Effect of a Dispersed Admixture on the Flow Pattern and Heat Transfer in a Supersonic Dusty-Gas Flow Around a Cylinder

A mathematical model of two-phase (gas-solid particle) flow which takes into account particle-particle collisions and the feedback effect of the admixture on the gas parameters is proposed. The dispersed phase is described by a kinetic equation of the Boltzmann type and the carrier gas by modified Navier-Stokes equations. Using this model, a supersonic uniform dusty-gas flow past a cylinder is calculated. The fields of the macroparameters of the admixture and the carrier medium are obtained. The dependence of the heat transfer at the stagnation point on the relative particle size and the free-stream admixture concentration is studied in detail. The ranges of these parameters on which particle collisions and the feedback effect of the admixture on the carrier-gas flow are important are found.     

Reduction of Peak Heat Fluxes by Supplying Heat to the Free Stream

A supersonic flow past a blunt body in the presence of an incident oblique shock wave is considered. It is shown that by supplying heat to the free stream it is possible substantially to reduce local heat flux peaks on the body surface. The integral heat flux on the body surface increases by only a small fraction of the heat released into the flow.     

Intensification of Heat Transfer in a Downward Liquid-Film Flow

Heat transfer in a film flow of the FC-72 dielectric liquid down a vertical surface with an embedded 150×150 mm heater is experimentally examined in the range of Reynolds numbers Re = 5–375. A chart of liquid-film flow modes is constructed, and characteristic heat-transfer regions are identified. Data on the dependence of heater-wall temperature and local heat flux at the axis of symmetry of the heater on the longitudinal coordinate are obtained. Local and mean heat-transfer coefficients are calculated. It is shown that enhanced heat transfer is observed in the region where rivulets starts forming in the low-Reynolds-number liquid-film flow.     

Laminar Heat Transfer of a Swirled Flow in a Conical Diffuser. Self-similar Solution

Heat transfer in a laminar swirled air flow in the divergent channel between a disk and a cone whose vertex touches the disk is studied. A self-similar solution of the Navier-Stokes and energy equations is derived using group analysis. An exact numerical solution of the problem is obtained for different radial-to-tangential velocity ratios at the channel inlet.     

Finite Element Modeling of Liquid Deuterium Flow and Heat Transfer in a Cold-neutron Source

A finite element simulation of flow and heat transfer in the moderator cell of a cold-neutron source (CNS), in which liquid deuterium subject to internal heat generation is flowing, is reported. The numerical scheme consists of a stabilized equal-order method. A time-accurate approach is adopted to resolve the large-scale eddies of the flow, with a Smagorinsky's model for the subgrid-scale effects. The thermal coupling follows a staggered strategy, with SUPG-type upwinding. A specific wall-law is developed that accounts for the correct partition of the heat deposited at the wall by radiation between the liquid deuterium and the helium gas flowing at the outer side of the wall. The average flow and thermal structure are presented. The turbulent fluctuations are both illustrated in physical space and decomposed into spectral components. The wavenumber spectrum suggests that adequate resolution of the large-scale eddies has been attained with just 200,000 nodes, while a DNS analysis would have required at least 1010 nodes. Usefulness of the approach in the design process of the CNS is highlighted.     

井内流动与传热的三维耦合数值模型

钻井过程中,井内的压力、流场及温度分布是钻井作业必需的重要参数。本文提出了一个描述井内流动和传热的三维数学模型,用SIMPLER方法获得了该数学模型的数值解。该数值模型考虑了温度、压力对钻井液的流变性、密度以及各种介质的热物理参数的影响。现场试验数据与数值模拟结果的对比表明：本文提出的数学模型及采用的数值计算方法是可行的。     

Friction and Heat Transfer in a Laminar Separated Flow behind a Rectangular Step with Porous Injection or Suction

Results of a numerical study of a laminar separated flow behind a rectangular step on a porous surface with uniform injection or suction are described. Two cases are considered: an unconfined flow past a step and flow evolution in a confined channel (duct). It is shown that mass transfer on the surface causes strong changes in the flow structure and substantially affects the position of the reattachment point, as well as friction and heat transfer. More intense injection leads first to an increase in the separation-zone length and then to its rapid vanishing due to boundary-layer displacement. Vice versa, suction at high Reynolds numbers Re _s > 100 reduces the separation-zone length. The duct flow has a complicated distribution of friction and heat-transfer coefficients along the porous surface owing to the coupled effect of the transverse flow of the substance and changes in the main flow velocity due to mass transfer. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 18–28, January–February, 2006.     

The Flow and Heat Transfer at Start-Up of an Arbitrarily Shaped Body in a Viscous Heat-Conducting Gas

The flow corresponding to the start-up of an arbitrarily shaped body in a viscous heat-conducting gas is analyzed. The established fact of fluid incompressibility at short times is used. In the first approximation, in the neighborhood of each point on the body surface the flow and heat transfer are proved to be the same as for an infinite plate coinciding with the tangential plane at this point. The corrections for the curvature of the body surface are found. For determining the flows near a cylinder of arbitrary shape and near a spherical bluntness, the start-up problems for a circular cylinder and a sphere are considered. The possibility of extending the results to the case of reacting gases is discussed.     

浮力对混合对流流动及换热特性的影响

用热线和冷线相结合的技术测量垂直圆管内逆混合对流流体的平均速度、 温度以及它们的脉动. 较详细地研究了浮力对逆混合对流的流动特性和传热特性的影响. 评 估了实验中采用的冷线测量温度补偿速度探头温度敏感的影响. 逆混合对流的传热结果用无 量纲参数Ω (Ω= Grd / Red2 )来表示，其中，基于管道直 径的雷诺数Red变化范围为900~18000, 浮力参数Ω变化范围为 0.004899~0.5047. 研究结果表明，浮力对逆混合对流的换热有强化作用. 随着葛拉晓夫数Grd的增加，温度脉动，流向雷诺正应力和流向温度通量增 大，并且在靠近壁面的流体区域尤其明显. 热线与冷线相结合的技术适合于研究非绝热的流 动测量，可以用于研究浮力对流动和换热特性的影响.     

旋转方形截面螺旋管内流动与传热特性

利用数值计算方法研究了旋转矩形截面螺旋管内的粘性流动，分析了在离心力，科氏力共同作用下曲线管道中的二次流动结构、轴向流速分布、截面温度分布、摩擦系数比以及管道Nusselt数比随各参数的变化情况。计算结果表明：当旋转方向和主流方向相同时，旋转的作用与增大Dean数的作用相同，使得管道摩擦系数变大，管道换热效果增强，而当旋转方向和主流方向相反时，管道内流动结构变化十分明显，当F≈-1．2时(F为科氏力与离心力之比)，二次流出现类似于直扭管内的鞍状流动结构，轴向速度类似于静止直管内的流动结构，管道内的摩擦系数与静止直管内的摩擦系数大约相等，换热效果减至最弱；挠率对流动结构以及摩擦系数比和Nusselt系数比的影响效果与F有关。     

Some Features of a Turbulent Separated Flow and Heat Transfer Behind a Step and a Rib. 2. Heat Transfer in a Separated Flow

Results of an experimental study of heat transfer in a separated flow behind a step and a rib are presented. The influence of the obstacle height (H = 6–30 mm) on heat and mass transfer and the structure of the thermal boundary layer is studied. The features of heat transfer in recirculation and relaxation zones of the separated flow are analyzed, and the effect of separation on intensification and suppression of turbulent heat transfer is determined.     

Direct Monte Carlo Simulation of Transverse Supersonic Rarefied Gas Flow around a Cylinder

Supersonic flow around a cylinder is investigated using the direct simulation Monte Carlo method over a wide rarefaction range: from the Knudsen number Kn = 0.1 to free-molecular flow. The effect of the cylinder temperature on the region of sharp nonequilibrium near the cylinder and the heat flux is studied.     

Flow and Heat Transfer in Underexpanded Air Jets Issuing from the Sonic Nozzle of a Plasma Generator

We present the results of an experimental investigation and numerical simulation of the gasdynamic structure of underexpanded dissociated-air jets and the heat transfer in these strongly nonequilibrium flows under the test conditions realized in the 100-kW electrodeless VGU-4 plasma generator of the Institute for Problems in Mechanics of the Russian Academy of Sciences (IPM RAS). The flow and heat transfer analysis is carried out on the basis of measurements of the static pressure in the plenum chamber, at the sonic nozzle exit, and on the low-pressure chamber wall, the stagnation pressure on the jet axis using a Pitot tube, and the heat transfer at the stagnation points of water-cooled models placed along the jet axis. The numerical simulation, based on complete Navier-Stokes equations, includes the calculation of (1) equilibrium air plasma flows in the discharge channel of the VGU-4 plasma generator; (2) underexpanded nonequilibrium dissociated-air jet outflow into the ambient space; and (3) axisymmetric jet flow past cylindrical models.     

下降液膜层流换热发展段中的积分分析

对等温竖直壁面上层流液膜发展段的流动换热进行了理论分析 ,用积分法得到并求解了速度和温度边界层的积分方程式 ,求得了发展段的流动和换热特性的变化规律 ,讨论了进口流态和普朗特数对换热的影响。     

Asymptotic Solution of the Problem of Heat Transfer between Two Plates and a Uniform Fluid Flow

For low Peclet numbers, analytic expressions are obtained for three highest terms of the asymptotic expansion of the solution of the convective heat-transfer problem for a system consisting of two parallel plates with identical lengths identical and constant surface temperatures and an infinite uniform fluid flow with a low Prandtl number.     

Heat,Water, and Solution Transfer in Unsaturated Porous Media: I -- Theory Development and Transport Coefficient Evaluation

A detailed theory describing the simultaneous transfer of heat, water, and solute in unsaturated porous mediais developed. The theory includes three fully-coupledpartial differential equations. Heat, water, andsolute move in the presence of temperature, T; matricpressure head, _m ; solution osmotic pressure head _o ; and solute concentration C gradients. Thetheory can be applied to describe the mass and energyin radioactive waste repositories, food processing,underground energy storage sites, buried electriccables positions, waste disposal sites, and inagricultural soil. Several transport coefficients forheat, water, and solute are included in the theory. The coefficients are evaluated for a silty clay loamsoil to clarify their dependence on water content (),T, and C. The thermal vapor diffusivity D _Tv first increased as increased to0.22 m³/m³ then decreased with furtherincreases in . D _Tv was 3 orders of magnitudegreater than either isothermal vapor D _mv orosmotic vapor D _ov , diffusivities at of0.20~m³/m³, T of 50°C, and C of 0.001mol/kg. All of the liquid and vapor water transport coefficients increased with increasing T. D _Tv decreased with increasing C to a greater extent thanD _mv and D _ov . The effective thermalconductivity decreased slightly with increasing C. Thesolute diffusion coefficient D _d was 6 to 7orders of magnitude greater than the thermal soluteand salt sieving diffusion coefficients at of0.20~m³/m³, T of 50°C, and C of 0.001 mol/kg.     

Calculation of Radiation Heat Transfer in Problems of Flow past Bodies with Account for Heat-Shield Coating Mass Loss

Flow past bodies with account for radiation heat transfer near the body nose is considered in connection with the problem of thermal protection of spacecraft entering planetary atmospheres. An approach based on the spherical harmonics method is used for taking radiation into account. The heating and ablation of the heat-shield coating is determined by numerically solving the heat conduction equation with a moving boundary. The thermal problem is solved together with the calculation of the vehicle trajectory, which makes it possible to estimate the effect of the coating mass loss on the trajectory parameters. The approach formulated is realized under the conditions of entry of a spherical segment and a spherically-blunted cone with equal mid-section radii into the Venusian atmosphere. Comparing the results makes it possible to choose the vehicle shape optimal with respect to the thermal regime.     

Heat Transfer and Pressure loss of a very shallow fluidized-bed heat exchanger Part 1. Experiment with a single row of tubes

A novel gas fluidized-bed heat exchanger with a very small static bed height has been developed for a heat-exchanging system using a low-pressure fan. This fluidized bed is composed of a multislit distributor, a single row of 8 mm diameter tubes, and glass beads 48–195 μm in diameter. The measured performance of heat transfer is excellent and that of fluidization is satisfactory, in spite of the static bed height being as small as 13 mm. In the best case, the test fluidized bed exhibited a heat transfer performance comparable to that of a conventional fluidized bed with a perforated plate distributor and a static bed height of 150 mm, and showed one-fourteenth the pressure loss.     

Flow and Heat Transfer of Viscous Fluids Saturated in Porous Media over a Permeable Non-isothermal Stretching Sheet

The present paper deals with the flow and heat transfer of a viscous fluid saturated in a porous medium past a permeable and non-isothermal stretching sheet with internal heat generation or absorption and radiation. Closed-form solutions to steady, two dimensional momentum equations with neglecting quadratic inertia terms and heat transfer equation are found using a similarity transformation. Asymptotic expressions of the temperature functions are also presented valid for both very large and very small modified Prandtl numbers. Attention is focused on the effects of porous parameter K, suction parameter R, radiation parameter Nr, viscosity ratio Λ, internal heat parameter α and Prandtl number P to the characteristics of flow and heat transfer.     

气固两相分支管流动及流量分配特性的研究

在水平T型分支管道中,用压缩空气对平均粒径为0．5mm砂石进行气固两相流试验。试验结果表明,当压缩空气的流速大于33m／s时,T型分支接头处没有固相沉积,两个分支管路分配的流量几乎相同。当压缩空气的流速小于33m／s时,分支接头处出现沉积,并且沉积量和分支管路的流量分配与分支管路上阀门开度有关:开度相同时,分支接头两侧的固相沉积量和流量分配相同;开度不同时,阀门开度小的一侧分支接头处的沉积量少,其分配的流量也少。