热泵储电系统中压降对效率的影响

构建了基于闭式布雷顿循环的热泵储电系统模型,通过热力学计算得到了状态参数和往返效率。闭式系统中压缩机和透平的进出口压力相互关联,压比随压降变化,引起压缩功与膨胀功改变,从而对往返效率产生重要影响。经对比分析,结果表明：压降升高会降低往返效率,储能过程压降升高造成储能功耗增大且释能发电量减少,释能过程压降升高只造成释能发电量减少;储能过程压降对效率的影响大于释能过程,低压侧压降的影响大于高压侧;按照影响程度从低到高,分别为储能过程高压侧压降、释能过程高压侧压降、储能过程低压侧压降和释能过程低压侧压降;在给定参数下,上述四个过程的压降从10kPa增至60kPa,往返效率降幅百分比分别为4.72%、5.79%、11.83%和20.63%。因此,在条件有限时,系统优化方向为首先降低释能过程低压侧的压降。本文构建的基于闭式布雷顿循环的热泵储电系统,可为热泵储电系统的设计与优化提供参考。     

集成外热源的超临界二氧化碳热泵储电系统性能研究

对基于超临界二氧化碳工质的热泵储电系统展开研究,建立了热力学与技术经济性分析模型,并对系统热力参数进行优化,分析了压缩机等熵效率、透平等熵效率、换热器压损以及最小换热温差等关键设备参数对系统性能的影响。此外,提出了以燃气轮机排气为外热源的集成系统构型,对独立热泵储电系统及集成外热源的系统性能进行分析。结果表明：独立储能系统的最高往返效率可达62.91%;集成外热源后,单位能量的投资成本降低,系统能量效率随放电时间和放电功率的增加而降低。     

冷水相变能热泵系统的性能系数与经济性分析

冷水相变能热泵系统是一种清洁能源供热供冷系统,性能系数和经济性是冷水相变能热泵系统的主要问题。根据冷水相变能热泵系统的运行原理,采用控制变量法实验分析了冰层厚度、冷水流量以及蒸发冷凝温度对系统能效比的影响,提出了一种冷水相变能热泵系统的运行调控方案并计算其经济性。研究表明：结冰厚度为8 mm时,系统有效能效比最大;系统制热量为744 kW时,相变机结冰期冷水流量应控制在70 t/h,排冰期冷水流量应控制在80 t/h;根据不同时间段的冷热负荷进行系统运行调控,与传统运行方式相比,冬季运行成本降低了4.72%,夏季运行成本降低了29.96%,系统能效比提高了5.6%;系统投资回报率为15.27%,投资回收期为7.67年,具有良好的经济性与节能性。     

基于TRNSYS对太阳能-空气源热泵系统性能研究

通过试验研究蓄热水箱,分别测量0.75 m和1.5 m螺旋盘管一天中进出水温度和流量等参数,对比分析二者制热量、耗功量、COP.结果表明,蓄热水箱采用0.75 m螺旋盘管系统COP低于采用1.5 m螺旋盘管系统COP.基于TRNSYS模拟软件,对太阳能集热器与空气源热泵采用串联和并联两种连接方式下的太阳能-空气源热泵系...     

相变储能太阳能热泵系统的试验研究

文章建立了相变储能太阳能热泵系统试验平台,介绍了系统的运行方式以及各个部分的运行原理,选取典型日进行试验,并对试验数据进行分析。分析结果表明:相变储能太阳能热泵系统能够满足北方农村的供暖需求,可以保证白天室内的温度达到22℃,COP的最大值为6.3;太阳能热泵系统停止工作后,相变储能箱可以保证室内温度达到供暖的需求温度7 h,起到了"削峰填谷"的作用,运行费用显著降低;相变储能太阳能热泵系统解决了单纯电加热供暖方式费用高、能耗高的问题,具有显著的节能性。     

蒸汽喷射式热泵变工况性能分析

采用数值模拟的方法对低压蒸汽增压利用系统中的蒸汽喷射式热泵在非设计工况下的操作性能进行研究，计算并分析了工作蒸汽压力和温度、引射流体压力及混合流体压力等热力参数对热泵操作性能的影响。数值结果表明：当混合流体的压力低于一定的数值时，喷射系数维持一定值；而热泵对引射流体压力的变化极为敏感，引射压力的微小变化可能导致热泵操作性能的急剧下降；提高工作蒸汽的压力并不一定能改善喷射泵的工作性能，这是因为提高工作蒸汽压力会增加额外的蒸汽量所致；喷射系数随工作蒸汽温度的升高而略有增大，并近似呈线性率。     

浅谈新型水源热泵空调系统

水源热泵空调系统与普通的中央空调系统相比，具有节能热回收以及系统简单，安装方便、操作灵活、适应性强等优点。本文简介其系统组成，工作原理设计要点。     

相变蓄热火墙的结构设计及其性能分析

应用计算流体力学软件分析确定火墙的内部构造形式。选择熔点较高,融解热较大的相变材料,将其封装、制成相变墙板应用于传统火墙壁面。通过计算和模拟分析得出,相变蓄热火墙是一种能有效吸收和利用火墙体内部烟气余热的采暖系统,这种创新式火墙具有较好的应用前景。     

Experimental study on thermal performance of a pumped two-phase battery thermal management system

Battery thermal management system (BTMS) is of great significance to keep battery of new energy vehicle (NEV) within favorable thermal state, which attracts extensively attention from researchers and automobile manufacturers. As one BTMS scheme, pumped two-phase system displays excellent cooling capacity owing to large amount of latent heat usage, while there is limited research efforts focusing on the feasibility of the BTMS scheme. This paper experimentally investigates thermal performance of a pumped two-phase BTMS heated by a dummy battery with relative high heat fluxes. The effects of heat fluxes, flow rates and cold source temperatures on thermal performance have been studied and conclusions have been drawn accordingly. The results show that the thermal performance of the system is generally enhanced with the increase of the refrigerant flow rates. When the heat flux and cold source temperature are 0.11 W/cm² and 10°C, respectively, t_avg and △t_max are decreased by 3.4°C and 0.5°C, respectively, when the refrigerant flow rate is increased from 0.20 to 1.67 L/min. Meanwhile, heat transfer coefficient is also improved with an increase of the flow rates, while the enhancements become less obvious under high heat flux. In addition, the t_avg and △t_max of cold plate surface are increased when the heat flux is elevated, while the t_avg at the low flow rate is increased slightly. However, the increase of △t_max is more obvious at the low flow rate, compared to that at high flow rate. When the heat flux is increased from 0.11 to 0.60 W/cm², t_avg is increased by 3.8°C under the flow rate of 0.2 L/min, while that at the flow rate of 1.67 L/min is almost doubled. Meanwhile, the heat transfer coefficient is increased monotonously at the low flow rate, while that at the high flow rate is first decreased and then increased. Besides, lower surface temperatures can be obtained with low cold source temperatures. However, cold source temperatures affect temperature uniformity less.     

Experimental investigation of start-up and transient thermal performance of pumped two-phase battery thermal management system

In this study, a pumped two-phase battery thermal management system was developed, and its start-up and transient thermal performances were experimentally evaluated. The start-up behavior was characterized, and the effects of the flow rate, heat flux, and cold-source temperature on the start-up and transient thermal performances were examined. Three start-up modes were observed: fluctuating growth, temperature overshoot, and smooth growth. The fluctuating growth start-up mode appears to be suitable for battery cooling. The transient performance was improved when the flow rate was decreased, which resulted in a quicker start-up and lower average temperature (t_avg) and maximum temperature difference (∆t_max). Reducing the flow rate from 0.99 to 0.20 L/min significantly shortened the start-up time, lowered t_avg and ∆t_max, and increased the heat transfer coefficient (α) when the steady state was reached. Increasing the heat flux initially improved and then weakened the transient performance of the pumped two-phase system. Increasing the heat flux from 1.1 to 2.8 W/cm² initially reduced the start-up time and t_avg to 350 seconds and 1.5°C, respectively, but they then significantly increased to 360 seconds and 13.5°C, respectively. The transient t_avg and ∆t_max decreased with the cold-source temperature (t_cs), while the start-up time was independent of changes in t_cs.     

A hyperbolic microscopic model and its numerical scheme for thermal analysis in an N-carrier system

We extend the concept of the well-known hyperbolic two-step model for micro heat transfer to the case of energy exchanges in a generalized N-carrier system. The model satisfies an energy estimate and hence is well-posed. Based on this result, a finite difference scheme is developed for solving the hyperbolic microscopic model. The scheme is shown to satisfy a discrete analogue of the energy estimate, implying that it is unconditionally stable. Finally, the scheme is tested by an example. The difference between the hyperbolic model and the corresponding parabolic model for a multi-carrier system is also compared.     

Transient thermal performance of ice slurries pumped through pipes

The paper examines the transient melting rates of ice slurries being pumped through pipes whose walls are initially warmer than the freezing temperature of the slurry. The application for this work is the new innovative pipe cleaning method known as ice pigging. Ice pigging consists of introducing a length of ice slurry consisting of small ice crystals in a fluid matrix of water and a freezing point depressant into a pipe. The ice slurry forms a semi-solid plug whose temperature is at the freezing temperature of ice at the prevailing operating conditions. The plug cools the pipe walls, which in turn results in some phase change within the slurry. The plug is propelled along the pipe by a pressurised fluid introduced behind the plug. This results in the pipe walls being exposed to large time-varying temperature changes, with the front of the plug receiving the greatest heat flux. The purpose of undertaking ice pigging is to clean the pipe walls with the high shear at between the walls and the semi-solid slurry.Analytical transient conduction theory is adopted to estimate the energy removed from the pipe wall as a result of the passing ice pig. This is used to develop equations predicting the amount of phase change occurring in the pig and hence estimate the distance it can travel before it has melted. The resultant model enables ice pig users to estimate how much ice slurry is required to undertake successfully a specific ice pigging task.     

太阳能膜蒸馏淡化系统试验及热性能分析

太阳能膜蒸馏淡化水是新型的水处理技术。通过太阳辐射量、水箱温度、膜通量等参数对系统运行影响的试验研究表明,即使在较寒冷的11月份,自然循环条件下水箱的温度也可维持在40℃以上,最高温度可达65℃,可以满足膜蒸馏系统运行的热源条件;在夏季,注入新水的太阳能膜蒸馏实验系统12 h的产水量为4.98kg,可为3口之家提供一天的健康饮用水。文章根据系统的热平衡条件,给出了太阳能膜蒸馏系统产水量的计算公式。     

Greenhouse floor heating system optimization using long-term thermal performance design curves

Steady-state design curves suitable for the determination of long-term thermal performance of the floor heating system are presented in the paper. The dominant design variables considered in the system synthesis are: pipe diameter and spacing, floor depth, greenhouse main air mass temperature, hot water temperature, water flow rate and plant canopy density. The design curves are generated for a wide range of these parameter values. The nomograms are presented in terms of the greenhouse heat gain per unit floor area as a function of the floor depth, with other variables as parameters. The set of design curves also includes the values of the rate of change of heat flux with the floor depth. This facilitates in design optimization by reducing the three dimensional search in geometric parameter, namely, pipe diameter and spacing, and floor depth, to a two dimensional search. The utility of nomograms is illustrated through a design example for a floor heated greenhouse located in the midwest region of the United States. The optimum parameter values for the floor heating system are estimated using the classical calculus technique.     

A solar thermal cooling and heating system for a building: Experimental and model based performance analysis and design

A solar thermal cooling and heating system at Carnegie Mellon University was studied through its design, installation, modeling, and evaluation to deal with the question of how solar energy might most effectively be used in supplying energy for the operation of a building. This solar cooling and heating system incorporates 52 m² of linear parabolic trough solar collectors; a 16 kW double effect, water-lithium bromide (LiBr) absorption chiller, and a heat recovery heat exchanger with their circulation pumps and control valves. It generates chilled and heated water, dependent on the season, for space cooling and heating. This system is the smallest high temperature solar cooling system in the world. Till now, only this system of the kind has been successfully operated for more than one year. Performance of the system has been tested and the measured data were used to verify system performance models developed in the TRaNsient SYstem Simulation program (TRNSYS). On the basis of the installed solar system, base case performance models were programmed; and then they were modified and extended to investigate measures for improving system performance. The measures included changes in the area and orientation of the solar collectors, the inclusion of thermal storage in the system, changes in the pipe diameter and length, and various system operational control strategies. It was found that this solar thermal system could potentially supply 39% of cooling and 20% of heating energy for this building space in Pittsburgh, PA, if it included a properly sized storage tank and short, low diameter connecting pipes. Guidelines for the design and operation of an efficient and effective solar cooling and heating system for a given building space have been provided.     

A stable finite difference scheme for thermal analysis in an N-carrier system

In this study, we extend the concept of the well-known parabolic two-step model for micro heat transfer to model the energy exchanges in a generalized N-carrier system with heat sources. We show that the multi-carrier system satisfies an energy estimate. Based on this result, a finite difference scheme is then developed for thermal analysis in the multi-carrier system. The developed numerical scheme is shown to satisfy a discrete analogue of the energy estimate, implying that it is unconditionally stable. The method is illustrated by several numerical examples.     

Automotive fuel cell engine test cell design and its thermal flow analysis

A test cell for automotive PEM fuel cell engine is introduced and designed. Similarities and differences of facilities between PEM fuel cell engine and inner-combustion engine are illustrated. It turns out that, the air treatment, exhaust gas, cooling and electrical facilities are quite similar, the fuel treatment, power load type, ventilation and air-conditioning are quite different, while the vibration isolation and noise elimination facilities are completely simplified. Furthermore, a thermodynamic model is proposed to analysis the heat flow in fuel cell engine test cell. The Monte Carlo Simulation method is applied to get the proportion of outgoing thermal flows. A thermal flow rule of 4.5/4.5/0.6/0.4 is proposed as rule of thumb for cell designer.     

斜坡式热气流发电试验模型的设计

分析了斜坡式热气流太阳能发电的可行性,介绍了斜坡式热气流发电的组成及基本原理.根据依山而建斜坡式热气流发电系统的思想,设计了一个高4m、宽1.5 m的试验模型.用有机玻璃做透明盖板材料;用铁板代替山体,在其后面设置了用于调控温度的电阻丝700W/m2.阐述了确定该试验模型各部分比例和结构参数的依据.对设计的试验模型进行了评价:与传统的塔式发电模型相比,该模型具有集热效率高、造价低的优点.