Effects Of Flow Parameters Research Articles

THERMAL DIFFUSION AND RADIATION EFFECTS ON UNSTEADY FREE CONVECTION FLOW IN THE PRESENCE OF MAGNETIC FIELD FIXED RELATIVE TO THE FLUID OR TO THE PLATE

The objective of this study is to investigated thermal diffusion and radiation effects on unsteady free convection chemically reacting fluid flow past an accelerated infinite inclined plate with variable temperature and mass diffusion under the influence of uniform transverse magnetic field when the magnetic lines of force are fixed relative to the fluid or to the plate studied in two cases, (i) when magnetic field fixed relative to the fluid (K=0), (ii) and the magnetic field fixed relative to the plate (K=1) have been considered. A general exact solution of the dimensionless governing partial differential equation is obtained by the usual Laplace transform technique without any restriction. The effect of flow parameters on velocity, temperature, concentration, heat transfer and the rate of mass transfer are studied though graphs and tables.

Effect of viscous dissipation on hydromagnetic fluid flow and heat transfer of nanofluid over an exponentially stretching sheet with fluid-particle suspension

AbstractThis paper considers the problem of steady, boundary layer flow and heat transfer of a nanofluid with fluid-particle suspension over an exponentially stretching surface in the presence of transverse magnetic field and viscous dissipation. The stretching velocity and wall temperature are assumed to vary according to specific exponential form. The governing equations in partial forms are reduced to a system of coupled non-linear ordinary differential equations using suitable similarity transformations. An effective Runge–Kutta–Fehlberg (RKF-45) is used to solve the obtained differential equations with the help of a symbolic software MAPLE. The effects of flow parameters—such as nanofluid interaction parameter, magnetic parameter, solid volume fraction of nanoparticle parameter, Prandtl number and Eckert number—on the flow field and heat-transfer characteristics were obtained and are tabulated. Useful discussions were carried out with the help of plotted graphs and tables. Under the limiting cases, c...

Balancing Energy Processes in Turbine Engines

Abstract The article discusses the issue of balancing energy processes in turbine engines in operation in aeronautic and marine propulsion systems with the aim to analyse and evaluate basic operating parameters. The first part presents the problem of enormous amounts of energy needed for driving fans and compressors of the largest contemporary turbofan engines commonly used in long-distance aviation. The amounts of the transmitted power and the effect of flow parameters and constructional properties of the engines on their performance and real efficiency are evaluated. The second part of the article, devoted to marine applications of turbine engines, presents the energy balance of the kinetic system of torque transmission from main engine turbines to screw propellers in the combined system of COGAG type. The physical model of energy conversion processes executed in this system is presented, along with the physical model of gasodynamic processes taking place in a separate driving turbine of a reversing engine. These models have made the basis for formulating balance equations, which then were used for analysing static and dynamic properties of the analysed type of propulsion, in particular in the aspect of mechanical loss evaluation in its kinematic system.

Analysis of flow parameters of a Newtonian fluid through a cylindrical collapsible tube.

In this research study, fluid flow through a cylindrical collapsible tube has been investigated. Of particular interest is the effect of flow parameters on the cross sectional area of a collapsible tube, flow velocity and internal pressure of the fluid. The flow parameters considered are longitudinal tension and volumetric flow rate. The tube is considered collapsible in the transverse direction, taken to be perpendicular to the main flow direction. Collapse happens when external pressure exceeds internal pressure and hence the tube results to a highly noncircular cross sectional area. The fluid flow in consideration is steady and incompressible. Equations governing the flow are non-linear and cannot be solved analytically. Therefore an approximate solution to the equations has been determined numerically. In this case, finite difference method has been used. A computer program has then been used to generate the results which are presented in form of graphs. The results show that the longitudinal tension is directly proportional to both the cross sectional area and internal pressure and inversely proportional to the flow velocity and that change in volumetric flow rate has no effect on the cross sectional area but it is directly proportional to the flow velocity and inversely proportional to the internal pressure.

Structural design and performance experiment of a single vortex combustor with single-cavity and air blast atomisers

The adoption of vortex combustion technology is a relatively recent phenomenon. Among such technology is the trapped vortex combustor, which demonstrates a wide range of stable combustion and low pollutant emissions and accordingly has good application prospects in the field of aeroengines. A new type of single-cavity vortex combustor with air blast atomisers is introduced in this paper. This study conducted a combustion experiment that detailed the influence of the mainstream parameters, fuel parameters and combustion organisation on the combustion characteristics of the liquid-fuelled combustor. The results of this experiment suggest that this new type of vortex combustor has a reasonably designed structure and demonstrates good combustion performance. In addition, pollutant emissions under a low power state are predicted using a semi-empirical formula in which the effects of flow parameters, fuel parameters and atomisation characteristics of the fuel supply equipment are considered. Furthermore, the predicted value obtained is consistent with the experimental value. The results of this study provide a reference for the structural design and engineering application of the vortex combustor.

Heat transfer and friction characteristics of an equilateral triangular solar air heater duct using inclined continuous ribs as roughness element on the absorber plate

An experimental study has been carried out to determine the effect on the heat transfer and friction characteristics of an equilateral triangular solar air heater duct using inclined continuous ribs as roughness element on the absorber plate. The experimental study encompasses the range of Reynolds numbers from 5600 to 28,000, relative roughness height (e/Dh) 0.021–0.043, relative roughness pitch (p/e) 8–16 and angle of attack (α ) 30–60°. The duct has an aspect ratio (W/H) of 1.15. The effect of flow parameters and roughness parameters on heat transfer and friction factor is discussed. The thermohydraulic performance parameter has been determined for the given range of flow parameters and roughness parameters.

Diffusion-Thermo and Radiation Effects on Unsteady MHD Flow Through Porous Medium Past an Impulsively Started Infinite Vertical Plate with Variable Temperature and Mass Diffusion

The objective of this study is to investigate diffusion-thermo (Dufour effect) and radiation effects on unsteady MHD free convection flow past an impulsively started infinite vertical plate with variable temperature and uniform mass diffusion in the presence of transverse applied magnetic field through porous medium. At time t > 0, the plate is given an impulsive motion with constant velocity u0 in the vertical upward direction against to the gravitational field. At the same time, the plate temperature is raised linearly with time t and the level of concentration near the plate is raised to \({{C}_{\rm w}^{\prime}}\). A magnetic field of uniform strength B0 is applied normal to the direction to the flow. The dimensionless governing equations are solved in closed form by Laplace transform technique. The effect of flow parameters on velocity, temperature, concentration, the rate of heat transfer and the rate of mass transfer are shown through graphs.

Magnetohydrodynamics and Radiation Effects on Unsteady Convection Flow of Micropolar Fluid Past a Vertical Porous Plate with Variable Wall Heat Flux

An analysis is presented for the problem of the unsteady two-dimensional laminar flow of a viscous incompressible micropolar fluid past a vertical porous plate in the presence of a transverse magnetic field and thermal radiation with variable heat flux. The free stream velocity follows an exponentially increasing or decreasing small perturbation law. A uniform magnetic field acts perpendicularly to the porous surface in which it absorbs the micropolar fluid with a suction velocity varying with time. The Rosseland approximation is used to describe radiative heat transfer in the limit of optically thick fluids. The effects of flow parameters and thermophysical properties on the flow temperature fields across the boundary layer are investigated. The method of solution can be applied for small perturbation approximation. Numerical results of velocity profiles of micropolar fluids are compared with the corresponding flow problems for a Newtonian fluid. Also, the results of the skin-friction coefficient and the couple stress coefficient at the wall are prepared with various values of the fluid properties.

Dufour Effects on Unsteady Hydromagnetic Radiative Fluid Flow past a Vertical Plate through Porous Medium

The objective of the present study is to investigate diffusion-thermo (Dufour effect) and radiation effects on unsteady MHD free convection flow past an impulsively started infinite vertical plate with variable temperature and uniform mass diffusion in the presence of transverse applied magnetic field through porous medium. At time t > 0, the plate is given an impulsive motion with constant velocity in the vertical upward direction against to the gravitational field. At the same time the plate temperature is raised linearly with time t and the level of concentration near the plate is raised to . A magnetic field of uniform strength is applied normal to the direction to the flow. The dimen- sionless governing equations are solved in closed form by Laplace-transform technique. The effect of flow parameters on velocity, temperature, concentration, the rate of heat transfer and the rate of mass transfer are shown through graphs.

Fluctuating Heat and Mass Transfer on Unsteady MHD Free Convection Flow of Radiating and Reacting Fluid past a Vertical Porous Plate in Slip- Flow Regime

In this paper, an analytical study on unsteady MHD free convective viscous incompressible flow of electricallyconducting fluid with periodic heat and mass transfer past an infinite vertical porous flat plate in slip flow regime is presented. A uniform magnetic field perpendicular to the plate is applied. The effects of thermal radiation and chemical reaction are included. The effects of flow parameters and thermo physical properties on the flow, temperature and concentration fields across the boundary layer are investigated. The forms of the wall shear stress, Nusselt number and Sherwood number are derived. The results are shown in figures and tables followed by a quantitative discussion.

Convective heat transfer for viscoelastic fluid in a curved pipe

In this paper, fully developed convective heat transfer of viscoelastic flow in a curved pipe under the constant heat flux at the wall is investigated analytically using a perturbation method. Here, the curvature ratio is used as the perturbation parameter and the Oldroyd-B model is applied as the constitutive equation. In the previous studies, the Dirichlet boundary condition for the temperature at the wall has been used to simplify the solution, but here exactly the non-homogenous Neumann boundary condition is considered to solve the problem. Based on this solution, the non-axisymmetric temperature distribution of Dean flow is obtained analytically and the effect of flow parameters on the flow field is investigated in detail. The current analytical results indicate that increasing the Weissenberg number, viscosity ratio, curvature ratio, and Prandtl number lead to the increase of the heat transfer in the Oldroyd-B fluid flow.

Numerical study of flow in a rotor-stator system with inward throughflow

A numerical study has been carried out to study fluid flow within a rotor-stator system with an inward throughflow and pre-rotation. Furthermore, the effect of flow parameters on the flow structure has been investigated. The entrainment coefficient, beta, of the rotating fluid and the rotating disc moment coefficient have been calculated. A correlation has been found for predicting the place of stagnation point. The results show the Batchelor type of flow with two separated boundary layers on the rotating and stationary discs. The numerical results are compared with the available measured data and generally, a good agreement has been encountered.

A novel restricted-flow etching method for glass

This paper presents a novel micro fabrication method based on the laminar characteristics of micro-scale flows. Therein the separator and etchant are alternatively arranged in micro channels to form multiple laminar streams, and the etchant is located at the site where the reaction is supposed to occur. This new micro fabrication process can be used for the high aspect ratio etching inside a microchannel on glass substrates. Furthermore, the topography of microstructure patterned by this method can be controlled by changing the flow parameters of the separator and etchant. Experiments on the effects of flow parameters on the aspect ratio, side wall profile and etching rate were carried out on a glass substrate. The effect of flow rates on the etching rate and the micro topography was analyzed. In addition, experiments with dynamical changes of the flow rate ratio of the separator and etchant showed that the verticality of the side walls of microstructures can be significantly improved. The restricted flowing etching technique not only abates the isotropic effect in the traditional wet etching but also significantly reduces the dependence on expensive photolithographic equipment.

The interior heat transfer characteristics of gas turbine blade due to sparse film cooling holes

The film cooling technique is one of the most useful cooling methods. At present, the midchord region of gas turbine blades in an aeroengine often adopt a sparse film cooling technique and impingement cooling technique at the same time. So the interior heat transfer characteristics on the inner side of blades due to the sparse film cooling holes have become a very complicated and interesting problem. In this paper, the heat transfer characteristics of impingement-cooling have been investigated experimentally. Through lots of experimental data, the effect of flow parameters and geometric parameters on heat transfer characteristics has been studied. Correlation equations obtained show good agreement with experimental data. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(3): 197–207, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20052

Transient mixed radiative convection flow of a micropolar fluid past a moving, semi-infinite vertical porous plate

The flow of viscous incompressible micropolar fluid past a semi-infinite vertical porous plate is investigated with the presence of thermal radiation field, taking into account the progressive wave type of disturbance in the free stream. The effects of flow parameters and thermophysical properties on the flow and temperature fields across the boundary layer are investigated. The Rosseland approximation is used to describe radiative heat transfer in the limit of optically thick fluids. Numerical results of velocity profile of micropolar fluids are compared with the corresponding flow problems for a Newtonian fluid. It is observed that, when the radiation parameter increases the velocity and temperature decrease in the boundary layer, whereas when Grashof number increases the velocity increases.

Void Fraction Measurement in Subcooled-Boiling Flow Using High-Frame-Rate Neutron Radiography

A high-frame-rate neutron radiography (NR) technique was applied to measure the void fraction distribution in forced-convective subcooled-boiling flow. The focus was experimental technique and error estimation of the high-frame-rate NR. The results of void fraction measurement in the boiling flow were described. Measurement errors on instantaneous and time-averaged void fractions were evaluated experimentally and analytically. Measurement errors were within 18 and 2% for instantaneous void fraction (measurement time is 0.89 ms), and time-averaged void fraction, respectively. The void fraction distribution of subcooled boiling was measured using atmospheric-pressure water in rectangular channels with channel width 30 mm, heated length 100 mm, channel gap 3 and 5 mm, inlet water subcooling from 10 to 30 K, and mass velocity ranging from 240 to 2000 kg/(m2·s). One side of the channel was heated homogeneously. Instantaneous void fraction and time-averaged void fraction distribution were measured parametrically. The effects of flow parameters on void fraction were investigated.

Some problems for bundle CHF prediction based on CHF measurements in simple flow geometries

A comparison of critical heat flux (CHF) fuel bundles data with CHF data obtained in simple flow geometries was made. The base for the comparison was primary experimental data obtained in annular, circular, rectangular, triangular, and dumb-bell shaped channels cooled with water and R-134a. The investigated range of flow parameters (pressure, mass flux, and critical quality) in R-134a was chosen to be equivalent to modern nuclear reactor water flow conditions ( p=7 and 10 MPa, G=350–5000 kg (m 2 s) −1, x cr=−0.1–1). The proper scaling laws were applied to convert the data from water to R-134a equivalent conditions and vise versa. The effects of flow parameters ( p, G, x cr) and the effects of geometric parameters ( D, L) were evaluated during comparison. The comparison showed that no one simple flow geometry can be used for accurate and reliable bundle CHF prediction in wide range of flow parameters based on local (critical) conditions approach. The comparison also showed that the limiting critical quality phenomenon is unique characteristic for each flow geometry which depends on many factors: flow conditions (pressure and mass flux), geometrical parameters (diameter or surface curvature, gap size, etc.), flow obstructions (spacers, appendages, turbulizers, etc.) and others.

Flow length effect in heat exchangers with turbulent flow at low prandtl number

This work brings out the effect of entry length on the mean overall heat transfer coefficient of a heat exchanger for turbulent flow with low Prandtl Number. For this purpose simple heat transfer correlations are proposed in the thermal entry length region and with these correlations the correction factors are calculated for selected special cases. The effect of flow parameters and total heat exchanger length has also been investigated. Finally comments are made regarding thermal boundary conditions and in its light the commonly used design method is assessed.

Oxides of nitrogen emissions from turbulent jet flames: Part I—Fuel effects and flame radiation

Measurements of oxides of nitrogen emission indices, flame radiant fractions, and visible flame dimensions were made for turbulent jet diffusion flames covering a wide range of flow conditions. Objectives of the study were to explain the observed scaling of NO x emissions with flow variables and to understand the interrelationships among NO x , flow conditions, and flame radiation. The flames were vertical and stabilized with hydrogen pilot flames on straight tube burners. Flow conditions were varied by changing the initial jet velocity and/or the burner tube diameter. Four burner sizes were used, with diameters ranging from 2.18 to 6.17 mm; and four fuel types, having a wide range of sooting tendencies, were employed: methane, ethylene, propane, and a 57% CO 43% H 2 (by volume) mixture. The ranges of Reynolds numbers and Froude numbers explored were 3,130–88,500 and 218 to 2.8 × 10 6, respectively. The effects of flow parameters and fuel type on radiant losses are shown to be important in determining the NO x emissions from simple jet flames. For high-temperature flames (T > 2050 K), overall NO x production rates for all four fuels were found to scale with characteristic flame temperatures deduced from the measured radiant fractions in a manner consistent with Zeldovich kinetics. This successful scaling of NO x production rates with global flame temperatures and residence times is consistent with, but does not prove, the view that much of the NO x emitted by jet flames is formed in large-scale eddies at the flame tip. NO x production rates higher than expected from the thermal mechanism alone are observed for the hydrocarbon fuels at lower flame temperatures (<2050 K), with the NO x production rates ranking in the same order as sooting tendencies. This suggests that gas-molecular radiation is more relevant than broadband radiation from soot for determining temperatures in NO formation zones. Prompt NO and/or other soot-NO interactions may also be important for the hydrocarbon fuels in this temperature regime. Previously reported Reynolds and Froude number dependencies for NO x production rates are examined and found to be consistent with flame heat loss characteristics.

Effects of Flow Parameters on the Cathodic Protection of a Steel Plate in Natural Seawater

Abstract A formula that describes the transport of oxygen to the surface of a metal under cathodic polarization in seawater is presented. The relation assumes turbulent flow conditions and a flat p...