Simulation of a pillow plate thermosiphon reboiler using an equivalent tube bundle geometry

Abstract

Pillow plate thermosiphon reboilers are innovative heat exchangers due to their compactness, flexible design options as well as high temperature and pressure resistance. Furthermore, thanks to their design they stabilize the recirculation flow and thus extend the operating range. However, due to their special geometry, available simulation tools do not allow for a quantitative rating or sizing. In this study, the geometry of a pillow plate apparatus is converted to an equivalent shell and tube geometry. It is investigated whether experimentally obtained results in a pillow plate thermosiphon reboiler can be reproduced by using that geometric equivalent in two industrial heat exchanger simulation tools. Eight experimental cases with varied operating pressures, submergences, and driving temperature differences are studied and compared to simulation results based on the geometrical equivalent. Both simulation tools provide acceptable results with deviations between +15% and −30% compared to the experimental determined circulation and heat flow. Additionally, they illustrate a special feature of the pillow plate thermosiphon reboiler: the pinch point appears at a shorter axial length than in a typical shell and tube thermosiphon reboiler, providing a larger area for evaporation.

Keywords

• Pillow plate
• Thermosiphon reboiler
• Simulation
• Pinch point
• Equivalent tube bundle