Theoretical Investigation of the Effect of the Thermal Conductivity of a Wall on the Processes of Free-Convective Heat Transfer in a Vertical Cylindrical Tank

The natural-convective heat transfer is studied in a vertical cylindrical tank with a heat-conducting wall. It is demonstrated that the theory of local self-similarity may be applied in the case of a uniform heat supply to the side wall in the quasi-stationary mode for a free-convective boundary layer. This theory enables one to derive simple analytical formulas for some hydrodynamic and thermal characteristics. The analytical results are compared with the numerical simulation results. The effect of the wall thermal conductivity on the heat-transfer processes in the mode of convection development is investigated numerically under conditions of short heating times.     

Functional Surfaces with Enhanced Heat Transfer for Spray Cooling Technology

In this study the effects of nano/microstructuring and surface chemistry on wettability, evaporation rate and the Leidenfrost temperature are experimentally investigated. The functional surfaces with two alternative patterns were originally fabricated via direct femtosecond laser surface processing of polished silicon wafer in air at a fluence slightly above ablation threshold. The droplet lifetime method was used to measure the evaporation rate of a water droplet (4.5 μL) at surface temperatures of 25–350°C and to determine the Leidenfrost temperature. Generally, after processing the functional surfaces with hierarchical surface morphology demonstrate enhanced wetting behavior, evaporation rate enhancement and positive shifts in the Leidenfrost temperature. The functional surfaces with a microgrooved surface pattern, extensively covered by flake-like nanostructures, exhibit strong superhydrophilicity, resulted in a significant temperature-dependent enhancement of evaporation rate (up to 6 times) and an increase of about 30°C in the Leidenfrost temperature relative to the polished surface. The functional surfaces with a microcratered surface pattern being only hydrophilic demonstrate a nearly twofold temperature-independent enhancement of evaporation rate. Thermostability tests showed the heating of the functional surfaces above 340°C to be resulted in a drastically deteriorated wettability and a reduction of evaporative heat transfer performance under repeated experiments.     

Unsteady Heat Transfer in HeII in Cylindrical and Spherical Geometries

The problem of evolution of strong heat pulses in superfluid helium interacting with quantum vortices induced by these pulses is investigated numerically on the basis of equations of hydrodynamics of superfluid turbulence. The “discontinuity decay” method (Godunov method) is used for the calculations. In order to study nonlinear effects, the initial equations are expanded to the second order in the amplitudes of pulses. The influence of the main flow parameters—heat flux and rest time—on temperature evolution is reported. The numerical investigations are carried out at the bath temperature of 1.4 K. The obtained results are compared with experimental data.      

筒型翅片管换热器空气侧换热模型分析与实验

本文对筒型翅片管换热器的空气侧流动特点进行了理论分析,基于现有换热模型提出了一种能够反映筒型翅片管换热器结构特点的集中参数形式的换热因子关联式.通过实验对比了筒型和普通型的换热因子,对理论分析进行验证,结果表明:现有换热模型对筒型翅片管换热器的预测误差较大,平均相对误差达到81.16％;对传统换热器预测较准,平均误差为...     

The Study of Heat Flux Measurement for Heat Transfer during Condensation at Pipe Surfaces

Technical Physics Letters - For the first time, heat transfer during condensation has been studied using gradient heat flux measurement. The applicability of the new method has been tested on a...     

Heat Transfer for Vertical Surfaces with Discrete Fins in the Case of Free Convection

A mathematical model of heat transfer has been developed and numerical calculations for a vertical surface with discrete fins arranged in staggered order have been carried out. The model accounts for the influence of the heat-conduction properties of the finning material and of the fin size on the conditions of heat transfer. A comparison of the results obtained with the existing numerical and experimental data has been made. This comparison shows that the discretization intensifies the heat-transfer process by 50–70%, and neglect of the heat-conduction properties of the fins leads to overstated values of the removed heat fluxes.     

圆柱型翅片管换热器变工况传热性能模拟与分析

基于分排参数模型,本文建立了圆柱型翅片管换热器的性能仿真计算模型,对换热器的传热性能进行计算,并进行实验验证。结果表明:换热量的平均相对误差最大,为6.31%;出风干球温度的平均相对误差最小,为0.61%。计算所得各性能参数与实验值吻合良好。根据仿真模型,对不同制冷工况下的换热器进行计算,研究了循环风量、水质量流量、进风干球温度以及进水温度的变化对换热性能的影响。分析换热器的变工况特性可预测其非设计工况下的换热性能,并为换热器的运行工况调节提供依据。     

Simulation of Heat and Mass Transfer in a Cylindrical Evaporator of a Loop Heat Pipe with a Rectangular Interface

High Temperature - The stationary heat and mass transfer in a cylindrical evaporator of a loop heat pipe with a thermal interface in the form of a rectangular parallelepiped and a heat source...     

高换热多分仓滚筒冷渣机在CFB电厂中的应用

针对攀枝花分公司锅炉配套RA型气垫床冷渣器换型改造为WWR-XP-20型高换热多分仓滚筒冷渣机后得以安全稳定运行的示例,介绍了冷渣机运行原理、技术参数和性能,重点阐述了冷渣器改造后机组运行的适应性和经济性,体现了该类型冷渣机节能降耗和减少环境污染的优点,符合国家目前的节能、环保政策要求。     

攻击角对涡产生器式圆管板式翅片强化传热的影响

利用萘升华传质／传热比拟实验方法，研究了翼形涡产生器攻击角的变化对圆管板式翅片换热和阻力的影响，分析了涡产生器式叉排圆管式翅片管换热器在不同翼形涡产生器攻击角下的传热与阻力特性，并应用传热因子对换热器板芯结构做了综合评价。     

长圆柱形果蔬冷激处理过程传热特性分析

为探究冷激过程中长圆柱形果蔬组织传热特性,建立并求解了长圆柱形果蔬冷激过程传热模型,以黄瓜为试材,0℃冰水混合物为介质进行冷激试验,实测了冷激过程中黄瓜不同位置的组织温度,对比分析了长圆柱形果蔬的传热特点。结果表明:计算结果和试验结果最大差值为2.22℃,果蔬组织按各向同性、热物性不变计算传热过程存在一定误差;半径方向,黄瓜组织不同位置温度响应速度不同,同一位置各时间段传热特点不同,应考虑果蔬表面特征、组织热物性差异的影响;两端换热对其内部温度场的影响较小,冷激最优工艺参数的确定可以果蔬中段为准。     

翼高对涡产生器式扁管板式翅片强化传热的影响

利用萘升华传质/传热比拟实验方法,研究了三角翼形涡产生器翼高的变化对扁管板式翅片换热和阻力特性的影响,分析了涡产生器式顺排扁管板式翅片管换热器在不同涡产生器翼高时的传热与阻力特性,为换热器设计提供了一定的理论依据.     

Numerical Simulation of Unsteady-State Heat Transfer under Conditions of Laminar Transverse Flow past a Circular Cylinder

Two-dimensional Navier-Stokes and energy equations are used to perform a numerical calculation of the parameters of unsteady-state flow and heat transfer under conditions of laminar transverse flow of a viscous incompressible fluid past a circular cylinder and at Re = 140. The process of formation of Karman vortex street is treated, as well as the cyclic heating of the near and far wakes behind the heated cylinder. Special attention is given to analysis of the behavior of the integral characteristics of flow and heat transfer, and the distributions of pressure, friction and heat-transfer coefficients on the cylinder surface, as well as to correlations of the parameters of flow and temperature at selected points in the vicinity of the cylinder. Evaluation is made of the effect of the factor of unsteadiness on the increment of power and heat loads in the process of flow past the cylinder.     

Heat Transfer from a Local Heat Source to Subcooled Liquid Film

An experimental investigation is performed of heat transfer from a local heat source to films of water and low-boiling dielectric liquid that flow down a vertical plate by gravity. The liquids are substantially subcooled. In the case of perfluorotriethylamine flow, regular structures are formed in the film at the threshold value of the heat flux density. After the heated layer of liquid comes to the film surface, three characteristic modes of heat transfer are observed, which are associated with the variation of the modes of liquid flow caused by thermocapillary convection. At low values of the Reynolds number of the film, a specific form of critical heat transfer is observed, which is characterized by disintegration of the jet into droplets and their separation from the heater.     

Transverse Evolution of Cylindrical Phonon Pulse in Superfluid Helium-4

No Heading The equations for the transverse evolution of the anisotropic phonon system are solved for the case of cylindrical symmetry. The angular distribution of the phonon-energy density is obtained at large distances from the heater.PACS numbers: 67.70.+n, 68.08.–p, 62.60.+v     

Heat Dissipation Performance of Porous Copper with Elongated Cylindrical Pores

The purpose of this paper is to investigate heat dissipation performance of porous copper with long cylindrical pores fabricated by a unidirectional solidification method. Three samples with porosity of 29.87%, 34.47% and 50.98% were chosen and cut into size of 60 mm （length） × 26 mm （width） × 2 mm （thickness） along the vertical direction of pore axis. Their heat dissipation performance was evaluated by a nonsteady method in air and compared to those of not only bulk copper but also bored coppers with porosity of 30.61% and 32.20%. It is found that the porous copper dissipated heat faster by a forced air convection than that by natural convection from 80 ℃ to room temperature and both porosity and pore size play an important role in the performance for the porous copper. Furthermore, the heat dissipation rate is higher when the forced air was circulated along the specimens than that perpendicular to the specimens for the porous copper. It is revealed that porous copper with bigger porosity and a proper pore size possesses a higher heat dissipation rate. It is concluded that the porous copper with elongated cylindrical pores has larger heat dissipation performance than both the bulk copper and the bored copper, which is attributed to its higher specific surface area. Application of the porous copper for heat dissipation is promising.     

Flow Pattern and Heat Transfer in a Cylindrical Annulus Under 1 g and Low-g Conditions: Experiments

We investigate the thermal convection in an annular cavity, with differentially heated inner and outer cylinders, under the influence of a dielectrophoretic (DEP) force. Applying a temperature gradient to a liquid creates buoyancy driven thermal convection. When additionally a radially acting DEP-force is applied by means of an alternating electric field, the pattern of this convective flow changes which also leads to a change in the heat transfer. Depending on the parameters, e.g. an axisymmetric structure with toroidal vortices appears. Another possible structure are columnar vortices, which extend through the annulus. To isolate the effect of the DEP-force, this experiment is not only conducted in the laboratory, but also in microgravity conditions during parabolic flights. By using DEP-induced convective flows in microgravity a comparable heat transfer as with buoyancy convection under Earth’s condition can be obtained. A better understanding of the heat transport mechanisms inside a dielectric liquid confined between two concentric cylinders can deliver solutions for the improvement of the heat transport in many technical applications.     

攻击角对纵向涡错排椭圆管板式翅片强化传热的影响

利用萘升华传质/传热比拟实验方法,研究了纵向涡产生器攻击角对椭圆管板式翅片换热和阻力特性的影响,分析了纵向涡错排椭圆管板式翅片换热器在不同纵向涡产生器的攻击角时的传热与阻力特性,为换热器设计提供了一定的理论依据.