Multi-objective optimal design of evaporative condenser using zeotropic working fluid

doi:10.16085/j.issn.1000-6613.2023-0771

Abstract

Abstract:

Applying evaporative condenser to zeotropic organic Rankine cycle can effectively improve the thermal economy of the system. After establishing the Kriging surrogate model of evaporative condenser, by taking the R601a component mass fraction, air flow rate and spray water flow rate flow as decision variables, and the heat exchange area and exergy efficiency as objective functions, analysis of influencing factors of the objective function was conducted, and multi-objective optimization was carried out using non-dominated sorting genetic algorithm and TOPSIS decision method. The results showed that in the analysis of influencing factors, the influence of air flow rate on the objective function was greater than that of spray water flow rate, and when the mass fraction of R601a was about 0.7, the heat exchange area had a minimum value and the exergy efficiency had a maximum value. In Pareto front, the mass fraction of R601a component had the best value range for the design of evaporative condenser, while the value range of air flow rate and spray water flow rate was wide, covering almost the whole range of variation. The scheme with low cost, small occupied space and high effective utilization of available energy was: R601a component mass fraction of 0.725, air flow rate of 81.017kg/s, spray water flow rate of 58.302kg/s, corresponding heat exchange area of 316.883m², and exergy efficiency of 0.428.

Key words: evaporative condenser, zeotropic, surrogate model, multi-objective, optimal design

摘要：

将蒸发式冷凝器应用于非共沸有机朗肯循环可以有效提高系统的热经济性。建立了蒸发式冷凝器的Kriging代理模型，以R601a组分质量分数、空气流量、喷淋水流量作为决策变量，换热面积和㶲效率为目标函数，开展了目标函数的影响因素分析，并采用非支配排序遗传算法和TOPSIS决策法开展多目标优化。结果表明，影响因素分析中，空气流量对目标函数的影响程度比喷淋水流量更大，而R601a组分质量分数为0.7左右时，换热面积有最小值且㶲效率有最大值；Pareto前沿中，R601a组分质量分数对蒸发式冷凝器的设计存在最佳的取值范围，而空气流量、喷淋水流量的取值范围较广，几乎涵盖其整个变化范围。成本低、占用空间小且对可用能的有效利用程度大的方案为：R601a组分质量分数0.725，空气流量81.017kg/s，喷淋水流量58.302kg/s。对应的换热面积为316.883m²，㶲效率为0.428。

关键词: 蒸发式冷凝器, 非共沸, 代理模型, 多目标, 优化设计

CLC Number:

TK124

XIONG Yuanfan, LI Huashan, GONG Yulie. Multi-objective optimal design of evaporative condenser using zeotropic working fluid[J]. Chemical Industry and Engineering Progress, 2024, 43(6): 2950-2960.

熊远帆, 李华山, 龚宇烈. 非共沸工质蒸发式冷凝器多目标优化设计[J]. 化工进展, 2024, 43(6): 2950-2960.

Figures/Tables 12

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参数	氨气	水蒸气
入口空气干球温度/℃	32.52	24.32
入口空气湿球温度/℃	24.91	21.36
质量流量/t·h^-1	1.51	2.56
工质冷凝压力/kPa	1460.30	21.00
冷凝传热系数/W·m^-2·℃^-1	858.17	864.28

参数	氨气	水蒸气
入口空气干球温度/℃	32.52	24.32
入口空气湿球温度/℃	24.91	21.36
质量流量/t·h^-1	1.51	2.56
工质冷凝压力/kPa	1460.30	21.00
冷凝传热系数/W·m^-2·℃^-1	858.17	864.28

参数	本文模型计算面积 /m²	文献[23]冷凝器换热面积 /m²	相对误差 /%
氨气	110.4185	114.28	3.38
水蒸气	110.6200	114.28	3.20

参数	本文模型计算面积 /m²	文献[23]冷凝器换热面积 /m²	相对误差 /%
氨气	110.4185	114.28	3.38
水蒸气	110.6200	114.28	3.20

参数	初始值	变化范围
空气干球温度t_db/℃	32.00	—
空气湿球温度t_wb/℃	27.00	—
空气压力P_air/kPa	101.33	—
冷凝工质	R601a/R245fa	—
R601a组分质量分数M	0.50	0~1.00
冷凝热负荷Q_cond/kW	2000.00	—
出口工质温度/℃	37.00	—
出口工质状态	饱和	—
空气流量G_a/kg·s^-1	118.035	78.69~157.38
喷淋水流量G_w/kg·s^-1	48.338	32.22~64.44
冷凝器长/m	5.00	—
冷凝器宽/m	3.00	—
换热管外径D_o/mm	25.00	—
换热管水平间距P_t/mm	50.00	—
换热管厚度δ/mm	2.50	—