System Design And Performance Simulation Of A New Silica Gel-Water Adsorption Chiller

The silica gel-water adsorption chiller has the large potential of industrialization in the filed of waste heat and solar energy and is one of the most competitive refrigeration system for being environment-friendly, energy-saving and low temperature-driving. In this paper, a novel silica gel-water adsorption chiller with high effectiveness, reliability and low operating cost is developed and its performance is simulated, which has solved the problems of low efficiency under low temperature heat source and high heat capacity ratio in a conventional system and simplified the implicated structure in an improved system. The results show that this chiller has a new structure, a high cyclic efficiency and high electric COP (Coefficient Of Performance), which can be effectively driven by 60 ~85℃heat source and meet the demand of design requirements greatly.Silica gel with diameter of 0.5-1.5mm is scanned by the scanning electron microscope (SEM), so it is very crucial to investigate heat and mass transfer of adsorber. A test rig is set up to investigate sorption properties of water on silica gel and its composites blended expanded graphite or binder depending on the weighing method. The sorption capacity of water on silica gel and its composites is measured accurately under vacuum, so a new sorption equation is fitted and adopted for silica gel-water chillers manufactured in China. The equation has an accuracy better than that of Freundlich equation and D-A equation compared to experimental data. Besides, the experiment results show that using composites blended expanded graphite or binder can shorten the cyclic time and improve SCP (Specific Cooling Power).With the purpose of solving the problems of high metal heat capacity ratio, poor performance of heat and mass transfer in the adsorber and bad reliability on those chillers, according to theoretical analysis and based on the adsorption chillers developed by the former researchers,a new 10 kW silica gel-water adsorption chiller is designed. Not only are system design steps proposed but also some key system parameters are gained, what's more important is that resolving the problem of no cooling power during some time of the cyclic time due to the existence of heat and mass recovery time and the valve switching one.Heat transfer of the finned tube adsorber is analyzed and calculated, and heat transfer between the adsorber and silica gel is numerically simulated through unsteady-state heat conduction theory, so the contact thermal resistance between them, the accurate heat transfer coefficient of the adsorbent side enhanced by fin and the total heat transfer coefficient of adsorber are obtained. A coil condenser and a capillary-assisted water evaporator is developed, their temperature difference of heat transfer, total heat transfer coefficient, heat transfer area and pressure drop are gained, respectively. Considering the particularity of closed cooling tower used by a new silica gel-water adsorption chiller, a tubular indirect evaporative cooler is designed which has a high cooling performance and compact structure, not only saves some copper products and cost of the evaporative cooler but also reduces the weight of the chiller and meets the needs of cooling power.Based on the special structure and thermodynamic cycle mode, the mathematic model for the dynamic operation of the designed chiller is built. Through the simulations, the operating characteristics of the chiller and the effects of the key parameters on the performance of the chiller under different working conditions are obtained, and the rationality and validity of the design work are evaluated.