In this study, the nucleus formation and bubble growth at beginning of boiling process in microchannels was investigated. Canonical molecular distribution was introduced to analyze characteristics of nucleate boiling when liquid molecular number is very small. The minimum bulk phase volume in which phase change was enable to occur was determined from thermodynamic theory of bubble formation in a superheated liquid and from the energy distribution of the molecules in the bulk phase at a given temperature and pressure. The comparison of the free energy decrease during nucleus formation on a flat wall and at a corner of walls indicates that nuclei more easily form at a corner than on a flat wall for wetting liquids. The experimental results demonstrated that the superheat temperature increased as diameter of microchannels decreased. The experimental measurements are in a quite agreement with theoretical predictions.

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