A novel membrane heat exchanger was proposed and analyzed. It was expected that the novel heat exchanger could be applied to the lithium bromide absorption chiller. Polyvinylidene fluoride hollow fiber module was adopted as the solution heat exchanger. The hot feed solution from the generator flowed into the lumen side of the membranes while the cold feed solution from the absorber flowed away from the shell side. Heat transfer and mass transfer occurred simultaneously in the membrane module, and only water vapor could diffuse across the membrane pore due to the water vapor pressure difference between the inside and outside of the membrane. Mathematical equations of the heat and mass transfer processes in the membrane heat exchanger were built, and the parallel flow process and the counter flow process were compared by numerical simulation. The simulation results show that the counter flow process was the better flow mode because the mean temperature difference was larger and the mass transfer was more steadily from the lumen side to the shell side. The heat caused by water vapor mass transfer may account for one-third of the total heat transfer. As a result, the membrane heat exchanger not only reinforced the heat recovery but also enlarged the deflation range and reduced the circulation rate and the heat loads of the generator and absorber. Eventually, the coefficient of performance of the heat exchanger was increased.
The polyvinylidene fluoride hollow fibre membrane air dehumidification tests were carried out between the liquid desiccant solutions and the wet air. Three liquid desiccant solutions of LiBr solution (50%), LiCl solution (35%) and CaCl2 solution (40%) were tested under different wet air conditions. The results showed that all the membrane dehumidification processes were stable. The air moisture content in the outlet of the membrane was maintained as 6.5 g/kg (da)–8.2 g/kg (da) when the air moisture content in the inlet of the membrane was operated from 17.1 g/kg (da) to 32.4 g/kg (da). The dehumidification amount of LiBr solution (50%) and LiCl solution (35%) was more productive. On this basis, a membrane-based air pre-dehumidification process for the capillary radiant air conditioning system was built. Since the ideal dew point temperature range of the indoor air is below 14–17°C according to the cold supply water, all the air moisture content at the membrane outlet is much lower than that of the ideal dew point temperature range, which means non-condensing occurs in the capillary tube surface. The membrane-based air pre-dehumidification process can easily form an adaptive regulation process of humidity with the capillary radiant air conditioning system under different environmental parameters.
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