基于三维圆锥设计的空气取水性能强化

Three-dimensional conical adsorbent design for enhancing atmospheric water harvesting performance

吸附剂材料和系统结构是影响吸附式空气取水效果的两大关键因素.目前,已开发的水凝胶、金属有机框架材料以及高吸湿复合物等吸附剂已具有非常优越的取水潜力,而传统的依靠材料堆积的系统结构,导致整体的吸附动力学特性较差,制约了系统的取水性能.为了解决这一问题,本文采用活性炭纤维浸渍氯化锂作为吸附剂,通过三维圆锥形结构设计,在不牺牲材料性能的前提下,优化了系统的传热传质性能,进而在吸附和解吸方面分别实现了1.6和1.3倍的性能提升.

Recently,atmospheric water harvesting(AWH),which could relieve serious water scarcity,has attracted widespread interest around the world.Sorption-based atmospheric water harvesting(SAWH),due to its portability,easy availability,wide suitability,and low energy consumption,overmatchs other AWH technologies,such as fog capture,dew collection,and water condensation based on refrigeration.As for the SAWH technology,adsorbent material and structural design of the SAWH device are the most significant factors that affect its performance.In terms of material,numerous developed hydrogels,MOFs,and hygroscopic composites have exhibited promising potential when applied in SAWH systems in a wide range of relative humidity.However,in terms of the device,research related to structural design and optimization is usually ignored.Conventional systemic structure by stacking numerous materials is frequently exploited to increase the dosage of adsorbent materials,in order to promote integral water productivity.Nevertheless,in this case systemic heat and mass transfer properties will worsen,which further leads to the degradations of sorption capacity per mass adsorbent and integral water productivity in time-limited processes.Therefore,both dosage of adsorbents and sorption capacity per mass adsorbent should be ensured to realize promising SAWH performance.In this work,a three-dimensional conical structure is proposed to satisfy the above requirements.It could increase the dosage of adsorbents in a limited projected area without impairing systemic adsorption and desorption kinetics.Therein,a flexible hygroscopic adsorbent material is acquired to be fixed and configured into a conical shape.In addition to the high preparation cost,excellent MOF usually is powdery,which is tough to be exploited in an AWH device.As for the hygroscopic hydrogel,its complicated fabrication method and weak rigidity impede its practical application.Therefore,these novel adsorbents are unsuitable to be assembled into conical structures.The commercial cheap active carbon fiber(ACF),which possesses a porous structure and high photothermal property,is very suitable as the network structure to hold the hygroscopic factor.By impregnating LiCl in ACF,the scalable outstanding ACF-LiCl(water uptake:2.2 g g^(-1) at 25°C and RH 60%)is developed to be configured into a three-dimensional cone shape(it is named as Cone;the control sample is named as Circle).A series of adsorption and desorption experiments have been conducted to demonstrate and explore the performance of Cone.Compared to conventional Circle,the systemic adsorption and desorption performances of Cone have been improved by 1.6 and 1.3 times,respectively.And the total water productivity of Cone is evaluated to be 1.5–2.1 times higher than that of Circle.It is mainly attributed to the innovative combination of super hygroscopic ACF-LiCl adsorbent and desirable conical structure.The exhibited ACF-LiCl adsorbent possesses considerable water capacity per mass material,while the promising conical structure with sufficient adsorbent materials endows the whole SAWH system with rapid dynamic property.Therefore,enough adsorbent dosage,impervious sorption capacity per mass material,and enhanced systemic heat and mass transfer property are together achieved to break through current bottlenecks in the SAWH field.The original strategy referring to SAWH’s structural design from 2 D to 3 D is firstly introduced in this work,which is beneficial to promoting sustainable development in the arid regions with affordable water.