Heat and Mass Transfer Performance Evaluation and Advanced Liquid Desiccant Air-Conditioning Systems
In recent years, liquid desiccant air-conditioning systems have attracted much attention for its prominent potential of energy saving. In such systems, dehumidifiers/regenerators are the core components where heat and mass transfer occurs. The heat and ma
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Heat and Mass Transfer Performance Evaluation and Advanced Liquid Desiccant Air-Conditioning Systems Yonggao Yin, Tingting Chen and Xiaosong Zhang
Abstract In recent years, liquid desiccant air-conditioning systems have attracted much attention for its prominent potential of energy saving. In such systems, dehumidifiers/regenerators are the core components where heat and mass transfer occurs. The heat and mass transfer coefficients determine the accuracy of mathematical model which were used to design the dehumidifiers/regenerators. So, in this paper, the methods to obtain heat and mass transfer coefficients are evaluated theoretically. In order to enhance the mass transfer process, the internally cooled/heated dehumidifier/regenerator is designed and investigated experimentally and theoretically. Further, several advanced liquid desiccant air-conditioning systems are also introduced. Results show that the proposed equivalent integral mean method has high accuracy in calculating the coupled heat and mass transfer coefficients. Unlike Lewis number which was often assumed as one for describing heat and mass transfer between air and water, the defined Le factor may deviate appreciably from one in the heat and mass transfer process between air and liquid desiccant. The internally heated regenerators help to develop zero-carryover gas– liquid contactors because of much higher performance than adiabatic regenerators under low solution flow rate. It also helps to reduce energy consumption because of the high regeneration thermal efficiency, which indicates that the internally heated regenerators are promising and deserve much more renovation and application.
Keywords Liquid desiccant Heat and mass transfer coefficient Le factor Internally cooled/heated Regeneration thermal efficiency Hybrid air-conditioning
List of Symbols A Cps Cpa
Mass transfer area, m2 Specific heat capacity of solution, kJ/kg °C Specific heat capacity of humid air, kJ/kg °C
Y. Yin (&) T. Chen X. Zhang School of Energy and Environment, Southeast University, Sipailou Road, Nanjing 210096, China e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 N. Enteria et al. (eds.), Desiccant Heating, Ventilating, and Air-Conditioning Systems, DOI 10.1007/978-981-10-3047-5_6
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Cpw H ha he hd hc hcw hs Ga Ma Ms Mw Mr kd r r0 ta ts tw va wa we Xs i o
Specific heat capacity of water, kJ/kg °C Height along solution flow direction, m Enthalpy of humid air, kJ/kg Enthalpy of air in equilibrium with solution, kJ/kg Mass transfer coefficient, kg/m2 s Heat transfer coefficient between air and solution, kW/m2 °C Heat transfer coefficient between water and solution, kW/m2 °C Enthalpy of liquid desiccant, kJ/kg Air flow rate, m3/s Air mass flow rate, kg/s Solution mass flow rate, kg/s Water mass flow rate, kg/s Moisture evaporation rate, g/s Mass transfer coefficient, m/s Vaporization heat of water, kJ/kg Vaporization heat of water at 0 °C, kJ/kg Air temperature, °C Solution temperature, °C Water temperature, °C Air velocity, m/s
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