Theoretical Study On The Vaporization Heat Of Organic Fluids

With the increasing development of science and technology,the world conventional primary energy consumption has risen to a level never reached before,and energy efficiency is also generally low.Organic Rankine Cycle(ORC)has been proven to be a promising solution to recover low-grade waste heat.Values of the vaporization heat can be obtained by means of experiment directly,but most of them are obtained at a given temperature such as normal boiling point.It is an important research direction to estimate the vaporization heat of organic fluids by theoretical methods due to lake of experimental data.In the paper,two theoretical methods are used to estimate the vaporization heat of organic fluids.The first theoretical method is the corresponding states principle.Based on the corresponding states principle,a new vaporization heat equation is presented by correlating the vaporization heat with the reduced temperature and the acentric factor.36 kinds of organic fluids are calculated by the equation.In order to further improve the calculation accuracy of the equation,36 kinds of organic working fluids,classified into the polar and the non-polar according to the molecular polarity and chemical bonds,are chosen to calculate the vaporization heat to verify the new equation.The second method is group contribution method.A new method is proposed by combining corresponding states principle with group contribution method.A new correlation of the vaporization heat is established by corresponding states principle,and then 4 type organic fluids,including alkanes,alcohols,esters,ethers,are divided into various groups.Finally,values of the vaporization heat of 4 type organic fluids are estimated.The vaporization heat of 36 kinds of working fluids has been estimated,and the average absolute deviations are 0.78% and 0.66% for the polar and the non-polar fluids.The results suggest that it is available and precise to apply the equation to the calculation of vaporization heat of organic working fluids.By comparing with other corresponding states principle correlations,the new equation shows a conspicuous improvement in the vaporization heat calculation.Based on the group contribution method,contribution values of 23 groups are obtained by correlating 1574 vaporization heat experimental data of 50 organic fluids,and the average absolute deviations are 0.83%,1.27%,0.65% and 1.2% for alkanes,alcohols,esters,and ethers.The total average deviation of 50 organic fluids is 0.92%.