The applicability of electrohydrodynamics (EHD) technique for in-tube boiling heat transfer enhancement of Rll in vertical tube was investigated experimentally. The test rig was similar to a separated heat pipe which consisted of a tube-in-tube heat exchanger with hot water or cold water flowing in the outer tube and refrigerant flowing through the inner tube. A coaxial stainless steel cylindrical electrode with an outer diameter (OD) of 2.5mm and a length of 800mm was inserted through the test section, which was a smooth stainless steel pipe with an inner diameter of 25mm. The experiments was conducted under different values of heat flux, electric high voltage, and superheat. It was found that Rl 1 exhibits an evident response to the EHD effect. An increase in the heat transfer coefficient of as high as 300% was obtained compared to the base case (absence of EHD effect). The electrical power consumption was found to be less than 0.3% of the corresponding heat transfer rate.