(350e) Experimental and Numerical Analysis of Single-Phase Flow in a Thermosyphon

Thermosyphons, or natural circulation loops, consist of circuits in which a flow pattern is developed driven by buoyancy forces originated by density differences. In the present work, the single-phase operation of a thermosyphon was evaluated by physical and numerical experiments, in order to obtain a model capable of representing flow and heat transfer behaviors. For physical analysis, an experimental facility containing one riser and one downcomer, which are jacketed glass tubes, and a phase-separating drum was used. The circulating water in the jacket of the pipes, coming from thermostatic baths, heats or cools the fluid inside the thermosyphon. Acetone was chosen as working fluid due its physical properties. As measurement experimental technique, particle image velocimetry (PIV) was applied to determine the axial velocity profile in the riser, in different conditions established for the water inlet temperatures in downcomer (35°C, 45°C and 55°C) and riser jackets (15°C above the inlet water temperature in the downcomer jacket). A commercial code was used for the numerical experiments, which were performed in the same conditions from the physical experiments. The 3-D computational fluid dynamic model was applied with the assumption that density is a polynomial function of the temperature only.  The axial velocity profile obtained by numerical simulations are in concordance with physical experimentation data, showing the higher velocities near the tube wall. The results also showed the magnitude increase of the circulation rate trough the thermosyphon with the increase of the temperature of the water in the jackets.