Perforated tubes are widely used in nuclear industries for many critical process and regulatory purpose. In pressurized heavy water reactors (PHWRs), perforated tubes are used in moderator system, in shutdown system for poison injection and in reactivity mechanism for housing the safety bank inside the core. In the moderator system and in poison injection loop the flow of fluid through perforated tubes match the requirement of the system. One is a steady state flow and the other is transient flow. The design of perforated tube involves arriving at the size of the holes, its spacing along the length and in the circumference. For PHWRs, the design is validated by rigorous experimentation. The paper offers a simplified analytical method along with detail theoretical steps required in arriving at the design of perforated tubes that can meet the end objective. For existing tubes, the given formulations can be used for estimating the flow profile. The paper presents case study of predicted flow through perforated tube and its validation by experimental results.