Abstract: The Visualization and start up performance of closed-loop plate pulsating heat pipe (PHP) with parallel channels with ethanol as the working fluid under different working conditions is experimentally studied. The influences of liquid filled ratio, inclination angle and heating power on flow pattern and start up performance are analyzed. Results show that flow pattern of working fluid include bubble flow, slug flow, mixed flow(slug flow and annular flow), but there is not complete annular flow in channels. Working fluid mainly distributed in medial position at filling ratio of 10%, and uniform is improved at filling ratio from 35% to 85%. There are slug flow (close to cooling end) and annular flow(close to heating end) in every channel during operating, and equilibrium position of annular flow moved to cooling end with power increasing. Pattern of PHP is smooth temperature increasing, and start up time decreases with heating power and inclination increasing，but it can not start up with 45°and 30°.

Key words: closed-loop with parallel channels;plate pulsating heat pipe;visualization;inclination;start-up performance