温度分层型水蓄冷槽斜温层的动态特性模拟

针对温度分层型水蓄冷槽提出了一种新型布水器开孔方式,研究了流量为1.0 m3/h时开孔角度分别为60°、90°、120°三种情况。采用计算流体力学(CFD)的方法分析了布水器的开孔角度对温度分层的影响,模拟在充冷过程中垂直高度方向的温度分布和蓄冷槽底部的速度分布情况,并进行了比较分析。结果表明,在开孔角度为90°时,布水器出流最为均匀,斜温层厚度最小,布水器性能最好。     

自然分层型水蓄冷槽布水器的模拟

介绍了自然分层型水蓄冷技术的国内外研究现状，分析影响自然分层型水蓄冷槽蓄冷特性的主要因素。采用CFD商业模拟软件FLUENT6对三种不同类型的布水器建立模型，模拟其充冷过程中的温度分布和速度场，并进行比较分析，优化布水器的设计。     

超临界压缩空气储能系统蓄冷换热器优化设计

蓄冷换热器是超临界压缩空气储能系统的一个重要组成部分.为探究蓄冷换热器中设计尺寸参数对蓄冷装置加工和蓄冷性能的影响,以固体氯化钠颗粒作为蓄冷材料设计了一种超临界压缩空气填充床式蓄冷换热器.根据系统的要求参数和压力容器尺寸的约束方程,以罐体质量和加工成本最小、冷量损失最小和蓄冷效率最高为原则对10 MW蓄冷换热器的整体尺...     

蓄冷空调系统运行评价方法研究及影响因素分析

通过对现有蓄冷空调系统运行过程中能耗和经济性评价方法的分析,为了更好的、全面的评价蓄冷空调系统运行过程中的能耗经济性,提出用单位冷量能效经济系数评价蓄冷空调系统运行过程中能效性和经济性,并对影响蓄冷空调系统运行过程中单位冷量能效经济系数变化的因素进行了初步的分析。     

新型定形板状相变材料的蓄/放热特性

对填充了新型定形板状相变材料的蓄热槽的蓄／放热特性进行了数值计算分析和实验比较。根据数值计算，对影响蓄热槽蓄／放热特性的主要因素——相变材料的几何尺寸、相变材料的导热系数、流体流速、对流放热系数、相变材料填充率等的影响规律进行了分析研究，计算出了蓄热槽内温度分布随时间的变化；并在实验台上测试了蓄热槽初始温度、流人和流出蓄热槽流体温度、作为蓄热体的相变材料测点温度随时间的变化，计算结果与实验结果具有较好的一致性。     

土壤源热泵系统的土壤蓄冷影响因素研究

以南京为例,运用Trnsys软件的模拟计算方法研究夏热冬冷地区土壤源热泵系统中土壤蓄冷的影响因素。Trnsys系统模型模拟了土壤源热泵系统中土壤在室外干球温度和土壤初始温度影响下,其蓄冷性能的变化。通过对模拟结果进行数据处理与分析,得出土壤初始温度是影响土壤蓄冷性能的主要因素。在土壤温度达到25℃时,建议停止向土壤散热,开启冷却塔蓄冷。     

流体流过带折流板通道时的流动及传热数值研究

对常物性流体在通道内的周期性充分发展层流流动和换热特性进行了二维数值计算分析。所研究的通道是由两平行平板布置于中心线位置的一系列折流板构成。平行平板保持温度恒定，折流板则分成完全导热和绝热两种情况，对不同几何参数，Re数和Pr数下的流动和换热性能进行了数值研究。文章还给出了系统流函数图和局部换热系数分布情况。     

三角扰流蛇形翅片管流动换热特性数值研究

蛇形翅片管作为空冷凝汽器基本换热面,其流动与换热性能对空冷电站经济性有着重要影响,基于此,对三角扰流蛇形翅片管的气侧换热及流动特性进行了数值研究,分析了流体温度、压力沿流程方向的变化规律以及迎面风速、扰流三角个数、扰流三角尺寸等因素对蛇形翅片管换热及流动性能的影响,结果表明三角扰流部位局部阻力是沿程阻力的25%～70%,扰流三角对换热有明显的促进作用,换热系数最大提高37%.本研究可为蛇形翅片管的设计及优化提供理论参考.     

冰蓄冷空调系统的评价方法

本文分析了影响冻蓄冷空调经济效益和社会效益的因素，建立了一个评价冰蓄冷空调经济性的模型，归纳出评价冰蓄冷空调系统社会效益和经济效益的五项指标，高峰用转移率，蓄冷率，制冷机容量变化率，性能系数降低率，增加投资回收年限。     

内燃机循环熵产分析和性能评价

引入无因次熵产数Ns表示内燃机热力性能完善程度，对内燃机循环进行热力分析。研究了内燃机热力性能参数压缩比ε、定容增压比λ、定压预膨胀比p等对循环热效率ηm和无因次熵产数Ns的影响。研究表明压缩比ε、定容增压比λ增大，循环热效率ηm和无因次熵产数Ns相应增大，定压预膨胀比p增大，则无因次熵产数Ns增大且循环热效率ηm降低。根据内燃机常规性能参数范围，选定最高温度最高压力，依据性能分析经过一系列优化计算，得到考虑无因次熵产数Ns尽可能小的优化性能参数。     

The effect of diffuser configuration on thermal stratification in a rectangular storage tank

This study is to systematically analyze the effect of various kinds of design factors on the stratification performance of a rectangular storage tank. Special interest is focused on the diffuser configuration, which crucially impacts the performance of a storage tank. Herein, a new diffuser shape is proposed, which exemplifies improved performance. Three-dimensional unsteady numerical experiments are conducted for four design parameters of a stratified thermal storage tank: Three design parameters with three levels (i.e., the Reynolds number=400, 800, and 1200; the Froude number=0.5, 1.0, and 2.0; and the area ratio of the diffuser to tank cross-section=0.0327, 0.0582, and 0.131) and one design parameter having two levels (i.e., diffuser type=radial plate type and radial adjusted plate type). Orthogonal array L₁₈(2×3⁷) is adopted for the analysis of variance. The result gives quantitative estimation of the various design parameters affecting the performance and helps to determine the main factors for the optimum design of a stratified thermal storage tank. In the range of parameters considered, the Reynolds number is found to be the most dominant parameter. Moreover, the diffuser shape plays a significant role on the performance of a stratified thermal storage tank.     

Diffuser design influence on the performance of solar thermal storage tanks

The effect of the inlet and outlet diffuser design on the performance of thermal stratification in a vertical water tank is investigated experimentally. Two sets of diffusers are used in the experiments, which are conducted with a moving thermocline (both up and down) for different flow rates. The results indicate that the preservation of the initial thermocline is excellent when using a settling mesh. It is also shown that the extraction efficiency of the tank is higher at low flow rates during charging, whereas it is lower at low flow rates during discharging.     

Numerical analysis of the discharging performance of a solar energy storage tank containing PCM modules

采用数值模拟软件FLUENT对含有相变储能模块的储热水箱(下文简称为相变储能水箱)和不含相变储能模块的普通水箱(直接进水)的释能工况进行数值模拟,并将模拟结果进行了对比.数值模拟结果表明水箱加入相变储能模块后,一方面相变储能模块的堆积起到了散流作用,减缓了进口水流造成的扰动;另一方面冷水进入水箱中通过相变储能模块缝隙时,相变储能模块对冷水有一定的加热作用.加入相变储能模块后,改善了释能过程的水箱内热分层效果,提高了储热水箱的释热总量.在流量为5 L/min时,相变储能水箱的释能效率比普通水箱的释能效率高7%,但是随着流量的增大,相变储能水箱的释能效率逐渐降低.     

A comparison of experimental thermal stratification parameters for an oil/pebble-bed thermal energy storage (TES) system during charging

Six different experimental thermal stratification evaluation parameters during charging for an oil/pebble-bed TES system are presented. The six parameters are the temperature distribution along the height of the storage tank at different time intervals, the charging energy efficiency, the charging exergy efficiency, the stratification number, the Reynolds number and the Richardson number. These parameters are evaluated under six different experimental charging conditions. Temperature distribution along the height of the storage tank at different time intervals and the stratification number are parameters found to describe thermal stratification quantitatively adequately. On the other-hand, the charging exergy efficiency and the Reynolds number give important information about describing thermal stratification qualitatively and should be used with care. The charging energy efficiency and the Richardson number have no clear relationship with thermal stratification.     

STUDY OF CHARGING OF STRATIFIED STORAGE TANKS WITH FINITE WALL THICKNESS

This paper presents a numerical and experimental study of finite wall thickness on stratification during charging of soar thermal storage tanks. A numerical two-dimensional spectral-element model has been used. Predictions of the model are compared with experimental data, and with a one-dimensional plug flow model. The fluid inlet effect on the stratification is minimized in the experiments by the use of a proper diffuser design with a settling mesh. Both heat conduction in the tank wall and the developing flow in the tank have a significant effect on stratification during charging at low flow rates. The one-dimensional plug flow model is shown to be inferior to the two-dimensional model in representing the experimental data. Yet, a simple one-dimensional flow model corrected for both centreline velocity and mixing effects has given comparable results to the more expensive two-dimensional model. © 1997 by John Wiley & Sons, Ltd., Int. J. Energy Res., vol 21, 411–427 (1997).     

Performance study of a partitioned thermally stratified storage tank in a solar powered absorption air conditioning system

Accurate modeling of solar heating or cooling with storage generally requires an accounting of the stratification within such storage tank, since overall system performance is significantly affected by the storage temperature distribution. In this study, a simple one-dimensional multi-node approach, taking into account of the axial heat conduction between nodes, has been used to theoretically analyze temperature stratification in the thermal storage tank. The results indicate that, for less collector area, the heat removal factor plays a major role in increasing the system performance, than the thermal stratification. Also, an optimum ratio of tank volume over collector area exists for a solar powered absorption air conditioning system. This paper also reviews the state of the art on different kinds of variable inlet design, and a simple new inlet design (partitioning the tank) has been introduced to effect better thermal stratification in storage tank.     

Review of Molten-Salt Thermocline Tank Modeling for Solar Thermal Energy Storage

Molten-salt thermocline tanks are a low-cost option for thermal energy storage in concentrating solar power systems. A review of previous experimental and numerical thermocline tank studies is performed to identify key issues associated with tank design and performance. Published models have shown that tank discharge performance improves with both larger tank height and smaller internal filler diameter due to increased thermal stratification and sustained outflow of molten salt with high thermal quality. For well-insulated (adiabatic) tanks, low molten-salt flow rates reduce the axial extent of the heat-exchange region and increase discharge efficiency. Under nonadiabatic conditions, low flow rates become detrimental to stratification due to the development of fluid recirculation zones inside the tank. For such tanks, higher flow rates reduce molten-salt residence time inside the tank and improve discharge efficiency. Despite the economic advantages of a thermocline tank, thermal ratcheting of the tank wall remains a significant design concern. The potential for thermal ratcheting is reduced through the inclusion of an internal thermal insulation layer between the molten salt and tank wall to diminish temperature oscillations along the tank wall. Future research directions are also pointed out, including combined analyses that consider the solar receiver and power generation blocks as well as optimization between performance and economic considerations.     

Three-dimensional analysis and investigation of the thermal and hydrodynamic behaviors of cylindrical storage tanks

A numerical analysis of the three-dimensional temperature and velocity fields in horizontal cylindrical storage tanks was performed. The phenomena of laminar natural convection and vertical stratification of temperature were considered. The developed three-dimensional transient computing code solves the equations of energy and momentum through the finite volume method. The simulation of fluid cooling process inside the tank showed the formation of stratified temperature profiles that matched those obtained experimentally. Based on several simulations, a correlation was proposed for determining the degree of thermal stratification inside the tank regarding thermal and geometrical parameters. From this correlation, an expression was proposed to predict the fluid temperature profiles along the time. This information is very important in many applications, such as in thermosiphon solar water heating systems, where the global efficiency of the system increases with the thermal stratification degree of the working fluid. Another case studied considered that the tank was connected to solar collectors, aiming at investigating the influence of the inlet jet position with and without a baffle plate on the preservation of the thermal stratification. Results showed that the baffle plate modified the velocity and temperature fields close to the inlet jet, allowing a better thermal stratification. Also the suitable choice of the inlet jet position allowed the formation of a more effective thermal stratification. Some other aspects of the internal dynamics of this kind of storage tank are presented and discussed. For the cases studied, the inlet jet next to the top led to a greater thermal stratification. However, it was verified that when the inlet jet temperature remains constant for a long period of time, and thus its temperature approaches the temperature of the water inside the tank, for the same height, the temperature profiles obtained become similar to the case of the inlet located at usual height of 2/3 of the diameter.     

Effect of obstacles with different opening means on thermal stratification in hot water storage tanks

为研究具有内置隔板的太阳能蓄热水箱隔板开孔尺寸及位置对其内部热分层效果的影响,对9种隔板开孔位置的太阳能蓄热水箱内温度场进行了数值分析,结果显示：在相同的流动参数及开孔面积条件下,隔板中心开1个圆孔的水箱热分层效果最好。对于多开孔的水箱,开孔位置对水箱内热分层影响不大,但对蓄热量影响显著。对于隔板中心开1个圆孔的水箱,在不同流动参数条件下,冷、热水出口温差随着冷水入口流速的增大呈先增后减的趋势,当冷水入口流速大于0.9 m/s时,减弱了热分层的稳定性。     

Fluid thermal stratification in a non-isothermal liquid hydrogen tank under sloshing excitation

To the safe space operation of cryogenic storage tank, it is significant to study fluid thermal stratification under external heat leaks. In the present paper, a numerical model is established to investigate the thermal performance in a cryogenic liquid hydrogen tank under sloshing excitation. The interface phase change and the external convection heat transfer are considered. To realize fluid sloshing, the dynamic mesh coupled the volume of fluid (VOF) method is used to predict the interface fluctuations. A sinusoidal excitation is implemented via customized user-defined function (UDF) and applied on tank wall. The grid sensitivity study and the experimental validation of the numerical mode are made. It turns out that the present numerical model can be used to simulate the unsteady process in a non-isothermal sloshing tank. Variations of tank pressure, liquid and vapor mass, fluid temperature and thermal stratification are numerically investigated respectively. The results show that the sinusoidal excitation has caused large influence on thermal performance in liquid hydrogen tank. Some valuable conclusions are arrived, which is important to the depth understanding of the non-isothermal performance in a sloshing liquid hydrogen tank and may supply some technique reference for the methods of sloshing suppression.