Neutron phase volumetry and temperature observations in an oscillating heat pipe

Abstract

An experimental investigation on a water filled 6-turn oscillating heat pipe (OHP) was conducted using neutron imaging. Using the neutron images, a method was developed to determine the volume fraction of liquid phase in different portions of the OHP while in operation. The results show that the volume fraction of liquid phase is highly nonuniform once the thermally excited fluid motion starts. Over the heat input range studied, during the steady state oscillating motion in an OHP, the volume fraction distribution of liquid phase was always less than 2.5% in the evaporator and greater than 80% in the condenser. Using this method, the startup behavior, pulsing and pause motions, circulation, and the relationship between the pulsing motion and circulation and temperature variations in the OHP were all determined as well. There is a notable synchronization between the entrance of liquid into the evaporator portion of the heat pipe and temperature oscillations.