The onset of nucleate boiling(ONB)in the porous media with internal heat source was experimentally investigated.This paper adopted electromagnetic induction heating method to heat the pebble bed stacked with 8mm diameter steel balls.The inflexion of wall temperature was used to determine ONB.The influence factors of ONB were analyzed at the superficial velocity ranging from 0.025 m穝-1 to 0.050 m穝-1

heat flux ranging from 7.5 kW穖-2 to 52 kW穖-2.The temperature of wall had an inflexion clearly because of enhancement of heat transfer.The superheat of wall and heat flux required at ONB were smaller when the location was closer to the exit because temperature gradient decreased in the boundary layer.The superheat of wall and heat flux required at ONB were higher when velocity was higher because heat transfer was enhanced.