Hydraulic conveying of snow

VIII. Blocking of snow/water mixture flow and criterion of stagnation of snow at pipe orifice

Abstract

Based on observations of flows, an outline of the blocking phenomenon of snow/water mixture flow in closed channels was given. It was confirmed that a characteristic blocking occurred due to the property of snow in the mixture flow, i.e. a tendency of snow blocks to adhere to each other and to form a densified plug in the channel compressed by the water pressure. Since the blocking was revealed to originate from the stagnation of the snow cluster, the criterion at on orifice in a horizontal pipe was investigated experimentally. With pipe diameter D=47∼90 mm and the areal contraction ratio K=0.068∼0.27, the dependence of the critical flow velocity V_st (below which snow clusters were arrested at the orifice) on D, on K, on snow volume fraction C in discharge, and on the property of snow was made clear as follows.
(1) When C<C^*, where C^* is 0.15 and 0.12 for granulated snow and fresh snow respectively, V_st is inversely proportional to D and independent of C. When C>C^*, snow clusters almost fill the pipe and V_st is inversely proportional to D and proportional to C. While, the influence of K on V_st is not significant over the whole experimental range of C.
(2) Fresn snow is apt to stagnate, and the critical values of DV_st with C<C^* and DV_st/C with C>C^* for fresh snow are 1.4 and 2 times the corresponding ones for granulated snow.
(3) Blocking is avoidable by applying the critical values of DV_st or DV_st/C obtained in this work as the criterion of stagnation.