Sensitivity of the Non-Equilibrium Approach for Mixture Condensation to Heat and Mass Transfer Correlations and Thermophysical Properties

Abstract

The prediction of mixture condensation is still complex due to coupled heat and mass transfer and insufficient data of thermophysical mixture properties. This article analyzes the impact of various heat and mass transfer correlations on the non-equilibrium approach for mixture condensation in a vertical plain tube. Furthermore, the influence of thermophysical properties from different databases is investigated. The results are shown for ethanol-water, but allow conclusions to other fluid mixtures. They indicate that the liquid heat transfer coefficient in the non-equilibrium approach dominates the qualitative behavior of the condensation process, but the vapor mass transfer coefficient can only decrease or increase the quantitative level of the effective heat transfer with minor impact. More importantly, the logarithm in the vapor mass transfer term is central for the prediction of the condensation heat transfer. As this logarithm contains VLE data, it proves that there is a strong connection between VLE and overall prediction of mixture condensation. A demonstration of available data for thermophysical mixture properties of ethanol-water shows significant deviations, which affect the calculations as well. Besides, data from our own experiments are presented for mixture viscosity of ethanol-water. It is recommended to focus not only on improved heat and mass transfer correlations, but also on thermophysical properties and VLE data for a precise prediction of mixture condensation.

Mixture Condensation of Ethanol/Water and Ethanol/Siloxane in a Vertical Double Pipe

“…Although the non-equilibrium method represents a more sophisticated description of the condensation process, the equilibrium method can also lead to satisfying results and keeps the benefit of less computing time. Still, these approaches coexist, and different aspects and adjustments of the approaches are investigated in current literature [8,9].…”

Measurements of Thermophysical Properties of Ethanol + Hexamethyldisiloxane and Ethanol + Octamethyltrisiloxane Mixtures in the Temperature Range of 293–343 K at 100 kPa

“…Similarly, the existing nonequilibrium and equilibrium approaches for the prediction of mixture condensation are highly dependent on mixture properties to fulfill the increment-wise update of all properties during the calculation. 15 In this context, Dorao and Fernandino 16 pointed out that the change of physical properties of mixtures is highly influential on the heat transfer performance, so that a lack of data may cause larger uncertainties than the choice of the calculation method itself, which was presented in an example by Zimmermann et al 17 The present work focuses on mixtures of the linear siloxanes hexamethyldisiloxane (MM) and octamethyltrisiloxane (MDM) with ethanol, which may eventually be used as potential new fluid mixtures in ORC or Kalina processes. Studies by Angelino and Di Paliano, 18 Wang et al, 19 and Abbas et al 20 showed the potential of siloxanes and their mixtures as working fluids in high-temperature ORC processes and experimental heat transfer coefficients are presented by Weith et al 10 and Zimmerman et al 21 Moreover, the increase of the sensible and latent heat capacity of siloxanes by mixing with ethanol as well as the availability, low-cost, and thermal stability of ethanol improve the usability in thermodynamic cycle processes.…”

“…Similarly, the existing nonequilibrium and equilibrium approaches for the prediction of mixture condensation are highly dependent on mixture properties to fulfill the increment-wise update of all properties during the calculation . In this context, Dorao and Fernandino pointed out that the change of physical properties of mixtures is highly influential on the heat transfer performance, so that a lack of data may cause larger uncertainties than the choice of the calculation method itself, which was presented in an example by Zimmermann et al…”