| The waste heat resource exists widely in the process of industrial production,it accounts for about 17%~67% of the full combustion heat emitted of fuel and recovery rate is up to 60%,the energy saving potential is huge.Converting waste heat to electric energy is an ideal energy saving way,organic rankine cycle power generation technology,low temperature steam turbine generator and semiconductor thermoelectric power generation technology are available generation modes,but they all have certain limitations.A novel heat-power conversion method was proposed based on the principles of reverse electro-dialysis and realized the conversion under the impetus of solution concentration,the heat-power conversion system consist of solution thermal separation part and reverse electro-dialysis cells part,it is adaptive to the grade and fluctuation of waste heat.NaCl aqueous solution possesses high conductivity and ionic activity,which is suitable to be used as working solution of cells,but it’s property of high latent heat of vaporization will reduce the efficiency of thermal separation part,proper solutions need to be found which can meet the thermodynamic characteristics in the process of thermal separation and the electrochemical characteristics in the process of reverse electro-dialysis at the same time.Conductivity and ionic activity are the two most important factors that affect the efficiency of heat-power conversion.In this paper,electrode conductance method is applied to determine the conductivitiy of metal salt-water binary solutions,metal salt-organic solvent(alcohols)binary solutions and metal salt-organic solvent(alcohols)-water ternary solutions and quarternary solutions.The effects of concentration,temperature,ionic radius and solvent type on conductivity are discussed from the angle of intermolecular interaction.Applying Castell-Amis empirical equation to correlate the experimental data.Electromotive force method is used to test and verify the accuracy of individual ionic activity coefficient of Li~+ and Cl~-through Na~+ and Cl~-ion selective electrode.Based on the experiments,the following conclusions are obtained: Ionic association and solvation are main factors that determine the conductivity of solution,in measured concentration and certain temperature range,conductivity increases with the increase of concentration and temperature,when the concentration of the solution system increases to a certain extent,the number of free ions will stop increasing and start to inform ion pair,then,conductivity has a maximum value.Conductivity increases with the increase of ionic radius.The polarity of the solvent and the solubility and dissociation degree of electrolyte in polar solvent determine the conductivity of the system.Castell-Amis equation can correlate the conductivity data well for the solution that conductivity first increase and then decrease with the increase of concentration.Na~+ and Cl~-selective electrodes can be used to measure the individual ionic activity coefficient of Li~+ and Cl~-.The advices to select the working solution for heat-power conversion cycle system are given as follows: Li I–ethanol solution has the best conductivity,the conductivity of LiCl–ethanol,LiBr–ethanol and CH3COOK–TFE solutions are relatively high,and high concentration solutions and low price can be obtained,they are suitable to be used as working solution of heat-power conversion system.In order to enhance the conductivity of solution,improving the solution concentration,working temperature and the mass rate of water in mixed solvent properly are available,but the increasing of energy loss,reduction of selection coefficient of ionic membrane and increasing of latent heat of vaporization should be noted. |
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