Experimental investigation of the thermal characteristics of single-turn pulsating heat pipes with an extra branch

In addition to some approaches such as changing the working fluid or number of turns in a pulsating heat pipe (PHP), geometrical changes are also appealing for enhancing the thermal performance of this type of heat pipes. The main idea of this investigation is to increase heat transfer rate by increasing flow circulation of working fluid. By placing an additional branch in the evaporator section, a secondary bubble pump was created which improved the circulation of fluid inside PHP. In order to investigate the impact of this additional branch, two similar one-turn copper heat pipes were fabricated. One of them was the conventional PHP and the other had an additional branch and is named additional branch PHP (AB-PHP). Thermal performances of these two types of heat pipes were investigated at different filling ratios (40, 50, 60, and 70%), inclination angles (0, 30, 60, and 90°), and heat inputs (from 5 to 150 Watts). Results showed that the thermal performance of the AB-PHP is considerably (up to 51%) better than the conventional PHP in the vertical orientation using filling ratios of 40% and 70%. Furthermore, comparing the performance of these two systems at the optimum filling ratio (60%) and different inclination angles indicated the better performance of AB-PHP in non-vertical positions including horizontal position. To better understand the effect of the additional branch in the AB-PHP, a Pyrex heat pipe similar to the copper type was fabricated and the flow circulation was visually analyzed.