车用内燃机变工况下有机朗肯循环系统性能的分析

通过试验和理论研究,得出了一台车用柴油机在全工况范围内可用排气能量的变化规律,据此设计了一套有机朗肯循环余热回收系统,分别采用纯工质R245fa和非共沸混合工质R416A作为系统的工作介质。针对车用柴油机有机朗肯循环联合系统,提出了有用功提升率评价指标。通过数值计算,研究了不同柴油机工况下,有机朗肯循环系统和联合系统工作性能的变化规律,得出了有机工质质量流量与柴油机可用排气能量的对应关系。研究结果表明:随着柴油机转速和转矩的增加,两种工质(纯工质R245fa和非共沸混合工质R416A)的有机朗肯循环系统的净输出功率均逐渐增加,最大值分别为30.39kW和28.03kW;两种工质的车用柴油机有机朗肯循环联合系统的有用功提升率最大分别为9.00%(纯工质R245fa)和9.70%(非共沸混合工质R416A);采用非共沸混合工质R416A的性能优于采用纯工质R245fa。     

亚临界有机朗肯循环系统的热经济分析与优化

以系统发电成本(electricity production cost,EPC)为评价指标,对用于回收工业锅炉烟气余热的有机朗肯循环(ORC)系统进行了热经济分析与优化。结果表明,随着蒸发器和冷凝器节点温差的增大,系统发电成本先减小、再增大,即存在一组最优的蒸发器和冷凝器节点温差使发电成本最小。分别以纯工质R245fa和R236ea、非共沸混合工质R141b/RC318和乙烷/丁烷为循环工质,得到了最小发电成本时有机朗肯循环系统的最优工作参数,以及对应的系统净输出功、热效率和火用效率。     

分级抽汽回热式太阳能低温有机朗肯循环系统的热力性能分析

研究了分级抽汽回热式太阳能低温有机朗肯循环系统的热力性能。以R600和R245fa作为循环工质,利用热力学第一定律和第二定律,在不同的蒸发温度和膨胀比的条件下,对分级抽汽回热式系统和基本有机朗肯循环系统的热力性能变化进行比较和分析,指出分级抽汽回热式系统的热效率和效率更高,产生的不可逆损失更小,具有更优越的性能。     

地热驱动非共沸工质有机闪蒸循环的热性能分析

非共沸工质具有变温相变特性,可有效改善有机闪蒸循环系统与冷源温度匹配差的问题,进而提高系统的循环性能。文章构建了有机闪蒸循环系统模型,其中,循环工质为R245fa/R601a混合物,热源温度为150℃。文章以净输出功率作为目标函数对有机闪蒸循环系统进行优化,研究了R245fa/R601a混合物的组分变化对有机闪蒸循环系统的闪蒸压力、质量流量、净输出功率和热效率的影响,并比较了以非共沸工质与纯工质作为循环工质时,有机闪蒸循环系统的净输出功率。模拟结果表明:当R245fa/R601a混合物的摩尔组分为3∶7时,有机闪蒸循环系统的净输出功率最大,为25.21 kW,与纯工质R245fa和R601a作为循环工质的有机闪蒸循环系统相比,分别增大了4.39%和5.66%,但以非共沸工质作为循环工质的有机闪蒸循环系统的热效率并不一定大于以纯工质作为循环工质;当R601a的摩尔组分为0～0.6时,以非共沸工质作为循环工质的有机闪蒸循环系统的热效率大于以纯工质作为循环工质;当R601a的摩尔组分为0.7～1时,以R245fa作为循环工质的有机闪蒸循环系统的热效率大于以非共沸工质作为循环工质。     

中低温热水发电系统循环参数和工质的选择

针对热源为80～150℃热水的有机朗肯循环（ORC）发电系统,以发电功率和效率为评价指标,分别分析了以R134a、R123和R245fa三种工质为循环介质时的系统,确定了最佳循环参数和工质。一般来说,最佳蒸发温度对应着最大的输出电功,且随着热流体温度的升高而升高;当热源温度大于120℃时,R134a的系统不存在最佳蒸发温度,此时输出电功随着蒸发温度的升高而增大。对于80～135℃的热水,工质R245fa的发电功率最大;当热水温度超过135℃时,工质R134a的发电功率最大。工质R245fa的发电效率始终是最大的。     

非共沸混合工质用于C-ORC系统的热力学分析

以低温烟气为热源,以R245fa、R152a及不同比例R245fa/R152a混合物为工质,提出新型的再热-抽汽-内回热联合有机朗肯循环(C-ORC)系统,基于美国NIST提供的制冷剂物性参数查询软件(REFPROP)及数学处理软件(MATLAB)混合编程,以净输出功和热效率为主要目标参数,分析系统性能随抽汽回热器出口温度、再热温度、不同比例混合工质的变化关系。结果表明,相同蒸发温度下纯工质R245fa的热力性能优于R152a,其最佳的抽汽回热器出口温度分别为70和55℃,抽汽回热器出口温度对系统的影响要大于再热温度的影响;混合工质分析中,在70℃抽汽回热器出口温度、105℃再热温度下,存在R245fa/R152a最佳质量分数比0.85/0.15,对应的净输出功为37.18 k W、热效率为18.52%、火用损为30.08 k W,其中蒸发器、冷凝器所占的火用损最大。     

分液冷凝有机朗肯循环系统R245fa/HFOs工质选择研究

有机朗肯循环是中低品位热能高效利用的有效技术之一,分液冷凝有机朗肯循环（LSCORC）是基于分液冷凝传热强化的新型热力循环。为寻找新型环保替代工质,建立LSCORC系统的热力学模型,以最大化净输出功为目标,重点考虑了雅各布数、冷热源换热匹配对系统性能的影响,对R245fa/HFOs工质进行了对比筛选。结果表明：工质的雅各布数越大,其净输出功越小;在基础工况下,R245fa/R1336mzz(Z)的热力性能及热经济性表现最佳;当热源参数变化时,雅各布数较小工质的性能表现普遍优于雅各布数较大的工质组合;当冷源参数变化时,在分液冷凝器两个流程中温度滑移和冷源温升匹配越好的工质组合,其系统净输出功越大。     

柴油机废热利用的ORC系统特性研究

以柴油发动机缸套水和尾气废热为热源,设计开发了有机郎肯循环ORC的热力循环系统及发电装置。在该系统中,采用R245fa作为循环工质,以板式蒸发器和冷凝器作为工质相变的换热元件,机械能与电能转化。ORC系统测试结果表明,在ORC系统和发动机长时间稳定运行,稳定发电量14.4kW,发电效率7.2%;净发电量12.45kW,净发电效率6.25%。在保持发动机稳定运行和冷却水全部进行大循环的前提下,发动机出水温度降低,有利于总发电量和净发电量的提升。     

基于定热源的两种有机朗肯循环系统的经济性分析

为了分析热源条件约束下两种有机朗肯循环系统的热力性能和经济性的差异,文章根据热力学理论,选取3种工质分别建立无内回热式有机朗肯循环系统和内回热式有机朗肯循环系统的热力模型和经济性模型。通过计算比较了两种系统的热力性能和经济性,并分析了排烟温度对系统经济性的影响。分析结果表明:当采用相同工质的两种系统的净功率相等时,所对应的排烟温度为等效排烟温度;当排烟温度高于等效排烟温度时,IORC系统的净功率高于ORC系统;当工质相同时,IORC系统的投资成本高于ORC系统,IORC系统的净功率高于ORC系统,且二者的差值较小,导致IORC系统的电力生产成本较高,经济性较低;排烟温度不受约束时,采用R123的ORC系统经济性最佳;当排烟温度不高于75℃时,采用R245fa的ORC系统经济性最佳。     

工质R123和R245fa的有机朗肯循环热力性能

在回收热量一定的条件下,运用热力学第一定律建立了有机朗肯循环热力分析模型,基于蒸发参数法展开了工质R123和R245fa的优选研究。计算结果表明:相同蒸发参数下,工质R123的循环热效率高于工质R245fa;相同蒸发温度下R123具有低压特性,这有利于系统的安全运行。从工质的环保性和热力性能来综合考虑,认为工质R123优于工质R245fa。     

Comparison of a Basic Organic Rankine Cycle and a Parallel Double-Evaporator Organic Rankine Cycle

ABSTRACT

The applications of zeotropic mixtures and multi-evaporator systems are two viable options to improve the performance of the organic Rankine cycle (ORC). This paper conducts the thermo-economic comparison of a basic ORC with R245fa/R600a and a parallel double-evaporator organic Rankine cycle (PDORC) with R245fa. Four indicators are used to evaluate the system performance: net power, cycle efficiency, area of heat exchangers, and area of heat exchangers per net power output. Submodels of condensers and evaporators are established specially for pure organic fluids and zeotropic mixtures. The performance optimization using genetic algorithm is conducted to compare the two systems quantitatively. The optimization indicates a zeotropic mixture is more profitable than a pure work fluid in a basic ORC with a worthy additional investment of heat exchanger. Though PDORC can increase net power obviously, it would decrease the thermo-economic performance of ORC.     

A comparative study of pure and zeotropic mixtures in low-temperature solar Rankine cycle

The paper presents an on site experimental study of a low-temperature solar Rankine cycle system for power generation. The cycle performances of pure fluid M₁ (R245fa) and zeotropic mixtures M₂ (R245fa/R152a, 0.9/0.1) and M₃ (R245fa/R152a, 0.7/0.3) are compared, respectively, based on the experimental prototype. The experiments have been conducted under constant volume flow rate of different fluids. The results show that, with the component of R152a increasing, the system pressure level increases and the power output varies accordingly, which provides an additional means of capacity adjustment. The collector efficiency and thermal efficiency of zeotropic mixtures are comparatively higher than pure fluid of R245fa in the experimental condition, which indicates that zeotropic mixtures have the potential for overall efficiency improvement. Due to the non-isothermal condensation of zeotropic mixture, the condensing heat could be partially recovered by adding an external heat exchanger. Thus, compared with pure fluid R245fa the system overall efficiency of zeotropic mixtures could be improved.     

Optimum composition ratios of multicomponent mixtures of organic Rankine cycle for engine waste heat recovery

With the temperature glide in saturation states, the mixture working fluids have the advantages in thermal energy conversion. In this study, through the investigation in optimum mass fractions of multicomponent mixture working fluids, the economic performance enhancement of the organic Rankine cycle system is obtained for recovering waste heat from engine. The zero ozone-depletion-potential and dry working fluids of R236fa, R245fa, and R1336mzz(Z) are selected as the components of multicomponent mixtures in the system. The net power output, heat transfer calculation, and apparatus cost evaluation are employed to evaluate the power cost of the organic Rankine cycle system. Parameters of temperatures of waste heat sources and efficiencies of expanders are taken into account. The comparisons of economic performances for single-component working fluid and multicomponent mixtures with optimum mass fractions are proposed. The results show that R245fa, having a levelized cost of energy, LCOE, of 8.75 × 10⁻² $/kW-h, performs the best for single-component working fluids, better than R236fa by 1.6% and R1336mzz(Z) by 8.3%. All the two-component mixtures are superior to their single-component working fluids in economic performance. Among the three two-component mixture working fluids, R1336mzz(Z)/R236fa has the lowest LCOE_min, 8.57 × 10⁻² $/kW-h, followed by R236fa/R245fa and R245fa/R1336mzz(Z). In addition, R236fa/R245fa/R1336mzz(Z) mixture, which has a LCOE_min of 8.47 × 10⁻² $/kW-h, economically outperforms all other working fluids and has a lower LCOE_min than R236fa/R245fa by 1.7% and R245fa/R1336mzz(Z) by 2%.     

低温余热有机朗肯循环发电系统工质选择

对有机朗肯循环系统工质的优化选择已逐渐从单一优化目标向多目标发展,但所选的优化目标及优化方法普遍存在主观性较强的问题.针对上述问题,从环保性、安全性等方面对工质进行初选,得到了R123、R245fa、R245ca和R601等9种工质,然后采用主成分分析法对工质的热效率、循环净功和不可逆损失等7个热力性能指标进行了分析计算,得到了两个较为客观的综合评价指标,并在不同蒸发温度下对工质的综合热力性能进行了分析.结果表明:R601做功能力较强,综合效率较高,是该循环系统较为理想的工质.     

Parametric Analysis of Dry Hydrocarbons on the Performance of Organic Rankine Cycle Improved by Working Fluid Reheating

In this paper, the performance of organic Rankine cycle with a two‐stage turbine and internal heat exchanger, considering different dry hydrocarbons as working fluid, has been analyzed. This thermodynamic analysis is done using Engineering Equation Solver version 8.379 software. The influence of working fluid reheating has been studied and the critical temperatures for the thermal and exergy efficiencies are determined. Results show that thermal and exergy efficiencies increase with working fluid reheating and also through a two‐stage turbine. RC‐318 is a good replacement for R‐236fa, R‐113 has a better efficiency than R‐236fa, R‐245fa, and iso‐butane and finally cyclohexane can achieve the highest efficiency. Although the maximum value of efficiencies for each one of working fluids are different, but all of these maximum values almost happen at a unique value of relative pressure of the cycle. The same result has been presented for variation of turbine inlet temperature.     

利用地热能的双压有机朗肯循环性能分析

根据地热利用系统回灌的要求,对热源在系统出口处的温度进行限制,研究了双压有机朗肯循环（DPORC）中的热量分配以及随运行时间的系统性能变化,针对5种不同的有机工质进行了计算分析。研究表明：系统热力学性能的最大值和有机工质流量的最小值在同样的k值（热源提供给高压循环的热量与热源为DPORC提供的热量比）处获得。而采用R600和R245fa系统的净输出功率较大;相比R601,采用R245fa可以将系统的净输出功率提高168.06 kW（5.55%）,热效率和效率分别可提高0.70%和2.86%。相比于单压有机朗肯循环（SPORC）,DPORC可以有效减小系统随运行时间净输出功率降低的幅度。经过40 a的运行,采用R601的系统净输出功率降低幅度最低（428.11 kW, 14.14%）,而采用R600系统的净输出功率降低幅度最大（526.75 kW, 16.55%）。     

Analysis of zeotropic mixtures used in low-temperature solar Rankine cycles for power generation

This paper presents the analysis of low-temperature solar Rankine cycles for power generation using zeotropic mixtures. Three typical mass fractions 0.9/0.1 (Ma) 0.65/0.35 (Mb), 0.45/0.55 (Mc) of R245fa/R152a are chosen. In the proposed temperature range from 25 °C to 85 °C, the three zeotropic mixtures are investigated as the working fluids of the low-temperature solar Rankine cycle. Because there is an obvious temperature glide during phase change for zeotropic mixtures, an internal heat exchanger (IHE) is introduced to the Rankine cycle. Investigation shows that different from the pure fluids, among the proposed zeotropic mixtures, the isentropic working fluid Mb possesses the lowest Rankine cycle efficiency. For zeotropic mixtures a significant increase of thermal efficiencies can be gained when superheating is combined with IHE. It is also indicated that utilizing zeotropic mixtures can extend the range of choosing working fluids for low-temperature solar Rankine cycles.     

Thermal matching performance of a geothermal ORC system using zeotropic working fluids

The thermal matching performance analysis is conducted for a geothermal organic Rankine cycle system using zeotropic mixtures as working fluids. The constant isentropic efficiency is replaced by internal efficiency of an axial flow turbine with given size for each condition, and the zeotropic mixtures of isobutane and isopentane is used as working fluids of the organic Rankine cycle, in order to improve thermal match in evaporator and condenser. The results showed the use of zeotropic mixtures leads to the prominent thermodynamic first law and second law efficiencies, especially at high minimum temperature difference in evaporator (Δt₁), and there exists an optimal thermal performance at some certain mole fraction of isopentane in zeotropic mixtures (x) and Δt₁. The geothermal organic Rankine cycle with x of 0.2 and Δt₁ of 16 K shows the maximal thermodynamic first law and second law efficiency in this research. The geothermal organic Rankine cycle system using zeotropic mixtures shows the optimal overall thermal performance at some certain x, which is not necessary to be the point with the maximal temperature glide. The use of zeotropic mixtures is not always lead to a high thermal to electricity efficiency compared to the pure working fluid, and its overall net power output of P_ORC is even lower than the pure working fluids compositions at some certain x.     

利用烟气余热的有机朗肯循环与苦咸水淡化联合系统

针对沿海和西北内陆地区淡水紧缺和工业烟气余热的排放问题,设计了一种有机朗肯循环与苦咸水淡化的联合系统对工业烟气余热进行有效回收,以生产淡水和电能。该联合系统将闪蒸法与有机朗肯循环进行有机结合,通过变参数法计算采用戊烷作为工质的有机朗肯循环的循环效率,确定该系统运行的最佳参数,并与水工质朗肯循环进行对比,证明了联合系统的优越性。