Time-Resolved Measurement of Enhanced Phase Change by a Fiber in an Oscillating Two-Phase Plug Flow

In this paper, we experimentally study the phase change enhancement of an oscillating two-phase plug flow in the presence of a wicking fiber. This oscillating flow is common in pulsating heat pipes (PHP) and self-oscillating fluidic heat engines (SOFHE). The main concerns in these devices are the startup and the amplitude of the oscillations that are governed by the phase change (evaporation-condensation). Herein, we suggest a simple and novel approach to manipulate the phase change by adding a fiber into the evaporator acting as a wicking structure. The experimental test rig is composed of a glass tube, with the inner diameter of 2mm that is filled with deionized water. The tube is heated at a closed end and cooled at the opposite open end. The fiber is inserted through the liquid plug all the way into the evaporator, effectively wicking liquid into the evaporator zone. Although self-oscillations are notoriously difficult to achieve with water, we showed that the fiber facilitates the start-up and yields stable oscillations with constant amplitude. The phase change rate and the oscillation amplitude significantly increase as we increase the fiber length inside the evaporator up to a certain length. However, the plotted phase change profile as a function of the position shows that the phasing of the phase change rate still has room for improvement.