Eulerian modeling of gas-solid multiphase flow in horizontal pipes

Abstract

Gas-solid flows in pipes are common in industrial applications, such as pneumatic conveying, fluidized beds, pulverized coal combustion, spray drying and cooling, etc. The prediction of the pressure drop is essential in design of the systems, while the addition of granular particles to the gas flow causes an enhancement of heat transfer from the heated wall to the bulk fluid. The fully developed and overall pressure drop and overall heat transfer prediction in gas-solid flows in horizontal pipes have been investigated numerically using the Eulerian-Eulerian (E-E) approach, accounting for four-way coupling. The Gidaspow drag model with the partial differential equation form of granular temperature model has been used for the simulations. For the prediction of fully developed pressure drop, fine particles (fly ash of size 20 to 150 μm) with the solid volume fractions of up to 0.1 have been considered. For the prediction of overall pressure drop and heat transfer, fine particles (flyash of size 30 to 50 μm) have been used in the simulations. A grid independence test has been conducted to get the accurate numerical results. The numerical results are in good agreement with the bench mark experimental data for the pressure drop and heat transfer. The effects of particle diameter, particle density, solid volume fraction, and gas phase Reynolds number on the fully developed pressure drop in gas-solid flows in a horizontal pipe of internal diameter 30 mm and length 3000 mm have been studied. It has been found that the pressure drop increases with an increase in the particle diameter, and reaches a peak value. After reaching the peak value, the pressure drop gradually starts to decrease. The pressure drop increases with increase in the particle density, solid volume fraction, and gas phase Reynolds number. Furthermore, the effects of solid particles on the overall (entrance as well as the fully developed region) pressure drop and heat transfer in gas-solid flows in a horizontal pipe of internal diameter 55 mm and length 5500 mm have been investigated. It has been observed that the pressure drop data are consistent. It increases with the particle size, gas phase Reynolds number, and solid loading ratio (SLR), under the present study operating conditions. The heat transfer data, i.e., the two-phase Nusselt numbers are not consistent with the gas phase Reynolds numbers. The heat transfer increases with respect to the gas phase Reynolds number fora low SLR. However, for the higher SLRs, the heat transfer first increases/decreases and then decreases/increases (after reaching a peak/nadir) with the gas phase Reynolds number. The heat transfer increases with increase in the SLR. Finally, a correlation for the two-phase Nusselt number has been developed using the non-linear regression analysis, which shows an accuracy of ±15%.