Collaborative Research: Enhanced Adsorption Cooling with Monolithic Nanoporous Adsorbents

采用单片纳米多孔吸附剂的高性能吸附冷却系统吸附冷却是蒸汽压缩空调的替代技术。它由低品位的热量，太阳能或工业过程或汽车发动机的废热提供动力。它使用环保的制冷剂，如水作为工作流体。吸附床是吸附冷却系统的核心，其中工作流体被吸附/解吸以补偿常规蒸气压缩循环中所需的功。吸附式制冷循环主要经历加热-解吸-冷凝和冷却-吸附-蒸发两个过程。制冷剂通过加热吸附材料并在冷凝器中冷凝而被解吸，而制冷剂在蒸发器中蒸发并通过冷却吸附材料而被吸附。床层的快速热响应是获得高性能的关键因素。填充床由于颗粒与颗粒接触差和颗粒与冷却表面接触差而具有低热导率，通常用于这种系统中。在这项研究中，一个创新的床将通过生长具有相当厚度的单片纳米多孔吸附剂层上的热交换器的铜翅片构造。该整料具有内部蒸气通道以降低蒸气扩散阻力，并且其热导率预计比填充床中的热导率高许多倍。 所提出的整料可用于高效和紧凑的吸附冷却单元。在研究的同时，高年级学生将接受设计环保冷却系统的培训。 一个完全不同的和潜在的变革吸附冷却系统将被开发。 该系统基于单片纳米多孔二氧化硅或铜。我们的研究计划将包括：制备整料，建立实验装置，模拟传热和传质过程，设计和建造使用纳米多孔整料的新床，并测量表面应力。首先，将通过完全去除纳米结构硅胶的残留溶剂来制备整料。硅胶的表面将覆盖一层液体石蜡，使得该过程将在高温下以温和的方式进行，以防止整料开裂。垂直支柱将被放置以形成蒸汽路径。在形成整料之后，可以移除柱。其次，将建立一个实验测量装置，以监测在所需的压力和温度下吸附剂质量随时间的变化。测量的数据将用于确定质量扩散系数、活化能和吸附热。在建模部分，将在纳米块体中产生的微孔中求解传热传质过程。该模型将依赖于解决在孔隙中的流动，以及在固相中的蒸汽的吸附和扩散过程。在两相之间的界面处，将应用质量和能量平衡。接下来，为了监测所开发的整料在吸附冷却系统中的性能，将通过在热交换器上生长厚的整料层来构造新的吸附床，这增加了吸附吸收。将对不同的设计配置进行测试，以得出最佳设计。计算比冷功率（SCP）和性能系数（COP），以评价新床的性能。在冷却系统的操作期间，单块纳米多孔材料可能经历来自液体的大的表面张力，这可能损坏纳米结构。因此，所开发的材料的机械稳定性将测试通过测量表面的原子力显微镜（AFM）的微悬臂梁上的材料涂层的表面应力。

High Performance Adsorption Cooling Systems Using Monolithic Nanoporous AdsorbentsAdsorption cooling is an alternative technology to vapor compression air conditioning. It is powered by low-grade heat, solar energy, or waste heat from industrial processes or automotive engines. It uses environmentally friendly refrigerants like water as the working fluid. The sorption bed is the core of an adsorption cooling system in which the working fluid is adsorbed/desorbed to compensate for the work needed in a conventional vapor compression cycle. To produce cooling, adsorption cycle undergoes two main processes: heating-desorption-condensation and cooling-adsorption-evaporation. The refrigerant is desorbed by heating the adsorbent material and condensing in the condenser while it vaporizes in the evaporator and is adsorbed by cooling the adsorbent material. Fast thermal response of the bed is the key factor that leads to high performance. Packed beds, which suffer from low thermal conductivity due to the poor particle-to-particle contact and poor particle-to-cooling surface contact, are regularly used in such systems. In this research, an innovative bed will be constructed by growing a monolithic nanoporous adsorbent layer with considerable thickness on copper fins of heat exchangers. The monolith has internal vapor channels to reduce vapor diffusion resistance and its thermal conductivity is expected to be many folds higher than those in packed beds. The proposed monoliths can be used in highly efficient and compact adsorption cooling units. In parallel to the research, senior students will be trained in designing environmental friendly cooling systems. A radically different and potentially transformative adsorption cooling system will be developed. The system is based on monolithic nanoporous silica or copper. Our research plan will include: preparing monoliths, building an experimental set-up, modeling the heat and mass transfer processes, designing and building new bed using nanoporous monoliths, and measuring surface stresses. First, monoliths will be prepared via complete removal of residue solvent of nanostructured silica gel. The surface of the silica gel will be covered with a layer of liquid paraffin so that the process will be carried out at high temperature and in a mild way to prevent the monolith from cracking. Vertical pillars will be placed to form the vapor paths. After forming the monoliths, the pillars can be removed. Second, an experimental measurement set-up will be built to monitor the change of the adsorbent mass as a function of time at a desired pressure and temperature. The measured data will be used to determine mass diffusion coefficient, activation energy, and heat of adsorption. In the modeling part, the heat and mass transfer processes will be solved in the micropores generated in the nano-monoliths. The model will rely on solving the flow in the pores as well as the adsorption and diffusion processes of vapor in the solid phase. At the interface between the two phases mass and energy balances will be applied. Next, to monitor the performance of the developed monoliths in adsorption cooling system, a new adsorbing bed will be constructed by growing a thick monolith layer on a heat exchanger, which increases adsorption uptake. Different design configurations will be tested to come up with the best design. Specific cooling power (SCP) and coefficient of performance (COP) will be calculated to evaluate the new bed performance. During the operation of the cooling system, the monolithic nanoporous material may experience large surface tension from liquid that may damage the nano structures. So the mechanical stability of the developed material will be tested by measuring the surface stresses of a layer of the material coated on a micro cantilever of Atomic Force Microscope (AFM).