Experimental investigation of oscillating motions in a flat plate pulsating heat pipe

An experimental study was conducted to evaluate the motion of vapor bubbles and liquid plugs within a flat plate pulsating heat pipe to determine the effects of working fluids (water, ethanol, Flutec PP2, and Flourinert), power input, filling ratio, and angle of orientation on the pulsating fluid flow. Experimental investigations quantify the position and velocity of the liquid-vapor interface for various conditions. Through the use of a Photron high speed camera, precise locations of the liquid-vapor interface were tracked and analyzed. Experimental data show that both the macromovement and oscillating motion of vapor bubbles and liquid plugs exist for a functional pulsating heat pipe. The amplitude of these oscillations was increased as more power was inputted into the pulsating heat pipe. The pulsating heat pipe investigated here would not function when charged with 50% high performance liquid chromatography grade water and positioned horizontally. On the other hand, the experimental results show that when the heat pipe was charged with ethanol, it created the largest amplitudes and velocities. The oscillating motion of vapor bubbles and liquid plugs including the macromovement is very sensitive to the tilted angle, and large increases in amplitude were observed when the angle was increased (bottom heating mode) from horizontal.