عنوان مقاله [English]
Introduction Material conveying in the industries is carried out in the different ways. Pneumatic conveyors are widely used in industries. The special benefits of these conveyors have led them in the short term to widely used in different industries. Transfer of materials without dust dispersion, the flexibility to choose the vertical, horizontal or diagonal tubing, low maintenance costs and manpower, adequate safety and reliability during conveying at the high amounts of materials, easy and automatic control are the some benefits of the pneumatic conveying systems
Materials and Methods The mean aperture and the coefficient of variation of sugar particles were determined by sugar crystal size distribution test. It is done based on the cumulative percentages of remaining sugar content on the sieve. The mean aperture (MA) and the coefficient of variation (CV) are obtained from the chart. 7 sieves are used for testing. The percentage of remaining sugar on each sieve was calculated. The amounts of D50% and D16% were calculated following the plotting the size of the sieves versus the cumulative percentage of the remaining sugar on each sieve graph. The conveying pressure drop includes the total pressure drop required for air alone (ΔPL), the material acceleration pressure drop (ΔPA), the friction and material collision pressure drop (ΔP*z), the pressure drop due to lifting and suspension of materials (ΔPG), and bends' pressure drop (ΔPB) in Pascal. Following determination of required power (293.42 w) to run the system, with a confidence coefficient of 3, a blower with a rated power of 700 w was selected. The amount of pressure produced by the selected centrifuge fan was measured by a pitot tube embedded in the blower outlet. The outlet air velocity was measured by a pressure gauge according to the principles of the pitot tube.
Results and Discussion The treatments and their levels consisted of pipe lengths at three levels (2, 4 and 6 m), inlet air velocity at five levels (13, 16, 19, 22 and 25 m/s) and mass flow rate of sugar at three levels (160, 180 and 200 kg/h). The statistical analysis was done as a factorial based on a completely randomized design. Analysis of variance and comparison of means were done using Duncan's test at 5% level in each case. Then, the effects of the factors on pressure drop, mean aperture and coefficient of variation of particle size were investigated. Analysis of variance of data shows that the effect of conveying length, mass flow rate of sugar particles and inlet air velocity as well as their interactions and the interaction of three factors on air and sugar pressure drop is significant at 1%. In all conveying lengths, an increase in air velocity and consequently increased sugar particles' velocity at each mass flow rate causes an increase in frictional pressure drop due to the particle's collision with the wall as well as air collision with the pipe wall at each length and the sugar mass flow rate level. Also, total pressure drop has increased with mass flow rate at any velocity. Analysis of variance of data shows that the effect of conveying length, mass flow rate of sugar particles, inlet air velocity, and the interaction of mass flow rate and air velocity on qualitative properties of sugar is significant at 1% level. Considering the significance of the effects of the main factors and interactions between air velocity and mass flow rate, the effect of every main factors and the interaction of air velocity and mass flow rate on qualitative characteristics of the sample was investigated. With increasing velocity in each mass flow rate, the mean aperture and coefficient of variation significantly decreased and increased, respectively. Also, with increasing mass flow at any velocity, the mean aperture decreased and the coefficient of variation increased. By increasing the mass flow rate, the effect of the air velocity on the mean aperture reduction and increase in coefficient of variation increases, and at higher velocities, the mass flow rate effect is more pronounced.
Conclusion The length of the pipe with a reduction by 15% in mean aperture and an increase of 137.5% in coefficient of variations than the initial sugar sample had the least effect on these two qualitative properties of sugar. With an increase in air velocity from 13 to 25 m/s, MA and CV values decreased by 20.27 and increased by 17.22, respectively. The velocity of 13 m/s with a reduction of 5.19% in the mean aperture and an increase of 6.69% in coefficient of variation compared to the initial sugar sample had the least effect on the size and the particle coefficient of variation size of the particles among all 5 velocity treatments. With the increase in particle mass flow rate of 160 to 200 kg/h, MA and CV values decrease by 16.49% and increase by 14.75%, respectively. The particle density increases with the mass flow rate.