Experimental investigation of steady and transient operations of a single-phase closed-loop vertical thermosyphon

Abstract An experimental investigation of a single-phase, closed-loop, vertical thermosyphon operating under steady and transient conditions, with water as the working fluid, is presented and discussed. With the dimensions and power inputs selected for this thermosyphon, it resembles a scaled-down and simplified laboratory model of buoyancy-driven cooling systems for electrical transformers. The steady and transient operations of this thermosyphon were investigated for the following series of power inputs: 50 W, 125 W, 200 W, 125 W, and 50 W. Each power input was kept constant until the steady-state operation was achieved; and then a step change in power input was imposed to study the time-varying excursion from one steady-state operation to that at the adjacent power level (up or down, depending on the position in the aforementioned series). With this strategy, the results for steady-state operation with a given power input also serve as reliable initial conditions for the transient excursion to the steady-state operation corresponding to the next chosen power input. A variety of results pertaining to both steady and transient operation of this thermosyphon are presented and discussed, including their special usefulness for validation of related mathematical models and numerical simulations. It is also demonstrated that a simple lumped-parameter approach can yield good estimates of the overall time needed for this closed-loop thermosyphon to adjust from steady-state operation at one value of the power input to that at an adjacent one imposed in a step-wise manner.