Each regular surface can be considered as a sum of isosceles triangles of different apex angle (epsilon). Triangular, square, hexagonal and circular plates consist of three, four, six and an unlimited number of triangles of apex angles epsilon = pi/3, pi/4, pi/6 and double-line arrow pointing right 0, respectively. Simplified theoretical consideration for extracted repeated fragments of the surface, describing it in the form of triangles, suitable for any polygon, has been performed. Two models of fluid flow over heated surfaces are proposed. The fluid flow direction in the first model was perpendicular to the leading edge and stream lines are parallel to each other. In the second one it has been assumed that fluid flows from the leading edge concentrically towards the apex angle of the considered triangular surface. In both models free boundary layers transform into plumes above the center of the plates. The solutions of these models are presented in the form of dimensionless Nusselt-Rayleigh relations with the function of apex angles as a polygon parameter. The results of experimental investigations of horizontal isothermal triangular, square, hexagonal and circular plates are presented. The free convection heat transfer experiments and visualization were carried out using plates of the same diameter d = 0.07 m of the circle inscribed in polygon and glycerine as the test fluid.