Experiments were carried out to explore the mechanisms of bubble lift-off from a vertical heated surface in subcooled pool boiling. The experiments were conducted at atmospheric pressure and distilled water was used as the test fluid. A high speed camera was used for observation of bubble behavior. The main experimental parameters were the static contact angle of the heated surface, the liquid subcooling, and the wall heat flux. The time variation of bubble size was measured through image

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... is. The growth force acting on the bubble was calculated using the measured time-evolution of the bubble size. The bubble growing on the vertical heated surface started to be extended in the horizontal direction when the sign of the growth force turned from negative to positive. It was hence considered that the growth force is one of the main causes of the bubble lift-off from a vertical heated surface. Furthermore, a correlation was developed for the bubble lift-off diameter considering the distribution of heat transfer rate around the bubble.