for both fluid and solid constituents are presented for some cases. Qualitative agreement with results using the classical approach (Darcy's law and additional terms to account for boundary and inertia effects, used as momentum equation) was obtained. (author)

Pore-Scale Hydrodynamics in a Progressively Bioclogged Three-Dimensional Porous Medium: 3-D Particle Tracking Experiments and Stochastic Transport Modeling

Science.gov (United States)

Carrel, M.; Morales, V. L.; Dentz, M.; Derlon, N.; Morgenroth, E.; Holzner, M.

2018-03-01

Biofilms are ubiquitous bacterial communities that grow in various porous media including soils, trickling, and sand filters. In these environments, they play a central role in services ranging from degradation of pollutants to water purification. Biofilms dynamically change the pore structure of the medium through selective clogging of pores, a process known as bioclogging. This affects how solutes are transported and spread through the porous matrix, but the temporal changes to transport behavior during bioclogging are not well understood. To address this uncertainty, we experimentally study the hydrodynamic changes of a transparent 3-D porous medium as it experiences progressive bioclogging. Statistical analyses of the system's hydrodynamics at four time points of bioclogging (0, 24, 36, and 48 h in the exponential growth phase) reveal exponential increases in both average and variance of the flow velocity, as well as its correlation length. Measurements for spreading, as mean-squared displacements, are found to be non-Fickian and more intensely superdiffusive with progressive bioclogging, indicating the formation of preferential flow pathways and stagnation zones. A gamma distribution describes well the Lagrangian velocity distributions and provides parameters that quantify changes to the flow, which evolves from a parallel pore arrangement under unclogged conditions, toward a more serial arrangement with increasing clogging. Exponentially evolving hydrodynamic metrics agree with an exponential bacterial growth phase and are used to parameterize a correlated continuous time random walk model with a stochastic velocity relaxation. The model accurately reproduces transport observations and can be used to resolve transport behavior at intermediate time points within the exponential growth phase considered.

Utilizing of inner porous structure in injection moulds for application of special cooling method

International Nuclear Information System (INIS)

Seidl, M; Bobek, J; Habr, J; Běhálek, L; Šafka, J; Nováková, I

2016-01-01

The article is focused on impact evaluation of controlled inner structure of production tools and new cooling method on regulation of thermal processes for injection moulding technology. The mould inserts with porous structure were cooled by means of liquid CO 2 which is very progressive cooling method and enables very fast and intensive heat transfer among the plastic product, the production tool and cooling medium. The inserts were created using rapid prototype technology (DLSM) and they had a bi-component structure consisting of thin compact surface layer and defined porous inner structure of open cell character where liquid CO 2 was flowing through. This analyse includes the evaluation of cooling efficiency for different inner structures and different time profiles for dosing of liquid CO 2 into the porous structure. The thermal processes were monitored using thermocouples and IR thermal analyse of product surface and experimental device. Intensive heat removal influenced also the final structure and the shape and dimensional accuracy of the moulded parts that were made of semi-crystalline polymer. The range of final impacts of using intensive cooling method on the plastic parts was defined by DSC and dimensional analyses. (paper)

Entropy generation in Poiseuille flow through a channel partially filled with a porous material

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Kumar Vikas

2015-01-01

Full Text Available In the present paper, a theoretical analysis of entropy generation due to fully developed flow and heat transfer through a parallel plate channel partially filled with a porous medium under the effect of transverse magnetic field and radiation is presented. Both horizontal plates of the channel are kept at constant and equal temperature. An exact solution of governing equation for both porous and clear fluid regions has been obtained in closed form. The entropy generation number and the Bejan number are also calculated. The effects of various parameters such as magnetic field parameter, radiation parameter, Brinkman number, permeability parameter, ratios of viscosities and thermal conductivities are examined on velocity, temperature, entropy generation rate.

Definition of a facility for experimental studies of two-phase flows and heat transfer in porous materials

International Nuclear Information System (INIS)

Reda, D.C.; Eaton, R.R.

1981-01-01

A facility-development effort is currently underway at Sandia National Laboratories in order to create an experimental capability for the study of two-phase, steam/water flows through a variety of porous media. The facility definition phase of this project is described. Equations are derived for the steady, adiabatic, macroscopically-linear two-phase flow of a single-component fluid through a porous medium, including energy transfer both by convection and conduction. These equations are then solved to give relative permeabilities for the steam and water phases as functions of known and/or measurable quantities. A viable experimental approach was thereby formulated, leading to the definition of facility components and instrumentation requirements, including the application of gamma-beam densitometry for the measurement of liquid-saturation distributions in porous media. Finally, a state-of-the-art computer code was utilized to numerically simulate the proposed experiments, providing an estimate of the facility operating envelope

Steady-state heat transfer in He II through porous superconducting cable insulation

International Nuclear Information System (INIS)

Baudouy, B.J.P.; Juster, F.P.; Meuris, C.; Vieillard, L.

1996-01-01

The LHC program includes the study of thermal behavior of the superconducting cables wound in the dipole magnet cooled by superfluid helium (He II). Insulation of these superconducting cables forms the major thermal shield hindering the He II cooling. This is particularly a problem in magnets which are subjected to thermal loads. To investigate He II heat transfer processes an experimental model has been realized which creates a one-dimensional heat transfer in such media. Insulation is generally realized by wrapping around the superconducting cable a combination of different kind of Kapton reg-sign tapes, fiber-glass impregnated by epoxy resin or Kevlar reg-sign fiber tapes. Steady-state heat transfer in He II through these multi-layer porous slabs has been analyzed. Experimental results for a range of heat flux show the existence of different thermal regimes related to He II. It is shown that the parameters of importance are a global geometrical factor which could be considered as an equivalent open-quotes permeabilityclose quotes related to He II heat transfer, the transfer function f(T) of He II and the thermal conductivity of the slab. The authors present and analyze results for different insulations as a function of the temperature

Studies on split heat pipe type adsorption ice-making test unit for fishing boats: Choice of heat pipe medium and experiments under unsteady heating sources

International Nuclear Information System (INIS)

Wang, L.W.; Wang, R.Z.; Lu, Z.S.; Chen, C.J.

2006-01-01

The split heat pipe type compound adsorption ice maker for fishing boats not only has the advantage of large volume cooling density but also has the advantage of less power consumption and high heat transfer performance. The available heat pipe media for the split heat pipe type compound adsorption ice maker, which are methanol, acetone and water are studied and compared in this paper, and the heat pipe medium of water shows the better performance for the reason of its stable heating and cooling process and high heat transfer performance. Considering the waste heat recovered from the diesel engine on fishing boats varies when the velocity of the fishing boat changes, the refrigeration performances at the condition of different values of heating power are studied while water is used as the heat pipe medium. Results show that the cooling power, as while as COP and SCP decrease when the heating power decreases. The highest COP and SCP are 0.41 and 731 W/kg, respectively, at the highest heating power of 4.2 kW, and the values decrease by 22% and 33%, respectively, when the heating power decreases by 15%. The values decrease by 32% and 51%, respectively, when the heating power decreases by 30%. The performance of the adsorption ice maker for the fishing boat with the 6160A type diesel engine is estimated, and the results show that the cooling power and ice productivity are as high as 5.44 kW and 1032 kg ice per day, respectively, even if the recovered waste heat decreases by 30% compared with the normal value. It can satisfy the ice requirements of such a fishing boat

Natural convection heat transfer in an anisotropic porous cavity heated from the side. 2nd Report. experiment by hele-shaw cell; Tosuiritsu ni ihosei wo yusuru howa takoshitsu sonai no sokuho kanetsu ni yoru shizen tairyu netsu dentatsu. 2. Hele shaw cell ni yoru jikken

Energy Technology Data Exchange (ETDEWEB)

Kimura, S; Okajima, A; Kiwata, T [Kanazawa University, Ishikawa (Japan). Faculty of Engineering

2000-11-25

Natural convection heat transfer and flow structure in an anisotropic porous medium of square cavity saturated with Boussinesq fluid has been studied experimentally using a Hele-Shaw cell. The permeability ratio defined by K=K{sub y}/K{sub x} was put to three different values; 0.4, 1 and 2.5. The convection patterns at three different permeability ratios are visualized for several different Rayleigh numbers by the pH indicator method. When K is 0.25, the visualized flow is mainly in the vertical direction. On the contrary for K=4 the convecting flow is in the horizontal direction. The average heat transfer coefficients are also measured, and the corresponding Nusselt number are plotted as a function of K. It is found that the corresponding Nusselt numbers are scaled with (KRa){sup 1/2}. The experimental results of flow pattern and heat transfer are accord with those obtained by our previous theory. (author)

CONVECTION HEAT TRANSFER IN A CHANNEL OF DIFFERENT CROSS SECTION FILLED WITH POROUS MEDIA

Directory of Open Access Journals (Sweden)

Ahmed A. Mohammad Saleh

2018-05-01

Full Text Available A forced convection heat transfer in ducts (circular, triangular, rectangular cross sections and (1m length with hydraulic diameter (0.1m filled with porous media (glass spheres 12 mm diameter is investigated experimentally at constant heat flux from the wall (1070W/m² with Reynolds number range of (12461-2500. Comparison was made between three ducts for local temperature distribution and local Nusselt number. The experimental results showed the effect of Reynolds number and cross section on the temperature profile and local Nusselt number,also empirical correlations for average Nusselt number and Peclet number were obtained for three ducts.

Porous stainless steel for biomedical applications

Directory of Open Access Journals (Sweden)

Sabrina de Fátima Ferreira Mariotto

2011-01-01

Full Text Available Porous 316L austenitic stainless steel was synthesized by powder metallurgy with relative density of 0.50 and 0.30 using 15 and 30 wt. (% respectively of ammonium carbonate and ammonium bicarbonate as foaming agents. The powders were mixed in a planetary ball mill at 60 rpm for 10 minutes. The samples were uniaxially pressed at 287 MPa and subsequently vacuum heat treated in two stages, the first one at 200 ºC for 5 hours to decompose the carbonate and the second one at 1150 ºC for 2 hours to sinter the steel. The sintered samples had a close porous structure and a multimodal pore size distribution that varied with the foaming agent and its concentration. The samples obtained by addition of 30 wt. (% of foaming agents had a more homogeneous porous structure than that obtained with 15 wt. (%. The MTT cytotoxicity test (3-[4,5-dimethylthiazol]-2,5-diphenyltetrazolium bromide was used to evaluate the mitochondrial activity of L929 cells with samples for periods of 24, 48, and 72 hours. The cytotoxicity test showed that the steel foams were not toxic to fibroblast culture. The sample with the best cellular growth, therefore the most suitable for biomedical applications among those studied in this work, was produced with 30 wt. (% ammonium carbonate. In this sample, cell development was observed after 48 hours of incubation, and there was adhesion and spreading on the material after 72 hours. Electrochemical experiments using a chloride-containing medium were performed on steel foams and compared to massive steel. The massive steel had a better corrosion performance than the foams as the porosity contributes to increase the surface area exposed to the corrosive medium.

Numerical study for Darcy-Forchheimer flow due to a curved stretching surface with Cattaneo-Christov heat flux and homogeneous-heterogeneous reactions

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Tasawar Hayat

Full Text Available The current investigation presents Darcy-Forchheimer flow of viscous fluid caused by a curved stretching sheet. Flow for porous space is characterized by Darcy-Forchheimer relation. Concept of homogeneous and heterogeneous reactions is also utilized. Heat transfer for Cattaneo–Christov theory characterizing the feature of thermal relaxation is incorporated. Nonlinear differential systems are derived. Shooting algorithm is employed to construct the solutions for the resulting nonlinear system. The characteristics of various sundry parameters are studied and discussed. Skin friction coefficient and heat transfer rate are numerically described. Keywords: 2D flow, Curved stretching surface, Darcy-Forchheimer porous medium, Cattaneo-Christov heat flux, Homogeneous-heterogeneous reactions

High Temperature Gas-to-Gas Heat Exchanger Based on a Solid Intermediate Medium

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R. Amirante

2014-04-01

Full Text Available This paper proposes the design of an innovative high temperature gas-to-gas heat exchanger based on solid particles as intermediate medium, with application in medium and large scale externally fired combined power plants fed by alternative and dirty fuels, such as biomass and coal. An optimization procedure, performed by means of a genetic algorithm combined with computational fluid dynamics (CFD analysis, is employed for the design of the heat exchanger: the goal is the minimization of its size for an assigned heat exchanger efficiency. Two cases, corresponding to efficiencies equal to 80% and 90%, are considered. The scientific and technical difficulties for the realization of the heat exchanger are also faced up; in particular, this work focuses on the development both of a pressurization device, which is needed to move the solid particles within the heat exchanger, and of a pneumatic conveyor, which is required to deliver back the particles from the bottom to the top of the plant in order to realize a continuous operation mode. An analytical approach and a thorough experimental campaign are proposed to analyze the proposed systems and to evaluate the associated energy losses.

Cosmic-Ray Feedback Heating of the Intracluster Medium

Energy Technology Data Exchange (ETDEWEB)

Ruszkowski, Mateusz [Department of Astronomy, University of Michigan, 1085 South University Avenue, 311 West Hall, Ann Arbor, MI 48109 (United States); Yang, H.-Y. Karen; Reynolds, Christopher S., E-mail: mateuszr@umich.edu, E-mail: hsyang@astro.umd.edu, E-mail: chris@astro.umd.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

2017-07-20

Active galactic nuclei (AGNs) play a central role in solving the decades-old cooling-flow problem. Although there is consensus that AGNs provide the energy to prevent catastrophically large star formation, one major problem remains: How is the AGN energy thermalized in the intracluster medium (ICM)? We perform a suite of three-dimensional magnetohydrodynamical adaptive mesh refinement simulations of AGN feedback in a cool core cluster including cosmic rays (CRs). CRs are supplied to the ICM via collimated AGN jets and subsequently disperse in the magnetized ICM via streaming, and interact with the ICM via hadronic, Coulomb, and streaming instability heating. We find that CR transport is an essential model ingredient at least within the context of the physical model considered here. When streaming is included, (i) CRs come into contact with the ambient ICM and efficiently heat it, (ii) streaming instability heating dominates over Coulomb and hadronic heating, (iii) the AGN is variable and the atmosphere goes through low-/high-velocity dispersion cycles, and, importantly, (iv) CR pressure support in the cool core is very low and does not demonstrably violate observational constraints. However, when streaming is ignored, CR energy is not efficiently spent on the ICM heating and CR pressure builds up to a significant level, creating tension with the observations. Overall, we demonstrate that CR heating is a viable channel for the AGN energy thermalization in clusters and likely also in ellipticals, and that CRs play an important role in determining AGN intermittency and the dynamical state of cool cores.

Mathematical Modeling of Electrolyte Filtration through the Porous Cathode Blocks during Aluminum Electrolysis with Regard Interblock Seams

Directory of Open Access Journals (Sweden)

Orlov Anton S.

2015-01-01

Full Text Available This article investigates electrolyte filtration in the bottom of the aluminum electrolyzer cathode device using the mathematical modeling. Penetration of molten electrolyte in the heat insulation part of the lining is one of the main reasons of electrolyzer premature shutdown, because it leads to bottom destruction and excessive heat loss. This problem is considered a two-phase filtration of incompressible immiscible liquids in an inhomogeneous non-deformable porous body. The verification of the model on the problem of water filtration pin a porous medium has confirmed its adequacy. With the help of the developed mathematical model the dynamics of the impregnation of the lining of the cathode and electrolyte device defined thermal balance baths. Research has identified the speed of penetration of the melt in the bottom of the bath during service of the electrolyzer.

Computational solutions for non-isothermal, nonlinear magneto-convection in porous media with hall/ionslip currents and ohmic dissipation

Directory of Open Access Journals (Sweden)

O. Anwar Bég

2016-03-01

Full Text Available A theoretical and numerical study is presented to analyze the nonlinear, non-isothermal, magnetohydrodynamic (MHD free convection boundary layer flow and heat transfer in a non-Darcian, isotropic, homogenous porous medium, in the presence of Hall currents, Ionslip currents, viscous heating and Joule heating. A power-law variation is used for the temperature at the wall. The governing nonlinear coupled partial differential equations for momentum conservation in the x and z directions and heat conservation, in the flow regime are transformed from an (x, y, z coordinate system to a (ξ,η coordinate system in terms of dimensionless x-direction velocity (∂F/∂η and z-direction velocity (G and dimensionless temperature function (H under appropriate boundary conditions. Both Darcian and Forchheimer porous impedances are incorporated in both momentum equations. Computations are also provided for the variation of the x and z direction shear stress components and also local Nusselt number. Excellent correlation is achieved with a Nakamura tridiagonal finite difference scheme (NTM. The model finds applications in magnetic materials processing, MHD power generators and purification of crude oils.

Distinguishing oil and water layers in a cracked porous medium using pulsed neutron logging data based on Hudson's crack theory

Science.gov (United States)

Zhang, Xueang; Yang, Zhichao; Tang, Bin; Wang, Renbo; Wei, Xiong

2018-05-01

During geophysical surveys, water layers may interfere with the detection of oil layers. In order to distinguish between oil and water layers in porous cracked media, research on the properties of the cracks, the oil and water layers, and their relation to pulsed neutron logging characteristics is essential. Using Hudson's crack theory, we simulated oil and water layers in a cracked porous medium with different crack parameters corresponding to the well log responses. We found that, in a cracked medium with medium-angle (40°-50°) cracks, the thermal neutron count peak value is higher and more sensitive than those in low-angle and high-angle crack environments; in addition, the thermal neutron density distribution shows more minimum values than in other cases. Further, the thermal neutron count and the rate of change for the oil layer are greater than those of the water layer, and the time spectrum count peak value for the water layer in middle-high-angle (40°-70°) cracked environments is higher than that of the oil layer. The thermal neutron density distribution sensitivity is higher in the water layer with a range of small crack angles (0°-30°) than in the oil layer with the same range of angles. In comparing the thermal neutron density distribution, thermal neutron count peak, thermal neutron density distribution sensitivity, and time spectrum maximum in the oil and water layers, we find that neutrons in medium-angle (40°-50°) cracked reservoirs are more sensitive to deceleration and absorption than those in water layers; neutrons in approximately horizontal (0°-30°) cracked water layers are more sensitive to deceleration than those in reservoirs. These results can guide future work in the cracked media neutron logging field.

Hydromagnetic thermosolutal instability of compressible walters' (model B' rotating fluid permeated with suspended particles in porous medium

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G Rana

2016-09-01

Full Text Available The thermosolutal instability of compressible Walters' (model B' elastico-viscous rotating fluid permeated with suspended particles (fine dust in the presence of vertical magnetic field in porous medium is considered. By applying normal mode analysis method, the dispersion relation has been derived and solved analytically. It is observed that the rotation, magnetic field, suspended particles and viscoelasticity introduce oscillatory modes. For stationary convection the Walters' (model B' fluid behaves like an ordinary Newtonian fluid and it is observed that the rotation and stable solute gradient has stabilizing effects and suspended particles are found to have destabilizing effect on the system, whereas the medium permeability has stabilizing or destabilizing effect on the system under certain conditions. The magnetic field has destabilizing effect in the absence of rotation, whereas in the presence of rotation, magnetic field has stabilizing or destabilizing effect under certain conditions.

Échangeur de chaleur et de matière à paroi poreuse. Application en récupération sur fumées Porous Heat and Mass Exchanger for Recovery from Flue Gases

Directory of Open Access Journals (Sweden)

Brunel G.

2006-11-01

least one condensable product. The first application under the responsibility of Chaudières Seccacier SA involved industrial or district heating. The aim was to transfer part of the heat and water from the flue gases of a condensation boiler to the air of combustion. The ECMP was substituted for a heat exchange system based on patents held by Chaudières Seccacier SA and Gaz de France. Its job was to perform heat and mass transferts between the two fluids in two successive phases in two direct combustion air/water and flue-gas/water contact columns (Fig. 1a. The simplification made possible by the ECMP (Fig. 1b stems from the performing of both operations in a single module. The two gases between which the heat and mass exchanges occur circulate on either side of a porous membrane, which, because of its hydrophilic nature and porous structure (pore diameters and porosity in particular, separates the two gases by a film of condensed water held in place by capillarity in its pores. In addition to the advantages of compactness and reliability thus obtained, this design defines the circulation spaces of the fluids (distance between two porous membranes, with both fluids being acted upon alternately according to the pressure drops requested by the user. This technique is thus based mainly on the choice of the porous medium (nature of the constituent material, structure so as to give the membrane the right properties for it to fulfill its heat and mass transfer and physical separation functions of the two fluids. In addition to these purely operational aspects, the membrane must also meet the technological constraints required by the manufacturing and the physical operating conditions. The analysis of the functional roles (heat and mass transfer, separation leads to a definition of the range of pore diameters capable of ensuring both mass transfer according to a kinetics compatible with the flow rates required by the evaporation and condensation phases and the capillary

Meso-scale modelling of the heat conductivity effect on the shock response of a porous material

Science.gov (United States)

Resnyansky, A. D.

2017-06-01

Understanding of deformation mechanisms of porous materials under shock compression is important for tailoring material properties at the shock manufacturing of advanced materials from substrate powders and for studying the response of porous materials under shock loading. Numerical set-up of the present work considers a set of solid particles separated by air representing a volume of porous material. Condensed material in the meso-scale set-up is simulated with a viscoelastic rate sensitive material model with heat conduction formulated from the principles of irreversible thermodynamics. The model is implemented in the CTH shock physics code. The meso-scale CTH simulation of the shock loading of the representative volume reveals the mechanism of pore collapse and shows in detail the transition from a high porosity case typical for abnormal Hugoniot response to a moderate porosity case typical for conventional Hugoniot response. Results of the analysis agree with previous analytical considerations and support hypotheses used in the two-phase approach.

Chaotic convection of viscoelastic fluids in porous media

Energy Technology Data Exchange (ETDEWEB)

Sheu, L.-J. [Department of Mechanical Engineering, Chung Hua University, Hsinchu, Taiwan (China)], E-mail: ljsheu@chu.edu.tw; Tam, L.-M. [Department of Electromechanical Engineering, University of Macau, Macau (China)], E-mail: fstlmt@umac.mo; Chen, J.-H. [Department of Mechanical Engineering, Chung Hua University, Hsinchu, Taiwan (China)], E-mail: chen@chu.edu.tw; Chen, H.-K. [Department of Industrial Engineering and Management, Hsiuping Institute of Technology, Taichung, Taiwan (China)], E-mail: kanechen@giga.net.tw; Lin, K.-T. [Department of Mechanical Engineering, Chung Yuan Christian University, Chung Li, Taiwan (China)], E-mail: willie@nanya.edu.tw; Kang Yuan [Department of Mechanical Engineering, Chung Yuan Christian University, Chung Li, Taiwan (China)], E-mail: yk@cycu.edu.tw

2008-07-15

Buoyancy-induced convection in a viscoelastic fluid-saturated porous medium was analyzed using an Oldroydian-type constitutive relation. An autonomous system with four differential equations was deduced by applying the truncated Galerkin expansion to the momentum and heat transfer equations. The four-dimensional system can be reduced to many systems provided in the literature such as the Lorenz system, Vadasz system, Khayat system, and Akhatov system. Depending on the flow parameters, the asymptotic behavior can be stationary, periodic, or chaotic. Generation of a four-scroll, or two-'butterfly', chaotic attractor was observed. Results also show that stress relaxation tends to precipitate the onset of chaos.

Viscous dissipation and radiation effects on MHD natural convection in a square enclosure filled with a porous medium

Energy Technology Data Exchange (ETDEWEB)

Ahmed, Sameh E., E-mail: sameh_sci_math@yahoo.com [Department of Mathematics, Faculty of Sciences, South Valley University, Qena (Egypt); Hussein, Ahmed Kadhim, E-mail: ahmedkadhim7474@gmail.com [College of Engineering, Mechanical Engineering Department, Babylon University, Babylon City—Hilla (Iraq); Mohammed, H.A. [Department of Thermofluids, Faculty of Mechanical Engineering, University Teknologi Malaysia (UTM), 81310 UTM Skudai, Johor Bahru (Malaysia); Adegun, I.K. [Department of Mechanical Engineering, University of Ilorin, Ilorin (Nigeria); Zhang, Xiaohui [School of Physics Science and Technology, School of Energy—Soochow University, Suzhou 215006, Jiangsu (China); Kolsi, Lioua [Unite de Metrologie en Mecanique des Fluides et Thermique, Ecole Nationale d’Ingenieurs, Monastir (Tunisia); Hasanpour, Arman [Department of Mechanical Engineering, Babol University of Technology, PO Box 484, Babol (Iran, Islamic Republic of); Sivasankaran, S. [Institute of Mathematical Sciences, University of Malaya, Kuala Lumpur 50603 (Malaysia)

2014-01-15

Highlights: • Ha decelerates the flow field. • Ha enhances conduction. • Magnetic field orientation is important. • Radiation parameter important. • Nu decreases as Ha increases. -- Abstract: Numerical two-dimensional analysis using finite difference approach with “line method” is performed on the laminar magneto-hydrodynamic natural convection in a square enclosure filled with a porous medium to investigate the effects of viscous dissipation and radiation. The enclosure heated from left vertical sidewall and cooled from an opposing right vertical sidewall. The top and bottom walls of the enclosure are considered adiabatic. The flow in the square enclosure is subjected to a uniform magnetic field at various orientation angles (φ = 0°, 30°, 45°, 60° and 90°). Numerical computations occur at wide ranges of Rayleigh number, viscous dissipation parameter, magnetic field orientation angles, Hartmann number and radiation parameter. Numerical results are presented with the aid of tables and graphical illustrations. The results of the present work explain that the local and average Nusselt numbers at the hot and cold sidewalls increase with increasing the radiation parameter. From the other side, the role of viscous dissipation parameter is to reduce the local and average Nusselt numbers at the hot left wall, while it improves them at the cold right wall. The results are compared with another published results and it found to be in a good agreement.

Macroscopic lattice Boltzmann model for heat and moisture transfer process with phase transformation in unsaturated porous media during freezing process

Directory of Open Access Journals (Sweden)

Song Wenyu

2017-06-01

Full Text Available In the current study, a macroscopic lattice Boltzmann model for simulating the heat and moisture transport phenomenon in unsaturated porous media during the freezing process was proposed. The proposed model adopted percolation threshold to reproduce the extra resistance in frozen fringe during the freezing process. The freezing process in Kanagawa sandy loam soil was demonstrated by the proposed model. The numerical result showed good agreement with the experimental result. The proposed model also offered higher computational efficiency and better agreement with the experimental result than the existing numerical models. Lattice Boltzmann method is suitable for simulating complex heat and mass transfer process in porous media at macroscopic scale under proper dimensionless criterion, which makes it a potentially powerful tool for engineering application.

Effect of rotation on peristaltic flow of a micropolar fluid through a porous medium with an external magnetic field

International Nuclear Information System (INIS)

Abd-Alla, A.M.; Abo-Dahab, S.M.; Al-Simery, R.D.

2013-01-01

In this paper, the effects of both rotation and magnetic field of a micropolar fluid through a porous medium induced by sinusoidal peristaltic waves traveling down the channel walls are studied analytically and computed numerically. Closed-form solutions under the consideration of long wavelength and low-Reynolds number is presented. The analytical expressions for axial velocity, pressure rise per wavelength, mechanical efficiency, spin velocity, stream function and pressure gradient are obtained in the physical domain. The effect of the rotation, density, Hartmann number, permeability, coupling number, micropolar parameter and the non-dimensional wave amplitude in the wave frame is analyzed theoretically and computed numerically. Numerical results are given and illustrated graphically in each case considered. Comparison was made with the results obtained in the presence and absence of rotation and magnetic field. The results indicate that the effect of rotation, density, Hartmann number, permeability, coupling number, micropolar parameter and the non-dimensional wave amplitude are very pronounced in the phenomena. - Highlights: • The effects of induced magnetic field and rotation in peristaltic motion of a two dimensional of a micropolar fluid through a porous medium • The exact and closed form solutions are presented • Different wave shapes are considered to observe the behavior of the axial velocity, pressure rise, mechanical efficiency, spin velocity, stream function and pressure gradient

Effect of rotation on peristaltic flow of a micropolar fluid through a porous medium with an external magnetic field

Energy Technology Data Exchange (ETDEWEB)

Abd-Alla, A.M., E-mail: mohmrr@yahoo.com [Maths Department, Faculty of Science, Taif University (Saudi Arabia); Abo-Dahab, S.M., E-mail: sdahb@yahoo.com [Maths Department, Faculty of Science, Taif University (Saudi Arabia); Maths Department, Faculty of Science, SVU, Qena 83523 (Egypt); Al-Simery, R.D. [Maths Department, Faculty of Science, Taif University (Saudi Arabia)

2013-12-15

In this paper, the effects of both rotation and magnetic field of a micropolar fluid through a porous medium induced by sinusoidal peristaltic waves traveling down the channel walls are studied analytically and computed numerically. Closed-form solutions under the consideration of long wavelength and low-Reynolds number is presented. The analytical expressions for axial velocity, pressure rise per wavelength, mechanical efficiency, spin velocity, stream function and pressure gradient are obtained in the physical domain. The effect of the rotation, density, Hartmann number, permeability, coupling number, micropolar parameter and the non-dimensional wave amplitude in the wave frame is analyzed theoretically and computed numerically. Numerical results are given and illustrated graphically in each case considered. Comparison was made with the results obtained in the presence and absence of rotation and magnetic field. The results indicate that the effect of rotation, density, Hartmann number, permeability, coupling number, micropolar parameter and the non-dimensional wave amplitude are very pronounced in the phenomena. - Highlights: • The effects of induced magnetic field and rotation in peristaltic motion of a two dimensional of a micropolar fluid through a porous medium • The exact and closed form solutions are presented • Different wave shapes are considered to observe the behavior of the axial velocity, pressure rise, mechanical efficiency, spin velocity, stream function and pressure gradient.

Study of the Effect of Turbulence and Large Obstacles on the Evaporation from Bare Soil Surface through Coupled Free-flow and Porous-medium Flow Model