A generalized corresponding states method for predicting the limits of superheat of mixtures: Application to the normal alcohols

Abstract

The limits of superheat of the normal alcohols from methanol to octanol and of ethanol/ n-propanol, n-propanol/ n-butanol, and n-butanol/ n-pentanol mixture were measured at atmospheric pressure. The results were predicted using a new method based on the generalized corresponding states principle (GCSP) in which properties of two reference substances were used to predict the superheat limits of the fluids studied. Ethanol and n-butanol, and the two components of each mixture studied, were used as reference fluids for predicting the superheat limits of the pure alcohols and mixtures respectively. Results showed that it is possible to predict superheat limits to well within the accuracy of measured values ( < 1%). The method requires only accurate vapor pressure correlations and acentric factors of the reference fluids, and an accurate method for predicting the variation of the true critical mixture temperature with composition. It is shown that the GCSP reduces to an expression for the superheat limit of a mixture which is a mole fraction weighted average of the limits of superheat of the individual components in solution when the mixture and its components satisfies certain conditions. In the general case, both linear and nonlinear variations of mixture superheat limit with mole fraction can be predicted with the proposed method. Considerable simpiflication using the GCSP over the approach based on classical homogeneous nucleation theory is derived from the fact that no mixture surface tension or bubble point pressure data are required.