To clarify the detailed heat-transport mechanism of a pulsating heat pipe, an experimental study wasconducted using a forced oscillation system. A liquid column was oscillated in a channel for a singlecomponent(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 thelatent heat transport due to the phase change occurred simultaneously because the gas phase consistedof 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 conductivityof the latent heat transport was determined according to the difference in effective thermal conductivitybetween the single-component system and the two-component system. The effective thermal conductivityof the sensible heat transport increased monotonically as the oscillation center moved to the heatingsection under the same amplitude and frequency. On the other hand, the effective thermal conductivityof the latent heat transport increased as the oscillation center moved to the cooling section under thesame 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 fluctuationin the single-component system. The results show that the liquid film formed by the oscillating liquidcolumn played an important role in the mechanism of the latent heat transport. They also show thatthe direct-contact condensation from the working-fluid vapor to the tip of the liquid column occurredwhen the liquid column moved from the cooling section to the heating section.
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