Heat transfer enhancement of pulsating heat pipes with novel structures

Pulsating heat pipes can work without wicking layers with high heat transfer performance, whereas their performance is unstable especially at low heating temperatures significantly limiting their applications. The structure of pulsating heat pipes is reported to affect their flow characteristics and thereby affect their heat transfer performance. This study proposed cross-bonding and fabric-like structures for pulsating heat pipes with a working fluid of R134a to improve the heat transfer performance of pulsating heat pipes under low heating temperatures. The effects of the filling ratios of R134a and heat pipe inclination angles were investigated experimentally to explore the thermal performance of the proposed pulsating heat pipe. The results indicated that the heat pipe with the fabric-like structure has the best thermal performance with unidirectional fluid flow and remarkable operation stability, the thermal conductivity of which was up to 3.54 times higher than that of the classical pulsating heat pipe. The infrared thermal image further showed the fabric-like structure contributes to the most uniform temperature distribution. In addition, the heat pipe with the cross-bonding structure can also enhance the heat transfer performance and operation stability compared with the classical pulsating heat pipe. The performance enhancement can be attributed to the flow resistance imbalance and heat regeneration of the backflow liquid caused by the horizontal tubes, which can guide the structure design of pulsating heat pipes for various applications in electronics cooling and low-temperature heat recovery.