Numerical Investigation of Effective Heat Conductivity of Fluid in Charging Process of Thermal Storage Tank

This paper presents a numerical case study of heat transfer mechanisms during the charging process of a stratified thermal storage tank applied in a specific adsorption heat pump cycle. The effective thermal conductivity of the heat transfer fluid during the charging process is analyzed through CFD simulations using Unsteady Reynolds-averaged Navier-Stokes equations (URANS). The aim of the study is to provide an equivalent thermal conductivity for a one-dimensional storage tank model to be used in a system simulation of the complete adsorption heat pump cycle. The influence of the turbulent mixing and also the advection effect due to fluid bulk motion are investigated. The results show that in the case considered here, the turbulence effect on the effective thermal conductivity is more considerable than the advection effect.

Operation Performance of Central Solar Heating System with Seasonal Storage Water Tank in Harbin

This paper presented a preliminary research on the central solar heating system with seasonal storage(CSHSSS)used in cold climate in China.A mathematical model of the solar energy seasonal storage water tank used in the central solar heating system was firstly developed based on energy conservation.This was followed by the simulation of the CSHSSS used in a two-floor villa in Harbin,and analysis of the impacts on storage water temperature of tank volume,solar collector area,tank burial depth,insulation thickness around the tank,etc.The results show there is a relatively economical tank volume to optimize the system efficiency,which decreases with increasing tank volume at the constant collector area,and increases with increasing collector area at the constant tank volume.Furthermore,the insulation thickness has obvious effect on avoiding heat loss,while the tank burial depth doesn't.In addition,the relationship between the solar collector efficiency and storage water temperature is also obtained,it decreases quickly with increasing storing water temperature,and then increases slowly after starting space heating system.These may be helpful for relevant design and optimization in cold climates in China and all over the world.

Thermal impact on storage tank of natural gas vehicle during discharge process

To reduce the influence of thermal effects during discharge process for natural gas applications as vehicular fuel,the authors established a mathematical model of methane storage tank system during discharge process and solved the equations by method of Newton-Raphson and iterative algorithm. The results reveal that the lowest temperature occurs in the center of tank with temperature drop of 49. 14 ℃,the average temperature drop of system is 42. 78 ℃,and the discharge amount is 2. 733 kg,with a performance loss approaching 24. 5% at the discharge rate of 1. 315 g/s. The inner temperature and discharge amounts can be changed by heating the wall of tank and increasing the thermal conductivity coefficient of adsorbents. Average temperature drop of system is about 20. 1 ℃ and discharge amount is up to 3. 2065 kg,corresponding to discharge efficiency loss of 11. 47% by changing the thermal conductivity from 0. 2 to 0. 5 and the wall temperature from 20 ℃ to 50 ℃. The research on discharge dynamic performance at different discharge rates indicates that the heat supplied by tank wall is larger than natural convection does.

Comparison and Performance Analysis of Heat Storage Equipment in Solar Heating System

Solar heating system is widely used recently. Heat storage equipment is the guarantee for steady performance of solar heating system. A design of latent heat storage exchanger with submerged coil was introduced with the structure, working principle, and the main advantages. This heat exchanger was integrated into solar heating system as the heat storage equipment. Advantage comparison of the designed heat exchanger in solar heating system with hot water tank was carried out. The analysis results show that the latent heat storage exchanger is superior to hot water tank obviously. The heat exchanger performance parameters and variations of these parameters are got： （1） with the increase of phase change material （PCM） volume ratio, heat storage equipment volume ratio decreases; （2） heat storage efficiency has the same varying tendency with outdoor and air temperature; while the bigger PCM volume ratio is, the weaker the effect of outdoor air temperature on heat storage efficiency is; （3） heat storage capacity and heat storage efficiency increase together; when PCM volume ratio is big, heat storage efficiency is high and the system can begin operating effcienfly and quickly; （4） with the increase of heat storage capacity, life cyde operation cost （LCOC） of system increases gradually in high speed; but with the increase of PCM volume ratio, the difference between the two systems LCOCs becomes smaller and smaller; （5） the reasonable range of PCM volume ratio is 0.5 - 0.7. Temperature characteristic analysis shows that, with the filled PCM, heat storage medium temperature presents several segments at different time, under conditions of different heat storage capacity and different PCM state.

Comprehensive Molten Salt Storage Shell and Supporting Structure Design and Analysis-Part I:A Conductive and Convective Theoretical Heat Transfer Analysis for Molten Salt Cylindrical Shells at 565℃ and 700℃

In this paper a full theoretical thermal analysis of a large molten salt container,80-foot in diameter and 46-foot high,including a four-foot elliptic shell roof,is presented for two temperatures,the standard 565℃ and a futuristic 700℃,which substantially improves the efficiency of the molten salt containers through the use of a highly stable chloride salt called SS700(SaltStream 700).The theoretical analysis includes conductive and convective heat transfer analysis in the steel container,elliptic roof shell,the fiberglass insulation,and firebrick insulation,and includes thermal insulation designs to safeguard against energy losses at high temperatures.The underlying soil and the high temperature concrete foundation were analyzed theoretically using conductive heat transfer,however the area surrounding the soil surface around the bottom of the molten salt storage tank had convective heat transfer analysis included.The final designs presented in this paper seek to limit heat losses to a maximum of 250 W/m^(2) while being able to operate at a minimum external ambient temperature of-10℃,which determines the thicknesses of the fiberglass and firebrick insulation.

Comprehensive Molten Salt Storage Shell and Supporting Structure Design and Analysis-Part II:A Conductive and Convective Numerical Finite Element Heat Transfer Analysis for Molten Salt Cylindrical Shells at 700℃,and Comparison with Theoretical Analysis

In this paper a finite element thermal analysis model-using COMSOL-of a large molten salt container,80-foot in diameter and 46-foot high that includes a four-foot elliptic shell roof,is presented for a futuristic 700℃ design,which uses a highly stable chloride salt called SS700(SaltStream 700)that improves the efficiency of the tank when compared to the traditional 565℃.The FEA(finite element analysis)includes conductive and convective heat transfer analysis in the steel container,elliptic roof shell,the fiberglass insulation,and firebrick insulation,and includes thermal insulation designs to safeguard against energy losses at high temperatures.The underlying soil and the high temperature concrete foundation were analyzed by finite element using conductive heat transfer,however the area surrounding the soil surface around the bottom of the MS storage tank had convective heat transfer analysis included.The finite elements analyses presented are to verify the final fiberglass and firebrick insulation designs,which seeks to limit heat losses to a maximum of 250 W/m^(2) while being able to operate at a minimum external ambient temperature of-10℃.These results are also compared to previously calculated theoretical results.

动态热条件下原油罐储维温过程主要影响因素分析

掌握原油罐储维温过程主要影响因素,对原油库实现节能降耗目的起重要作用。在建立动态热条件下含蜡原油罐储维温过程三维理论模型的基础上,提出了加热盘管空间结构、周向效应对罐内对流传热的影响,划分了内、外因素影响区以及过渡区域;采用多元非线性回归的方法,建立不同季节边界位置主控影响因素模型,定量表征了罐边界油温与内、外因素之间的作用机制。结果表明:罐内大涡结构受无加热盘管区域局部湍涡影响,导致大涡结构向无盘管区域发生偏移。罐底低温区域受盘管周向效应影响较大,罐顶边界油品受内外因素影响大,形成最大厚度1.79 m的外界环境影响区;罐壁受保温层影响,只形成了内部维温热流影响区;冬季罐底形成了0.13 m的外界土壤影响区。

聚氨酯型固-固相变储能材料对沥青调温效果的影响研究

聚氨酯型固-固相变储能材料可以有效提高沥青的相变储能能力,从而在调节路面温度的同时,减小温度波动。基于上述背景,针对聚氨酯型固-固相变储能材料对沥青调温效果的影响展开研究。确定相变材料的分类标准,并分别研究其储能原理及具体应用情况,完成对聚氨酯型固-固相变储能材料特性的分析。在此基础上,定义周期性储热边界条件,根据沥青调温过程中内聚能密度的变化形式,推导相变储能材料的能量变化规律,从而确定聚氨酯型固-固相变储能材料对沥青调温效果的影响能力。

池火灾环境下喷涂涂料液化石油气储罐热响应机理试验研究

以无机水性非膨胀型防火涂料为研究对象、以涂层厚度为主要影响因素,进行了池火灾环境下的液化石油气罐热响应试验,研究了喷涂防火涂料后池火灾环境中储罐的壁温响应、毁坏时间和失效模式。结果表明:无机水性非膨胀型防火涂层对于迟滞储罐在火灾作用下发生爆炸的时间效果显著。对于民用液化石油气储罐,充装水平相同时,涂层厚度2 cm的储罐在池火灾环境下的持续时间是裸罐的6.91倍,涂层厚度3 cm的储罐持续时间是涂层厚度2 cm储罐的1.20倍,涂层厚度4 cm的储罐持续时间是涂层厚度3 cm储罐的1.05倍。增加涂层厚度对迟滞储罐在池火灾环境下毁坏时间的效果逐渐降低,因此,建议储罐涂层厚度以3 cm为宜。研究结果对池火灾环境下储罐的安全防护应用和防火涂料研究具有一定的意义。

双层相变材料复合水箱蓄热特性研究

以双层相变材料复合水箱为研究对象,通过数值模拟和实验研究的方法,对该水箱的蓄热特性进行模拟分析与实验验证,对比分析单、双层相变材料复合水箱的热特性,探究双层相变材料位置对复合水箱蓄热特性的影响规律。研究结果表明,与单层相变材料复合水箱相比,双层相变材料复合水箱的热分层更好,蓄热能力得到提升,双层相变材料复合水箱较普通水箱的蓄热量提高9.7%。双层相变材料距离进出水口位置较远时,相变材料完成熔化的时间更接近,更有利于蓄热水箱的热分层。

计及蓄热罐与管网虚拟储能热电联供系统的经济运行优化分析

本文建立计及蓄热罐与管网虚拟储能热电联供系统模型,探讨不同储能装置配置(如无储能装置、含虚拟储能、含蓄热罐、含蓄热罐与虚拟储能)下负荷场景、燃煤价格、管网长度对系统运行成本的影响。结果表明:含蓄热罐与虚拟储能的储能配置使得热电联供系统的运行成本大幅降低,且当热电负荷波动较大时,运行成本降幅更大,如工业负荷场景下降幅达26.12%;燃料价格上涨使得系统运行成本线性增加,但相比于无储能装置,含储能装置系统的运行成本仍然较低,经济性更好;由于管网储能容量限制以及管网热损的影响,存在一个最佳管长使得系统运行成本最小。

基于贝叶斯网络的储油罐区事故情景分析

为确定储油罐区事故引发多米诺效应中各关键节点因素的重要性,基于情景构建过程中不同发展阶段的孕灾环境、处置措施和演化结果等要素,引入贝叶斯网络方法,提出1种在储油罐区事故情景构建下的演化网络,通过敏感性和影响强度分析,筛选出事故发展过程中的关键节点,并通过提炼事故支链来论证事故演化网络构建的合理性。研究结果表明:在事故进程中,火灾熄灭、火势隔离、人员撤离、危化品残存、全员撤离、组织搜救节点因素对多米诺效应的影响较大;提炼的各事故支链符合情景构建演化趋势,说明该事故演化网络具备一定合理性。研究结果可为储油罐区事故应急辅助决策技术的建设提供支持和参考。

液氦储罐高真空多层绝热结构影响研究

为了明确液氦储罐真空多层绝热结构的最佳层密度,采用Lockheed模型研究热流密度与层密度的关系,确定最佳层密度,探讨绝热层厚度、环境温度、绝热空间真空度对液氦储罐绝热性能的影响。研究结果表明:液氦储罐最佳层密度为41层/cm;绝热层真空度减小,热流密度下降,真空度下降到一定值后,热流密度几乎不再下降;热流密度与环境温度、绝热层厚度分别呈正、负相关,当厚度增加到一定值后,热流密度下降速率减小。在实际确定绝热层厚度和真空度时,应兼顾经济性和绝热性能。研究结果可为液氦储罐高真空多层绝热结构的设计提供参考。

光伏蓄能恒温库系统数值模拟分析

为进一步降低热泵系统冬季能耗,减少恒温库能源消耗情况,本文提出了一种新型光伏驱动蓄能型恒温库系统。基于TRNSYS仿真系统,构建了太阳能-热泵蓄能型热力耦合数学模型,对该恒温库系统进行数值模拟和理论分析。结果显示,在新型光伏驱动蓄能型恒温库系统运行下,库内温度可以稳定维持在-2.0~3.7℃保持24 h,在稳定运行过程中热泵系统运行效率保持在3.0~4.0,系统平均性能系数(COPa)可以达到1.9,系统运行功率在0~0.7 kW,系统24 h累计制热量达到了18.0 kW·h,日平均累计消耗市电仅6.8 kW·h。结果表明,该系统可以为节能型恒温库提供一种设计依据。

低温贮箱SOFI/VD-MLI结构传热分析

针对聚氨酯泡沫与变密度多层组合绝热(SOFI/VD-MLI)结构传热特性分析,确定了满足地面及空间阶段液氮、液氧、液态甲烷贮箱漏热量要求的SOFI/VD-MLI组合绝热结构最小厚度为117mm,其中SOFI为77 mm,VD-MLI为40 mm。分析表明,在满足漏热量要求时,SOFI/VD-MLI组合绝热结构中SOFI厚度大于VD-MLI厚度;随着冷端温度降低,SOFI厚度明显增加,VD-MLI厚度基本保持不变,且空间阶段热端温度223 K对应的SOFI厚度变化量明显大于空间阶段热端温度323 K;随着空间阶段热端温度升高,SOFI厚度逐渐减小,VD-MLI厚度逐渐增加,但SOFI/VD-MLI组合绝热结构总厚度基本维持不变。同时,从质量经济性角度对贮箱SOFI/VD-MLI组合绝热结构进行分析,结果表明,满足地面及空间阶段液氮、液氧、液态甲烷贮箱漏热量要求的SOFI/VD-MLI组合绝热结构单位面积质量为5.022 kg,且单位面积质量受SOFI厚度影响较大,VD-MLI厚度影响较小。

基于斜温层等效容积的大型蓄热罐动态特性分析

斜温层蓄热罐可以提高热电联产(combined heat and power,CHP)机组在供热期间的调峰能力,因此逐渐向大型化发展,但设计参数对蓄热罐的性能影响较大,且采用目前的性能评估方法效率较低。为此,建立大型蓄热罐的物理模型及数学模型,研究蓄热过程中斜温层的形成及变化过程,提出斜温层等效容积的概念,同时分析结构参数及运行参数对斜温层等效容积的影响。结果表明:形成稳定斜温层后,随着蓄热量的增加,斜温层厚度变化不大,采用斜温层等效容积可以更高效的评估蓄热罐的性能。比较不同工况下蓄热罐等效容积的相对变化量可知,不同影响因素对斜温层等效容积的影响从高到低排序依次为布水器布置、蓄热流量、高径比和冷热水温差。研究成果为大型蓄热罐的性能评估提供了一种新参考。

考虑热储灵活配置与热网水力热力特性的电热综合能源系统优化规划

电热综合能源系统优化规划可以定量决策电热耦合系统转型,在规划层面充分开发风电消纳路径。为此,提出一种考虑热储灵活配置与热网水力热力特性的电热综合能源系统优化规划方法。基于变流量-变温度策略构建热网模型,建立电力系统与灵活热源-热网-热储协同规划模型。提出预定参数型、功率平衡下最优投资型、变流量温度下最优投资型、时间系数离散型4种热储建模方法,实现热储灵活配置,采用二项式凸松弛和大M法将非线性规划模型转化为混合整数二阶锥规划模型求解。通过算例分析验证了所提方法可以有效提升规划方案的经济性,保证系统运行可行性,实现风电高比例消纳。

半地下坐地式LNG储罐电伴热系统的设计

相较于传统架高式液化天然气(Liquefied Natural Gas, LNG)储罐,坐地式或半地下坐地式LNG储罐因采用低承台结构,本体的一部分会与周围土壤直接接触,且无空气流通空间,储罐内部的低温将通过储罐本体传导至罐外,影响储罐周围土壤温度;当土壤温度≤0℃时,土壤冻胀隆起,导致储罐受力不均。针对这一问题,首先分析了LNG储罐保冷结构,研究了不同保冷材料的导热系数,计算出储罐不同位置处的漏热量,并根据计算结果选择电伴热系统设计方案,最后采用软件建模仿真分析,进一步验证电伴热系统设计的合理性。电伴热系统可消除低温对储罐周围土壤造成的影响,且能保证储罐本体温度的一致性和连续性,有效避免罐内LNG沸腾。研究成果可为半地下坐地式LNG储罐在进行电伴热系统设计时提供借鉴。

碘离子推力器储罐性能影响因素数值研究

碘离子推力器主要应用于小型卫星的姿态控制和位置保持,其依靠碘工质的升华和电离产生推力。碘工质储供系统的加热方式和结构参数对其工作性能有很大影响。采用动网格方法对离子推力器储罐中碘工质升华相变过程进行数值模拟,讨论储罐加热方式和径高比对其性能的影响。结果表明:从质量流量、流量稳定性和预热时间3个参数综合考虑,四周伴热加热、辐射加热和接触加热3种方式中,接触加热性能最好。在接触加热方式下,储罐径高比对流量变化几乎无影响,流量稳定性很好。对于以大推力为设计目的的碘离子推力器,储罐径高比越小越好,径高比为0.2时的质量流量相比于径高比为1.4时增大了9.0%。对于以高响应速度为设计目的的碘离子推力器,储罐径高比越大越好,径高比为0.2时的预热时长相比于径高比为1.4时增大了80%。

基于Fluent的单罐蓄热特性模拟分析

采用熔盐储热是解决高效、低成本储能与实现减碳减排目标之间矛盾的一种有效途径。以熔融盐为储热介质,熔盐蓄热单罐储热系统能够实现太阳能―热能的有效转换,并可以用来存储和释放能量。选取不同几何形状的内壳式蓄热单罐模型,利用Fluent数值软件,计算各模型的PCM(Phase Change Material,简称PCM)平均温度和热罐内部液相分数并进行对比分析,结果显示,四棱柱管壳式储热罐的蓄热量较好,蓄热速率较大且储热性能更优。选择四棱柱管壳式蓄热罐作为研究对象,通过改变导热流体的进口温度和流速以及相变材料的导热系数,分析不同工况下PCM平均温度的变化:当导热流体进口温度从597 K上升到747 K时,管壳式蓄热罐中的PCM平均温度由394 K升高到441 K;在导热流体进口速度由0.3 m/s上升到2.2 m/s的过程中,蓄热罐中的PCM平均温度由446 K上升到473 K;导热系数在0.277 W/(m·K)增加到1.277 W/(m·K)的过程中,PCM平均温度增高约27 K。该研究可为蓄热单罐的优化设计及应用提供一定参考。