To close this gap in the literature, in a first step, we have elaborated a comprehensive database on the condensation heat transfer of pure n-propanol, isopropanol, isobutanol, and acetone on the outside of horizontal low-finned tubes with different fin geometries using a test rig implemented at the Technical University of Munich. Since it is often necessary to condense mixtures in the chemical industry, e.g., in distillation processes, the experimental data include heat transfer coefficients for mixture condensation of the investigated pure substances. The measurements cover the entire composition range and contain heat flux variations relevant for industrial applications in the range of 15 to 35 kW/m².
The second part of the study aims to investigate the influence of non-condensing gases, such as nitrogen, on condensation heat transfer on low-finned tubes. Even a small amount of non-condensing gas can significantly reduce the heat transfer [3]. The experimental results obtained on low-finned tubes are compared with the heat transfer measurements on a cylindrical plain tube.
Using the experimental data, we examine the applicability of calculation models available in the literature for the condensation of chemicals [2]. Therefore, the calculated outer heat transfer coefficients are compared with the measurements.
The study shows that the outer heat transfer coefficient during condensation of the pure substances n-propanol, isopropanol, isobutanol, and acetone can be enhanced significantly by using low-finned tubes. However, the investigated models from the literature are not suitable for describing the condensation of chemicals on low-finned tubes. We attribute this to the fact that the models are developed with measurement data on the condensation of refrigerants.
Except for close-boiling mixtures, the heat transfer in binary systems is reduced compared to the condensation of the corresponding pure substances due to additional thermal resistance in the vapor phase. In a model comparison, we show that the film model of Colburn and Drew [4], which can be used to predict the condensation heat transfer of mixtures, stands in good agreement with our measurements.
The investigations provide a thorough database on the condensation heat transfer of pure substances and binary systems on plain and low-finned tubes. Along with the model comparison, the presented results can help promote the use of condensers with low-finned tubes in the chemical industry.
[1] J.Y. Ho, K.C. Leong, A critical review of filmwise natural and forced convection condensation on enhanced surfaces, Appl. Therm. Eng. 186 (2021) 116–437, doi: 10.1016/j.applthermaleng.2020.116437.
[2] T. Losher, H. Klein, S. Rehfeldt, Modeling the condensation heat transfer on horizontal low-finned tubes, Chemie Ingenieur Technik 96 (10) (2024) 1364–1375. doi: 10.1002/cite.202300184.
[3] T. Losher, S. Schlecker, H. Klein, S. Rehfeldt, Experimental investigation of the impact of noncondensing gas on the condensation of n-propanol on a low-finned tube, Applied Thermal Engineering 244 (2024) 122775. doi: 10.1016/j.applthermaleng.2024.122775.
[4] A. P. Colburn, T. B. Drew, The condensation of mixed vapors, Transactions of the American Institute of Chemical Engineering 33 (1937) 197–215.