Tham khảo tài liệu 'blast cleaning equipment_4', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 136 4 Blast Cleaning Equipment Reynolds number Fig. Relationships between Reynolds number relative roughness and friction parameter Wille 2005 . 1-hydraulically smooth 2-hydraulically rough limit kH mm Bohl 1989 . This value is one order of magnitude lower than the typical values for the thickness of the laminar boundary layer see Fig. . The Reynolds numbers for the flow in blast cleaning hoses usually exceed the value ReH 105 see Fig. . Therefore the rather simple can be applied for the estimation of the friction number for most blast cleaning applications. Hose Diameter Effects The equations mentioned above deliver the following relationship between pressure drop and hose diameter Apa a dH5 This equation illuminates the overwhelming influence of the hose diameter on the pressure loss. A precise physical deviation delivers a power exponent value somewhat smaller than 5. This influence is graphically expressed in Fig. which shows results of measurements of the pressure drop in hoses with different diameters. The rapid pressure drop in the hose with the small diameter of dH 19 mm can be recognised. These experimental results agree very well with results calculated from . More values calculated with are plotted in Fig. . The graphs show among others that pressure drop reduces at higher air pressures. This phenomenon can be explained with which suggests that the air density increases with an increase in pressure. Higher air density means lower air volume which in turn reduces the air flow velocity in the hose. Equation shows that lower air flow velocity leads to less pressure drop. More relationships are displayed in Fig. . The graphs show the relationship between hose length and air flow velocity in the Pressure Air Hose Lines 137 Fig. Effect of hose diameter on experimentally estimated pressure loss in air hoses Neumann 1985 . Air flow rate 2A min hose diameter 1 - dH 19 mm 2 -dH .
