光致蒸发式太阳能苦咸水淡化系统功能化水体热性能研究

Research shows that low efficiency and high cost have become the biggest obstacles for solar brackish water desalination technology, which is caused by the structural mismatch of low efficiency between the solar collector system at high temperature and low efficiency of the brackish water desalination system at low temperature. This project proposes the novel idea of light-evaporation type solar brackish water desalination system, i.e., by utilizing the high efficient concentrating solar energy system to produce high strength solar energy and send directly the strong light to the brackish water to produce the vapor. Meanwhile, the high temperature vapor can then be generated and supplied into the conventional brackish water desalination system to produce freshwater. The coupling for the solar concentration collecting temperature and the brackish water desalination temperature will be achieved. Specifically, the functionlization of brackish water, which can directly absorb the sunlight, is the key to achieve the idea above mentioned. In this project, the conversion process from radiation to heat in functioned brackish water will be researched. The relationship between exergy loss, energy conversion efficiency and radiation, parameters of water body will be analyzed. The concentrating theory matched with brackish water desalination unit will be investigated. Then this project will mainly analyze basis convection heat transfer and phase change heat transfer process in the function process between radiation and functioned brackish water. With the solution of these problems, the high matching of the solar concentrating collector and the brackish water evaporation desalination unit will be achieved so that it can provide a new theory for the low cost and large scale solar brackish water desalination technology.

研究表明，推广太阳能苦咸水淡化技术的最大障碍在于效率低与成本高，究其原因，是由于太阳能集热系统在高温段时效率低，而苦咸水淡化系统在低温段时效率低的结构不匹配造成的。本课题提出了光致蒸发式太阳能苦咸水淡化新思路，即将太阳光经聚光器汇聚后，直接入射到功能化苦咸水中，从而产生蒸汽，然后蒸汽进入传统苦咸水淡化装置中生成淡水，实现了太阳能集热温度与苦咸水淡化温度的高效耦合，而对苦咸水进行功能化并使水体具有较强吸光性能是上述思想实现的关键。本课题拟研究功能化苦咸水水体中辐射到热量的转换过程，分析火用损失、能量转化效率等与辐射和水体参数之间的关系，探索与功能化苦咸水蒸发相匹配的聚光理论,着重对强光与功能化水体作用中对流换热、相变传热等热物理过程进行研究。这些问题的解决，为实现太阳能聚光集热部件与苦咸水蒸发淡化部件的高效匹配，以及低成本、高效率太阳能苦咸水淡化技术的应用提供新的理论基础。

聚焦太阳能在含深色多孔颗粒苦咸水水体内光热直接转化，是实现辐射到热能转化的关键，属于学科交叉研究课题，此过程中涉及到的部分基础科学问题尚未明晰。本项目利用热力学、传热传质学、光学、材料学等学科交叉理论和方法，开展功能化水体与光束相互作用机理研究，内容涵盖了功能化苦咸水光吸收特性研究、复合抛物面聚光设计理论探索、环形封闭小空间苦咸水液膜蒸发性能分析、光致蒸发式太阳能苦咸水淡化系统热性能研究等。通过研究掌握了影响功能化水体内光热直接转化的因素，获得了强化苦咸水液膜蒸发的方法，认识了太阳能聚光集热温度与苦咸水淡化温度耦合的关系。通过4年的科学研究，取得了一定的创新性研究成果，包括：1.在功能化苦咸水水体与入射光线相互作用方面，搭建了水体光吸收特性测试试验台，测试分析了深色多孔颗粒材质、粒径、丰度等参数与水体光吸收特性之间的关联，拟合出水体光吸收比与沸腾程度的函数关系；2.设计了新型复合抛物面聚光器，利用光学仿真软件对聚光器光热性能进行验证和校核，给出了可用于光致蒸发苦咸水的聚光器光学参数，搭建了复合抛物面聚光集热性能测试台，对设计结果进行了验证，研究了聚光器内嵌玻璃管接收体光热高效转化性能；3.建立了环形封闭小空间苦咸水液膜蒸发传热传质模型，得到了气水二元混合气体自然对流传热系数计算方法，给出了特征尺寸对水蒸气自然对流传热的影响机理；4.搭建了光致蒸发式太阳能苦咸水淡化性能测试台，研究了太阳能对水体温升、光热转化效率的影响。研究成果为突破太阳能苦咸水淡化系统集热单元在高温段时效率低而淡化单元在低温段时效率低的结构不匹配技术瓶颈提供了参考，丰富了太阳能利用中热辐射工程热力学的内涵，推动了太阳能苦咸水淡化技术低成本、高效率、规模化应用。