Electrical Conductivity And Electrical Convertibility Of The Metal Salt-Organic Solvent-Water Systems

There are a variety of the low-grade thermal energy,such as the industrial waste heat,solar energy,geothermal energy,etc.A novel closed type heat-electricity conversion technology driven by the low-grade thermal energy has proposed by our research group,which combining the reverse electrodialysis（RED）technology with the low temperature multi-effect distillation technology.With the continuous concentration conversion of the working solution,the whole power generation system can realize the two conversions of from the low-grade thermal energy to solution salinity gradient energy（SGE）by the low-temperature multi-effect distillation technology firstly,and then from the SGE to electric energy by the reverse electrodialysis technology.The effluent from the outlet of the RED cells is directed back to the generator for regeneration again.This operating cycle allows for heat-electricity conversion continuously.The working solution is a key factor that affects the energy conversion efficiency of the whole power generation system.The suitable working should have the characteristics of the low latent heat of vaporization,the low boiling point and high electrical conductivity.In this paper,the metal salt-organic solvent-water ternary system was selected as the main research object,and the electrical conductivity and electrical conversion of which were investigated.Firstly,the effects of solution composition（solutes,solvents and additives）,concentration,temperature and other vital factors on the electrical conductivity of the solution were tested.Further,a ternary solution with high electrical conductivity was preferably to be used,and the electrical conversion characteristics of which was tested by means of a newly established RED cells system.The influences of the key factors（such as the solution concentration ratio,the solution flow rate,the operating temperature,the membrane spacing and spacer material）on the power of RED cells was experimented.In addition,the acid resistance and alkali resistance of the ion exchange membrane were tested from the viewpoint of further practicality.Based on the previous research on the physical chemical properties of the binary potassium acetate（KAc）solutions,here,the conductivity characteristics of KAc-methanol-H₂O and KAc-ethanol-H₂O were investigated in this paper.The experimental results showed that with the proportion of water in the mixed solvent increased,the electrical conductivity of the solution was increased continuously;the increase of solution temperature also caused the increase of the electrical within the experimental temperature range;the electrical conductivity of the KAc-methanol-H₂O was bigger than that of the KAc-ethanol-H₂O solution under the same experimental conditions.The electrical conversion test results of the KAc-methanol-H₂O solution were as follows.The output power density（OPD）of the RED cells gradually increased with the increase of the concentration ratio of the concentrated and dilute solutions at the inlet,but the optimal concentration ratio may exist to maximize the OPD.Within the experimental flow rate range,the output voltage and power density of the RED cells increased with increasing flow rate.It also can be seen that the larger the membrane spacing,the smaller the OPD.Besides,the OPD was be improved by elevating the operating temperature.When using KAc-methanol-H₂O as the working solution,the OPD of the RED cells was found to be larger than that of the KAc-ethanol-H₂O solution.Finally,the OPD was observed to be enlarged by using the metal spacer due to the reduction of the resistance.From the perspective of the actual engineering,it is necessary to do a good job of the anti-corrosion of the metal space.