Research On The Performance Of Mixed Solutions To Substitute Single Desiccant In Liquid Desiccant System

The liquid desiccant technology has wide application prospects in aspects of temperature and humidity independently controlled air conditioning systems and drying compressed air system.In the liquid desiccant system,the desiccant directly exchanges heat and mass with the air,which directly affects the efficiency and performance of the system.In view of the shortcomings of dehumidification performance or expensiveness of a single desiccant currently used,many scholars have studied the mixed solution.However,due to the limited selection of the best cost-effective ratio,the dehumidification capacity and economics of the solution cannot be guaranteed at the same time.Based on this problem,this article starts mixed solutions substitute single solutions research from the point of view of having the same dehumidification capacity and more economical efficiency.The main research contents and results are as follows:First of all,the thermal properties such as the vapor pressure,viscosity,and specific heat capacity of the mixed solution were measured.The result revealed that the calcium chloride/lithium bromide mixed solution has the same characteristic as the calcium chloride/lithium chloride solution whose vapor pressure value satisfies the simple mixing rule calculation model.The mixed solution ratio scheme can be deduced from this model.A simple mixed model of the extreme ratio of the high temperature calcium chloride/lithium chloride mixed solution was corrected.The corrected formula was accurate and relatively high;the viscosity of the calcium chloride/lithium bromide mixed solution increased with the increase of the calcium chloride content.According to the measurement results,a viscosity fitting formula is proposed;DSC differential thermal analysis method has higher accuracy for measuring dehumidified solutions,and the specific heat capacity of calcium chloride/lithium chloride mixed solution and calcium chloride/lithium bromide mixed solution all satisfy the simple mixing rule.In the model,the difference between the experimental value and the calculated value is within 2%.Secondly,according to the vapor pressure prediction mixing rule,a substituting scheme of a mixed solution of calcium chloride/lithium chloride substituting a high concentration of lithium chloride is proposed.And the dehumidification performance of three mixed solutions with different ratios and pure solution was studied on the compressed air liquid desiccant test bed.The dehumidification performance of the pure solution and the mixed solutions at different air pressures,air flow rates,solution temperatures and the economics of the solution are mainly compared.The results showed that the dehumidification performance of the mixed solution and the pure solution was not much different.The maximum moisture content of the outlet air was different by 0.1g/kg.The mixed solution with 44% mass concentration had good dehumidification performance at 0.15 Mpa air pressure,and the 49% mixed solution was 58% cheaper than the pure solution.It can be seen that using a mixed solution reduces the cost of liquid desiccant solution and improves the drying efficiency.Then,a falling film liquid desiccant test bed was built.The low temperature heat source driven and the heat pump driven liquid desiccant air conditioning system conditions were simulated through experiments.The dehumidification and regeneration performance of the pure solution of lithium chloride,lithium bromide,and its calcium chloride/lithium chloride,and calcium chloride/lithium bromide mixed solutions was compared,which are commonly used in the two liquid desiccant air conditioning systems,.The dehumidification performance of the pure solution and the mixed solution under each working condition is similar.Except for steam pressure,other thermal properties have little effect on the dehumidification performance of the solution.However,due to the mixed solutions are added with the calcium chloride solution on the basis of the pure solution,the solution vapor pressure curve is changed,resulting in a higher vapor pressure than the pure solution under the regenerating conditions.The regeneration performance of the mixed solution is better than that of pure solution.At the same time,the mass transfer performance of the mixed solution under different working conditions was explored in combination with the thermal properties of the solution,and the formula for the mass transfer coefficient of the mixed solution was proposed.Finally,based on the characteristics of solution dehumidification performance,regeneration performance,pump consumption,solution cost and other factors affecting the efficiency of the liquid desiccant air conditioning system,the pure solution and the mixed solution were evaluated.The conclusion is that the mixed solution has obvious advantages in terms of regeneration performance and solution cost.The evaluation of mixed solutions is better than that of pure solution.The mixed solution as a new type of desiccant that replaces the pure solution has broad research and application prospects.