By combination of infrared thermal imaging technique and high-speed visualization method

the surface temperature distribution of condenser in a pulsating heat pipe (PHP) and operating state of working fluid inside the PHP are obtained and the relationship between them and heat transfer performance of the PHP is analyzed. The results indicate that the working fluid sequentially exhibits three quasi-steady operation modes with the increasing heat load viz. small pulsation in single pipe

large pulsation among different pipes and unidirectional circulation. In addition

in the condenser the dominated flow patterns are dispersed bubbles and vapor plugs

and the proportion of the dispersed bubbles decreases with increasing heat load. The difference in strength of heat and fluid flow in the PHP leads to the different characteristics of temperature distribution in the condenser

implying that the infrared thermal image of condenser is an important evidence to the evaluation of working fluid operation and heat transfer performance of the PHP.