Study On The Performance Of The Liquid Desiccant Dehumidification System Based On The Rotating Packed Bed

Liquid desiccant dehumidification system has the potential of high energy efficiency and improving indoor quality.Dehumidifier and regenerator are the key components of the liquid desiccant dehumidification system,which directly affect the performance of the system.The liquid in the traditional packed tower forms a liquid film on the packed surface by gravity,which has the disadvantages of the thick liquid film,low flow rate,and long retention time on the packed surface.These will increase the amount of solution circulation and reduce the gasliquid heat and mass transfer performance and the control of heat and mass transfer process.Compared with the traditional packed tower,the rotating packed bed(RPB)has the advantages of a large gas-liquid contact area,high heat and mass transfer coefficient,small volume,low liquid holding capacity,fast dynamic response,and no fear of vibration.This thesis applies the rotating packed bed to the traditional liquid desiccant air conditioning system.The heat and mass transfer characteristics and dehumidification and regeneration performance of the RPB dehumidifier/regenerator are investigated.The dynamic characteristics of the RPB dehumidifier/regenerator are researched.The system design method is proposed and the performance evaluation is made.Firstly,the hydrodynamic model and the heat and mass transfer model of RPB are established.The hydrodynamic properties of liquid and gas in RPB are studied.The air side pressure drop model and liquid flooding characteristic curve of RPB are put forward.The influence of operating parameters on motor energy consumption is analyzed theoretically,and the influence of operating parameters on air side pressure drop is analyzed experimentally.The liquid flooding characteristic curve and heat and mass transfer process model are verified through experiment data.Secondly,the heat and mass transfer characteristics and dehumidification performance of the RPB are studied.The effects of the air and solution inlet parameters and operation parameters on the performance indices are investigated.Based on the experimental results,the correlation expressions of heat and mass transfer coefficients are developed.It is concluded that the heat and mass transfer coefficients of RPB dehumidifier are ranging from 22.3 to 37.3 k W.m-3.°C-1 and from 21.2 to 35.8 kg.m-3.s-1 which are far higher than the heat and mass transfer coefficients of the traditional dehumidifier.Again,the heat and mass transfer performance and regeneration performance of the RPB regenerator are studied.The effects of the air and solution inlet parameters and operation parameters on the performance indices are investigated.Compared with the traditional regenerator,the mass transfer coefficient of the RPB regenerator is ranging from 12.5-35.6 kg.m-3.s-1 which is far higher than the traditional regenerator of 1.12-4.64 kg.m-3.s-1.On this basis,the dynamic models of RPB dehumidifier/ regenerator are established.The dehumidifier startup process,solution inlet temperature change process,inlet concentration change process,regenerator startup process,and solution inlet temperature change process are analyzed.The dynamic response process of air outlet temperature,outlet humidity ratio,moisture removal rate,dehumidification effectiveness,and regeneration effectiveness are investigated.The time constant of the RPB dehumidifier is only 1/6 of that of the traditional dehumidifier,and the time constant of the RPB regenerator is only 1/10 of that of the traditional regenerator.Finally,the design method of the RPB liquid desiccant dehumidification system is proposed and the performance analysis model is presented.The energy consumption composition and cost structure of the RPB liquid desiccant dehumidification system are analyzed.The COP and TAC under different loads are analyzed,and the energy consumption of the traditional dehumidification system is compared.A genetic algorithm model for the optimal design was proposed.Through the calculation of the optimal design model,a higher COP could be obtained,up to 0.331 in the case.Meanwhile,the TAC was also significantly reduced compared with the previous design.