Simulation of Thermosiphon Reboilers Using Wire Matrix Inserts at Lower Operating Range

Abstract

Heat transfer enhancement to enlarge the operating range enables a more efficient use of thermosiphon reboilers. For this purpose, the use of wire matrix inserts in thermosiphon reboilers was studied experimentally and via simulation. The boiling of water/glycerol as a wide boiling mixture with an elevated viscosity was investigated at a sub-atmospheric pressure of 0.2 bar abs and a submergence of 110%. With varied driving temperature differences, single-phase reboiler inlet velocities from 0.01 m·s^-1 to 0.16 m · s^-1 were induced coupled with heat fluxes ranging from 1 kW·m^-2 to 22 kW·m^-2. By using inserts, the reboiler showed significant improvement of fluid dynamics and thermal performance and could be operated at lower temperature differences. The simulation confirmed the advantageous usage of inserts. However, the heat transfer was underestimated possibly resulting from the neglected subcooled boiling and deficits in the flow boiling model for the wide-boiling mixture at low pressures.

Acknowledgments

Yan Lu would like to thank the German Federal Environmental Foundation (Deutsche Bundesstiftung Umwelt [DBU], Osnabrueck, DE) for her Doctoral Scholarships. We thank CALGAVIN Ltd. for providing the inserts and the continuing support. The contributions of Alvaro Ferre, Adrian Waßmann, and Lukas Kilzer through their student projects are gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Yan Lu

Yan Lu received in 2015 a M.Sc. Degree (with honors) in Mechanical Engineering at the Technische Universität Braunschweig, Germany. Currently, she is a doctoral candidate at the same university under the supervision of Prof. Dr.-Ing. Stephan Scholl, and works in the research group of Innovative Equipment and Plant Concepts in the Institute for Chemical and Thermal Process Engineering. Her topic of research is the energy-efficiency enhancement of thermosiphon reboilers by using wire matrix inserts in the lower operating range.

Katharina Jasch

Katharina Jasch is Senior Research Manager in the Institute for Chemical and Thermal Process Engineering at Technische Universität Braunschweig, Germany, and is responsible for the research group Innovative Equipment and Plant Concepts. She received her doctor’s degree in Heat Transfer in Microstructures from Technische Universität Braunschweig, Germany, in 2012. Her research activities include improved operation of thermal separation devices such as thin film evaporators or thermosiphon reboilers under challenging process conditions. Furthermore, she pursues the incorporation of new methods from the field of machine learning into classical methods for improved understanding and advanced modeling of complex mechanism.

Stephan Scholl

Stephan Scholl is Professor of Chemical and Thermal Process Engineering and Director of the respective Institute at Technische Universität (TU) Braunschweig. From 1979 to 1984 he studied Mechanical Engineering with a specialization in Energy and Process Engineering and received his Dr.-Ing. degree in 1991 at TU Munich. After 11 years with BASF AG, Ludwigshafen, Germany, he joined TU Braunschweig in 2002. His main research areas are innovative equipment and plant concepts, fouling and cleaning, sustainable production processes as well as process technologies for active compounds.