Study On Performance Of Liquid Desiccant Outdoor Air Processor Driven By Heat Pump

With the national emphasis on energy-saving and emission-reduction,as well as the increasing requirements of the people on the indoor air quality,traditional air conditioning no longer meets the needs of the modern market,so the liquid desiccant technology coming gradually into people's view.However,there is a lack of research in the performance on the winter-humidification of the liquid desiccant technology and the uniformity of the flow field in the tower.Applying combined experimental analyses and numerical simulations,this thesis aims to analyze the dependence of humidification performance in winter on the filler and determine the optimal configuration of the packing in the tower.Firstly,design and feasibility analysis are performed for an outdoor air processor with a nominal air volume of 500 m3/h and the liquid desiccant technology under the heat balance of heat pump.The unit consists of a solution circulation system,a heat pump system,a wind system,an electrical control system and a test system.The unit is characterized with a single solution tank to achieve the dynamic balance of solution concentration,and an auxiliary condenser with a power of 6kW to achieve the energy balance of the heat pump system.Based on the theoretical analysis of the lgp-h plot of the heat pump system and related technology research,the feasibility of the design of the unit is determined in turn,and the construction of the test bench is accomplished.Secondly,the cold tests of the unit are carried out based on the constructed test bench,mainly including the tests of the wind system,the water system and the heat pump system.By the sealing property of the bench is first tested and a system air leakage rate within ± 20% is observed,ensuring the reliability of experimental data.Then through the smoke streamers,tracer and chemical colorimetric method,the uniformity of the flow in the tower is analyzed qualitatively and quantitatively.According to the experiment of the water system,the relationship between the optimal number of holes and the flow rate of the liquid distributor is determined.The flow coefficient of gravity pipe discharge is about 0.56 from the experimental results.The commissioning of the heat pump system mainly includes the on-off states of the auxiliary condenser,the continuous adjustment of the expansion valve,the influence of the flow regulation of the pump and fan on the system performance.The optimal range of the expansion valve opening is found in the integral of 2.5-3.5.According to the results of cold state experiment,the optimal control strategy of each subsystem is developed.Then,the optimal packing form and the optimization strategy are determined through numerical simulation method.According to the geometrical relationship between the normal lines of the packing plates,four simulation conditions areformulated and the cross arrangement of the normal lines can produce the best uniformity of the flow from the simulations.Additionally,the form and structural parameters of the bottom packing are the key factors that affect the distribution of air flow.Based on the comparison of the simulation results of four conditions,the concept of the transition layer of the flow uniformity is defined,and the optimization simulation of the height of the transition layer is performed,producing the relationship between the optimal height of the transition layer and the wind speed at the cross section of the packing tower.The simulation results provide theoretical guidance for the determination of the number and height of the packing plate.Finally,the cold state experiment and simulation results are used to guide the hot state test of the packing performance in winter condition.Through comprehensive analyses of the air supply temperature,humidification,heat transfer/mass transfer coefficient and heating/humidification performance coefficient at the conditions of SKB-350 Y,7090 wet curtain,multi-faceted hollow sphere and empty tower,the 7090 wet curtain condition exhibits the best comprehensive performance,and the corresponding mass transfer coefficient and heat transfer coefficient are 4.37 kg/m3/s and 23.83 W/m2/?,respectively.The results show that the comprehensive performance of structured packing is better than that of bulk packing,and the empty tower condition shows the worst performance.Individual fillers have their own strengths from the perspective of heat transfer or mass transfer.The experimental results have some reference significance for the application of different packing in the design of the unit.In addition,the relationship between the solution concentration and the liquid level is determined from the experiment,which can be used to achieve the visualization and the real-time control of the solution concentration of unit during the operation.