基于金属氢化物高温蓄热的氢热耦合传递机理

目前大多数可再生能源如太阳能具有间歇性和不稳定性的问题,因此高效蓄热技术成为了发展太阳能的一个关键途径。金属氢化物高温蓄热技术作为热化学蓄热中最有前途的方法之一,受到了人们的广泛关注。为了实现金属氢化物高温蓄热技术的工程应用,明确其氢热耦合传递机理至关重要。本研究采用数值模拟的方法,通过建立反应器的多物理场耦合模型,讨论了不同时刻下床层内部参数的分布,得到了反应锋面的形成和移动机理以及非均匀反应的形成机理;此外,结合反应器内部氢压、接触热阻和床层热阻的变化规律,明确了不同阶段下金属氢化物高温蓄热技术的控制环节;最后,依据金属氢化物高温蓄热技术的工程应用挑战,提出了相应的研究策略。     

Numerical studies of simultaneously developing laminar flow and heat transfer in microtubes with thick wall and constant outside wall temperature

The effects of wall axial heat conduction in a conjugate heat transfer problem in simultaneously developing laminar flow and heat transfer in straight thick wall of circular tube with constant outside wall temperature are numerically investigated. The results show that the heat transfer process is most sensitive to wall-to-fluid conductivity ratio k_sf, and when k_sf ? 25 the increasing tube thickness and the decreasing k_sf could make the inner wall surface approaching the uniform heat flux condition. It turns out that the basic function of the wall axial heat conduction for the cases studied is to unify the inner wall surface heat flux.     

Reactor dosimetry for VVERs RPV lifetime assessment

A state of the art review of Reactor Dosimetry used for reactor pressure vessel irradiation damage assessment and lifetime evaluation of the Russian type VVER reactors is presented. The necessity of prospective studies in Reactor Dosimetry for improvements that will reduce the neutron fluence uncertainty and in this way to substantiate the extension of NPP lifetime is summarized by specialists in Reactor Dosimetry from countries operating VVER reactors such as Russia, Ukraine, Czech Republic, Finland, Hungary, and Bulgaria, together with specialists from Western European countries such as France, Spain, Germany, Belgium, The Netherlands, and UK, operating PWR and BWR type reactors.     

Reactivity control options of space nuclear reactors

This paper compares two ex-core control options of the gas-cooled Submersion Subcritical Safe Space (S^4) reactor with a fast neutrons energy spectrum: (a) rotating BeO drums with 120° thin segments of enriched B₄C in the BeO radial reflector; and (b) sliding segments in the BeO radial reflector. Investigated are the effects on the beginning-of-life (BOL) excess reactivity, reactivity depletion rate and operation life, and the spatial neutron flux distributions and fission power profiles in the core. Also investigated is the effect of reducing the thickness of the enriched B₄C segments in the control drums on the BOL excess reactivity, when one or two of the 6 drums are stuck in the shutdown position. Reducing the thickness of the B₄C segments from 0.5 mm to 0.238 mm, with one drums stuck in the shutdown position, increases BOL cold and hot-clean excess reactivity from +$1.71 and +$0.47 to +$2.38 and +$0.89, respectively. These reactivity values are almost identical to those of the reactor with one of the six reflector segments stuck open in the shutdown position. Results also showed that the control options made little difference in the reactor performance. The power peaking in the reactor core with sliding reflector segments is slightly lower and the spatial power profiles are relatively flatter. The operation life of the reactor with a sliding reflector segments control, when operating at a nominal thermal power of 471 kW, is only 22 full power days longer than with rotating drums control.     

横摇条件下九通道系统两相流动不稳定性研究

对横摇条件下并联多通道系统的两相流动不稳定性进行了理论研究。基于横摇条件的均匀流模型,通过控制容积积分法建立了并联九通道系统的分析模型。用吉尔方法对系统控制方程组进行了求解。分析了在横摇条件下并联九通道系统入口段和上升段及加热功率对管间脉动不稳定性的影响,得到了相应的不稳定性边界。在低含汽率、高含汽率及低过冷度数区域,系统均不稳定。同时,在高含汽率区域会出现倍增周期现象及混沌现象。     

高压真空断路器用散热器的自然对流换热特性

为提高高压真空断路器的运行安全,以一种新型高压真空断路器为背景,采用计算流体动力学方法研究了不同环境温度下,圆柱形散热器竖直肋片间自然对流换热特性。结果表明:采用扩大计算区域和设置压力边界条件的方法来模拟计算自然对流换热是恰当的。在散热器肋片缝隙的进口处,气体温度较低、流速较小;在肋片缝隙中部,气体温度升高、流速较大;越靠近肋片根部,气体温度越高,但由于粘性阻力大,所以在肋片根部速度较小。在相同的环境温度下,随着肋片温度的逐渐升高,肋片的换热能力也逐渐升高;在相同的肋温情况下,随着环境温度的逐渐升高,肋片的换热能力逐渐下降。所得的肋片缝隙内自然对流的流动换热特性、肋片表面的平均Nu数对高压真空断路器散热器肋片的热力设计和进一步优化设计有重要的意义。     

The influence of distributed generation penetration levels on energy markets

Planning of national energy policies brings new dilemmas with the introduction of distributed generators (DG). Economic theory suggests that a perfectly competitive market would lead to efficient pricing. In the absence of competition, regulators play a fundamental role in attracting reasonably priced finance in order to maintain, refurbish and increase the infrastructure and provide services at a reasonable cost. Energy market price equilibrium is mainly dependent on suppliers, generators, energy sources and demand, represented by conventional utility grid users. Its behavior is similar to that of other commodities. As generation becomes less centralized with the increasing economic viability of renewable energy sources, new suppliers are being connected to the grid. Such evolution means the transition from a monopolistic market to a broader and more open environment, with an increasing number of competitors. We make use of variational inequalities to model a hypothetical DG market in different scenarios, from monopoly, to oligopoly, to open market. Such an approach enables different equilibrium outcomes due to different DG penetration levels. Based on these findings, we argue that energy policies for such markets must be developed according to each specific stage of the grid's lifecycle. We show how energy policies and market regulations may affect such a transition, which may be catastrophic if not managed properly, and which is dependent on the energy mix.     

Chemical conversion of wood by treatment in a semi-batch reactor with subcritical water

Sugi (Cryptomeria japonica D. Don) wood meal was extracted with subcritical water in a semi-batch reactor. About 70–90% by weight of the sugi wood meal was converted into water-soluble compounds. The main components of the water-soluble compounds were monosaccharides and oligosaccharides, as a result of hydrolysis of cellulose and hemicellulose. White precipitates appeared in the solution after settling for 48 h. X-ray diffractometry clearly showed that precipitates had crystallized into cellulose II. High yield of total saccharides (including the precipitates) was obtained at 310–320 °C, 25 MPa and 65 g min⁻¹ water flow rate from a wood meal charge of 2.0 g, while the decomposition reaction was completed within about 20 min. Moreover, the yield increased to more than 60% when the wood meal was pretreated for improved wettability. It is shown that saccharides can be produced from sugi wood powder quickly and effectively by treatment in subcritical water.     

人工神经网络在预测流动沸腾曲线中的应用

选用20世纪60年代以来的实验数据，应用人工神经网络分析入口欠热度、质量流速、压力等主要参数对沸腾曲线的影响。在整个传热区内，热流密度随入口欠热度的增加而增大；在过渡沸腾和膜态沸腾区，热流密度随质量流速的增加而增加；压力起重要的作用，除膜态沸腾区外，增加压力能强化传热。除泡核沸腾外，稳态和瞬态的流动沸腾曲线的差异很小。