The present application discloses a cassette assembly including an inlet cassette plate, an outlet cassette plate, and a separation layer disposed therebetween. The inlet cassette plate defines an inlet flow path and an inlet channel extending therefrom. The outlet cassette plate is configured to be arranged in a stack with the inlet cassette plate and defines an outlet flow path and an outlet channel extending therefrom. The separation layer extends from a first lateral end to a second lateral end. The inlet flow path is configured to be in fluid communication with the outlet flow path through the separation layer. The inlet channel defines an effective inlet surface area of the separation layer and the outlet channel defines an effective outlet surface area of the separation layer. The effective inlet surface area defines a first width towards the first lateral end and a second width towards the second lateral end.