On stratified variable thermal conductivity stretched flow of Walter-B material subject to non-Fourier flux theory

The objective here is to examine the characteristics of non-Fourier flux theory in flow induced by a nonlinear stretched surface. Constitutive expression for an incompressible Walter-B liquid is taken into account. Consideration of thermal stratification and variable thermal conductivity characterizes the heat transfer process. The concept of boundary layer is adopted for the formulation purpose. Modern methodology for the computational process is implemented. Surface drag force is computed and discussed. Salient features of significant variables on the physical quantities are reported graphically. It is explored that velocity is enhanced for a larger ratio of rate constants. The increasing values of thermal relaxation factor correspond to less temperature.

     

Transient flow and heat transfer mechanism for Williamson-nanomaterials caused by a stretching cylinder with variable thermal conductivity

The utilization of nanometre-sized solid particles in working fluids has been seriously recommended due to their enhanced thermal characteristics. This suspension of solid particles in base fluids can significantly enhance the physical properties, such as, viscosity and thermal conductivity. They are widely used in several engineering processes, like, heat exchangers, cooling of electronic equipment, etc. In this exploration, we attempt to deliver a numerical study to simulate the nanofluids flow past a circular cylinder with convective heat transfer in the framework of Buongiorno’s model. A non-Newtonian Williamson rheological model is used to describe the behavior of nanofluid with variable properties (i.e., temperature dependent thermal conductivity). The leading flow equations for nanofluid transport are mathematical modelled with the assistance of Boussinesq approximation. Numerical simulation for the system of leading non-linear differential equations has been performed by employing versatile, extensively validated, Runge–Kutta Fehlberg scheme with Cash–Karp coefficients. Impacts of active physical parameters on fluid velocity, temperature and nanoparticle concentration is studied and displayed graphically. It is worth to mention that the temperature of non-Newtonian nanofluids is significantly enhanced by higher variable thermal conductivity parameter. One major outcome of this study is that the nanoparticle concentration is raised considerably by an increasing values of thermophoresis parameter.

     

Magnetohydrodynamic three-dimensional nonlinear convective flow of viscoelastic nanofluid with heat and mass flux conditions

The present research focuses on three-dimensional nonlinear convective flow of viscoelastic nanofluid. Here, the flow is generated due to stretching of a impermeable surface. The phenomenon of heat transport is analyzed by considering thermal radiation and prescribed heat flux condition. Nanofluid model comprises of Brownian motion and thermophoresis. An electrically conducting fluid is accounted due to consideration of an applied magnetic field. The dimensionless variables are introduced for the conversion of partial differential equations into sets of ordinary differential systems. The transformed expressions are explored through homotopic algorithm. Behavior of different dimensionless parameters on the non-dimensional velocities, temperature and concentration are scrutinized graphically. The values of skin friction coefficients, Nusselt and Sherwood numbers are also calculated and elaborated. It is visualized that the heat transfer rate increases with Prandtl number and radiation parameter is higher.

     

Thermal convection of MHD Blasius and Sakiadis flow with thermal convective conditions and variable properties

Microsystem Technologies - A theoretical study on the effect of magnetohydrodynamic field on the classical Blasius and Sakiadis flows of heat transfer characteristics with variable conditions and...     

Dynamic temperature control with variable heat flux for high strength steel

We propose a dynamic temperature control (DTC) scheme for high strength steel to obtain the desired temperature and properties of steel in the run-out table (ROT) process. A control model with variable heat flux is developed to reduce the temperature deviation from the actual temperature of the strip, the temperature drop due to water cooling. The control concept uses field data and a timetemperature transformation (TTT) diagram. A ROT dynamic simulator (RoDys) with four simulation modes using the control model is developed to achieve the desired steel properties. The effectiveness of the proposed control scheme is verified from simulation results under a disturbance of the rolling speed. Using a hot strip mill field test, we show that the performance of the temperature control is significantly improved by the proposed control scheme.     

On MHD radiative Jeffery nanofluid flow with convective heat and mass boundary conditions

Neural Computing and Applications - The prime objective of present exploration is to study effects of magnetohydrodynamic, Joule heating and thermal radiation on an incompressible Jeffrey nanofluid...     

可变电压源在热导检测器中的应用

在可变电压源电路中,通过传感器上的电流恒定,改变桥路中支路电阻比值大小,能够一定程度上提高热导检测器(TCD)的灵敏度。同时还分析了可变电压源在铼钨丝与热敏电阻(NTC)作为传感器上的应用,在铼钨丝(130Ω)作为传感器实验中,其它条件相同时,通过铼钨丝上电流分别在20mA、40mA、60mA的比较,发现桥路输出信号与铼钨丝上通过电流的3.5次方成比例。在热敏电阻(NTC)作为传感器实验中,选择材料常数β值大的热敏电阻作为传感器,有利于提高桥路的信号输出。     

The effects of variable viscosity and thermal conductivity on a thin film flow over a shrinking/stretching sheet

The effects of variable viscosity and thermal conductivity on the flow and heat transfer in a laminar liquid film on a horizontal shrinking/stretching sheet are analyzed. The similarity transformation reduces the time independent boundary layer equations for momentum and thermal energy into a set of coupled ordinary differential equations. The resulting five-parameter problem is solved by the homotopy perturbation method. The results are presented graphically to interpret various physical parameters appearing in the problem.     

The heat transfer from a sphere in free convective flow

We consider the free convective flow over the surface of a sphere whose temperature is suddenly raised to a value greater than that of its surroundings. Numerical solutions of the Navier-Stokes equations are obtained for finite values of the Prandtl and Grashof numbers. The heat-transfer characteristics are examined, and where possible compared with earlier results obtained from boundary-layer theory in the high Grashof number limit.     

Application of homotopy analysis method for fin efficiency of convective straight fins with temperature-dependent thermal conductivity

In this paper, the homotopy analysis method (HAM) has been used to evaluate the efficiency of straight fins with temperature-dependent thermal conductivity and to determine the temperature distribution within the fin. The fin efficieny of the straight fins with temperature-dependent thermal conductivity has been obtained as a function of thermo-geometric fin parameter. It has been observed that the thermal conductivity parameter has a strong influence over the fin efficiency. The series solution is developed and the reccurance relations is given. Comparison of the results with those of the homotopy perturbation method (HPM) and the Adomian decomposition method (ADM), has led us to significant consequences. The analytic solution of the problem is obtained by using the HAM. The HAM contains the auxiliary parameter ?$?$, which provides us with a simple way to adjust and control the convergence region of solution series. By suitable choice of the auxiliary parameter ?$?$, we can obtain reasonable solution for large values of τ$\tau$ and η$\eta$.     

An optimal solution for magnetohydrodynamic nanofluid flow over a stretching surface with constant heat flux and zero nanoparticles flux

This article examines the hydromagnetic three-dimensional flow of viscous nanoliquid. A bidirectional linear stretching surface has been used to create the flow. Novel features regarding Brownian motion and thermophoresis have been studied by employing Buongiorno model to examine the slip velocity of nanoparticle. Viscous liquid is electrically conducting subject to uniform applied magnetic field. Problem formulation in boundary-layer region is performed for low magnetic Reynolds number. Simultaneous effects of constant heat flux and zero nanoparticles flux conditions are utilized at boundary. Appropriate transformations correspond to the strongly nonlinear ordinary differential expressions. The resulting nonlinear systems have been solved through the optimal homotopy analysis method. Graphs have been sketched in order to analyze that how the temperature and concentration profiles are affected by various physical parameters. Further the coefficients of skin-friction and heat transfer rate have been numerically computed and discussed. Our findings show that the temperature distribution has a direct relationship with the magnetic parameter. Moreover, the temperature distribution and thermal boundary-layer thickness are higher for hydromagnetic flow in comparison with the hydrodynamic flow.

     

Computer acquisition and analysis of skin temperature and heat flow data from heat flux transducers

A computer-controlled system for the collection and analysis of skin temperature and heat flow data originating from an array of heat flux transducers is describe. The systems is based on a program (‘THERMAL’) that reads, stores, prints and displays skin temperatures and heat flow data every 2 min for up to 4 h. It also simultaneously calculates important environmental physiology parameters such as mean skin and mean body temperatures as well as mean heat flow according to four different combinations of transducers such as the established 3-, 4-, 7- and 12-point (site) formulae. Core temperature, heart rate and environmental condition indices such as dry bulb, wet bulb and globe temperatures are also continuously monitored.     

Mixed convective heat and mass transfer in a vertical wavy channel with traveling thermal waves and porous medium

We investigate the problem of mixed convection heat and mass transfer through a vertical wavy channel with porous medium. The flow is generated by the periodic thermal waves prescribed at the wavy walls of the channel. The equations of momentum energy and concentration are solved subject to a set of appropriate boundary conditions by assuming that the solution consists of a mean part and a perturbed part. The effects of various pertinent parameters on flow, heat and mass transfer characteristics are discussed numerically and explained graphically.     

On the forced convective heat transport in a droplet-laden flow in microchannels

Recently, a great deal of attention has been focused on development of microfabricated devices for manipulating minute amounts of liquids. In particular, an extensive experimental work is devoted to generation, motion and manipulation of drops in microfluidic channels, or digital microfluidics. In the present work the numerical approach based on volume-of-fluid method, combined with the piece-wise linear interface reconstruction scheme, is implemented for modeling of droplet motion and forced heat transport in a droplet-laden laminar flow in a circular microchannel. The simulations show a very good agreement with asymptotic results concerning the motion of spherical and slender drops in confined laminar flows. The effective rates of the forced heat transfer in a droplet-laden flow are found to be superior over that in single-phase Poiseuille flow. The enhancement is anticipated to be a result of the flow disturbance in the carrier fluid due to propagation of a train of translating drops and efficient convective transport within drops due to internal circulation.

Unsteady flow of a reactive variable viscosity non-Newtonian fluid through a porous saturated medium with asymmetric convective boundary conditions

This article examines the thermal effects in an unsteady flow of a pressure driven, reactive, variable viscosity, third-grade fluid through a porous saturated medium with asymmetrical convective boundary conditions. We assume that exothermic chemical reactions take place within the flow system and that the asymmetric convective heat exchange with the ambient at the surfaces follow Newton’s law of cooling. The coupled nonlinear partial differential equations governing the problem are derived and solved numerically using a semi-implicit finite difference scheme. Graphical results are presented and discussed qualitatively and quantitatively with respect to various parameters embedded in the problem.     

Measurements and modeling of two-phase flow in microchannels withnearly constant heat flux boundary conditions

Two-phase forced convective flow in microchannels is promising for the cooling of integrated circuits. There has been limited research on boiling flow in channels with dimensions below 100 μm, in which bubble formation and flow regimes can differ from those in larger channels. This work develops single and multi-channel experimental structures using plasma-etched silicon with pyrex glass cover, which allow uniform heating and spatially-resolved thermometry and provide optical access for visualization of boiling regimes. Boiling was observed with less than 5°C of super-heating in rectangular channels with hydraulic diameters between 25 and 60 μm. The channel wall widths are below 350 μm, which minimizes solid conduction and reduces variations in the heat flux boundary condition. Pressure drop and wall temperature distribution data are consistent with predictions accounting for solid conduction and homogeneous two-phase convection     

Wavelet strategy for flow and heat transfer in CNT-water based fluid with asymmetric variable rectangular porous channel

In the present work, the characteristics of physical model unsteady nanofluid flow and heat transfer in an asymmetric porous channel are analyzed numerically using wavelet collocation method. Using similarity transformation, unsteady two-dimensional flow model of nanofluid in a porous channel through expanding or contracting walls has been transformed into a system of nonlinear ordinary differential equations (ODEs). Then, the obtained nonlinear system of ODEs is solved via wavelet collocation method. The effect of various emerging parameters, such as nanoparticle volume fraction, Reynolds number (Re), and expansion ratio have been analyzed on velocity and temperature profiles. Numerical results have been presented in form of figures and tables. For some special cases, the obtained numerical results are compared with exact one and found that the results are good in agreement with exact solutions.

     

Electromagnetic imaging for shape and variable conductivity

We consider the inverse problem of determining both the shape and the conductivity of a two-dimensional (2D) conducting scatterer from the knowledge of the far-field pattern of TM waves by solving the ill-posed nonlinear equation. Based on the boundary condition and measured scattered field, a set of nonlinear integral equations is derived and the imaging problem is reformulated into an optimization problem. Satisfactory reconstructions are achieved by the genetic algorithm. Numerical results demonstrate that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In addition, the effect of Gaussian noise on the reconstruction results is investigated. The numerical results show that multiple incident directions permit good reconstruction of shape and, to a lesser extent, conductivity in the presence of noise in measured data. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14, 433–440, 2004.     

Problem of flow distribution with variable nodal flow rates

The hydraulic circuit theory created to model hydraulic systems such as pipeline transportation systems usually considers the flow distribution problem with specified flow rates of the medium to be transported to and from the transportation system at individual nodes. This paper investigates the case of practical interest where the medium flow rates at individual nodes are not fixed but depend on the pressure at these nodes.     

Significance of Arrhenius activation energy in flow and heat transfer of tangent hyperbolic fluid with zero mass flux condition

Microsystem Technologies - The current endeavor scrutinizes the flow of tangent hyperbolic fluid over a moving stretched surface. The characteristics of heat transfer are conferred by utilizing...