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Research of Water Harvesting Performance of Water Harvesting Device Based on Condensation Surface with Microstructures

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【Author in Chinese】 袁帅

【Supervisor】 李松晶

【Author's Information】 哈尔滨工业大学, 机械电子工程, 2018, 硕士

【Abstract in Chinese】 随着水资源的日益缺乏,人类活动范围的进一步扩大,如何在取水困难的干旱半干旱地区获取干净的淡水资源,为野外考察、野战部队、紧急救援等应用场合提供淡水补给正在受到越来越多的关注。大气作为清洁水资源的载体逐渐成为重要的淡水来源。近年来,基于空气制冷、吸附解吸附以及雾滴取水等方法的空气取水技术增出不穷。其中吸附解吸附技术因其具有便携性而最具有研究价值。但是,目前的研究重点大部分在于提高吸附剂的吸附性能,而忽略了冷凝水的移除效率,而后者对空气取水装置的取水效率有至关重要的影响。收到自然界中具备空气取水能力的动植物体表形貌的启发,本文依据仿生学原理提出了基于微流控产业常用的PDMS材料制作空气取水装置的冷凝面,并通过改变其表面微观结构,促进水滴的合并与移除,从而提高空气取水装置的取水效率。本文依据液滴在平面上的受力平衡与导热系数的理论推导,提出了液滴在冷凝面上的最佳尺寸模型,即在该尺寸下完成水滴的自移除,可以保证冷凝面具有最佳换热效率,从而有利于冷凝水的持续产生;同时也防止液滴生长过小而减小取水装置的整体效率。本文完成了所提出的PDMS冷凝面的设计与制备,并搭建了可实现恒温恒湿控制的实验平台,对不同表面微结构的PDMS冷凝面在不同相对湿度及过冷度条件下的冷凝及移除效果进行了实验研究。利用图像处理技术,对PDMS冷凝膜上的水滴数量、液滴覆盖面积、液滴平均直径等特性进行了定量分析。本文完成了基于PDMS冷凝膜的便携式空气取水装置的整体设计与制作。确定了变色硅胶吸附剂的最佳吸附时间。搭建了实验平台,对空气取水装置在解吸附过程中水蒸气的温湿度变化进行了测量,分析了装置的工作状态和性能,确定了最佳解吸附时间。通过重复实验对装置连续工作的稳定性进行了实验验证。通过对比实验证明了被动式空气散热的必要性。

【Abstract】 With the gradual depletion of water resources and the further expansion of human activities,how to obtain fresh water in arid and semi-arid areas with difficult water resources is being paid more and more attention.In such places,fresh water would be crucial for field investigation,field troops,emergency rescue and other applications.As a large container of clean water resources,the atmosphere has gradually become an important source of fresh water.In recent years,water harvesting technology based on air cooling,adsorption desorption and water droplet extraction has increased.Among these technologies,adsorption-desorption technology shows the most research value because of its portability.However,the main focus of the present study is to improve the adsorption properties of the adsorbents,while ignoring the removal efficiency of the condensed water,which has a vital effect on the efficiency of the water output of the water harvesting devices.Inspired by the surface morphology of the animal and plants with the ability of water harvesting in nature and based on the principle of bionics,this paper proposes the condensation surface of the water harvesting device based on the PDMS material commonly used in the microfluidic industry,and promotes the combination and removal of water droplets by changing the surface microstructure of its surface,thus improving the water output of water harvesting device.Based on the theoretical deduction of the force balance and thermal conductivity of the droplets on a plane,the optimum size model of the droplet on the condensing surface is proposed.The self-removal of the water droplets under this size can ensure that the condensation surface has the best heat transfer efficiency,which is beneficial to the continuous production of condensate water and also prevents the droplets from growing.Smaller size droplets would reduce the overall efficiency of the water intake device.In this paper,the design and preparation of the PDMS condensing surface were completed,and an experimental platform for constant temperature and constant humidity control was built.The effect of condensation and removal of water droplets from PDMS condensing surface with different surface microstructures under various conditions of different relative humidity and supercooling was experimentally investigated.Using image processing technology,the number of droplets,the area covered by droplets and the average diameter of droplets on PDMS condensate film were quantitatively analyzed.The whole design and manufacture of portable water harvesting device based on PDMS condensate membrane has been completed in this paper.The optimum adsorption time of the discolourant silica gel adsorbent was determined.The experimental platform was set up to measure the temperature and humidity of the water vapor during the desorption process.The working state and performance of the device were analyzed,and the optimum desorption time was determined.The stability of the continuous operation of the device is verified by repeated experiments.The necessity of passive air cooling is proved by comparative experiments.

【Keywords in Chinese】 空气取水吸附解吸附微结构冷凝自移除
【Key words】 water harvestingadsorbent-desorbentmicrostructurecondensationselfremoval
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