有机朗肯循环系统中蒸发器和冷凝器夹点温差的优化与匹配研究

发布时间：2018-03-23 10:46

本文选题：蒸发器和冷凝器　切入点：夹点温差　出处：《重庆大学》2014年硕士论文

【摘要】：能源问题已经成为全球经济发展的最大压力之一。现代工业生产中造成了大量低温余热的排放，因此回收低温余热能源将其用来发电有很大的意义。目前应用最广泛的低温余热发电系统主要是有机朗肯循环系统(Organic Rankine CycleSystem，ORCs)。作为ORCs中的关键部件，蒸发器和冷凝器的性能对整个系统有很大影响，而其中重要的操作参数夹点温差的选择和匹配，成为ORCs研究的又一新问题。因此，本课题运用热经济学原理，拟对有机朗肯循环系统中的蒸发器和冷凝器夹点温差进行优化和匹配。研究的主要内容如下： ①以R600a为工质，构建亚临界ORCs的蒸发器热经济性模型，分别从火用回收和火用损失两个角度来探讨蒸发器夹点温差对蒸发器性能的影响，并对夹点温差进行优化，分析相关操作参数和经济参数等对优化结果的影响。结果表明：存在最佳的蒸发器夹点温差ΔTe,opt，使蒸发器的性能最佳；从火用回收的角度优化的蒸发器夹点温差与从火用损失的角度优化的结果相比略大；本部分优化的蒸发器夹点温差的范围为5 12K，优化结果与经济因素有关；最优蒸发器夹点温差随余热烟气与工质的热容率之比R的增大而增大，随蒸发器预热段换热系数KeA、蒸发段与预热段换热系数比1、热量火用价ce的增大而减小；流动火用损失对最优蒸发器夹点温差的影响很小，，可以忽略。 ②以采用纯工质R601a、R245fa，混合工质R13I1/R601a、R245fa/R601a的亚临界ORCs为研究对象，分析蒸发器和冷凝器夹点温差对系统性能的影响，通过分析影响因素，对二者进行优化和匹配。结果表明：存在最优的蒸发器夹点温差ΔTe,opt和最优的冷凝器与蒸发器夹点温差比yopt；ΔTe,opt范围为3 6K，与其他文献中提到的范围相比偏小；yopt优化结果范围为0.8 1.5；优化结果受以下几个参数如冷凝器与蒸发器换热系数之比2、混合工质在冷凝器中的露点温度T1a、混合工质的组分变化的影响较大；而工质在蒸发器中的泡点温度T3a、余热烟气的质量流量mg、进口温度Tgi等对优化的结果影响很小。并对四种不同工质R601a、R245fa，R13I1/R601a、R245fa/R601a的优化结果进行了比较分析。 ③以采用R143a为工作流体的跨临界ORCs为研究对象，分析蒸发器和冷凝器夹点温差对系统性能的影响及影响二者优化的因素，并将优化的结果与亚临界ORCs的结论进行比较分析。结果表明：跨临界ORCs中也存在ΔTe,opt和yopt；冷凝器与蒸发器换热系数之比2、工质在膨胀机的出口压力P1、烟气的质量流量mg和进口温度Tgi都会影响ΔTe,opt和yopt。
[Abstract]:Energy has become one of the biggest pressures on global economic development. At present, the most widely used low temperature waste heat power generation system is organic Rankine cycle system ORCs, which is a key component in ORCs. The performance of evaporator and condenser has a great influence on the whole system, and the choice and matching of the temperature difference of the important operating parameters become another new problem in the research of ORCs. The temperature difference between evaporator and condenser in organic Rankine circulatory system is optimized and matched. The main contents of the study are as follows:. 1 using R600a as working medium, the thermal economic model of subcritical ORCs evaporator is constructed. The influence of temperature difference at pinch point of evaporator on evaporator performance is discussed from exergy recovery and exergy loss respectively, and the temperature difference of pinch point is optimized. The effects of relevant operation parameters and economic parameters on the optimization results are analyzed. The results show that the optimum temperature difference between evaporator pinch points 螖 Teopt makes the evaporator performance the best. Compared with the result from exergy loss, the optimized temperature difference of evaporator from exergy recovery angle is slightly larger than that from the angle of exergy loss, the range of temperature difference of evaporator pinch point of this part is 5 ~ 12K, and the optimization result is related to economic factors. The optimal temperature difference increases with the increase of heat capacity ratio R of waste heat smoke to working fluid, and decreases with the increase of heat transfer coefficient KeA in preheating section of evaporator, the ratio of heat transfer coefficient of evaporation section to preheating section of evaporator and the heat exergy value ce of evaporator. The effect of exergy loss on the temperature difference of the optimal evaporator is negligible. (2) the subcritical ORCs with pure working fluid R601a / R245faand mixed refrigerant R13I1 / R601a / R245fa / R601a was used as the research object to analyze the effect of temperature difference between evaporator and condenser on the performance of the system. The results show that there are optimal temperature difference between condenser and evaporator, and the range of 螖 Teopt is 3 ~ 6K, which is smaller than the range mentioned in other literatures, and the optimal ratio of temperature difference between condenser and evaporator is yopt.The results show that the optimum temperature difference between evaporator and condenser is smaller than that mentioned in other literatures. The optimum results were influenced by the following parameters, such as the ratio of condenser to evaporator heat transfer coefficient 2, the dew point temperature T 1a of mixed working fluid in the condenser, and the change of composition of mixed working fluid. However, the Bubble point temperature T 3a, the mass flow rate of waste heat flue gas, and the inlet temperature Tgi have little effect on the optimized results, and the optimized results of R245fa1 / R601a / R245far / R601a of four different working fluids are compared and analyzed. Taking transcritical ORCs with R143a as working fluid as the research object, the influence of temperature difference between evaporator and condenser on the system performance and the factors influencing their optimization are analyzed. The optimized results are compared with the results of subcritical ORCs. The results show that there are 螖 Teopt and yop t in transcritical ORCs, the ratio of heat transfer coefficient between condenser and evaporator is 2, the working fluid is at the outlet pressure of expander P1, and the mass flow of flue gas is obtained. Both the dose of mg and the inlet temperature Tgi could affect 螖 Teanopt and yop _ t.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM617

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