Vízügyi Közlemények, 1961 (43. évfolyam)

4. füzet - IX. Képek a Föld különböző részeinek vízépítési munkáiról

(60 > The two fundamental hydraulic factors of hydraulic material transport are: a.) transportation velocity to be used, b.) the friction loss occuring during transportation. These two factors depend on a.) the properties of the solid material transported (specific gravity, particle size, shape, etc.), b.) the properties of transporting fluid medium (specific gravity, viscosity, density, etc.), c.) the properties of the slurry (concentration, temperature, etc.) and d.) the characteristics of the pipeline in which transport takes place (diameter, roughness, gradient, etc.). The relationships known to exist between the above factors are as yet of purely empirical character. The results yielded by the empirical formulae differ from each other. One of the defects of these formulae is, that the effect of changes in each individual factor on the phenomenon has not been investigated separately by the authors. The other reason for the inconsistencies is that a narrow range of the parameters has only been explored, and the experiments failed to truly represent the phenomenon, etc. For determining the transport velocity, the knowledge of the critical velocity of the slurry is necessary. This is the velocity at which the solid part of the slurry is still in motion in the "entire length of the conduit. Energy consumption is lowest at the critical velocity, the knowledge of which is thus necessary also for economical operation. The friction loss may, according to practical experience, be higher, or lower than in the case of clear water. In the cases shown in Figs. 1/b, 1 a and 1/c the friction loss of slurry is, in the higher velocity ranges equal, lower and always higher than with clear water, respectively. When designing a transport installation, various aspects have to be taken into consideration, such as the lowest energy consumption, wear of the conduit, capacity of the installation, safety factor, etc. Beyond these, special requirements arise with almost every individual installation, and the selection of the governing factor requires careful consideration and thorough familiarity with the subject. Design formulae and the fields of application thereof are described in Chapter III of the paper. The practical application of every method is illustrated by preparing an example for each with a material of finer (material A), and of coarser (material B) gradation. The results obtained by computation are represented in a graphical form. The grain-size distribution curves of the materials used are shown in Fig. 2. The following methods are described: a.) The method of G. N. Roer

: The first of the Soviet investigators relied primarily on experience gained on earth moving jobs fox* developing his formulae. Eq. (1) is suitable for determining the critical velocity of homogeneous materials, while Eq. (2) applies to mixed ones. Computation results are represented in Fig. 3. FricLion losses are determined from Eq. (3). Those for clear water are computed by the formula of Pawlowsky, using a roughness coefficient n = 0,012 — 0,010. Values of the settling velocity ,,\V" involved in the formula were substituted according to the compilation by Gontsharov (Table III). The values obtained for the friction loss are plotted in Fig. 4. The computation method is subjected to a critical discussion. b.) The method of S. G. Goryunow

: On the basis of experimental results obtained at the laboratory of the VNIIG Institute, Leningrad, a table has been compiled for determining the friction loss. According to Goryunow, Eq. (5) applies to slurry, where ghe presence of the solid material is taken into consideration by introducing the coefficient of additional resistance Я„. The resistance coefficient of clear water К can be determined from Eq. (6). In compiling the table (see Tables V to XII) the relationship = f (v, C, d) has been taken into consideration. When using the computation method, the following limitations should be remembered: 1.) the ranges are primarily valid for material of mostly uniform particle size, 2.) the method cannot be suggested for finely graded material, 3.) the method is suitable for soils only and 4.) it is restricted to high velocity ranges.