A new dry-spot model for high heat flux nucleate boiling region and critical heat Aux (CHF) is proposed. The new concept of dry area formation based on Poisson distribution of active nucleation sites and the critical active site number is introduced. It is shown that CHF can be determined without any correction factor based on information on the boiling parameters such as active site density and bubble diameter, etc., in the nucleate boiling region. It turns out that the present model well explains the mechanism on how parameters such as flow modes and surface wettability influences CHF. (C) 1997 Elsevier Science Ltd.