Abstract
Internally-cooled dehumidifiers are efficient liquid desiccant dehumidifiers, whose performance is mainly determined by the device structure and operating conditions. Based on energy and mass conservation in the air, solution, and cooling water in the device, mathematical models are built and their theoretical performance is simulated and analyzed in this paper. A novel measure of dehumidification efficiency is introduced to evaluate the performance of internally-cooled dehumidifiers, in which the equilibrium humidity ratio of the inlet solution is calculated according to the minimum temperature in the inlet solution and the cooling water. Numerical simulations show that a counter flow between air and solution is always the most efficient, followed by cross flow, and parallel flow is the least efficient. Cooling water with the same flow direction as the solution performs better than that with a counter flow, with approximately a 5% improvement in efficiency. Compared with CaCl2, the dehumidification efficiency of a LiCl solution is greater by 60%, while its exergy efficiency is less by 16%. Dehumidification efficiency can be improved with the number of air-solution heat transfer units (NTUa-s) increasing, and reduced with the air mass flow rate raised. With NTUa-s increasing, exergy efficiency can be improved, and an increase in mass flow rate of cooling water results in a decrease of efficiency. Higher solution concentration and lower inlet temperature of solution and air can achieve both higher dehumidification efficiency and exergy efficiency.
概要
目 的
目前关于内冷型溶液除湿器的研究均基于特定的装置结构和流型, 限制了其普遍应用. 本文采用基于传热单元数的传热传质数学模型, 通过数值模拟研究了各种流型、 结构和流体参数的影响.
创新点
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1.
提出一种新的除湿效率定义;
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2.
引入火用效率评价内冷型除湿器的性能;
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3.
分析不同流型、 结构和流体参数下除湿器除湿效率和火用效率;
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4.
研究结论不受特定装置和流体参数的限制, 为内冷型除湿器的设计优化提供了建议.
方 法
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1.
建立内冷型除湿器的物理和数学模型;
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2.
通过实验数据与模拟数据的对比, 验证模型的正确性;
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3.
建立除湿效率和火用效率的数学模型;
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4.
通过不同流型、 结构和流体参数的模拟数据, 分析其对除湿效率和火用效率的影响.
结 论
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1.
本文提出了一种新的除湿效率定义, 解决了内冷型除湿器在某些工况下除湿效率超出 0~1 范围的问题; 溶液入口平衡含湿量根据入口溶液和冷却水的最低温度计算, 并且新的除湿效率综合考虑了冷水的代价, 可以更好地评价除湿器的除湿性能.
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2.
对于内冷型除湿器, 三种空气与溶液间流型的除湿效率和火用效率总是逆流最好, 叉流其次, 顺流最差; 溶液与冷水之间的流型对两种效率影响不大, I 流型比 II 流型提升 5% 左右.
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3.
LiCl 溶液的除湿效率高于 CaCl2 溶液, 可以提高 60%, 但 LiCl 溶液的火用效率低于 CaCl2 溶液, 可降低 16%.
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4.
在设计内冷型除湿器时应采用较大的空气与溶液间传热单元数, 并建议在其运行过程中使用浓度较高的溶液及入口温度较低的溶液和空气, 以达到更高的除湿效率和火用效率.
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Dong-gen PENG designed the research and edited the manuscript, Shun-yi LI processed the corresponding data and wrote the first draft of the manuscript, Dan-ting LUO conducted the research, Yu-ting FU revised the manuscript, Xiao-song CHENG helped organize the manuscript, and Yin LIU revised and edited the final version.
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Dong-gen PENG, Shun-yi LI, Dan-ting LUO, Yu-ting FU, Xiao-song CHENG, and Yin LIU declare that they have no conflict of interest.
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Project supported by the National Natural Science Foundation of China (No. 51766010), the Knowledge Innovative Team of High-efficient Refrigeration in Nanchang City of China (No. 2018-CXTD-004), the Special Fund Project for Graduate Innovation of Nanchang University (No. CX2018058), the Zhihui Zhengzhou 1125 Talent Gathering Plan Innovation and Entrepreneurship Leading Team, and the Study Plan for Young and Middle-aged Teachers in Nanchang University, China
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Peng, Dg., Li, Sy., Luo, Dt. et al. Efficiency comparison and performance analysis of internally-cooled liquid desiccant dehumidifiers using LiCl and CaCl2 aqueous solutions. J. Zhejiang Univ. Sci. A 21, 44–63 (2020). https://doi.org/10.1631/jzus.A1900241
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DOI: https://doi.org/10.1631/jzus.A1900241
Key words
- Liquid desiccant
- Internally-cooled dehumidifiers
- Performance comparison
- Dehumidification efficiency
- Exergy efficiency