Su Awarded NSF Grant for Enhanced Adsorption Cooling
ChE Associate Professor Ming Su was awarded an $160K NSF grant for “Enhanced Adsorption Cooling with Monolithic Nanoporous Adsorbents”.
Abstract Source: NSF
Adsorption 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).