Numerical and experimental investigation of a counter-current two-phase thermosyphon with cascading pools

An innovative design of a counter-current two-phase thermosyphon is investigated for the in-plane cooling of flat product structures. The thermosyphon features multiple pools staggered along the entire evaporator section, in which liquid flowing toward the bottom of the thermosyphon can be stored. The pools are used to cascade the working fluid to the evaporator end cap. Liquid accumulates in the pools until they overflow, thereby spreading the working fluid across the entire evaporator length rather than creating one liquid pool at the bottom end cap. Multiple of such thermosyphons operating in parallel can be used for low-gradient planar cooling of vertically oriented surfaces. A numerical model using a control volume approach is developed to predict and to validate the experimental results of this innovative design. The main advantages of the control volume approach are the adaptability of the entire model and the fast computational speed in comparison to elaborate fluid dynamics models. Empirical correlations are used for the modeling of the heat transfer coefficients and friction factors of the counter-current flow. A proof of principle is given by observing a prototype that was milled into a copper bar. Next to logging temperature measurements, the prototype had a glass top plate to visually record the working fluid behavior. The model presented is well suitable for the early stages of thermosyphon design studies and for the impact evaluation of design changes.