高温超导带材多场特性测试系统研制进展(Ⅱ)

考虑到第一代高温超导带材多场特性测试系统采用液氮浸泡的方式进行材料冷却,这极大地限制了其应用范围。另外,封闭的杜瓦结构对于超导材料在变形过程中的电磁特征难以实现有效观测,这成为弄清超导材料变形导致其载流能力下降物理机制的主要瓶颈。为此,我们采用制冷机直接冷却方式,获得了最低6.59K的样品温度。采用PID温度控制,实现了从6.59K至300K样品温度的精确控制,控温精度为0.1K。采用外置式的加载装置,通过机械传动实现对试样的准静态拉伸,其最大拉伸应变可达20%。自行设计了一种高温超导导线,采用制冷机一级冷头直接冷却,实现了密闭杜瓦容器中最大可达600A的电流输入。最后,在杜瓦瓶设置直径50mm的光学观察窗,采用磁光镜像的方法实现了超导材料电磁特性的原位观测。     

Effect of surroundings on the transient energy transfer in a layer of radiating gas

Summary An analysis is presented for the transient cooling or heating of a stagnant layer of hot radiating gas surrounded by a cold gas capable of absorbing and emitting radiation. Scattering of radiation is neglected, and energy transfer by conduction and convection is considered to be negligible compared with radiation. The gas is assumed to be perfect and in local thermodynamic equilibrium. The heating of a cold gas by a diffuse and a collimated radiation flux incident on the boundary of the gas from some external source is considered, and the dependence of physical and radiative properties on temperature is taken into account. The problem is formulated exactly using radiative transfer theory. A scheme is developed for the numerical solution of the nonlinear integrodifferential equations of energy conservation. Starting with arbitrary, but given, initial temperature profiles, temperature distributions and local radiative fluxes are predicted as a function of time for a wide range of physically interesting conditions.     

Numerical modelling of solidification processes of semitransparent materials using the enthalpy and the finite volume methods

Solidification of a semitransparent medium was investigated. It was found that internal radiation cooling decreases temperature in the liquid and contributes to development of a two-phase region (mushy zone) not only for binary medium but also for pure substance. Such factors as conduction–radiation parameter, albedo, optical thickness and contrast in radiative properties of both phases exert significant impact on the location, width, composition and temperature distribution in the mushy zone.     

The concrete columns as a sensible thermal energy storage medium and a heater

This study investigated storage possibility of sensible thermal energy in the concrete columns of multi-storey buildings and the heating performance of the indoors with the stored energy. In the suggested system, the dry air heated in an energy center will be circulated in stainless steel pipes through columns. The sensible thermal energy would firstly be stored by means of forced convection in column medium. Then, the stored thermal energy will transfer by natural convection and radiation from the column surfaces to indoor spaces. The transient thermal calculations are realized for a flat of the 11-storey building in Kayseri city of Turkey. The thermal energy requirement of the flat is nearby 5.3 kW as an average of a winter season. The simplified transient calculations were carried out over a concrete hollow cylindrical column having outer radius of 0.31 m and inner radius of 0.05 m corresponding an averaged column section in the sample flat. The flow temperature was selected between T = 350 and 500 K, which are considerably lower than the temperature of 573 K assumed as a limit for thermal strength of the concrete in the literature. The flow velocity ranges were selected between V = 1.0 and 5.0 m/s. The initial temperature was assumed as 293 K. After the first energy charging process of 23 h, for T = 350 K and V = 1.0 m/s, the total heat flux from the column surfaces into indoors are nearby 5.5 kW. The first charging time required to reach the energy requirement of 5.3 kW is decreased by increasing the flow velocity and temperature. Also for 5.0 m/s–350 K and 5.0 m/s–450 K, this time can decrease to 10 and 4.5 h, respectively. In addition, with 4.0 m/s–360 K or 2.0 m/s–400 K, after the energy charging of 8 h, the energy requirement of 5.3 kW can be provided by the energy discharging of 16 h and the energy charging of 8 h during 7 days. The results are very attractive in terms of the building heating systems of the future.     

复合材料层合板在加工固化后期降温速率对残余热应力的影响

本文采用非线性有限元方法，对材料性质与温度有关的复合材料层合板在加工固化后期降温过程中的温度速场和热应力场进行了分析，对降温度速率对板中固化残余热应力的影响进行了研究，获得一些对层合板固化成型工艺和固化残余热应力分析模型的选取均有意义的结果。     

Snow melting with radiative heating

This paper is concerned with the melting of a packed snow heated by the radiative energy which is the blackbody radiation having source temperature of 3200 °K and short radiative energy. A transfer of the radiation in snow is significantly affected by both the porosity of snow and water saturation. The internal melting in snow is greatly characteristic for radiative heating which is to be produced by absorbing of a comparatively short wave radiation. In this study, an analysis is attempted to predict the variation of snow density, the moving rate of dry-wet interface of snow due to percolation of melt water, and the transient temperature distribution in dry snow zone located under wet snow zone.     

Determination of thermal conductivities of Sn–Zn lead-free solder alloys with radial heat flow and Bridgman-type apparatus

The variations of thermal conductivities of solid phases versus temperature for pure Sn, pure Zn and Sn–9 wt.% Zn, Sn–14 wt.% Zn, Sn–50 wt.% Zn, Sn–80 wt.% Zn binary alloys were measured with a radial heat flow apparatus. The thermal conductivity ratios of liquid phase to solid phase for the pure Sn, pure Zn and eutectic Sn–9 wt.% Zn alloy at their melting temperature are found with a Bridgman-type directional solidification apparatus. Thus, the thermal conductivities of liquid phases for pure Sn, pure Zn and eutectic Sn–9 wt.% Zn binary alloy at their melting temperature were evaluated by using the values of solid phase thermal conductivities and the thermal conductivity ratios of liquid phase to solid phase.     

Heat exchange between a selectively emitting liquid and a laminar gas flow in the presence of an external source of radiation

An investigation is conducted in the solution of a number of practical problems of the radiative and combined heat exchange in nonuniform systems having widely different physical properties. The processes of thermal interaction between the ocean and the atmosphere have been treated in the paper [1], the effect of thermal radiation on the melting and solidification of semitransparent crystals has been investigated in [2], the flow of a selectively emitting gas around the lateral surface of an object evaporating under the action of radiative heating has been discussed in [3], and heat transfer from a jet to the molten mass of glass in a glassmaking furnace tank has been investigated in [4]. The radiative and combined heat exchange between a selectively emitting liquid and a transparent heat-conducting laminar gas flow in the case of a specified external thermal radiation field is discussed in this paper. The energy conservation equations are set up taking into account the heat transfer by radiation, convection, and molecular thermal conduction. A differential approximation is used in calculating the values of the radiation fluxes. A system of fundamental computational equations is solved by the method of finite differences and iterations and by the Runge-Kutta method. The results of the calculations are presented in the form of graphs.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 116–122, May–June, 1976.     

Numerical analysis of interaction between non-gray radiation and forced convection flow over a recess using the full-spectrum k-distribution method

In the present work, the interaction between non-gray radiation and forced convection in a laminar radiating gas flow over a recess including two backward and forward facing steps in a duct is investigated numerically. Distributions of absorption coefficients across the spectrum (50 cm^?1 < η < 20,000 cm^?1) are obtained from the HITRAN2008 database. The full-spectrum k-distribution method is used to account for non-gray radiation properties, while the gray radiation calculations are carried out using the Planck mean absorption coefficient. To find the divergence of radiative heat flux distribution, the radiative transfer equation is solved by the discrete ordinates method. The effects of radiation–conduction parameter, wall emissivity, scattering coefficient and recess length on heat transfer behaviors of the convection–radiation system are investigated for both gray and non-gray mediums. In addition, the results of gray medium are compared with non-gray results in order to judge if the differences between these two approaches are significant enough to justify the usage of non-gray models. Results show that for air mixture with 10 % CO₂ and 20 % H₂O, use of gray model for the radiative properties may cause significant errors and should be avoided.     

Experimental study of the effect of spray inclination on ultrafast cooling of a hot steel plate

The ultrafast cooling that occurs during high mass flux air-atomized spray impingement on a hot 6 mm thick stainless steel plate has been studied experimentally in terms of the nozzle inclination between 0° and 60°. The average mass flux of water used in the study accounts to 510 kg/m² s. The coolants used in the study are pure water and surfactant water of 600 ppm concentration. The initial temperature of the plate has been maintained at 900 °C, which is the temperature of a hot strip on run-out table in steel industry. The transient surface heat flux and temperature histories have been estimated by an inverse heat solver using measured temperature input data. Heat transfer results demonstrates that optimum cooling efficiency (~2.76 MW/m², 194 °C/s) for pure water has been achieved at 30° nozzle orientation. The inclined nozzle has not been found beneficial when surfactant water is used as the coolant.     

Thermal radiation effect on non-Darcy natural convection with lateral mass transfer

 A boundary layer analysis has been presented to study the influence of thermal radiation and lateral mass flux on non-Darcy natural convection over a vertical flat plate in a fluid saturated porous medium. Forchheimer extension is considered in the flow equations, and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. Similarity solution for the transformed governing equations is obtained and the combined effect of thermal radiation and fluid suction/injection on the heat transfer rate is discussed. Numerical results for the details of the velocity and temperature profiles as well as Nusselt number have been presented. Received on 7 July 1999     

G—10CR玻璃布／环氧层压板低温剪切力学性能

纤维复合材料极低温力学性能的试验研究国内尚处于空白阶段。利用国际间的多国合作计划,采用三点弯曲和层间剪切两种试验方法,对G－10CR玻璃布／环氧层压板的低温剪切性能进行了对比研究。试验结果发现该材料低温下的剪切强度较室温有明显增加,且低温下表现出了和室温不同的破坏机制。     

用于低温风洞的新颖制冷方法

描述了用于低温风洞的新颖制冷系统,利用热交换器回收排气冷量预冷压缩空气,然后再用热分离器将其降至深低温作风洞气源．原理性实验结果证实新制冷方法的可行性．讨论了新制冷方法产生的有一定压力的低温空气作引射气源,引射驱动回流型风洞的特性．其制冷方法与现有低温风洞喷雾液氮制冷相比,由于仅需压缩空气而无需液氮,造价更便宜．更由于能量利用合理,效率高,因而运行成本可显著降低．     

Numerical computation of natural convection in an isosceles triangular cavity with a partially active base and filled with a Cu–water nanofluid

This paper discusses the results of a study related to natural convection cooling of a heat source located on the bottom wall of an inclined isosceles triangular enclosure filled with a Cu water-nanofluid. The right and left walls of the enclosure are both maintained cold at constant equal temperatures, while the remaining parts of the bottom wall are insulated. The study has been carried out for a Rayleigh number in the range 10⁴ ≤ Ra ≤ 10⁶, for a heat source length in the range 0.2 ≤ ε ≤0.8, for a solid volume fraction in the range 0 ≤ ?≤0.06 and for an inclination angle in the range 0° ≤ δ≤45°. Results are presented in the form of streamline contours, isotherms, maximum temperature at the heat source surface and average Nusselt number. It is noticed that the addition of Cu nanoparticles enhances the heat transfer rate and therefore cooling effectiveness for all values of Rayleigh number, especially at low values of Ra. The effect of the inclination angle becomes more noticeable as one increases the value of Ra. For high Rayleigh numbers, a critical value for the inclination angle of δ = 15° is found for which the heat source maximum temperature is highest.     

Effect of the storage tank thermal insulation on the thermal performance of an integrated collector storage solar water heater (ICSSWH)

The thermal behavior of an integrated collector storage solar water heater (ICSSWH) is numerically studied using CFD simulations. Based on the good agreement between the numerical results and the experimental data from literature, we propose a geometrical change allowing limiting the main disadvantage of this solar system which is its high night losses due to the non-insulated storage tank surface. A second 3D CFD model of an ICSSWH in which the storage tank is partially insulated is developed and three values of this tank thermal insulated fraction are studied. Numerical results show that the partially insulated tank based ICSSWH presents lower thermal losses during the night and this night thermal losses coefficient is reduced from 14.6 to 11.64 W K^?1 for the tank thermal insulation fraction τ = 1/4. Similarly, the modified system presents the advantage of its lower thermal losses even during the day. Regarding the thermal production, it is seen that the modified system presents higher water temperature at night and that for all the tank thermal insulation fractions. Concerning the operation of this modified system during the day, the water temperature is lower during the day and that up to 16 h but the water temperature which achieves 324 K for the storage tank thermal insulation fraction τ = 1/8 still sufficiently high to satisfy a family hot water needs.     

Radiative gasdynamics of the nose surface of the Apollo-4 command module at its superobrital reentry

The problem of the radiative gasdynamics of the Apollo-4 command module superorbital entry in the dense terrestrial atmosphere is numerically solved in the two-dimensional formulation of flow past an aerodynamic nose shield on the entry velocity range V_∞ = 10.7?5.75 km/s and the altitude range H = 91.5?35.0 km. The specific regions of the trajectory with strongly nonequilibrium flow in the shock layer, the most high-heat areas of the trajectory, and the regions with strong radiative-gasdynamic interaction in a relatively dense and strongly rarefied oncoming flow are highlighted. The density distributions of the convective and radiative heat fluxes over the body surface are obtained. The spectral composition of the thermal radiation is studied. The results of the calculations are compared and found to be in good agreement with the experimental flight data.     

Heat dissipation structure research for rectangle LiFePO4 power battery

Under hard acceleration or on a hill climb of (hybrid) electronic vehicles, the battery temperature would increase rapidly. High temperature decreases the battery cycle life, increases the thermal runaway, and even causes a battery to explode, that making the management of battery temperature an important consideration in the safety using of electronic vehicles. A study of increasing heat transfer area from the beginning design phase has been conducted to determine and enhance the heat dissipation on the battery surface. Both experiment and simulation methods were used to analyze the cooling performance under identical battery capacities and heights. Optimal external dimensions and cell sizes with the consideration of better battery workability was obtained from the analysis. The heat transfer coefficients were investigated in order to regulate the battery temperature under safety operating range. It was found that the temperature of the experiment battery would be controlled under safety critical when the cell was designed for 180 mm × 30 mm × 185 mm sizes and the surface heat transfer coefficient was 20 W m^?2 K^?1 at least.     

Economic and technical assessment of the desiccant wheel effect on the thermal performance of cross flow cooling towers in variable wet bulb temperature

Performance improvements of cross flow cooling towers in variable wet bulb temperature were performed. A conventional mathematical model is used to predict desiccant wheel effect on the performance of cooling tower. It is found that by using optimum parameters of desiccant wheel, the inlet air wet bulb temperature into the cooling tower would decrease more than 6 °C and outlet water temperature would decrease more than 4 °C.     

The influence of sidewall cooling on boundary layer pressure fluctuations for a two-dimensional supersonic nozzle

Broadband root-mean-square (rms) values and frequency spectra for pressure fluctuations in the supersonic boundary layer on a Mach 3 DeLaval nozzle sidewall and in the freestream are reported for both adiabatic and cooled surface conditions. The flat sidewall of the nozzle contained four sections independently cooled by liquid nitrogen. During the experiments, the flat sidewall was operated (1) adiabatically, (2) cooled in an approximately uniform manner to ?40°C, and (3) cooled in a nonuniform manner. For all thermal boundary conditions on the sidewall, a dynamic pitot probe was traversed through the boundary layer and into the freestream to measure the broadband pressure fluctuations from 30 Hz to 100 kHz. The influence of sidewall cooling on the measured pressure fluctuations was dependent on the unit Reynolds number. Compared with the pressure fluctuations measured with an adiabatic sidewall, uniform cooling of the sidewall was found to reduce the rms pressure fluctuations in both the boundary layer and the freestream by approximately 50% at the highest stagnation pressures used (unit Reynolds numbers above 44,000/cm). Uniform cooling of the sidewall increased rms pressure fluctuations for lower stagnation pressures (unit Reynolds numbers below 44,000/cm). A reduction in the pressure fluctuation amplitude within the boundary layer resulted in a corresponding reduction in the pressure fluctuation amplitude in the test section freestream. Tests using a nonuniform temperature distribution on the sidewall indicated that cooling the portion of the sidewall covering the nozzle throat had the most influence on the pressure fluctuations in the boundary layer and in the freestream.     

Messungen und Berechnungen von adiabaten Oberflächentemperaturen bei der Verdunstung einer katalytisch zerfallenden Flüssigkeit in einen heißen Gasstrom

The effectiveness of evaporation cooling of a wall with high thermal loading can be improved if the fluid undergoes an endothermic reaction as it passes through the wall. In the past, fuels with high molecular weight have been proposed as “reacting” cooling liquids. In the present paper the applicability of a boundary layer prediction procedure to the calculation of adiabatic surface temperature is investigated. The system considered involved the evaporation of a catalytically split solution of hydrogen-peroxide which, although not suitable for reaction cooling processes, contains all the associated problems. The discrepancies between measured and predicted surface temperatures are, in all cases below 2°K for free stream temperatures up to 500°K.