Semi-open heat pipes were studied experimentally in this work. A new kind of semi-open heat pipe with fluid swirl backflow was developed on the basis of the traditional semi-open heat pipe. Heat transfer characteristics during operation and start-up of closed heat pipe、traditional semi-open heat pipe and swirl flow semi-open heat pipe were investigated. The swirl orifice' s backflow effect on enhancing the working limitation was obtained. Heat exchangers or waste heat boilers made of swirl flow semi-open heat pipes and semi-open heat pipes have been successfully used in high or variable gas temperature engineering applications.