This thesis presents results of an experimental investigation of frost formation on cooled tube under cross air flow. Frost formation, as a physical phenomenon, is very often observed in the nature. Frost structure forms on surfaces whose temperature lies below the solidification temperature of the condensed water steam. The frost structure is porous and consists of ice crystal and humid air. In the most cases of industrial practice the porous frost structure is undesirable because of its negative influence on the operating condition of the equipment. This is due to the reduced heat transfer between the surrounding air and the cooled surfaces caused by the growing isolation layer. In particular the frost structure reduces the refrigerating capacity of the chillers and raises the exergy loses and the operating expenses. In addition, the increasing frost structure reduces, e.g., in the air duct, the cross-sectional area for the flow of humid air and increases at the same time the flow resistance as well as the pressure drop. From the present state of knowledge it becomes clear that quite extensive research projects were carried out on the area of the frost formation. Relatively few works however, enclose experimental investigations of the frost formation on cooled tubes. The development of the measuring technique, new optical measurement techniques and applications for identification of the geometry of the frost structure and accurate humidity sensors allow exact measurements of the frost thickness and the mass of the condensed steam. New hydrophobic structures and their potential application possibilities in the refrigeration technology as a heat transmitting surface were not yet completely investigated. It would be interesting to know whether surfaces with hydrophobic properties can reduce the isolation effect of the growing frost layer. Therefore the aim of the present work is - to realize experimental investigations of the frost structure on tube and then to derive suitable correlation equations for the most important frost parameters. Most often the heat conductivity of frost structure is given as a function of its density. Therefore it is necessary to derive the density as a function of all varying parameters. The parametric study includes an analysis of influence of the following varying parameters on the frost structure: air temperature, relative air humidity, surface temperature, Reynolds number in the duct, structure and roughness of the surface, geometry of the duct, diameters of the test body and time. The following physical dimensions were calculated: average frost density, frost volume, frost growth rate, mass and mass flow of the condensed steam and as well as the total heat flux. As a test body a plain polished copper tube with a diameter of 15.0 mm and length of 85.0 mm was used. This tube was installed crosswise in the test section of the 6 meter long duct. The thickness and the volume of frost layer were measured by using a non contact visual method (CCD Camera). Humidity sensors with integrated thermocouple were used for the measurement of the mass of condensate and the total flux. It was observed that increasing air parameters like temperature, humidity and air velocity accelerate both the frost growth and the density increase. A decrease in the tube temperature caused an increase in mass flux of the condensate and results in a faster density growth. Additionally, two surfaces with higher roughness, and a surface with a self-cleaning and superhydrophobic Lotus coating were tested. The results show that the frost density is higher on a smoother surface. A visual observation proved that in the initial phase more smaller droplets condensed on a rougher surface due to a higher density of nucleation sites. The droplets solidify and build ice dendrites faster than on a less rough surface and isolate the cold surface. This reduces the condensate mass flux. The average density therefore is smaller on a rougher surface. Finally two correlations were derivated: for mass of condensate and for average frost density as a function of all parameters. For directly technical applications these correlations were shown in diagrams.