Working characteristics and heat transfer performance of pulsating heat pipes of non-capillarity size have been experimentally and analytically studied. The pulsating heat pipes (PHPs) were made of round tubes of 10 mm in inside diameter and the working fluid of the heat pipe was water. The experimental apparatus consisted mainly of a heating part, an adiabatic part, and a cooling part. The tubes of the heating part was made of Duplex stainless steel that can be heated by an induction heater. Two kinds of the cooling part were used for the variation of operating pressure. A water circulation type was suitable for the subatmospheric operating pressure of the working fluid and a pool type was for the operating pressure higher than the atmospheric pressure. The ranges of the major experimental parameters in this study were 10 ~ 110 kW/m2 of heat flux and 60 ~ 80% of fluid charging ratio.
The experimental results showed that the thermal resistance of the pulsating heat pipe decreased as the heat flux increased or the charging ratio was reduced, but a possibility of dryout increased at high heat flux or low charging ratio.
Heat transfer characteristics of pulsating heat pipes of non capillarity size were analytically modeled based on the Shafii's simple model. The governing equations of continuity, momentum and energy were solved using the Runge-Kutta method to predict the behavior of vapor plug and liquid slug. The calculation showed the oscillation behavior of vapor plug and liquid slug.