The article presents the results of an experimental study on the effect of two-dimensional roughness and Influence of the Prandtl number (Pr) on heat transfer when a liquid film flows down a vertical surface. The following coolants were used in the experiments: network water, distilled water and ethyl alcohol.
The experiments were carried out in the range of the Prandtl number (Pr) from 3 to 19, the Reynolds number (Re) varied from 100 to 45000. The experimental results obtained for a smooth surface are in good agreement with the existing literature data.
As a result of the study, it was found that the creation of a two-dimensional roughness on the heat-transfer surface causes a significant increase in the intensity of heat transfer. At the same time, the degree of intensity of heat transfer increases noticeably with an increase in the Prandtl number.
It has also been established that the two-dimensional roughness has a great influence on the critical value of the Reynolds number - Re_cr. In this case, the value of Re_cr for rough surfaces depends to a large extent on the Prandtl number.
The obtained results indicate that the use of the method of artificial roughness to heat transfer enhancement in the corresponding heat transfer installations will lead to a significant increase in the efficiency of such installations.