Radiation Absorption Effects Research Articles

Combined influence of radiation absorption and Hall current effects on MHD double-diffusive free convective flow past a stretching sheet

Abstract An analysis has been carried out on the influence of radiation absorption, variable viscosity, Hall current of a magnetohydrodynamic free-convective flow and heat and mass transfer over a stretching sheet in the presence of heat generation/absorption. The fluid viscosity is assumed to vary as an inverse linear function of temperature. The boundary-layer equations governing the fluid flow, heat and mass transfer under consideration have been reduced to a system of nonlinear ordinary differential equations by employing a similarity transformation. Using the finite difference scheme, numerical solutions to the transform ordinary differential equations have been obtained and the results are presented graphically. The numerical results obtained are in good agreement with the existing scientific literature.

Effects of Thermophoresis, Dufour, Hall and Radiation on an Unsteady MHD Flow past an Inclined Plate with Viscous Dissipation, Chemical Reaction and Heat Absorption and Generation

This paper investigates study of MHD(Magnetohydrodynamics) flow of viscous incompressible fluid past an inclined porous plate embedded in porous medium with the effects of Thermophoresis, Dufour, Hall, radiation, viscous dissipation, chemical reaction and heat generation or absorption. Non dimensional partial differential equations of governing equations of flow are solved numerically by applying Crank-Nicolson finite difference method for different values of parameters. Velocity, temperature, concentration profiles are discussed through graphs for different values of parameters and skin friction coefficients, Nusselt number and Sherwood number are discussed through tables.

Unsteady mixed convection of a micropolar fluid past a circular cylinder due to time-dependent free stream velocity and temperature

Unsteady mixed convection boundary-layer flow of an electrically conducting micropolar fluid past a circular cylinder is investigated taking into account the effect of thermal radiation and heat generation or absorption. The reduced non-similar boundary-layer equations are solved using the finite difference method. It is found that the magnitude of the friction factor and the couple stress significantly increases due to the increase of the mixed convection parameter, the conduction-radiation parameter, the surface temperature parameter, the heat absorption parameter and the frequency parameter. However the magnitude of the heat transfer rate decreases with these parameters. The converse characteristics are observed for the Prandtl number. The magnitude of the couple stress and the heat transfer rate is seen to decrease whereas the magnitude of the skin factor increases with increasing the vortex viscosity parameter. The magnetic field parameter reduces the skin factor, couple stress and heat transfer rate. The amplitude of oscillation of the transient skin factor and couple stress gradually increases owing to an increase of $\xi$. But the transient heat transfer rate is found to be oscillating with almost the same amplitude for any value of $\xi$. The amplitude of oscillation of the transient skin factor and couple stress increases with an increase of $S$ and $\xi$ while the amplitude of the transient heat transfer rate increases with increasing Pr and $S$.

Magneto Convective Flow of a Non-Newtonian Fluid through Non-Homogeneous Porous Medium past a Vertical Porous Plate with Variable Suction

Radiation absorption and chemical reaction effects on unsteady MHD free convective flow of a viscoelastic fluid past a vertical porous plate in the presence of variable suction and heat source is considered. A uniform magnetic field is assumed to be applied in the transverse direction of the flow. The set of non-linear partial differential equations is transformed into a set of ordinary differential equations by super imposing a solution with steady and unsteady part. The set of ordinary differential equations is solved by using regular perturbation scheme. The expressions for velocity, temperature and species concentration fields are obtained and the expressions for Skin friction, Nusselt number and Sherwood number are also derived. The effects of numerous physical parameters on the above flow quantities are studied with the help of graphs and tables.

Effects of variable permeability and radiation absorption on magnetohydrodynamic (MHD) mixed convective flow in a vertical wavy channel with traveling thermal waves

An analysis has been carried out to study the effects of radiation absorption and first-order chemical reaction on unsteady mixed convective flow of a viscous incompressible electrically conducting fluid through a porous medium of variable permeability between two long vertical non conducting wavy channels in the presence of heat generation. The unsteadiness in the flow is due to traveling thermal wave imposed on the walls. The governing equations are solved subject to the relevant boundary conditions with the assumption that the solution consists of a mean part and a perturbed part. The zeroth-order, the first order and the total solution of the problem are numerically evaluated and displayed graphically for pertinent parameters. This model finds applications in studying fixed-bed catalytic reactors and packed bed heat exchangers.

An enhanced multi-component vaporization model for high temperature and pressure conditions

An enhanced multi-component vaporization model was proposed to simulate the vaporization process of fuel droplets under high ambient temperatures and pressures. In the present model, the heat flux of conduction, enthalpy diffusion, and radiation absorption in the gas phase are calculated by Fourier’s law, the multi-component diffusion sub-model, and a simplified analytical solution of the radiative heating, respectively. A surface temperature sub-model was employed to evaluate the average temperature within the droplet and the surface temperature of the droplet. For calculation of vapor–liquid phase equilibrium, a real and an ideal gas approach was used for high and low ambient temperatures and pressures, respectively. Moreover, the dependence of gas physical properties on temperature and pressure is also considered. Based on the enhanced vaporization model, extensive verifications for different multi-component droplets were conducted, and the results indicate that satisfactory agreements between the predictions and measurements can be achieved. Finally, the multi-component vaporization model was applied to investigate the vaporization characteristics of practical fuel droplets with a wide range of diameters at high ambient temperatures and pressures, and the effects of radiation absorption and real gas behavior on the vaporization process were understood. It is found that the influence of radiation absorption on the vaporization behavior strongly depends on the droplet diameter and the ambient temperature, and the effect of ambient pressure on the average vaporization rate is determined by the ambient temperature. Considering the compromise between computational accuracy and efficiency, a pressure criterion (P′) was introduced for the choice of ideal or real gas approaches, and a diameter criterion (D′) was also defined to decide whether to consider the radiation absorption in the vaporization model.

Ignition of deflagration and detonation ahead of the flame due to radiative preheating of suspended micro particles

We study a flame propagating in the gaseous combustible mixture with suspended inert solid micro particles. The gaseous mixture is assumed to be transparent for thermal radiation emitted by the hot combustion products, while particles absorb and reemit the radiation. Thermal radiation heats the particles, which in turn transfer the heat to the surrounding unburned gaseous mixture by means of thermal heat transfer, so that the gas phase temperature lags that of the particles. We consider different scenarios depending on the spatial distribution of the particles, their size and the number density. In the case of uniform spatial distribution of the particles the radiation causes a modest increase of the temperature ahead of the flame and corresponding modest increase of the combustion velocity. In the case of non-uniform distribution of the particles (layered dust cloud), such that the particles number density is relatively small in the region just ahead of the flame front and increases in the distant regions ahead of the flame, the preheating caused by the thermal radiation may trigger additional independent source of ignition. Far ahead of the flame, where number density of particles increases forming a dense cloud of particles, the radiative preheating results in the formation of a temperature gradient with the maximum temperature sufficient for ignition. Depending on the steepness of the temperature gradient formed in the unburned mixture, either deflagration or detonation can be initiated via the Zel'dovich's gradient mechanism. The ignition and the resulting combustion regimes depend on the number density profile and, correspondingly, on the temperature profile (temperature gradient), which is formed in effect of radiation absorption and gas-dynamic expansion. The effect of radiation preheating as stronger as smaller is the normal flame velocity. The effect of radiation heat transfer in the case of coal dust flames propagating in layered particle-gas deposits cloud can result in the spread of combustion wave with velocity up to 1000 m/s and it is a plausible explanation of the origin of dust explosion in coal mines.

Effect of chemical reaction and radiation absorption on the unsteady MHD free convection Couette flow in a vertical channel filled with porous materials

This paper deals with effect of chemical reaction and radiation absorption on the unsteady MHD natural convection flow in a vertical channel filled with porous materials. One of the plate moves with a constant velocity in the direction of fluid flow while the other plate is stationary. A uniform magnetic field acts perpendicular to the porous plate, which absorbs the fluid with a suction velocity varying with time. The dimensionless governing equations for this problem are solved analytically using two-term harmonic and non-harmonic perturbation series method. The results of the analytical solutions for velocity, temperature and concentration profiles of both phases are graphically presented and discussed. It is noteworthy to mention that growing permeability and channel width parameter lead to increase in the fluid velocity profile. Results in the present work have been compared with other works in literature and an excellent agreement is found.

Effects of Thermal Radiation and Radiation Absorption on Flow Past an Impulsively Started Infinite Vertical Plate with Newtonian Heating and Chemical Reaction

A perfect solution to the present natural convective flow problem of a vertical transfinite plate owing to the impulsive motion in the ubiety of first ordered chemical reaction, radiation absorption, radiation, Newtonian heating and species concentration in its plane is evolved by applying the method of Laplace transforms in closed form at the plate. Exact results for velocity, temperature, concentration fields are prevailed and expressions for heat and mass transfer rates are also found. The effects are analyzed for the respective invariables for both ammonia and water vapor.

Effect of Addition of Energetic Nanoparticles on Droplet-Burning Rate of Liquid Fuels

A droplet stream combustion experiment was developed to understand the effect of reducing droplet size to a micrometer scale on the combustion characteristics of nanofluid fuels, which are liquid fuels with a stable suspension of nanoparticles. Pure ethanol and ethanol with aluminum nanoparticles at varying concentrations (up to 5 wt%) and droplet sizes were studied. The effect of particle addition on the droplet-burning rate was determined, and the mechanisms that are responsible for that effect were identified. The results show that the droplet-burning rate increases with increasing particle concentration. For example, with a 5 wt% addition of 80 nm aluminum nanoparticles, the burning rate increased by 140%. The burning rate enhancement is mainly attributed to strong radiation absorption of the nanoparticles suspended within the droplets, which provides more energy from the exothermic reaction (the flame) to the liquid phase (the droplets) for vaporization, thus increasing the burning rate. The radiation absorption effect becomes increasingly important as the droplet size increases.

Application of a Novel CO2 DC Thermal Plasma Torch Submerged in Aqueous Solution for Treatment of Dissolved Carboxylic Acid

A novel direct current (DC) plasma torch, operating with a gas mixture consisting of carbon dioxide and hydrocarbon (methane), has been adapted and used for the first time for treatment of a solution containing dissolved carboxylic acid. Compared with conventional DC thermal plasma torches, this novel torch has high plasma enthalpy, high thermal conductivity, low cost and often readily available operating gas (CO2) and long electrode life-time. Performance of this CO2/CH4 DC thermal plasma torch submerged in aqueous solution was investigated for decomposition of dissolved organic contaminants. Sebacic acid was selected as a representative of organic pollutants in wastewater of chemical process industries. Effect of different operational conditions including treatment time, initial solution pH, and the reactor pressure as well as the role of oxidizing agents such as (H2O2) were investigated on decomposition rate of sebacic acid and its intermediate products. It was shown that the submerged CO2/CH4 DC thermal plasma could decompose carboxylic acid. The highest decomposition rate was obtained at neutral solution pH. Adding H2O2 could significantly enhance the decomposition rate due to synergetic effect of ultraviolet radiation (UV) absorption and hydrogen peroxide oxidation. Photo-oxidation was also proposed as the decomposition mechanism with the novel CO2/CH4 plasma torch based on its high level of UV. This work shows the ability of this novel plasma torch for treatment of organic acids in liquids and solutions and therefore offers a new application for the CO2/CH4 thermal plasma in wastewater treatment.

The effects of gas-phase and in-depth radiation absorption on ignition and steady burning rate of PMMA

Although well studied, there are still interesting features about the ignition and steady burning rate behaviour of PMMA when heated by thermal radiation. In this contribution, the dependence on external heat flux of ignition delay time and steady mass flux of PMMA are investigated numerically. Ignition is modelled by the critical mass flux criterion. The heat transfer model includes effects of heat lost by out gassing, change of volume during degradation and absorption of radiation in both condensed and gaseous phases. Model results are compared to experimental data for both ignition delay time and quasi-steady mass flux across a range of heat fluxes from 20 to 210kWm−2 and the importance of both gas-phase and condensed-phase radiation absorption effects are discussed.

Chemical reaction and radiation absorption effects on the flow and heat transfer of a nanofluid in a rotating system

The aim of this paper is to study the effects of radiation absorption and chemical reaction on MHD free convection heat transfer flow of a nanofluid bounded by a semi-infinite flat plate in a rotating frame of reference. The plate is assumed to oscillate in time with steady frequency so that the solutions of the boundary layer are the similar oscillatory kind. The entire system rotates about the axes normal to the plate. The dimensionless governing differential equations for this investigation are solved analytically using perturbation method. The effects of various important parameters entering into the problem on velocity, temperature, skin friction and Nusselt number within the boundary layer are discussed for Cu–water-based nanofluid with the help of graphs. The predicted consequences obviously point out that the presence of nanoparticles in the base fluid improves the heat transfer process significantly. The results also show that the values of Nusselt number in case of nanofluid are more pronounced than that of micropolar fluid.

Kinetic modelling of Escherichia coli inactivation in a photocatalytic wall reactor

A kinetic model of the photocatalytic inactivation of Escherichia coli in an annular wall reactor is presented. The model is based on a reaction scheme that involves a series of events in which bacteria are progressively damaged and eventually led to cell lysis. The model explicitly takes into account radiation absorption effects. Photocatalytic inactivation experiments were carried out in a photoreactor operated in a closed recirculating circuit with a reservoir tank and irradiated with a 6W black light lamp situated in the axis of the reactor. Immobilization of TiO2 Aeroxide P25 has been carried out by the dip-coating procedure onto the inner-tube wall of the annular reactor. Experimental results for different TiO2 layer thicknesses were used to estimate the kinetic parameters of the model. Good agreement between model predictions and inactivation experiments was achieved in the whole range of TiO2 thicknesses studied.

Remarkable magnetic properties of amorphous hydrogenated carbon nanostructured thin films

AbstractAmorphous hydrogenated carbon thin films with 3d metal nanoparticles were deposited on Si and glass‐ceramic substrates by reactive ion‐plasma magnetron sputtering. Thin films have a high complex permittivity ε * and permeability µ * (ε ′ ≈ 1000–10000, ε″ ≈ 100–1500, μ ′ ≈ 10–70, µ ″ ≈ 0.4–10), what can stipulate by anomalous electromagnetic microwave radiation absorption effect. The magnetic parameters as shape of hysteresis loop, values of coercive force, remanence and saturation magnetization were determined from vibrating‐coil magnetometer measurements. The mechanism of absorption in the material under study is described. Obtained results demonstrate a good promise to use this material for the absorption of electromagnetic microwave radiation. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Hall Currents, Thermal Radiation and Radiation Absorption on Mixed Convective Heat and Mass Transfer Flow Past a Stretching Sheet

In the present work we study the combined influence of chemical reaction, Hall currents and radiation absorption on convective heat and mass transfer flow of a viscous electrically conducting fluid past a stretching sheet. The equations governing the flow of heat and mass transfer have been solved by Galerkin finite element analysis with three nodded line segments. The velocity, temperature and concentration have been analysed for different values of M, m, R, N, N1, Sc and Q1. The rate of heat and mass transfer on the plate has been evaluated numerically for different variations.

Effects of Hall current and radiation absorption on MHD micropolar fluid in a rotating system

The objective of this paper is to study the effects of Hall current and radiation absorption on MHD free convection mass transfer flow of a micropolar fluid in a rotating frame of reference. A uniform magnetic field acts perpendicular to the porous surface in which absorbs micropolar fluid with a constant suction velocity. The entire system rotates about the axes normal to the plate with uniform angular velocity Ω. The dimensionless governing equations for this investigation are reduced to a system of linear differential equations using regular perturbation method, and equations are solved analytically. The influence of various flow parameters of the flow field has been discussed and explained graphically. The present study is of immediate interest in geophysical, cosmically fluid dynamics, medicine, biology, and all those processes which are greatly embellished by a strong magnetic field with a low density of the gas.

Kinetic modeling of arsenic (III) oxidation in water employing the UV/H2O2 process

In a previous study it has been shown that the combination of hydrogen peroxide and UVC radiation is an effective and feasible process to oxidize arsenic in water. In this work, a kinetic model for the photo-oxidation of As (III) is presented. An initial concentration of 200μg/L of As (III) was used. The model was based on mechanistic reaction steps and included the modeling of the local radiation absorption effects. The evaluation of the radiation field inside the reactor was achieved by solving the radiative transfer equation for the homogeneous system. Both dark and photochemical arsenic oxidation rates were incorporated in the complete kinetic expression. Three parameters were estimated and a simplified model that only considered photoactivated reactions was developed. The rates obtained from these simplifications were compared with the rates from the complete model and showed a satisfactory concordance. The study was carried out in a cylindrical reactor operated in batch recirculation mode and two germicidal lamps were used (λ=254nm) as the source of radiation. Experimental runs were performed varying the hydrogen peroxide concentration and incident radiation. Both models rendered a good representation of the experimental data.

Chemically Reacting Hydromagnetic Unsteady Flow of a Radiating Fluid Past a Vertical Plate with Constant Heat Flux

The combined effects of thermal radiation absorption and magnetic field on an unsteady chemically reacting convective flow past an impulsively started vertical plate is studied in the presence of a constant wall heat flux. Boundary layer equations are derived and the resulting approximate nonlinear partial differential equations are solved numerically using a semi-discretization finite difference technique. A parametric study of all parameters involved is conducted, and a representative set of numerical results for the velocity, temperature, and concentration profiles as well as the skin-friction parameter and Sherwood number are illustrated graphically to show typical trends of the solutions. Further validation with previous works is carried out and an excellent agreement is achieved.

MHD non-Darcian flow through a non-isothermal vertical surface embedded in a porous medium with radiation

The effect of MHD on steady two-dimensional laminar mixed flow about a vertical porous surface is numerically analyzed. Also the effects of radiation and heat generation and absorption are considered. A power law variation of temperature along the vertical wall is assumed. The nonlinear boundary-layer equations were transformed and the resulting differential equations were solved by an implicit finite difference scheme (Keller box method). Numerical results for the velocity distribution and the temperature distribution are presented for various values of Prandtl number Pr, magnetic parameter, porous medium parameter and internal heat generation or absorption coefficient. Further validation with previous works is carried out.