What is the flow direction during cross-flow filtration?

In cross-flow filtration, the flow direction is primarily parallel to the filter membrane rather than perpendicular. This method involves liquid, often referred to as the feed stream, traveling along the surface of the filter. As the liquid moves across the filter, it helps to carry away the particles and solutes, preventing the filter from clogging.

When considering the options, the correct flow direction indicated in the answer refers to liquid moving horizontally over the surface of the filter. This orientation allows for the effective separation of particles while minimizing fouling, which is a common challenge in filtration processes. The movement either left to right or right to left (the specifics of horizontal movement) symbolizes the cross-flow nature of this filtration method, ensuring that the liquid continually sweeps away accumulated particles and enhances the efficiency of the filtration system.

In contrast, upward flow paths through the filter or inward directions towards the filter do not accurately represent the cross-flow operation, as these would typically describe more traditional dead-end filtration methods where the flow directly penetrates the filter, increasing the likelihood of blockage and reduced efficiency.