Abstract: This paper reviews the factors affecting the distribution of nucleation site density in nucleate boiling and then uses fractal theory to discuss the relationship between boiling surface microstructure information and nucleation site density and study the data of nucleation site density in two boiling experiments: one is to investigate the change of nucleation site density during the course of aging process, the other is to investigate the difference of the nucleation site density on two boiling surfaces made of different materials. The result of experimental data analysis shows that the relationship between nucleation site density and minimum nucleation radius is fractal. Fractal dimensions are calculated and different fractal dimensions correspond to different boiling surfaces. Fractal dimension is a quantitative parameter describing boiling surface character.

Key words: nucleation site density, minimum nucleation radius, fractal dimension