Porous Medium Temperature Research Articles

Solutions for a flame propagation model in porous media based on Hamiltonian and regular perturbation methods

This article extends the exploration of solutions to the issue of flame propagation driven by pressure and temperature in porous media that we introduced in earlier papers. We continue to consider a p-Laplacian type operator as a mathematical formalism to model slow and fast diffusion effects, that can be given in the non-homogeneous propagation of flames. In addition, we introduce a forced convection to model any possible induced flow in the porous media. We depart from previously known models to further substantiate our driving equations. From a mathematical standpoint, our goal is to deepen in the understanding of the general behavior of solutions via analyzing their regularity, boundedness, and uniqueness. We explore stationary solutions through a Hamiltonian approach and employ a regular perturbation method. Subsequently, nonstationary solutions are derived using a singular exponential scaling and, once more, a regular perturbation approach.

Temperature distribution and dissipation in a porous media (coal)–CO2 system

In order to master the temperature and dissipation law of the porous media-CO2 system, the distribution of temperature and adsorption field in porous media during intermittent CO2 injection was studied by using self-developed adsorption device and experimental platform of diffusion seepage. The results show that the distribution of high temperature in porous media is isotropic. The effect of CO2 on the temperature field mainly occurs in the self-heating stage of coal, and the high temperature area moves towards gas injection port. The gas migration rate is the highest in the first gas injection. The cooling rate decreases with the increase of gas injection times. Combined with the logistic function relationship between adsorption capacity and temperature, the porous medium CO2 adsorption field was constructed, and it was found that the adsorption field is stable under low temperature oxidation. Therefore, temperature variation mechanism of confined space porous media-CO2 system was established, and quadrilateral of coal spontaneous combustion prevention was proposed. By analyzing the heat transfer process of coal-CO2 system, the thermodynamic entransy dissipation was introduced.

Finite element modeling of energy storage materials alumina using heat recovery in packed pebble bed heat exchanger

The studies of thermal energy storage material Alumina (Al 2 O 3 ) as a function of average bed temperature. Aluminum oxide is engineering properties and uses commercially available. Alumina is one of the most cost-effective and widely used materials in the family of ceramics. The raw materials, from which this high-performance technical grade ceramic is made aluminum oxide, commonly referred to as alumina high strength characteristics of the material. Aluminum oxide is used in the energy storage of heat exchanger. The Al 2 O 3 pebbles are 6 mm to 14 mm and are randomly dumped and packed in a 450 mm long hollow tube of 45 mm inner diameter. The tube was fully covered the asbestos ropes to reduce the heat loss. Hot air from a source was used to flow in the packed bed at various inlet conditions of velocity varying from 2 to 3 m/s. The spheres were heated from an inlet temperature of 32 °C. The experimental work was done in the heat exchanger is given to air in the multistage compressor and diesel engine exhaust. Waste heat energy was stored in the pebbles. The experimental results indicated that the increased porous media temperature increased the outer surface temperature, increased the heat transfer rate with an increase in the average bed temperature of 342 K to 402 K. The entire results obtained by using experimentation were cross verified using Finite Element Analysis modeling. Finally the results of both experimental and Finite Element Analysis Modeling were found to be in good co-relation.

Simulation on flow behavior of particles and its effect on heat transfer in porous media

Mastering flow and heat transfer of fluids in porous media is significant in the development of oilfield. A three-dimensional porous model with anisotropic pore structure is developed, and flow and heat transfer behaviors of particles are simulated using CFD-DEM method incorporating with the coupled convective-conductive heat flow model. The interphase forces including drag force, lubricating force and thermophoretic force are considered comprehensively. Comparisons of the predicted results are also made and in a good agreement with the classical experimental results by Rimon. Simulation results show that the temperature in porous media rises along with the mixing and contact between particles and liquid. The migration of moving particles is restricted in pore spacing, and thus narrows the apertures of fluid channel, increases the local instantaneous liquid velocity. Moving particles are preferred to decelerate and deposit at a low porosity. The velocities of particles and frequency of collision increase while contact force and granular temperature decrease with an increase of porosity. With the increase of particle temperature, the temperature gradient around hot particles enlarges and the number of trapped particles goes up affected by thermophoretic force. The intensity of convection heat decreases at lower liquid velocity, and the heat conduction between particles is regarded as the main heat transfer mechanism.

Pore-scale investigation on the thermochemical process in uniform and gradient porous media considering immiscible phase

In the present study, the complex thermochemical process in uniform and gradient porous media is investigated by the thermochemical dissolution model based on the lattice Boltzmann method considering immiscible phase. The two immiscible phase flow, solute transport and heat transfer are solved by Shan-Chen multicomponent lattice Boltzmann model, mass transport lattice Boltzmann model and multicomponent thermal lattice Boltzmann model, respectively. The immiscible phase, undissolved solid component and porosity gradient effects on the thermochemical process are investigated. For the solid, the dissolvable component is considered and updated by Volume of Pixel method. The results show that the immiscible phase and its initial distribution considerably affect the solid dissolution, acid transport and the average temperature in porous media. The undissolved solid component and the porosity gradient influence the thermochemical process significantly.

Flame stability and combustion characteristics of liquid fuel in a meso-scale burner with porous media

To overcome difficulties of complete evaporation and mixing of liquid fuel in limited resident time and space, a self-evaporation meso-scale burner is proposed. Combustion characteristics at various inlet conditions are experimentally investigated. Results show that liquid n-heptane can be evaporated completely in porous media without external heating. Porous media temperature near fuel outlet is closely related to flame stability and significantly affected by air flow. Generally, using larger fuel flow rate and keep the porous media temperature near fuel outlet below the boiling point can prevent the flame from violent oscillation or extinction. When the porous media temperature near fuel outlet is much lower than boiling point, increase of porous media temperature changes fuel evaporation process and increases fuel velocity, which increases the flame length and soot. However, when porous media temperature is higher than the boiling point, improvement of porous media temperature has negligible effect on flame shape. Evaporation performance of n-heptane in low-temperature porous media is better than that of ethanol and dodecane. Ethanol and dodecane can evaporate completely with external heating and the flame is stable. Therefore, targeted heat management based on the characteristics of selected fuel is required to achieve stable and efficient combustion.

Thermodynamic simulation of porous-medium combustion chamber under diesel engine-like conditions

Currently, one of the most important issue of the diesel engines is the non-homogeneity of the in-cylinder fuel-air mixture. Non-homogeneous mixture causes the non-uniform heat release and high-temperature gradient in the combustion chamber that followed by the production of unburnt hydrocarbons, carbon monoxide, nitrogen oxides and soot. Homogenous combustion decreases the production of the emissions. One novel method for achieving homogenous combustion is the use of porous medium (PM) within the combustion chamber of engine so as to separate the mixture formation process from combustion process. The present article thermodynamically investigates the effect of utilizing PM in a constant-volume combustion chamber via solving the energy equations for both the solid and fluid phases considering the chemical reaction of the fuel combustion. At first, numerical result is validated according to the experimental result of diesel fuel injection in a constant-volume combustion chamber with PM. Then, effects of the initial mixture and PM temperature, the porosity of the PM, the mean pores diameter as well as the use of fuels such as decane, isooctane, methanol, ethanol, propane and hydrogen on combustion initiation, and also pressure and temperature of the combustion chamber studied.

An Assessment of Coupling Algorithms in HTR Simulator TINTE

This paper evaluates the performance of neutronic and thermal-hydraulic coupling algorithms in transient problems based on the high-temperature gas-cooled reactor simulator TINTE. In particular, the operator splitting semi-implicit (OSSI), Picard iteration, and Jacobian-free Newton-Krylov (JFNK) methods are compared by a practical engineering model. The OSSI method is employed in the original TINTE. The fully implicit algorithms TINTE-Picard and TINTE-JFNK are implemented in this study. Several special numerical technologies are discussed to improve the performance of JFNK. First, a novel JFNK variant is employed to deal with the multiscale coupling between local fuel sphere temperature and global solid porous media temperature. Second, the preconditioning strategy is determined by making a balance between performance and code burden. Finally, the scaling modifications of the Jacobian matrix and perturbation size are investigated to solve the ill-posed problem. What is more, the framework of TINTE-Picard and TINTE-JFNK is presented, and the key points of implementation are discussed. Numerical results indicate that the advanced coupling algorithms Picard and JFNK can achieve higher computational performance than the original semi-implicit coupling algorithm in TINTE due to the accuracy and stability advantage.

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

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.

Experimental study of the low-pressure-vaporization of water in different porous media

The present study aims to evaluate the benefits of using porous media (PM) to enhance the rate of the low-pressure-vaporization (LPV) of water. An experimental characterization of the process of low-pressure-vaporization (LPV) of water is presented considering four different types of porous media and different initial conditions. This characterization involves the measurement of the time evolution of the porous media temperature and of the total and the vapor pressure inside the vaporization chamber, as well as the indirect determination of the saturation pressure, the mass of water vaporized, its specific rate of vaporization and of the energy removed by this phenomenon. A direct comparison between the evolution of the LPV of water in porous media and the LPV of free water was also made for two selected situations. The results show that the evolution of the LPV parameters, namely the temperature decrease and the rate of energy removal, are strongly dependent on the volume of the water initially contained in the porous medium which in turn, depends essentially of the medium microstructure. The significant differences found between the evolution of the LPV parameters in free water and in porous media are related to different boiling onset mechanisms, which is strongly dependent on the surface tension of the liquid water in the whole LPV process in PM. The practical result of these effects is an increased vaporization rate and an enhanced surface heat transfer capability that justify the use of porous media in a wide variety of applications.

Numerical Simulation of Convection Heat Transfer in a Plate Channel with Sintered Copper Porous Ribs

Convection heat transfer in a plate channel periodically fitted with sintered copper porous ribs attached to a copper plate was numerically studied. The local thermal equilibrium model was adopted in the energy equation to evaluate the temperature of fluid and solid. The effect of porosity, Reynolds number and heat flux applied to the copper plate on the heat transfer characteristic of the porous media was investigated respectively. The numerical results show that the heat transfer can be enhanced by increasing Reynolds number, decreasing the porosity and the heat transfer enhancement of the porous media took effect significantly when subjected to high heat flux. Detailed development of the porous media temperature field and the Nusselt number of the wall as a function of Reynolds number for different porosity and heat flux were also presented.

NUMERICAL SIMULATION OF A THREE-LAYERED RADIANT POROUS HEAT EXCHANGER INCLUDING LATTICE BOLTZMANN SIMULATION OF FLUID FLOW

This paper deals with the hydrodynamic and thermal analysis of a new type of porous heat exchanger (PHE). This system operates based on energy conversion between gas enthalpy and thermal radiation. The proposed PHE has one high temperature (HT) and two heat recovery (HR1 and HR2) sections. In HT section, the enthalpy of flowing high temperature gas that is converted to thermal radiation to gas enthalpy takes place. In each section, a 2-D rectangular porous segment which is assumed to be absorbing, emitting and scattering is present. For theoretical analysis of the PHE, the gas and solid are considered in non-local thermal equilibrium and separate energy equations are used for the two phases. Besides, in the gas flow simulation, the lattice Boltzmann method (LBM) is applied to obtain the velocity distribution through the porous segments. For the purpose of thermal analysis of the proposed PHE, volume-averaged velocities through the porous matrix obtained by LBM are used in the gas energy equation, and then the coupled energy equations for gas and porous medium of each section are numerically solved using finite difference method. The radiative transfer equation is solved by discrete ordinates method to calculate the distribution of radiative heat flux in the porous medium. The numerical results consist of the gas and porous media temperature distributions. The variation of radiative heat flux are also presented. Furthermore, the effects of scattering albedo, optical thickness and inlet gas temperature on the efficiency of the proposed PHE are investigated. It is revealed that this type of heat exchanger has high efficiency in comparison to conventional one. Also, the present numerical results for a porous radiant burner are compared with theoretical finding by the other investigator and good agreement is found.

Numerical study on the realization of compression ignition in a type of porous medium engine fueled with Isooctane

The working process of a porous medium (PM) engine, characterized as periodic contact type and fueled with liquid fuel as Isooctane, is simulated by using an improved version of KIVA-3V. A modified volume-averaged method is proposed for describing the interaction between fuel droplets and the solid phase of the PM. The improved version of KIVA-3V was validated by simulating the experiment of Zhdanok for the superadiabatic combustion of CH 4–air mixtures under filtration in a packed bed. Good agreement between experimental data and computational results for the speed of combustion wave is achieved. The influences of initial PM temperature, PM structure and valve opening timing on the realization of compression ignition in the PM engine are also verified. Initial PM temperature is the crucial factor in guaranteeing the realization of the compression ignition of the PM engine. Considering influential factors, such as the properties of the PM, the compression ratio, the equivalence ratio, and the heat transfer between gas and solid phase of the PM should obtain optimized initial PM temperature. The variation in PM structure affects the convective heat transfer between the gas and solid phase and the dispersion effect of the PM. Compression ignition all can be realized in PM engines with four kinds of PM. Compression ignition is achieved at the considered four valve opening timings. Value opening timing has influence on the average temperature of the PM engine and the working of the PM engine does not allow earlier or later valve opening timing.

Simulation of a porous medium (PM) engine using a two-zone combustion model

Porous medium (PM) engine was a new type engine based on the technique of combustion in porous medium, which can realize homogeneous and stable combustion. In this paper, the combustion and working processes of a specific PM engine were simulated by a two-zone model considering the influences of the mass distribution, heat transfer from the cylinder wall, mass exchange between zones and the heat transfer in porous medium. Influences of operating parameters, e.g. intake temperature and pressure, compression ratio, the excess air ratio on the performance of the PM engine were discussed. It was found out that the porous medium, acting as a heat recuperator, can significantly enhance the evaporation of liquid fuel and preheat the mixture, which promotes the ignition and combustion in the cylinder; and that the initial PM temperature and the compression ratio are critical factors controlling the compression ignition of the mixture.

Quantifying Volatile Organic Compounds in Porous Media: Effects of Sampling Method Attributes, Contaminant Characteristics and Environmental Conditions

Understanding how sampling methods can impact the accuracy of volatile organic compound (VOC) measurements in samples of soil and subsurface porous media is often critical to sound decision making during characterization and remediation of VOC contaminated sites. In this study, the accuracy of VOC measurements was investigated using an experimental apparatus packed with sandy porous media and contaminated with known levels of VOCs, which could be sampled using different methods under variable, but controlled, conditions. Five sampling methods were examined representing different degrees of porous media disaggregation and duration of atmospheric exposure (MDE) that can occur during sample acquisition and preservation in the field. Three pervasive VOCs were studied (1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene) at low and high concentration levels. Five porous media temperatures were examined ranging from 5 to 80 degrees C to represent ambient or thermal remediation conditions and two water saturation levels were used to mimic vadose zone and groundwater zone conditions. The results of this research demonstrated that sampling method attributes can impact the accuracy of VOC measurements in porous media by causing negative bias in VOC concentration data ranging from near 0 to 90% or more. The magnitude of the negative bias is dependent on the attributes of the sampling method used (i.e., level of MDE) and interactions with key contaminant properties and environmental conditions (i.e., VOC KH, porous media temperature, water saturation level).

Numerical study of the working mechanisms and influential factors affecting a compression ignition engine with a closed porous medium chamber

This study simulated the working process of a porous medium (PM) engine, characterized as periodic contact type and fuelled with natural gas (methane (CH4)), by using an improved version of KIVA-3V to understand the working mechanism of the PM engine. The effects of the initial PM temperature, the PM structure and the valve opening timing on the compression ignition of the PM engine were also investigated. The improved version of KIVA-3V was validated by simulating the experiment made by Zhdanok et al. on the superadiabatic combustion of CH4—air mixtures under filtration in a packed bed. Computational results are in good agreement with experimental data for the speed of the combustion wave. Simulation results for the PM engine show that the initial PM temperature is the key factor in guaranteeing the onset compression ignition of the PM engine at a given compression ratio. The variation in PM structure affects the convective heat transfer between the gas and solid phase and the dispersion effect of the PM. The working of the PM engine does not allow later or earlier valve opening timing.

Numerical study on the compression ignition of a porous medium engine

Homogeneous and stable combustion can be realized in a porous medium (PM) engine where a chemically inert PM is mounted in the combustion chamber. To understand the mechanism of the PM engine, we simulated the working process of a PM engine fueled with natural gas (CH4) using an improved version of KIVA-3V and investigated the effects of the initial PM temperature, the PM structure as well as the fuel injection timing on the compression ignition of the engine. The improved version of KIVA-3V was verified by simulating the experiment of Zhdanok et al. for the superadiabatic combustion of CH4-air mixtures under filtration in a packed bed. The numerical results are in good agreement with experimental data for the speed of combustion wave. Computational results for the PM engine show that the initial PM temperature is the key factor in guaranteeing the onset of compression ignition of the PM engine at a given compression ratio. The PM structure affects greatly both convective heat transfer between the gas and solid phase in the PM and the dispersion effect of the PM. Pore diameter of the PM is a crucial factor in determining the realization of combustion in the PM engine. Over-late fuel injection timing (near TDC) cannot assure a compression ignition of the PM engine.

Dynamics of quantum liquids in confinement, theory and experiment.

Liquid (4)He immersed in porous media such as aerogel, Vycor, and Geltech silica are excellent examples of bosons in disorder and confinement. Of special interest is the impact of disorder on Bose-Einstein condensation (BEC), on the elementary excitations of the superfluid and on their connection to the superfluid properties. Indeed, the modifications induced by disorder can be used to reveal the interdependence of BEC, the excitations and superfluidity. To date, the superfluid properties in porous media are much more completely documented than BEC or the excitations. In this paper, we review measurements of the excitations by neutron scattering, focusing particularly on their temperature dependence and the existence of phonon-roton excitations at higher temperatures. The weight of single excitation response at higher temperatures suggests the existence of localized BEC above the superfluid-normal transition temperature in porous media. We sketch several recent predictions made for BEC, the excitations, and the superfluid properties in disorder. Connections with other "Dirty Bose systems" are made.

Effects of magnetic field and variable viscosity on forced non‐darcy flow about a flat plate with variable wall temperature in porous media in the presence of suction and blowing

This paper presents a study of the effect of a magnetic field and variable viscosity on steady two‐dimensional laminar non‐Darcy forced convection flow over a flat plate with variable wall temperature in a porous medium in the presence of blowing (suction). The fluid viscosity is assumed to vary as an inverse linear function of temperature. The derived fundamental equations on the assumption of small magnetic Reynolds number are solved numerically by using the finite difference method. The effects of variable viscosity, magnetic and suction (or injection) parameters on the velocity and temperature profiles as well as on the skin‐friction and heat‐transfer coefficients were studied. It is shown that the magnetic field increases the wall skin friction while the heat‐transfer rate decreases.

Blowing/suction effect on non-Darcy forced convection flow about a flat plate with variable wall temperature in porous media

The effect of blowing/suction on steady two-dimensional laminar non-Darcy forced convection flow over a flat plate with variable wall temperature in a porous medium is numerically analyzed. The nonlinear uncoupled boundary-layer equations were transformed, and the resulting partial differential equations were solved by Keller box method. Numerical results for the dimensionless velocity profiles, the temperature profiles, the local friction coefficient and the local Nusselt number are presented for various combinations of parameters. In general, it is observed that in the suction (blowing) case both the local friction coefficient and the local Nusselt number increase (decrease). The local Nusselt number is more sensitive to the blowing/suction parametersf w than the local skin friction coefficient. The local Nusselt number enhances with the increase of Rek, Pr, and λ. Moreover, the local Nusselt number becomes nearly constant when ξ is very small (pure fluid flow) and ξ is very large (pure Darcy flow).