三角转子膨胀机在有机朗肯循环中应用分析

基于中低温太阳能驱动的有机朗肯循环应用背景,分析三角转子机械作为膨胀机的运行特征,通过建立含泄漏影响的运行过程热力学模型对膨胀机性能进行计算,分析以R245fa为工质在单个膨胀周期内膨胀机内部的热力学性能,包括进气角度、形状因子、偏心距和轴距系数等型线设计参数对膨胀机性能的影响。结果显示,三角转子膨胀机可实现较大的膨胀压比,所讨论的因素会对质量流量、输出功率、膨胀压比和容积效率产生影响,适当选择结构参数可优化膨胀机的性能。     

有机朗肯循环中滚动活塞式膨胀机膨胀比最优化研究

针对容积式膨胀机出口压力与冷凝器内背压不同导致不可逆损失现象的存在,改进并设计了可变膨胀比的滚动活塞式膨胀机,并分析其工作原理。以R245fa为工质,研究了蒸发器内有机工质无过热、膨胀机无泄漏条件下,系统参数变化对膨胀机最佳膨胀比的影响。结果表明:膨胀机的最佳膨胀比受膨胀机效率的影响很小,而受发生温度和冷凝温度的影响较大,蒸发温度越高,最佳膨胀比越大,冷凝温度越高,最佳膨胀比越小,当系统某参数变化时,可以通过调节系统的其他参数使膨胀机处于最佳膨胀比下运行。为膨胀机膨胀比的设计和运行工况的选择提供参考依据。     

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。     

氦气涡轮一维特性预估方法研究

为探究以氦气作为闭式布雷顿循环动力系统工质的涡轮特性,基于氦气与空气的物性差异对损失模型进行修正,绘制涡轮特性曲线,构建一种特殊工质轴流透平一维特性快速预估方法,并通过三维仿真进行验证。研究表明：对损失模型进行修正后,一维预估得到的特性参数更加接近CFD计算结果;在设计点工况下,总温比的误差由0.53%降为0.42%,等熵效率的误差由7.8%降为0.23%;在非设计工况(50%,70%,100%设计转速)下,特性预估结果也较为准确。该方法可实现氦气涡轮特性快速预估,减少计算量。     

带膨胀机的二氧化碳跨临界循环水源热泵系统运行特性实验研究

虽然二氧化碳跨临界循环成为最具潜力的工质替代技术，但其循环的效率还是比常规工质循环低，因此开发膨胀机提高二氧化碳跨临界循环系统运行效率是推动实际应用的关键问题。本文给出了二氧化碳膨胀机的设计特点，同时利用实验手段对带膨胀机的二氧化碳跨临界循环水源热泵系统进行测试，了解膨胀机的运行特性以及对系统的影响，同时改变外部参数条件，了解系统运行规律。通过实验表明，膨胀机的运行效率与膨胀机的转速有关，而且存在极值。系统的运行也受其影响，但系统性能系数是一个综合作用的结果，应对系统运行参数进行优化。     

混合工质组分对ORC系统性能影响实验研究

针对低品位热能的特点,利用搭建的有机物朗肯循环(ORC)系统实验装置,对采用不同组分混合工质R600a/R601a的ORC系统性能进行实验研究,获得系统和部件特性随组分的变化规律。实验结果表明:随着混合工质中的R600a组分的增大膨胀比减小,下降幅度为38.4%,涡旋膨胀机效率受R600a组分变化的影响较小,在60%附近上下波动;净发电功率、工质吸热量和蒸发过程温度滑移量都随着R600a组分的增大先增大后减小,在R600a组分为0.4处,混合工质具有最大的净发电功率、吸热量和温度滑移量,净输出功率比纯R601a高出25%。这说明非等温相变特性可以使混合工质的吸热过程更好地与热源流体的放热过程相匹配,从而提高热能利用率,增加发电功率。     

储能过程设计参数对压缩空气储能系统性能影响研究

本文针对蓄热式压缩空气储能系统建立数学模型,利用MATLAB调用REFPROP软件获取不同状态下空气物性参数,进行总体计算程序开发,在储能系统输出功率为100 MW、膨胀机进口前压力及膨胀级数被固定的前提下,分析了压缩机不同总压比和级数对系统性能的影响。结果表明:对于固定压缩机级数,随着总压比的增加,储能系统效率降低,系统热能利用率降低,节流损失增加,系统热力学性能下降,而储释能工质质量流量降低,储气密度增加,体积减小;对于固定压缩机总压比,随着级数增加,储能系统效率降低,系统热能利用率降低,节流损失基本保持不变。     

一种波瓣式导管在潮流涡轮上的应用研究

导管通过扩压与引射作用提高涡轮的流通率与动能转化率,从而提高涡轮的效率。导管过度扩压将会引起流动分离,降低导管的扩压与引射效果,因此限制了涡轮效率的提高。设计一种具有较强引射作用的扩张导管,导管出口采用波瓣形状;采用CFD方法模拟了不同动能转化率下导管流通率及涡轮总效率的变化曲线,其中,不同动能转化率对应的涡轮工作状态采用激盘模型进行模拟,结果表明,该导管式涡轮理论效率最高可以达到145%。选取涡轮最高效率点对应的动能转化率与导管流通率作为涡轮的设计依据,基于能量守恒定律与叶元体理论设计了一台水平轴涡轮。对该涡轮性能的数值预报结果表明,涡轮输出功率可达到117%。     

有机朗肯循环系统损实验研究

可再生能源及余热发电是低品位能源一种高效利用模式,有机朗肯循环发电系统比水蒸气发电机组更适用于低温热源发电。设计并搭建了热源功率为100kW的导热油模拟热源的有机朗肯循环发电系统,研究冷热源参数恒定不变、膨胀机转速变化时发电系统主要设备的损失和所占比例。主要结论为:当膨胀机转速增加时,蒸发器、膨胀机和工质泵的损失增大,而冷凝器设备损失减少;定量分析膨胀机转速为3000r/min时,蒸发器损失为51.8%,占有机朗肯循环系统损失的1/2以上,工质泵损失最小,仅为1.8%。     

汽液两相螺杆膨胀机的定熵膨胀功率特性

本文探讨了以汽水混合物为工质的螺杆膨胀机的定熵膨胀功率特性,提出了峰值功率膨胀比的概念,分析了进口工质参数,工质预节流等对螺杆膨胀机定熵膨胀功率的影响。     

基于遗传算法的汽油机朗肯循环余热回收系统的优化

为了更加高效利用汽油机排气余热,分析了某款汽油机排气余热回收潜力,建立了基于蒸发器和活塞式膨胀机的汽油机-朗肯循环联合余热回收系统模型。利用遗传算法,同时考虑膨胀机输出功、排气利用率、蒸发器效率和膨胀机绝热效率,以膨胀机输出功和系统总效率为优化目标,以蒸发压力和膨胀机转速为优化变量,对汽油机4个工况下朗肯循环系统的最佳运行参数进行了研究。结果表明,在整个发动机转速范围内,排气最大可利用效率均高于46%,转速越高则排气品质越高。在不同工况下存在最优的膨胀机转速和蒸发压力。经过优化,在选取的4个工况下,功率提高率均在6%以上,最高达到7.08%。     

Cascaded waste‐heat recovery as a green technology for energy sustainability in power generation

In this work, the Cascaded waste‐heat recovery (WHR) is analyzed from the thermodynamic point of view. Typically, WHR is most effective with small gas turbines and old machines which have a relatively higher design mass flow per kW and higher exhaust temperatures than new designs. The working fluid used in the WHR technology is propane, which vaporizes and condenses at low temperatures. The temperature of the heat source, the outlet pressure of the two expanders, and the mass flow rate of the working fluid are assumed as working variables of the technology. The effect of these variables on the thermal efficiency and power output is evaluated. The obtained results are analyzed and discussed. The results of the calculation are also compared with similar published studies. The overall efficiency considering the gas turbine upstream ranges from about 35% up to 39%. The highest efficiency and power output of the WHR alone at 900 K heat source temperature, 800 kPa condenser pressure, and 100 kg/s mass‐flow rate are 30% and 18 MW, respectively, for two‐expander WHR, and 18% and 9 MW, respectively, for single expander WHR. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimal Performance Characteristics of Subcritical Simple Irreversible Organic Rankine Cycle

Based on the theory of finite time thermodynamics, a subcritical simple irreversible organic Rankine cycle (SSIORC) model considering heat transfer loss and internal irreversible losses is established in this paper. The total heat transfer surface area is taken as a constraint, and R245fa is adopted as working fluid of the cycle in the performance optimization. The evaporator heat transfer surface area and mass flow rate of the working fluid are optimized to obtain the maximum power output and thermal efficiency of the SSIORC, respectively. In addition, the influences of the internal irreversibilities on the optimal performances are also investigated. The results show that when the evaporator heat transfer surface area is varied, the relationship between power output and thermal efficiency is a loop-shaped curve, and there exist maximum power output and thermal efficiency points, respectively. However, the two maximum points are very close to each other. When the mass flow rate of the working fluid is varied, the relationship between power output and thermal efficiency is a parabolic-like curve. With the decreases of expander and pump irreversible losses, the performances of the irreversible SSORC are close to those of the endoreversible SSORC with the only loss of heat transfer loss.     

Finite time thermodynamic analysis of an irreversible regenerative closed cycle brayton heat engine

This communication presents the parametric study of an irreversible regenerative Brayton cycle with nonisentropic compression and expansion processes for finite heat capacitance rates of external reservoirs. The power output of the cycle is maximized with respect to the working fluid temperatures and the expressions for maximum power output and the corresponding thermal efficiency are obtained. The effect of the effectiveness of the various heat exchangers and the efficiencies of the turbine and compressor, the reservoir temperature ratio and the heat capacitance rate of heating and cooling fluids and the cycle working fluid on the power output and the corresponding thermal efficiency has been studied. It is seen the effect of cold side effectiveness is more pronounced for the power output while the effect of regenerative effectiveness is more pronounced for the thermal efficiency. It is found that the effect of turbine efficiency is more than the compressor efficiency on the performance of these cycles. It is also found that the effect of sink-side heat capacitance rate is more pronounced than the heat capacitance rate on the source side and the heat capacitance rate of the working fluid.     

Performance evaluation of a low-temperature solar Rankine cycle system utilizing R245fa

A low-temperature solar Rankine system utilizing R245fa as the working fluid is proposed and an experimental system is designed, constructed and tested. Both the evacuated solar collectors and the flat plate solar collectors are used in the experimental system, meanwhile, a rolling-piston R245fa expander is also mounted in the system. The new designed R245fa expander works stably in the experiment, with an average expansion power output of 1.73 kW and an average isentropic efficiency of 45.2%. The overall power generation efficiency estimated is 4.2%, when the evacuated solar collector is utilized in the system, and with the condition of flat plate solar collector, it is about 3.2%. The experimental results show that using R245fa as working fluid in the low-temperature solar power Rankine cycle system is feasible and the performance is acceptable.     

Parametric analysis and optimization for a combined power and refrigeration cycle

A combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the absorption refrigeration cycle. This combined cycle uses a binary ammonia–water mixture as the working fluid and produces both power output and refrigeration output simultaneously with only one heat source. A parametric analysis is conducted to evaluate the effects of thermodynamic parameters on the performance of the combined cycle. It is shown that heat source temperature, environment temperature, refrigeration temperature, turbine inlet pressure, turbine inlet temperature, and basic solution ammonia concentration have significant effects on the net power output, refrigeration output and exergy efficiency of the combined cycle. A parameter optimization is achieved by means of genetic algorithm to reach the maximum exergy efficiency. The optimized exergy efficiency is 43.06% under the given condition.     

Carbon Dioxide as Working Fluids in Transcritical Rankine Cycle for Diesel Engine Multiple Waste Heat Recovery in Comparison to Hydrocarbons

In consideration of the high-temperature characteristic of engine's waste heat and stricter environmental regulations, natural substance, including CO_2 and hydrocarbons, have been treated as promising working fluid for diesel engine waste heat recovery due to its environment friendly and excellent physical and chemical properties. This paper presented a comprehensive performance analysis on transcritical Rankine cycles for diesel engine multiple waste heat recovery using hydrocarbons and CO_2 as working fluid. The optimal turbine inlet pressures corresponding to maximum net power output, maximum exergy efficiency and minimum electricity production cost(EPC) were obtained. The effect of working fluid on these optimal pressures has been discussed. For fluids with low critical temperature, the optimal pressure corresponding to maximum net power output is lower than the one for maximum exergy efficiency, while the opposite results can be found for fluid with high critical temperature. Then, the effect of various working fluid properties in transcritical cycle performance is discussed. Comparison results show that CO_2 obtains only more power output than Ethane, Propane and Propene, but CO_2 is capable of absorbing more energy from engine coolant and regeneration heat with comparable total heat transfer areas and has an advantage in turbine size, particularly for hydrocarbons with high critical temperature.     

Analysis of a combined power and cooling cycle for low‐grade heat sources

This paper presents a parametric analysis of a combined power/cooling cycle, which combines the Rankine and absorption refrigeration cycles, uses ammonia–water mixture as the working fluid and produces power and refrigeration, while power is the primary goal. This cycle, also known as the Goswami Cycle, can be used as a bottoming cycle using waste heat from a conventional power cycle or as an independent cycle using low‐temperature sources such as geothermal and solar energy. Optimum operating conditions were found for a range of ammonia concentration in the basic solution, isentropic turbine efficiency and boiler pressure. It is shown that the cycle can be optimized for net work, cooling output, effective first law and exergy efficiencies. The effect of rectification cooling source (external and internal) on the cycle output was investigated, and it was found that an internal rectification cooling source always produces higher efficiencies. When ammonia vapor is superheated after the rectification process, cycle efficiencies increase but cooling output decreases. Copyright © 2010 John Wiley & Sons, Ltd.     

An integrated power generation system combining solid oxide fuel cell and oxy-fuel combustion for high performance and CO2 capture

An integrated power generation system combining solid oxide fuel cell (SOFC) and oxy-fuel combustion technology is proposed. The system is revised from a pressurized SOFC-gas turbine hybrid system to capture CO₂ almost completely while maintaining high efficiency. The system consists of SOFC, gas turbine, oxy-combustion bottoming cycle, and CO₂ capture and compression process. An ion transport membrane (ITM) is used to separate oxygen from the cathode exit air. The fuel cell operates at an elevated pressure to facilitate the use of the ITM, which requires high pressure and temperature. The remaining fuel at the SOFC anode exit is completely burned with oxygen at the oxy-combustor. Almost all of the CO₂ generated during the reforming process of the SOFC and at the oxy-fuel combustor is extracted from the condenser of the oxy-combustion cycle. The oxygen-depleted high pressure air from the SOFC cathode expands at the gas turbine. Therefore, the expander of the oxy-combustion cycle and the gas turbine provides additional power output. The two major design variables (steam expander inlet temperature and condenser pressure) of the oxy-fuel combustion system are determined through parametric analysis. There exists an optimal condenser pressure (below atmospheric pressure) in terms of global energy efficiency considering both the system power output and CO₂ compression power consumption. It was shown that the integrated system can be designed to have almost equivalent system efficiency as the simple SOFC-gas turbine hybrid system. With the voltage of 0.752 V at the SOFC operating at 900 °C and 8 bar, system efficiency over 69.2% is predicted. Efficiency penalty due to the CO₂ capture and compression up to 150 bar is around 6.1%.     

Transient response of waste heat recovery system for hydrogen production and other renewable energy utilization

In this paper, a 1 kW ORC experimental system is built. Using R123 as the working fluid, transient responses of Basic ORC (BORC) and ORC with a regenerator (RORC) are both tested under critical conditions. A total of four experiments are carried out, including: (1) Case 1: the working fluid pump is suddenly shut down; (2) Case 2: the working fluid is overfilled or underfilled; (3) Case 3: the torque of the expander is suddenly loss. (4) Case 4: the cooling water pump is suddenly shut down. All the major quantities such as the output power and torque of the expander, temperatures and pressures at the inlet and outlet of the expander, temperatures at the inlet and outlet of the condenser are measured. The transient responses of the two systems under the controlled critical conditions are tested and compared, some physical explanations are provided. It is found that RORC is more stable than BORC because of the regenerator. Regenerator should act as a “pre-heater” or “pre-cooler” under the critical conditions thus improving the stability of RORC. When the working fluid in the system is underfilled or leaked, the system performance is extremely unstable. Otherwise, when the working fluid is overfilled, the trend of the curves are similar to the optimal working condition but with weaker performances. We also find that if the working fluid pump is shut down when working fluid is overfilled, the rotation speed and shaft power output of the expander will increase significantly, the unique phenomenon can be used to estimate whether the working fluid in the system is overfilled.