基于CEFR的超临界二氧化碳循环系统特性分析

通过建立基于中国实验快堆CEFR的超临界二氧化碳布雷顿再压缩循环模型,研究各运行参数对循环效率的影响规律及各参数间的关联机制。经分析,循环最高温度恒定的假设无法反映反应堆参数特性,对布雷顿系统进行针对性优化。研究表明,全程超临界和跨临界循环对分流率和循环温度等运行参数具有不同的需求,布雷顿循环的回热性能直接决定了系统的效率,且循环系统中存在最优运行工质流量,经对比分析给出了系统循环的优化循环方案。     

环保型CO2热泵系统的理论分析与性能测试

由于CFCs和HCFCs等人工合成制冷剂对环境产生不利影响,CO2作为自然工质得到了日益重视.CO2的临界温度为31℃,一般采用跨临界循环方式,但其循环性能低于合成工质.对跨临界CO2热泵系统性能进行的热力学分析和实验测试表明:当气体冷却器出口温度一定时,跨临界CO2热泵循环存在一个最优运行压力;在相同工况下,随着蒸发温度的升高,系统的性能系数逐渐增大:气体冷却器出口温度越低,整个系统运行的效率越高.因此,在跨临界CO2热泵系统设计和运行过程中,应综合考虑蒸发温度、气体冷却器出口温度以及运行压力的影响,使系统性能最优.     

波动热源下ORC发电系统的动态运行特性

ORC(有机朗肯循环)是实现中低温热源热功转换的关键技术。以R245fa为工质,采用单螺杆膨胀机,在120℃不稳定热源下实验研究了ORC发电系统在变负载下的动态运行特性及系统主要运行参数随波动热源的变化。实验结果表明:增大负载容量,维持膨胀机做功状态所需工质流量增加,膨胀机入口压力变大,单位工质吸热量变小,膨胀机入口温度及过热度降低。但由于系统整体吸热量变大,系统冷凝压力及冷却水入口温度就增加。系统的发电功率与效率也随负载的提升而不断增大,最大分别为4.61 kW与5.76%。受热源温度正弦波动的作用,系统主要运行参数出现不同程度的波动,冷凝压力的变化是造成系统不稳定的主要原因。     

CO2与R41跨临界朗肯循环低温发电系统比较分析

本文以R41为工质的跨临界朗肯循环低温发电系统进行了热力性能分析,并与CO_2跨临界发电系统进行比较,结果表明:R41和CO_2系统均存在一个最优进口压力使得热效率在相同的膨胀机进口温度下达到最大值,且膨胀机进口温度越高,对应的最优压力也越大。同热效率一样,系统均存在一个最优进口压力使得净功在相同的膨胀机进口温度下达到最大值,且R41系统比CO_2系统所作的最大净功平均提高52.6%,最优进口压力平均降低41.6%,系统火用效率平均提高24.8%。     

中温地热能驱动的跨临界有机朗肯-蒸气压缩制冷系统的火用分析

建立中温地热能驱动跨临界有机朗肯−蒸气压缩制冷系统的火用分析热力学模型,采用R143a作为系统循环工质,探讨膨胀机入口压力、地热流体进口温度、冷凝温度、蒸发温度对火用效率的影响规律,分析系统各个部件的火用损失。计算结果表明：合理的膨胀机入口压力应该小于1.8倍临界压力;存在最佳的地热流体进口温度使得系统的火用效率最大;降低冷凝温度和提高蒸发温度都可以提高?效率,但需要增加换热器等效换热面积作为代价;冷凝器、发生器、膨胀机、节流阀、压缩机、蒸发器、工质泵的火用损失依次降低;随着地热流体进口温度升高,冷凝器及发生器的火用损失所占的比例增大,其它部件的火用损失对应的比例则降低。本文可以为跨临界有机朗肯−蒸气压缩制冷系统的设计提供依据。     

CO_2制冷技术的研究发展

二氧化碳作为一种高效、节能、环保的制冷剂,具有广泛的应用前景和可观的经济价值。但由于其采用跨临界循环,工作压力远远高于常规制冷剂,对设备的承压能力提出了较高要求。这一特点限制了二氧化碳制冷系统的推广和应用,所以为了在提高系统运行安全性、稳定性的同时,达到更高的效率,需要探索新型二氧化碳制冷装置。而这一装置需充分利用二氧化碳性质及其循环特点。文中简要介绍了二氧化碳制冷剂的发展史、性质、跨临界制冷循环技术的完善过程及其应用情况。     

工质跨临界物性变化及S-CO_2透平气动分析

超临界二氧化碳透平被广泛用于太阳能发电系统中,但局部损失导致该透平流动中部分区域工质处于亚临界区。为了探究二氧化碳在跨临界区物性对透平的影响,进行了喷管实验和单级轴流透平的热力气动设计、三维造型及数值模拟。结果表明:二氧化碳物性在跨临界区急剧变化,易产生流动分离和回流等现象;设计透平在各工况下喷嘴尾缘、动叶吸力面前缘等局部压降区域易出现跨临界现象,并伴随有透平效率不同程度降低;增大出口压力、升高温度、调整转速或优化翼型,均可避免跨临界情况发生,从而提高透平效率。     

跨临界CO2热泵系统性能研究

建立了跨临界CO_2热泵热水系统及其主要部件的数学模型并进行了模拟,利用自行搭建的跨临界CO_2热泵实验台进行了相关的实验研究。分析比较了气冷器的出口水温、气冷器的制热量与系统COP_h值(跨临界CO_2热泵系统)的仿真值与实验值,结果表明实验值与仿真值较为吻合,建立的系统模型准确性较高。利用仿真与实验的手段,研究了不同的冷却水流量和冷却水温度对跨临界CO_2热泵系统的性能影响。研究结果表明:系统运行时外部参数冷却水温度和流量及蒸发温度的变化将引起系统性能参数(制热量Q、系统COP_h值)变化,尤其是气冷器进口水温对系统性能的影响最大,为了保证气冷器中CO_2工质实现跨临界循环,降低气冷器进口水温是关键因素。     

4-kW有机朗肯循环系统运行特性实验研究

针对分布式发电系统的多工况运行需求,测试了采用R123工质的4.0 kW级有机朗肯循环实验机组在150℃热源条件下,基于工质流量和膨胀机转速控制的多工况运行特性和输出性能。结果表明：机组在膨胀机转速1 000～1 200 r/min性能最佳,提高工质流量可明显改善机组性能;膨胀机输出功和净功效率随工质流量变化趋势相反,在大流量下获得最大输出功3.7 kW,在小流量下取得最大热效率6.41%。涡旋膨胀机内容积比相对较小,机组在测试工况下均运行于欠膨胀状态,其等熵效率在50.0%～60.0%,随工质流量和膨胀机转速的增大而增大。     

中温地热能驱动的跨临界有机朗肯-蒸气压缩制冷系统的性能分析

跨临界有机朗肯?蒸气压缩制冷系统可以使工质与地热流体更好地匹配,减小系统的不可逆性。本文建立该系统的热力学模型,利用EES软件编程,分别对以R143a、R218及R125为工质的系统进行性能分析。计算结果表明,相比R218及R125,以R143a为工质的系统的性能是最佳的。为了避免膨胀机内产生湿蒸气,对于一定的膨胀机进口温度,膨胀机入口存在一个极限压力,并且存在一个最优压力使得系统的性能最佳。地热流体温度的升高可以提高系统的制冷能力,但系统的性能系数则随之先增大后减小;随着地热流体干度的增加,地热流体释放的潜热会大大增加系统的制冷量,而系统的性能系数保持不变。冷凝温度及蒸发温度对系统性能有着重要影响,其中冷凝温度的影响更为明显。以R143a为工质的跨临界有机朗肯?蒸气压缩制冷系统的最佳性能优于以R245fa为工质的亚临界有机朗肯-蒸气压缩制冷系统的最佳性能。     

Simulation of the optimal heat rejection pressure for transcritical CO2 expander cycle

In order to optimize and control transcritical CO₂ refrigeration cycle, a mathematical model was developed to simulate the system performance. The simulation results show that a maximum COP exists at the optimal heat rejection pressure not only for throttle valve cycle but also for expander cycle. Also, the optimal heat rejection pressures of the throttle valve cycle are greater than those of the expander cycle under the same condition. In order to further obtain correlation of the optimal heat rejection pressure for transcritical CO₂ expander cycle, it is necessary to analyze the impact degree of compressor efficiency, expander efficiency, gas cooler outlet temperature and evaporation temperature. Based on the simulation results, the values of the optimal heat rejection pressure for the expander cycle were regressed in terms of gas cooler outlet temperature and evaporation temperature at given compressor efficiency and expander efficiency. Finally, two types of polynomial correlations were obtained. One is cubic form, with an average deviation of less than 0.5% and the other is simplified form, with an average deviation of less than 1%. It is, therefore, convenient to use either correlation to simulate the performance of transcritical CO₂ expander cycle.     

Simulation of the optimal heat rejection pressure for transcritical CO<Subscript>2</Subscript> expander cycle

In order to optimize and control transcritical CO₂ refrigeration cycle, a mathematical model was developed to simulate the system performance. The simulation results show that a maximum COP exists at the optimal heat rejection pressure not only for throttle valve cycle but also for expander cycle. Also, the optimal heat rejection pressures of the throttle valve cycle are greater than those of the expander cycle under the same condition. In order to further obtain correlation of the optimal heat rejection pressure for transcritical CO₂ expander cycle, it is necessary to analyze the impact degree of compressor efficiency, expander efficiency, gas cooler outlet temperature and evaporation temperature. Based on the simulation results, the values of the optimal heat rejection pressure for the expander cycle were regressed in terms of gas cooler outlet temperature and evaporation temperature at given compressor efficiency and expander efficiency. Finally, two types of polynomial correlations were obtained. One is cubic form, with an average deviation of less than 0.5% and the other is simplified form, with an average deviation of less than 1%. It is, therefore, convenient to use either correlation to simulate the performance of transcritical CO₂ expander cycle.     

基于CO_2跨临界循环的冷热电联供系统热力学分析

基于低品位能源利用冷热电联供技术,以常规燃煤电厂排出温度为150℃的烟气为余热利用对象,提出了CO2跨临界循环冷热电联供系统模型,分析了膨胀机入口压力和温度等参数对系统性能的影响.结果表明:压缩机入口过热度对系统性能系数、经济性能系数的影响很小;系统性能系数随着高压膨胀机入口压力、低压膨胀机入口温度和膨胀机效率的升高而增大,随着高压膨胀机入口温度、低压膨胀机入口压力和制冷蒸发温度的升高而减小;系统总不可逆损失随着高压膨胀机入口压力的升高存在最小值.     

Modeling and simulating the transcritical CO2 heat pump system

In this paper, a mathematical model for steady-state simulation of transcritical CO₂ water-to-water heat pump system with an expander has been developed. It is used to simulate the performance of transcritical CO₂ system with CO₂ expander prototype. Simulated results are compared with experimental data to verify the accuracy of the simulation model. The comparison results show the average deviation of about 15% for COP_c(cooling coefficient of performance) and COP_h(heating coefficient of performance), about 17% for cooling and heating capacity at experimental high pressure ranges. With this model, which has been validated in a limited high pressure range, the influence of water mass flow rate and water inlet temperature of both evaporator and gas cooler on the performance of transcritical CO₂ expander system is analyzed. The results show that decreasing inlet temperature and increasing mass flow rate of cooling water cannot only increase the system performance but also reduce the optimal heat rejection pressure, at which the maximum COP (coefficient of performance) can be obtained. For chilling water, increasing its inlet temperature and mass flow rate is favorable for increasing the system performance, while the optimal heat rejection pressure does not vary very much.     

CO2跨临界循环地源热泵的研究

给出了CO2跨临界循环地源热泵的系统流程，并在考虑输气系数和绝热效率的基础上，与R22和R134a等进行了循环性能比较。结果表明，用于需要较高供水温度的空调系统或热水供应系统时，CO2可具有和常规工质相当的性能。同时对于一特定的CO2地源热泵，分析了在热水流量和热水温度变化时的运行特性，并讨论了CO2地源热泵容量调节的方法。     

Performance investigation of transcritical carbon dioxide two-stage compression cycle with expander

The trend toward the energy efficiency improvement for transcritical carbon dioxide refrigeration cycles has led to the development of the two-stage compression process. Three different variations of transcritical carbon dioxide two-stage compression cycles with expanders are investigated by using thermodynamics analysis. They are the two-stage compression at optimal intermediate pressure (TCOP) cycle, two-stage compression with expander driving high-pressure stage (TCDH) cycle and two-stage compression with expander driving low-pressure stage (TCDL) cycle, respectively. The performance of the TCOP cycle and the single-stage compression with expander (SCE) cycle is mainly discussed and compared for a wide operating condition. It is found that the COP and exergy efficiency of the TCOP cycle are on average 9% higher than those of the SCE cycle. At given design points, the COP of the TCDH cycle outperforms the other options, showing 11.32%, 9.65% and 0.72% performance improvement over the TCDL cycle, SCE cycle and the TCOP cycle, respectively. If design and structure are also taken into account, the TCDH cycle is a feasible option since the expander and the auxiliary compressor are integrated into one unit; thus, the transfer loss and leakage loss can be decreased greatly. The key problem is to adopt some measures that control the operating conditions to avoid deviating from the design point.     

跨临界制冷循环的适用条件及在CO2制冷系统中的应用研究

在热力学第一、第二定律的基础上研究了跨临界制冷循环若干适用条件。详细分析了跨临界制冷循环对环境温度、制冷压力和温度、回热温差的要求，得出了启动危机、最小制冷高低压差等概念，将这些成果用于CO2制冷剂的分析。获得了相应的数据。可供研究CO2跨临界制冷系统应用。     

Exergy analysis of transcritical carbon dioxide refrigeration cycle with an expander

In this paper, a comparative study is performed for the transcritical carbon dioxide refrigeration cycles with a throttling valve and with an expander, based on the first and second laws of thermodynamics. The effects of evaporating temperature and outlet temperature of gas cooler on the optimal heat rejection pressure, the coefficients of performance (COP), the exergy losses, and the exergy efficiencies are investigated. In order to identify the amounts and locations of irreversibility within the two cycles, exergy analysis is employed to study the thermodynamics process in each component. It is found that in the throttling valve cycle, the largest exergy loss occurs in the throttling valve, about 38% of the total cycle irreversibility. In the expander cycle, the irreversibility mainly comes from the gas cooler and the compressor, approximately 38% and 35%, respectively. The COP and exergy efficiency of the expander cycle are on average 33% and 30% higher than those of the throttling valve cycle, respectively. It is also concluded that an optimal heat rejection pressure can be obtained for all the operating conditions to maximize the COP. The analysis results are of significance to provide theoretical basis for optimization design and operation control of the transcritical carbon dioxide cycle with an expander.