Experimental study and analysis of heat and mass transfer ability of counter-flow packing tower and liquid desiccant dehumidification system

- Experiments of counter-flow packing towers with height of 0.7 m and 2.1 m were conducted.
- The heat and mass transfer ability of system should be considered in the flow path design process.
- The system COP cross points of flow paths are caused by heat and cold offset and the concentration difference of the solution circulation.

The purpose of air-conditioning systems is to provide a suitable indoor environment with respect to temperature, humidity and fresh air. Liquid desiccant dehumidification constitutes an effective method for extracting moisture from humid air with less energy consumption. Current studies mainly focus on dehumidification system under certain heat and mass transfer ability (number of mass transfer units NTUm). This paper will investigate NTUm of counter-flow packing tower and its influence on system performance. An experiment including a counter-flow packing tower was conducted. When the height of tower was 0.7 m, the volumetric mass transfer coefficient was between 1-4 kg/(m3·s) and NTUm presented a range between 0.9-1.4, when air flow rate changes from 1 kg/(m2 s) to 2.5 kg/(m2 s). When the height changed to 2.1 m, the NTUm of the tower presented a variation from 3.3 to 4.3. Furthermore, a simulation model is developed, which is validated by experimental data and past research results. The influence of NTUm on total circulation flow path is mainly caused by heat and cold offset and an NTUm value approximately of 4 constitutes a suitable value of increasing heat and mass transfer ability. Comparing three typical flow paths, when NTUm is lower than 3.5, inter-stage circulation presents improved performance in system COP. When NTUm is large, total circulation is efficient. The system COP cross points of flow paths are caused by heat and cold offset and concentration difference of the solution circulation between the dehumidifier and the regenerator, which can be quantified by loss coefficient ε and χ respectively. The heat and mass transfer ability of the system should be considered in the designing process of flow path configuration to obtain an efficient performance for different range of NTUm.