Chapter 3 - Fluid flow

Abstract

The chapter focuses on the fluid flow. Transportation of fluids is important in the design of chemical process plants. In the chemical process industries (CPI), pipework and its accessories, such as fittings, makeup 20% to 30% of the total design costs and 10% to 20% of the total plant investment. The aim in the design of the fluid flow is to choose a line size and piping arrangement that achieve minimum capital and pumping costs. Constraints on pressure drop and maximum allowable velocity in the process pipe is to be maintained. The flow of compressible fluids through pipelines and other restrictions is often affected by changing conditions of pressure, temperature, and physical properties. The densities of gases and vapors vary with temperature and pressure. Determining the maximum fluid flow rate or pressure drop for the process design often has a dominant influence on the density. As the pressure decreases because of piping and component resistance, the gas expands and its velocity increases. A limit is reached when the gas or the velocity cannot exceed the sonic or critical velocity. Even if the downstream pressure is lower than the pressure required in reaching the sonic velocity, the flow rate can still not increase above that evaluated at the critical velocity.