Research On Optimization Of Flow Path Structure And Air Treatment Process In Liquid Desiccant Dehumidification Systems

The conventional air-conditioning systems generally adopt condensation dehumidification to simultaneously undertake the heat and humidity load of air,existing problems as high requirement of energy grade,weak heat-humidity ratio,cold and heat offsets.As a new alternative,the liquid desiccant dehumidification dehumidifies or humidifies the air relying on the vapor pressure difference between the solution and air as the driving force.This can make up for the drawbacks of condensation dehumidification and increase the energy utilization.This study carried out a numerical simulation research for the liquid desiccant dehumidification system,and the influence mechanisms of systemic flow paths and parameters on the air treatment processes were firstly analyzed.Then the various parameters for each liquid desiccant flow path were reasonably designed,and the pros and cons of all flow paths were compared.Finally,the new optimization of liquid desiccant dehumidification flow path was proposed.The models of various components of the typical liquid desiccant systems were developed.The simulation results of the core components as dehumidifier and regenerator were compared with the experimental results,and the average absolute deviation was within9.8 %.Based on the systemic models,the influence of every part of solution flow,cooling/heating capacity and flow paths with different cooling/heating modes and solution circulation types on the air process lines and liquid desiccant dehumidification effect was respectively researched.The effect of the cooling/heating mode was more obvious than that of the cooling/heating capacity by comparing the influence degree of different factors.The dehumidification/regeneration air process lines had similar characteristics under the same cooling/heating mode.The liquid desiccant dehumidification effect was mainly determined by the cooling mode,and it could be improved when pre-cooling the solution.The corresponding dehumidification amount was 2.4 g/kg and 2.2 g/kg.The solution circulation type had larger influence than the solution flow on the air process lines and liquid desiccant dehumidification effect.Taking the own-side solution for dehumidification and regeneration could promote to improve the liquid desiccant dehumidification effect.Under the design conditions,the optimal dehumidification effect was achieved when the circulation solution flow is 0.05 kg/s.Therefore,the liquid desiccant flow path is the crucial factor that influences the air state changes,and optimizing the flow path is an important way to improve the system operation.Including 6 cooling/heating modes and 5 solution circulation types,there are 30 kinds of liquid desiccant flow paths divided in total.Under the fixed supply air state as 19 ℃/9 g/kg,the optimal flow path was determined in view of the cooling/heating capacity,cooling/heating source temperature and system energy consumption.The cooling and heating capacities mainly depended on the heat exchange loss caused by the cold and heat offsets of the circulation solution,and the heating capacity was also affected by the enthalpy difference between the inlet and outlet regeneration air.Adopting the own-side solution for dehumidification and regeneration was beneficial to reduce the heat exchange loss.In order to decrease the requirement of the heating source temperature,enthalpy difference between the inlet and outlet regeneration air and heating capacity,the solution should be selected as the heating object.As the heat pump was used to provide cooling and heating capacities,the air was preferred to be pre-cooled before the liquid desiccant dehumidification process when the exhaust heat temperature was lower than 29 ℃.When the exhaust heat temperature was higher than 29 ℃,the solution was preferred to be pre-cooled.The power consumption of the two preferred flow paths was equal at 2.5 k W as the exhaust heat temperature was 29 ℃.Considering the two optimal flow paths and existing air conditioning equipment,a new type of single-channel dual-cold sources liquid desiccant fresh air unit and corresponding designed conditions were proposed.