Experimental investigation of thermal performance of Pulsating heat pipe at angles close to the horizon

Pulsating heat pipes (PHPs) are one of the devices that can transfer a lot of heat while being simple and inexpensive. in industrial applications one of the major weaknesses of PHPs is their poor performance at angles close to the horizon. Previous studies have mostly been at 90, 60, 30, and 0 degree angles and have reported the weakness of PHPs in the 30 to zero angle range, but detailed studies has not been performed in this range. Therefore, the main purpose of this study is to experimentally investigate the performance of PHP at angles of deviation close to the horizon and to provide a more accurate critical inclination angle. the performance of PHPs was evaluated for the best filling percentage (60%) at different angles 0 to 90 degrees. the results showed that by reducing the PHP angle from 90 degrees to 15 degrees, the difference in thermal resistance for different heat input powers was very small, but this difference increased from angle of 10 to 0 degrees. Further studies showed that the percentage of difference in thermal resistance between angles 15, 10 and 5 with the average value of thermal resistance is 3%, 12% and 36%, respectively. Thus, it was found that the main weakness of pulsating heat pipes is from an angle of about 10 to 0 degrees.