This work restricts the term multiphase only to disperse flows, where one of the phases is present in the form of particles, droplets or bubbles, which are suspended within the continuous phase. The dispersed elements can vary in size. The proposed method uses the classes method in the Euler-Euler framework to handle the flow’s polydisperse nature. With this approach, every droplet/bubble/particle class is treated like a different phase in the calculation, i.e. every size class has its continuity and momentum equation. However, the pressure is shared among all phases. The derived model is tested for various polydisperse flows, which display the developed model’s capability to predict such complex dynamic behaviour. These test cases include complex bubbly flows and dense spray (where droplet sizes vary significantly).