Improved semi-empirical correlations for the evaporation and condensation of zeotropic mixtures
Final Report Abstract
Boiling and condensation of gases or gas mixtures can achieve high heat flux densities during the phase change of the fluid. This is used in various energy and process engineering processes, including the vapor compression cycle, which is used worldwide billions of times in air conditioning and refrigeration systems or heat pumps. Mixtures become increasingly important as working fluids in place of the conventional pure substances, since stricter ecological and safety requirements can be met through a suitable combination of the properties. At the same time, suitable calculation equations are required for the heat transfer in evaporators and condensers of the given cyclic processes, as the phase change behavior of the zeotropic fluid mixtures entails an increased complexity. The overall project aims to improve model equations for the calculation of mixture boiling and condensation on the basis of the experimental investigations. For this purpose, two coordinated experimental apparatuses will be designed in the first funding phase, one of which will be used at the project partner LTTT in Bayreuth for investigating mixture boiling and the second in Hannover at IfT for mixture condensation. Furthermore, the relevant thermophysical properties of the selected ethanol-siloxane mixtures are measured at both locations by existing measuring equipment and the data are published in journal articles. These data are a necessary for the model approaches known from the literature and are thus used for comparative calculations. Due to the investigation of three ethanol-siloxane mixtures with varying compositions and operating conditions, it is possible to work out impact factors, which influence the heat transfer during mixture boiling or condensation and they are implemented as generalized mixture parameters in the suggested model approaches. For mixture boiling, heat transfer coefficients can be calculated with an accuracy of approx. 12 % using the new correlation. The so-called superposition approach for mixture condensation offers an explicit calculation for compositiondependent heat transfer coefficients, which achieves a deviation of 10 % on average compared to experimental data based on low computation requirement and property data.
Publications
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Sensitivity of the Non-Equilibrium Approach for Mixture Condensation to Heat and Mass Transfer Correlations and Thermophysical Properties. Journal of Heat Transfer, 143(9).
Zimmermann, Conrad; Dagli, Cagatay Necati; Arnautovic, Zlatan & Kabelac, Stephan
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Isobaric vapor-liquid equilibrium for ethanol/water and binary linear siloxane mixtures at 100 kPa. Fluid Phase Equilibria, 556, 113371.
Arnautovic, Z.; Weith, T.; Heberle, F. & Brüggemann, D.
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Density and Viscosity of Linear Siloxanes and Their Mixtures. Journal of Chemical & Engineering Data, 68(2), 314-329.
Arnautovic, Zlatan; Kutzner, Sebastian; Weith, Theresa; Heberle, Florian & Brüggemann, Dieter
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Measurements of Thermophysical Properties of Ethanol + Hexamethyldisiloxane and Ethanol + Octamethyltrisiloxane Mixtures in the Temperature Range of 293–343 K at 100 kPa. Journal of Chemical & Engineering Data, 68(9), 2223-2237.
Arnautovic, Zlatan; Zimmermann, Conrad; Hamza, Maya; Heberle, Florian; Kabelac, Stephan & Brüggemann, Dieter
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Mixture Condensation of Ethanol/Water and Ethanol/Siloxane in a Vertical Double Pipe. Chemie Ingenieur Technik, 95(5), 724-731.
Zimmermann, Conrad; Lubos, Nico; Dagli, Cagatay Necati & Kabelac, Stephan
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Enhanced heat transfer correlation for nucleate boiling of fluid mixtures. International Journal of Heat and Mass Transfer, 231, 125804.
Arnautovic, Zlatan; Welzl, Matthias; Heberle, Florian & Brüggemann, Dieter
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Experimental Heat Transfer Coefficients for Zeotropic Mixture Condensation of Hexamethyldisiloxane/Octamethyltrisiloxane and Ethanol/Hexamethyldisiloxane. Chemie Ingenieur Technik, 96(8), 1123-1130.
Zimmermann, Conrad; Lubos, Nico & Kabelac, Stephan
