基于气隙式膜蒸馏的溴化锂吸收式制冷系统COP的优化

doi:10.16085/j.issn.1000-6613.2020-2212

摘要/Abstract

摘要：

针对传统的溴化锂吸收式制冷系统难以利用低品位热源的问题，将气隙式膜蒸馏（AGMD）技术引入到溴化锂吸收式制冷系统中，是使其能够利用低品位热源的一种新的工艺流程。本文根据已有的1H,1H,2H,2H-全氟癸基三乙氧基硅烷（FAS）-Al₂O₃管式复合膜的膜蒸馏性能数据，对典型的基于AGMD的溴化锂吸收式制冷系统进行了热力计算。结果发现制冷系统的性能系数（COP）值较小，仅为0.280，因而需要对其工艺流程作进一步的优化。经热力学分析确定了优化的方案：在膜发生器浓溶液出口处增加回路，从而改进了原制冷系统的工艺流程。研究结果表明，制冷系统的COP值会随着回流比的增大而增大。当回流比达到8时，COP值可达到0.765，相较于改进前的系统增大了1.74倍，大大改善了制冷系统的性能。

关键词: 气隙式膜蒸馏, 溴化锂吸收式制冷, 性能系数, 优化设计, 热力学过程, 平衡

Abstract:

Aiming at the problem that traditional lithium bromide absorption refrigeration systems can hardly use low-grade heat sources, we introduced the air gap membrane distillation (AGMD) technology into the system and established a new process to make use of low grade heat source. According to the existing AGMD data of the FAS (1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane)/Al₂O₃ tubular composite membrane, the thermal calculations were completed for a typical lithium bromide absorption refrigeration system based on AGMD. The results show that the coefficient of performance (COP) of the refrigeration system is small, only 0.280, so the process needs to be further optimization. After thermodynamic analysis, an optimum process was determined: adding a loop at the outlet of the membrane generator to improve the original process of the refrigeration system. The results indicate that the COPincreases with the increase of the reflux ratio. When the ratio reaches 8, the COP could reach 0.765, which is 1.74 times greater than that of the system before improvement and greatly improves the performance of the refrigeration system.

Key words: air gap membrane distillation (AGMD), lithium bromide absorption refrigeration, coefficient of performance (COP), optimal design, thermodynamics process, equilibrium

中图分类号:

TQ02

宋永, 李恋, 陈志. 基于气隙式膜蒸馏的溴化锂吸收式制冷系统COP的优化[J]. 化工进展, 2021, 40(S1): 150-155.

SONG Yong, LI Lian, CHEN Zhi. COP optimization analysis of a lithium bromide absorption refrigeration system based on AGMD[J]. Chemical Industry and Engineering Progress, 2021, 40(S1): 150-155.

图/表 6

图1 基于膜发生器的单效LiBr吸收式制冷系统Ⅰ—热源；Ⅱ—膜发生器；Ⅲ—节流阀；Ⅳ—蒸发器；Ⅴ—吸收器；Ⅵ—溶液泵；Ⅶ—溶液热交换器；Ⅷ—调节阀

表1 选取的节点参数

序号	名称	节点号	温度/℃	饱和蒸汽压/kPa	质量分数/%	焓值/kJ?kg^-1
1	蒸发器出口处冷剂蒸汽	1'	5	0.872	—	2508.58
2	吸收器出口处稀溶液	2	35	0.859	55.7	266.702
3	冷凝器出口处冷剂水	3	29	4.007	—	121.432
4	冷凝器进口冷剂蒸汽	3'	77.32	—	—	2637.21
5	膜发生器出口处浓溶液	4	74.65	7.346	55.985	345.05
6	膜发生器进口处稀溶液	5	80	8.666	55.7	356.676
7	热交换器出口处稀溶液	7	58.45	—	55.7	313.244
8	热交换器出口处浓溶液	8	51	—	55.985	298.27

图2 基于膜发生器的LiBr吸收式制冷系统的优化Ⅰ—热源；Ⅱ—膜发生器组件；Ⅲ—节流阀；Ⅳ—蒸发器；Ⅴ—吸收器；Ⅵ—溶液泵；Ⅶ—溶液热交换器；Ⅷ—溶液三通；Ⅸ—调节阀；Ⅹ—溶液泵；Ⅺ—调节阀；Ⅻ—混合器

表2 相关工作状态参数

名称	温度/℃	饱和蒸汽压/kPa	焓值/kJ·kg^-1
蒸发器出口处冷剂蒸汽	$t 1'$	$p 1'$	$h 1'$
吸收器出口处稀溶液	$t 2 n$	$p 2 n$	$h 2 n$
热交换器出口处稀溶液	$t 7 n$	—	$h 7 n$
热交换器出口处浓溶液	$t 8 n$	—	$h 8 n$

表2 相关工作状态参数

名称	温度/℃	饱和蒸汽压/kPa	焓值/kJ·kg^-1
蒸发器出口处冷剂蒸汽	$t 1'$	$p 1'$	$h 1'$
吸收器出口处稀溶液	$t 2 n$	$p 2 n$	$h 2 n$
热交换器出口处稀溶液	$t 7 n$	—	$h 7 n$
热交换器出口处浓溶液	$t 8 n$	—	$h 8 n$

图3 回流比对热源工作状态的影响

图4 回流比对COP的影响

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