雪の水力輸送に関する研究-5-直管における圧力損失に対する諸因子の影響

概要

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The pressure drop of a snow/water mixture in smooth walled straight pipes of circular cross section (inner diameter D=40 mm and 77 mm), the flow rate and the snow volume fraction C at discharge were measured for both fresh and granulated snow in the range of 0< C<0.3 and 3 < Fr <210, where Froude number Fr= Um2/ (|1-s|gD) and s is the density ratio of ice to pure water. An increase of the frictional force at the pipe wall due to snow mixing increased the pressure drop in a horizontal pipe. This pressure drop increased with C when the flow velocity Um was low, but it approached that measured for pure water with increasing Um. In a vertical pipe the pressure drop decreased with C for an ascending flow, and increased for a descending flow. This was due to gravity coupled with a reduction of the mean density of the mixture. In a horizontal pipe, fresh snow gave a slightly higher value to the hydraulic gradient i than granulated snow at intermediate values of C and Fr. The additional pressure drop coefficient defined by φ= (i-iw) / (Ciw), where iw is the hydraulic gradient for water, can be expressed as a function of Fr, irrespective of D, C, and Um. Equations for the additional pressure drop coefficient for horizontal and vertical flows are also presented as determined from experimental results.