Experimental investigation of heat transport with oscillating liquid column in pulsating heat pipe using forced oscillation system

To clarify the detailed heat-transport mechanism of a pulsating heat pipe, an experimental study was conducted using a forced oscillation system. A liquid column was oscillated in a channel for a single-component (liquid ethanol and vapor ethanol) system and a two-component (liquid ethanol and air) system. In the single-component system, the sensible heat transport due to the oscillating flow and the latent heat transport due to the phase change occurred simultaneously because the gas phase consisted of only working-fluid vapor. In the two-component system, only sensible heat transport occurred, because the gas phase consisted of air at the atmospheric pressure. The effective thermal conductivity of the latent heat transport was determined according to the difference in effective thermal conductivity between the single-component system and the two-component system. The effective thermal conductivity of the sensible heat transport increased monotonically as the oscillation center moved to the heating section under the same amplitude and frequency. On the other hand, the effective thermal conductivity of the latent heat transport increased as the oscillation center moved to the cooling section under the same amplitude and frequency until the tip of the oscillating liquid column reached the heating section. The vapor-mass fluctuation was estimated according to the measurement of the vapor-pressure fluctuation in the single-component system. The results show that the liquid film formed by the oscillating liquid column played an important role in the mechanism of the latent heat transport. They also show that the direct-contact condensation from the working-fluid vapor to the tip of the liquid column occurred when the liquid column moved from the cooling section to the heating section.