This paper is concerned with the effects of fine particle concentrations in a carrier fluid on the pressure fluctuation and water hammer phenomena in coarse solid-liquid flows. When fine particles were mixed with the carrier fluid, pressure fluctuations were reduced. This is due to the suppression of fluid turbulence. However, there was little effect of the fine particles on the reduction of pressure fluctuations at lower velocities because the movement of dunes dominated the pressure fluctuation, considerably suppressing the fluid turbulence. It was discovered from a power spectral density function that the existence of fine particles in the carrier fluid reduced the frequency of pressure fluctuations. The maximum surge pressure, due to water hammer, increased in relation to additions of the fine particle concentrations, resulting from the increase in mixture density. It is advantageous to the reduction of pressure loss and pressure fluctuations to mix fine particles with the carrier fluid. However, the maximum surge pressure increases when fine particles are mixed with the carrier fluid. Therefore, the concentrations of fine particles should be determined by taking into account both of the above mentioned effects.
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