Mal-distribution of gas-solid flow through identical parallel paths

Abstract

Two-phase flow in identical parallel paths is associated with various industrial applications in which the two phases are distributed among parallel branches, with common inlet and outlet manifolds. Evidence in the literature shows that the distribution of multi-phase flow travelling through identical parallel paths can be significantly nonuniform. This may have many harmful operating consequences in practice. In order to provide a better understanding of this fluid mechanics phenomenon, a fundamental analytical and numerical study is performed on the distribution of gas-solid pneumatic flow passing across a ‘Y branch’. While many steady-state gas-solid distribution solutions, including a uniform distribution, are the outputs of the governing equations, instability analysis is performed to examine the stability of the solutions. In addition, the behaviour of the system is analysed using computational fluid dynamics. The results indicate that the uniform distribution is the stable output in this case. Next the distribution of gas-solid flow through identical parallel cyclones is investigated based on an analytical model which includes a semi-empirical equation from the literature for cyclone pressure drop. Using the proposed model, many steady-state distribution solutions are obtained. The solution with maximum energy consumption is considered as the unlikely solution of the system. The results indicate that the nonlinearity of the system can cause the distribution to be non-uniform for high solids loadings, whereas lower loadings will result in distributions that are uniform, or so close to being uniform that experimental results will not be able to distinguish difference between the flows. Moreover a number of experimental studies were carried out for a pair of identical standard cyclones of diameter 101.6 mm on the distribution of dilute gassolid flow. The results are compared with the proposed cyclone model. The model can be used for multi-paths (>2) as well. Finally, available techniques, to make the distribution of gas-solid flow through parallel paths uniform, are presented.