Study Of Heat And Mass Transfer In Dehumidifying Process For A Liquid Desiccant System With Solar Energy

Liquid desiccant system with solar energy is an effective air conditioning system without pollution to the environment. It uses liquid desiccant to remove the water in the air, the weak liquid desiccant solution can be regenerated under temperature of 80 celsius, the flat and vacuum tube solar energy collection device can reach such temperature. It uses water as its working medium, consuming less electricity than traditional air conditioning system. In addition, the liquid desiccant has a high energy storage capacity. Therefore, a lot of researches have been conducted in recent years.In this paper, numerical simulation of the heat and mass transfer in dehumidifier was taken under the convective boundary condition, and the dehumidifying experimental study was also made for different liquid desiccant solutions.Most scholars had done the numerical calculation of heat and mass transfer in dehumidifier under constant temperature and adiabatic boundary conditions, which are two ideal boundary conditions. In fact, when the liquid desiccant solution in dehumidifier was cooled by the cooling liquid outside of the dehumidifying unit, the wall temperature of the unit cannot be considered as constant. In order to approach a practical boundary condition, numerical calculation of the heat and mass transfer for falling liquid film of laminar flow in dehumidifier was taken under the convective boundary condition in this paper, the temperature and concentration distribution of the falling liquid film was obtained. It is found that the temperature and concentration of the falling liquid film at small convective heat transfer coefficient are close to that of the adiabatic boundary condition, on the contrary, the one at larger convective heat transfer coefficient is similar with constant temperature boundary condition. This proves that the numerical method is correct. In addition, the influences of absorption heat and Lewis number on the temperature and concentration of liquid film were analyzed. At last, the optimized height of falling liquid film dehumidifier in the vertical direction of the dehumidifier was presented under the given operation conditions. The influence of the inlet solution concentration, solution flow rate, inlet air flow rate and temperature, air humidity on the absorbed process were studied for different liquid desiccants (calcium chloride, lithium chloride and calcium chloride mixture), and the dehumidifying effects of various mixture ratios on lithium chloride and calcium chloride mixture were also analyzed. The results show that the CELD (Cost-Effective Liquid Desiccant, the mixture ratio is 1:1) is more economical than pure lithium chloride solution, while its dehumidifying performance is better than calcium chloride solution.On the basis of the experimental study, the heat and mass transfer in dehumidifying process under the given operation conditions were calculated according to the presented numerical model for falling liquid film of laminar flow in liquid desiccant air conditioning system. The calculated results and the experimental data are coincided. It means that the numerical model proposed in this paper is satisfactory.