Visualization of the working fluid in a flat-plate pulsating heat pipe by neutron radiography

Abstract

Behaviors of the working fluid in a flat-plate pulsating heat pipe (PHP), made of aluminum alloy, in the bottom- and top-heating orientations were visualized by neutron radiography. The PHP has the square channel with side length of 1.2 mm and closed-end serpentine with 22 turns. The working fluid is R1336mzz(Z), and the filling ratio is 50%. The adiabatic section of the PHP (between the heating and cooling sections) is irradiated with the neutron beam and visualized the distribution of working fluid at certain time intervals. The results indicate that the initial distribution of the working fluid does not affect the startup characteristics of oscillation of the working fluid in regard to the specifications of flat-plate PHP used in this study. As for the PHP in the bottom-heating orientation, when heat input is 80 W, the working fluid is distributed from the heating section to the cooling section in every other channel. The working fluid distributed in the channel changes over time. When heat input is increased to 120 W, the working fluid tends to be located far from the heating section, intermittently reaches the heating section, and heat-transfer performance of the PHP is degraded. As for the PHP in top-heating orientation, when heat input is 80 W, the working fluid tends to distribute in the cooling section and intermittently reaches the heating section. When the heat input is increased to 120 or 160 W, the working fluid oscillates greatly, the amplitude and frequency of the oscillation increase, and the working fluid reaches the heating section more frequently. As a result, the working fluid is likely to boil in the heating section, and heat transfer performance of the PHP is improved.