Investigation of the effect of transverse thermal dispersion on forced convection in porous media

Summary In this paper an analytical study of the effect of the transverse thermal dispersion on fully developed forced convection in a parallel-plate channel filled with an isotropic fluid saturated porous medium is carried out. It is assumed that the momentum flow in the channel is governed by the Brinkman-Forchheimer-extended Darcy equation. The objective of the present research is to determine in which situations thermal dispersion can significantly influence heat transfer in the channel.     

Influence of natural and forced convection on the characteristics of heterogeneous combustion of a carbon particle

The little-studied problem of the effect of natural and forced convection on the stationary (combustion) and critical (ignition and extinction) high-temperature states of a carbon particle with account for radiative heat exchange with the cold walls of the processing setup is considered. The effect of molecular and convective heat and mass exchange of a carbon particle with a gas on the critical diameter of the particle d_e at which the particle is spontaneously extinguished (a jumpwise transition from combustion to oxidation) is analyzed. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 1050–1055, November–December, 1998.     

Uniform suction/blowing effect on forced convection about a wedge: Uniform heat flux

Summary The effect of constant suction/blowing on steady two-dimensional laminar forced flow about a uniform heat flux wedge is numerically analyzed. 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, the temperature distribution, the local skin friction coefficient and the local Nusselt number are presented for various values of Prandtl number Pr, pressure gradient parameterm and suction/blowing parameter . In general, it has been found that the local skin friction coeffcient and the local Nusselt number increase owing to suction of fluid. This trend reversed for blowing of fluid. In addition to, as the blowing effect is strong enough, i.e. –0.65, the flow separation only occurred in the case ofm=0.0.Notation C Constant defined in Eq. (4.2) - C _f Local skin friction coefficient, 2v(u/y) _y=0/U ² - f Dimensionless stream function defined in Eq. (5.3) - g Gravitational acceleration - h Local heat transfer coefficient - k Thermal conductivity - m Pressure gradient parameter, /(2–) - Nu _x Local Nusselt number,hx/k - Pr Prandtl number,v/ - q _w Wall heat flux - Re _x Local Reynolds number,U x/v - T Temperature - T _w Wall temperature - T Temperature of ambient fluid - u Velocity component in thex-direction - U Potential flow velocity,Cx ^m - v Velocity component in they-direction - V _w Surface mass transfer - x Coordinate along the wedge surface - y Coordinate normal to the wedge surface - Thermal diffusivity - Angle factor of the wedge - Pseudosimilarity variable defined in Eq. (5.2) - Suction/blowing parameter defined in Eq. (5.1) - Total angle of the wedge - Dimensionless temperature defined in Eq. (5.4) - Kinematic viscosity - Stream function     

强制对流换热实验测试系统的研制

运用虚拟仪器技术,研制了一套强制对流换热实验台自动化测试系统.测试系统实现了温度和风速的精确测量,以及风机转速和加热功率的自动控制,测试软件可以直观地观察整个换热过程中各个测量点的状态变化情况,进而得到整个实验过程从启动到稳态过程的全部数据,并对测量结果进行了不确定度分析,系统平均换热系数测量不确定度为4.9W/(m2.℃).     

A numerical study of similarity solutions for combined forced and free convection

Summary The similarity equations for combined forced and free convection flow over a horizontal plate when the wall temperature is inversely proportional to the square root of the distance from the leading edge are solved by introducing a scaling similar to that for the Blasius equation. The technique is also applied to the local similarity equations for the case of a constant wall temperature.With 7 Figures     

Development of a roller quenching apparatus for the production of amorphous phases

The details of an apparatus designed to produce amorphous phases by rapid quenching from the melt are described. A drop of molten material is squeezed between two copper rollers rotating against each other at 5000 RPM and a thin foil of the material is produced. The system produces cooling rates of the order of 10⁵ K/sec. Details of the development and construction are mentioned.     

Parametric study of unsteady forced convection with pressure gradient

By an extension of differential method, this paper has successfully examined the unsteady forced convection heat transfer from a flow over a flat plate. Transient state is inherent to a sudden change on the heat flux density at the surface of a plate. The general case where the pressure along the direction of flow is not constant is presented. The differential momentum and heat transfer equations are solved numerically. The results are given for different values of pressure gradient parameter m, in the cases of attached boundary layer, and for several values of Prandtl number corresponding to usual fluids (0.71 ⩽ Pr ⩽ 100). The dependences of transient behaviours with Pr number and parameter m are evidenced from the evolutions in time of temperature profile, Stanton number, and duration of unsteady process. Solutions given from the beginning of transient state to the ultimate steady state are discussed. Moreover, analytical solutions, as function of Pr and m, are deduced for Stanton number and duration of unsteady regime.     

Simulation of forced convection in non-Newtonian fluid through sandstones

Numerical simulation is carried out to study forced convection in non-Newtonian fluids flowing through sandstones. Simulation is carried out using lattice Boltzmann method (LBM) for both shear-thinning and shear-thickening, by varying the power law index from 0.5 to 1.5 in Carreau–Yasuda model. Parameters involved in LBM and Carreau model are identified to achieve numerical convergence. Permeability and porosity are varied in the range of 10^?10–10^?6 and 0.1–0.7, respectively, to match actual geometrical properties of sandstone. Numerical technology is validated by establishing Darcy's law by plotting the graph between velocity and pressure gradient. Consequently, investigation is carried out to study the influence of material properties of porous media on flow properties such as velocity profiles, temperature profiles, and Nusselt number.     

Effect of plate orientation on quenching characteristics

Abstract

The effect of position on the face of a steel plate on the quenching process during cooling from a typical austenitisation temperature has been examined. In addition, the effect of plate orientation on the quenching mechanism has been investigated. The most significant effect of these parameters on the quenching process relates to the length of the vapour blanket stage, which is very sensitive to position on the surface of the specimen. This has considerable importance in relation to the production of unhardened regions. A markedly different mechanism of heat transfer during nucleate boiling at different positions on the face did not give rise to corresponding differences in the surface heat transfer coefficients at this stage in the quench. The investigation of heat transfer in the surface of the plate has been supported by still photographs that clearly show the different processes at different positions and orientations of the plate. In particular they show violent disruption of the surrounding quenchant as large packets of vapour are nucleated in quick succession on the underside of a horizontal plate.

MST/3032     

Similarity and the formation of correlations for forced convection to supercritical pressure fluids

Investigation of heat transfer to supercritical pressure helium seems to be following a pattern like that of supercritical pressure water. The aim of the paper is to demonstrate the conditions under which heated tubes carrying variable property fluid will have similar heat transfer performance. It is shown how these conditions follow from the governing equations, and their application to the planning and interpretation of experiments is demonstrated using supercritical pressure water data. Recent experimental data and correlations for supercritical pressure helium are examined.     

薄壁圆柱壳构件受迫振动的响应特征研究

针对固支-自由约束条件下受径向谐波激励或径向冲击激励的薄壁圆柱壳构件,开展其受迫振动下的响应特征分析。首先基于Love壳体理论建立了薄壁圆柱壳构件的动力学模型,然后,根据固支-自由约束条件特点,采用轴向梁函数和周向三角函数组合的振型函数以及振型叠加法,获得了考虑粘性阻尼的薄壁圆柱壳模态坐标振动方程,进而求解受径向谐波激励或冲击激励的振动响应。通过一个具体算例,进行了不同位置上的响应幅度与相位的变化分析,并对比了模态阻尼比和激励力幅值对响应幅值的影响。     

Heat transfer correlations for the forced convection boiling of R12-R13 mixtures

Correlations for predicting the local heat transfer coefficient during forced convection boiling of mixed refrigerants have been developed for four compositions of binary mixtures of R13 and R12. Of the several correlations examined with nearly equal promise, the Lavin-Young type has been found the best. Generalized correlations have also been developed for all mixture compositions. Effect of concentration factor, CF, has resulted in marginal improvement of the correlations. Liquid and vapour phase Prandtl numbers have also been found to affect the generalized correlations for predicting the local heat transfer coefficient.     

A quenching apparatus for the gaseous products of the solar thermal dissociation of ZnO

Rapid cooling for avoiding the recombination of Zn vapor and O₂ derived from the solar thermal dissociation of ZnO is investigated using a thermogravimeter coupled to a quenching apparatus. The ZnO sample, which is placed in a cavity receiver and directly exposed to concentrated solar irradiation, underwent dissociation in the temperature range 1,820–2,050 K at a rate monitored by on-line thermogravimetry. The product gases were quenched by water-cooled surfaces and by injection of cold Ar at cooling rates from 20,000 to 120,000 K/s, suppressing the formation of ZnO in the gas phase and at the walls. Zinc content of the collected particles downstream varied in the range 40–94% for Ar/Zn(g) dilutions of 170 to 1,500.

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Study of forced convection in the presence of a liquid-porous-medium interface

Exact solutions of the problem of forced convection of an incompressible fluid (gas) are obtained for a number of geometries with the presence of an interface between an "ideal" fluid and a saturated porous medium. A generalization of the Darcy law allowing for viscous effects that are substantial at the boundaries of a porous body is used to model flow in a porous layer. The flow velocity as a function of the Darcy number is studied. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 6, pp. 895–901, November–December, 1997.     

Analysis of forced convection micropolar boundary layer about a permeable sphere

The heat transfer characteristics and local skin friction for forced convection flow of micropolar fluid over an isothermal or a constant-heat-flux surface of sphere with surface mass transfer have been studied. The problem was formulated by applying a suitable variables transformation and the solutions were obtained by an implicit finite difference method. Numerical results were carried out for a wide range of mass transfer parameters as the Prandtl number at 0.7 or 7 with several values of material parameters of the micropolar fluid. The variations of the local friction factor and local Nusselt number are plotted and discussed.     

Heat transfer in forced convection of fluid in porous sintered metals

The present state of the problem is analyzed and latest results presented for studies of heat transfer during the flow of fluid within porous sintered metals.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 1, pp. 5–13, January, 1976.     

Boundary-layer analysis of forced convection with a plate and porous substrate

Summary. The classical boundary-layer analysis of Blasius and Pohlhausen for forced convection from a flat plate in the presence of a uniform external stream is extended to the case where a thin layer of a porous medium is attached to the plate. It is found that the effect of the porous layer is to increase the heat flux as represented by a Nusselt number, and to within the approximations made this increase is independent of the Darcy number. The deviation increases with the Prandtl number, and also increases with the new parameter defined by Eq. (9).