A Computational Study of the Evaporation Characteristics of an Air-Blast Atomized, Kerosene Spray in Porous Media

2004 ◽  
Author(s):  
Chendhil Periasamy ◽  
Sathish K. Sankara Chinthamony ◽  
S. R. Gollahalli
Keyword(s):  
Thermal Conductivity ◽  
Porous Medium ◽  
Porous Media ◽  
Vapor Concentration ◽  
Inlet Temperature ◽  
Swirl Number ◽  
Medium Temperature ◽  
Air Blast ◽  
Air Inlet ◽  
Complete Vaporization

The evaporation characteristics of an air-blast atomized kerosene spray in porous media in a 2D-axisymmetric coflow environment were studied numerically. A swirling primary air stream with varying intensity was used to aid the atomization process. The effects of non-Darcy flow in porous medium were modeled using a modified form of Ergun equation. Local thermal equilibrium between the fluid mixture and porous medium was assumed. Conductive and transient heat flux terms in the energy equation were modified to include the effective thermal conductivity and thermal inertia of the solid region respectively. The effective thermal conductivity was defined as the volumetric average between solid and fluid media. First, the temperature characteristics of the porous medium, arising from different source terms, were obtained. Complete vaporization of kerosene was achieved when the maximum temperature of the porous medium was at 590 K. The effects of porous medium temperature, primary air swirl number, fuel flow rate, and secondary (coflow) air inlet temperature on vaporization were analyzed. For all cases, kerosene vapor concentration profiles at five different axial locations in the domain (0.08, 0.12, 0.13, 0.14, and 0.19m from the nozzle) were obtained. An increase in secondary air inlet temperature from 373 K to 473 K increased the completeness of evaporation from 94% to 97%. When the swirl number was increased from 0.14 to 0.34, the peak vapor concentration was reduced by 31% and more vapor spread radially. The porous medium temperature was found to be a crucial factor in obtaining the complete vaporization of the spray.

A Parametric Simulation of the Evaporation in Liquid-Fueled Porous Burners

2006 ◽  
Author(s):  
Chendhil Periasamy ◽  
S. R. Gollahalli
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Heat Source ◽  
Strong Dependence ◽  
Equation Model ◽  
Vapor Concentration ◽  
Inlet Temperature ◽  
Medium Temperature ◽  
Air Inlet ◽  
Fuel Flow

This paper presents a computational parametric study of evaporation processes in liquid-fueled, simulated porous media burners using a two-energy equation model. The effects of porous medium heat source, porous medium structure, fuel flow rate, and air inlet temperature on evaporation characteristics were determined. Predicted steady-state axial temperature profiles within the porous media and radial vapor concentration profiles at 5 cm downstream of the porous medium are presented. Vapor concentration results showed a strong dependence on porous medium temperature, which, in turn, depended on the strength of the heat source and the effectiveness of heat transfer between porous medium and coflow air. Simulations with different porosities demonstrated that the peak vapor concentration decreased as porosity increased. The peak vapor concentration dropped by 42 % when porosity was increased from 0.5 to 0.87. Under higher fuel flowrate conditions, the extent of completeness of evaporation decreased, showing that much stronger heat source was needed to maintain the complete evaporation. When the coflow air temperature was increased, the peak vapor concentration was found to increase and the vapor concentration spread more radially.

Numerical Study on the Performance of a Tube With Inserted Porous Media of Various Thermal Conductivities

2016 ◽  
Author(s):  
Tariq Amin Khan ◽  
Wei Li
Keyword(s):  
Thermal Conductivity ◽  
Porous Medium ◽  
Porous Media ◽  
Velocity Profile ◽  
Fluid Transport ◽  
Energy Transport ◽  
Numerical Study ◽  
Darcy Number ◽  
Local Thermal Equilibrium ◽  
Working Fluid

Numerical study is performed on the effect of thermal conductivity of porous media (k) on the Nusselt number (Nu) and performance evaluation criteria (PEC) of a tube. Two-dimensional axisymmetric forced laminar and fully developed flow is assumed. Porous medium partially inserted in the core of a tube is investigated under varied Darcy number (Da), i.e., 10−6 ≤ Da ≤ 10−2. The range of Re number used is 100 to 2000 and the conductivity of porous medium is 1.4 to 202.4 W/(m.K) with air as the working fluid. The momentum equations are used to describe the fluid flow in the clear region. The Darcy-Forchheimer-Brinkman model is adopted for the fluid transport in the porous region. The mathematical model for energy transport is based on the one equation model which assumes a local thermal equilibrium between the fluid and the solid phases. Results are different from the conventional thoughts that porous media of higher thermal conductivity can enhance the performance (PEC) of a tube. Due to partial porous media insertion, the upstream parabolic velocity profile is destroyed and the flow is redistributed to create a new fully develop velocity profile downstream. The length of this flow redistribution to a new developed laminar flow depends on the Da number and the hydrodynamic developing length increases with increasing Da number. Moreover, the temperature profile is also readjusted within the tube. The Nu and PEC numbers have a nonlinear trend with varying k. At very low Da number and at a lower k, the Nu number decreases with increasing Re number while at higher k, the Nu number first increases to reach its peak value and then decreases. At higher Re number, the results are independent of k. However, at a higher Da number, the Nu and PEC numbers significantly increases at low Re number while slightly increases at higher Re number. Hence, the change in Nu and PEC numbers neither increases monotonically with k, nor with Re number. Investigation of PEC number shows that at very low Da number (Da = 10−6), inserting porous media of a low k is effective at low Re number (Re ≤ 500) while at high Re number, using porous material is not effective for the overall performance of a tube. However, at a relatively higher Da number (Da = 10−2), high k can be effective at higher Re number. Moreover, it is found that the results are not very sensitive to the inertia term at lower Da number.

scholarly journals Design and Performance Investigation of a Compact Catalytic Reactor Integrated with Heat Recuperator

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 447
Author(s):  
Qiang Chen ◽  
Mingming Mao ◽  
Min Gao ◽  
Yongqi Liu ◽  
Junrui Shi ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Porous Media ◽  
Ignition Temperature ◽  
Catalytic Combustion ◽  
Methane Concentration ◽  
Inlet Temperature ◽  
Catalytic Reactor ◽  
Heat Recirculation ◽  
Heat Recuperator ◽  
Reaction Performance

The catalytic combustion has the advantage of lower auto-ignition temperature and helps to expand the combustible limit of lean premixed gas. However, the intake needs to be preheated to certain temperature commonly through an independent heat exchanger. Similar to the principles of non-catalytic RTO combustion, this paper presents a similar approach whereby the combustion chamber is replaced by a catalytic combustion bed. A new catalytic reactor integrated with a heat recuperator is designed to enhance the heat recirculation effect. Using a two-dimensional computational fluid dynamics model, the performance of the reactor is studied. The reaction performances of the traditional and compact reactors are compared and analyzed. Under the same conditions, the compact reactor has better reaction performance and heat recirculation effect, which can effectively decrease the ignition temperature of feed gas. The influences of the inlet velocity, the inlet temperature, the methane concentration, and the thermal conductivity of porous media on the reaction performance of integrated catalytic reactor are studied. The results show that the inlet velocity, inlet temperature, methane concentration, and thermal conductivity of porous media materials have important effects on the reactor performance and heat recirculation effect, and the thermal conductivity of porous media materials has the most obvious influence. Moreover, the reaction performance of multiunit integrated catalytic reactor is studied. The results show that the regenerative effect of multiunit integrated catalytic reactor is further enhanced. This paper is of great significance to the recycling of low calorific value gas energy and relieving energy stress in the future.

Spray Impingement and Evaporation Through Porous Media

2004 ◽  
Author(s):  
Sathish K. Sankara Chinthamony ◽  
Chendhil Periasamy ◽  
S. R. Gollahalli
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Flow Rate ◽  
Mass Flux ◽  
Ceramic Foam ◽  
Vapor Concentration ◽  
Combustion Heat ◽  
Liquid Mass ◽  
Spray Impingement ◽  
Carbon Ceramic

This paper presents an experimental study on spray impingement and fuel evaporation processes in porous media. Aviation-type kerosene (Jet-A) was used as the fuel and an open-cell, silicon carbide coated, carbon-carbon ceramic foam was used as the porous medium. The fuel was sprayed into a coflowing, preheated air environment using an air-blast atomizer. A Phase Doppler Particle Analyzer (PDPA) was used to measure Sauter mean diameter (SMD), liquid mass flux, and axial velocity of the droplets. The porous medium was resistively heated to simulate heat feedback from the combustion zone. An organic vapor analyzer, based on catalytic oxidation, was used to measure the concentration of kerosene vapor downstream of the porous medium. The temperature and flow rate of coflow air were held constant, while the fuel flow rate, and hence, the overall equivalence ratio, was varied from 0.3 to 0.6. Higher liquid mass flux was recorded away from the spray core region, due to the swirling action of atomizing air. Surface temperature measurements of porous media revealed the uniformity of thermo-electrical properties of the medium. Vapor concentration measurements with combustion heat feedback (a heat input of 33 kW/m2) increased the average vapor concentration by 63% and 43% than that of no heat feedback case for 0.3 and 0.6 equivalence ratios respectively.

Numerical Prediction of Evaporation Processes in Porous Media Combustors

2007 ◽  
Author(s):  
C. Periasamy ◽  
A. Saboonchi ◽  
S. R. Gollahalli
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Numerical Study ◽  
Mean Value ◽  
Pollutant Emissions ◽  
Fuel Spray ◽  
Vapor Concentration ◽  
Fuel Vapor ◽  
Computational Domain ◽  
The Mean

This paper presents a numerical study of evaporation characteristics of liquid fuel spray in porous media. A two-energy equation model was employed to predict solid and gas phase temperatures. Governing equations were solved on a two-dimensional axisymmetric computational domain of 2.15 × 20 cm. An air-blast atomizer model was used to inject kerosene fuel spray on to the porous medium. Combustion in porous media was simulated by using a uniform volumetric heat source in the porous region. Numerical results were obtained with a commercial code Fluent 6.0. For a heat feedback rate of 1% of average heat input, the porous medium attained a temperature of 465 K. This data agreed well with experimental data obtained by infrared imaging. With an increase in heat feedback rate, the porous medium temperature also increased. Surface temperature distribution in porous media for different heat feedback rates was predicted. Results indicate that the transverse distribution was uniform within 1.5% of the mean value. Droplet diameter was smaller in spray core upstream of porous medium and increased radially due to the swirling action imparted to the atomizing air. Transverse vapor concentration results downstream of porous medium show that the distribution was uniform within 5% of the mean value, which demonstrates that porous medium uniformly distributes the fuel vapor-air mixture. The spatially homogeneous reactant mixture is important to achieve good combustion, reduce pollutant formation, and minimize instabilities in practical combustors. Effects of equivalence ratio and flame temperature on transverse vapor concentration profiles were also numerically studied. Porous media combustors could be used in gas turbine and industrial burner applications to reduce pollutant emissions.

scholarly journals Thermal Investigations of Double Pass Solar Air Heater with Two Types of Porous Media of Different Thermal Conductivity

2021 ◽  
Vol 39 (1A) ◽  
pp. 79-88
Author(s):  
Jalal M. Jalil ◽  
Shrooq J. Ali
Keyword(s):  
Thermal Conductivity ◽  
Porous Medium ◽  
Stainless Steel ◽  
Porous Media ◽  
Thermal Efficiency ◽  
Wire Mesh ◽  
Solar Air Heater ◽  
Steel Wool ◽  
Double Pass ◽  
Air Heater

This study describes an experimental investigation of the thermal efficiency of stainless steel mesh and steel wool as a porous medium in the lower channel of a double pass solar air heater. An experimental setup was planned and developed. Various types of porous media with high thermal conductivity and with different porosities have been tested. The effects of the porosity of wire mesh, the thermal conductivity of porous media, mass flow rate, and the intensity of radiation have been studied. Experimental results show that thermal efficiency with using porous media is greater than without using porous media. When used steel wool as a porous medium, the thermal efficiency reached 79.82 percent while it can be achieved 76.  The percent by using stainless mesh as porous material. The reduction in porosity increasing thermal efficiency. The thermal efficiency of multi-pass solar air collector when used steel wool as porous media is 6, 12.6 and31.7percent higher than without porous media at porosity 98.75, 97.5, and 96.25percent. While it can increase 8.1 and 28.5 percent at porosity 97.875 and 95.75 percent when using stainless steel as porous media.

Numerical Analysis of Wooden Porous Media Effects on Heat Transfer From a Staggered Tube Bundle

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Mohammad Layeghi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Porous Medium ◽  
Porous Media ◽  
Numerical Analysis ◽  
Pressure Drop ◽  
Tube Bundle ◽  
Numerical Data ◽  
Darcy Number ◽  
Finite Volume Approach

A numerical analysis of forced convective heat transfer from a staggered tube bundle with various low conductivity wooden porous media inserts at maximum Reynolds numbers 100 and 300, Prandtl number 0.7, and Darcy number 0.25 is presented. The tubes are at constant temperature. The extended Darcy–Brinkman–Forchheimer equations and corresponding energy equation are solved numerically using finite volume approach. Parametric studies are done for the analysis of porous medium thermal conductivity and Reynolds number on the local Nusselt number distribution. Three different porous media with various solid to fluid thermal conductivity ratios 2.5, 5, and 7.5 are used in the numerical analysis. The results are compared with the numerical data for tube bundles without porous media insert and show that the presence of wooden porous media can increase the heat transfer from a tube bundle significantly (more than 50% in some cases). It is shown that high conductivity porous media are more effective than the others for the heat transfer enhancement from a staggered tube bundle. However, the presence of a porous medium increases the pressure drop. Therefore, careful attention is needed for the selection of a porous material with good heat transfer characteristics and acceptable pressure drop.

Second Law Analysis in a Partly Porous Double Pipe Heat Exchanger

2005 ◽  
Vol 73 (1) ◽  
pp. 60-65 ◽  
Author(s):  
Nadia Allouache ◽  
Salah Chikh
Keyword(s):  
Thermal Conductivity ◽  
Porous Medium ◽  
Heat Exchanger ◽  
Effective Thermal Conductivity ◽  
Entropy Generation ◽  
Inlet Temperature ◽  
Two Fluids ◽  
Annular Gap ◽  
Double Pipe ◽  
Pipe Heat

A combination of the first and second laws of thermodynamics has been utilized in analyzing the performance of a double pipe heat exchanger with a porous medium attached over the inner pipe. The goal of this work is to find the best conditions that allow the lowest rate of entropy generation due to fluid friction and heat transfer with respect to the considered parameters. Results show that the minimization of the rate of entropy generation depends on the porous layer thickness, its permeability, the inlet temperature difference between the two fluids, and the effective thermal conductivity of the porous substrate. An increase in the effective thermal conductivity of the porous medium seems to be thermodynamically advantageous. Unexpectedly, the fully porous annular gap yields the best results in terms of the rate of total entropy generation.

Modeling Liquid Spray Evaporation in Heated Porous Media With a Local Thermal Non-Equilibrium Model

2004 ◽  
Author(s):  
Chendhil Periasamy ◽  
Sathish K. Sankara Chinthamony ◽  
S. R. Gollahalli
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Porous Media ◽  
Equation Model ◽  
Vapor Concentration ◽  
Computational Domain ◽  
Equilibrium Models ◽  
Radial Profiles ◽  
Energy Equations ◽  
Non Equilibrium

The situations such as rapid evaporation, and significant heat generation/convective heat transfer, typically encountered in liquid-fueled porous media combustors, warrant the use of local thermal non-equilibrium models. Knowledge of fuel vaporization and mixing is important to understand the combustion characteristics. In this paper, a two-energy equation model is presented to account for the non-equilibrium between the solid and liquid phases. In this approach, two energy equations for solid and gas phases were solved. Kerosene fuel, issued from an air-blast atomizer, was injected on to a heated porous medium. Governing equations were applied on a 2-D axisymmetric, computational domain of 20.3 cm × 2.5 cm. Computer simulations were conducted using a commercial code Fluent 6.0. Heat transfer from combustion porous medium was simulated by setting a volumetric heat source in the porous region. Accordingly, the peak temperatures in porous media varied from 473 K to 590 K. Axial temperature profiles within the porous media were obtained with equilibrium and non-equilibrium models. Results indicated that the equilibrium models slightly underpredicted the peak temperature. Using non-equilibrium models, radial profiles of kerosene vapor concentration were obtained at different axial locations and the results showed that the thermal effects of the porous medium dominated in the evaporation process. Numerical results were also compared with available data and the agreement was found to be good.

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