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A discrete population balance equation for binary breakage

The numerical solution of the population balance equation is frequently achieved by means of discretization, ie, by the method of classes. An important concern of discrete formulations is the preservation of 2 chosen moments of the distribution, eg, numbers and mass, while remaining flexible on the grid and kernels applied. Existing formulations for breakage are either able to perserve only one moment or restricted by the choice of grid and kernels. Two types of kernel functions for the description of breakup rate exist, ie, total breakup model and partial breakup model. The first type states the total breakup rate of a mother particle and requires a daughter size distribution function. The other type gives the breakup rate between a mother and a daughter particle directly. Existing formulations are known to work well for the former type but inefficiently for the latter one due to the need of additional numerical integrations. The particular focus of the present work lies in developing an efficient formulation for this type of kernels. A discrete formulation of the breakup terms due to binary breakage is proposed, which allows a direct implementation of both types of breakup kernels and an efficient solution of the population balance equation, making it favorable for the coupling to computational fluid dynamics codes. The results for a pure breakage process obtained by using the new formulation and various kernels are compared with those by a reference formulation as well as analytical solutions. Good agreement is achieved in all test cases, and numerical efficiency of the new formulation for partial breakup models is evidenced.