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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。 相似文献
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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。 相似文献
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蒸汽喷射式热泵变工况性能分析 总被引:4,自引:1,他引:4
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。 相似文献
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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。 相似文献
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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, tavg and △tmax 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 tavg and △tmax of cold plate surface are increased when the heat flux is elevated, while the tavg at the low flow rate is increased slightly. However, the increase of △tmax 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, tavg 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. 相似文献
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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 (tavg) and maximum temperature difference (∆tmax). Reducing the flow rate from 0.99 to 0.20 L/min significantly shortened the start-up time, lowered tavg and ∆tmax, 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 tavg to 350 seconds and 1.5°C, respectively, but they then significantly increased to 360 seconds and 13.5°C, respectively. The transient tavg and ∆tmax decreased with the cold-source temperature (tcs), while the start-up time was independent of changes in tcs. 相似文献
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Weizhong Dai 《International Journal of Heat and Mass Transfer》2009,52(9-10):2379-2389
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. 相似文献
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G. Quarini E. Aislie D. Ash A. Leiper D. McBryde M. Herbert T. Deans 《Applied Thermal Engineering》2013,50(1):743-748
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. 相似文献
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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. 相似文献
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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. 相似文献
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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. 相似文献
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Xinfeng Zhang Minghui Luo Wei Dai Chuanqi Yao Jiwen Wang Daojin Huang Chunyang Wang 《International Journal of Hydrogen Energy》2018,43(36):17409-17419
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. 相似文献