A mechanistic approach to laminar flow through an abrupt enlargement

The flow of highly viscous fluids in pipeline fittings has previously been of little interest to mechanical engineers. More recently it has become more topical because design methods for emergency pressure relief systems on polymerization reactors need to be improved. The abrupt enlargement is of particular importance in this respect, because it regularly occurs on pipeline systems and is also an integral component part of other pipeline fittings such as orifice plates and valves. The energy loss mechanisms that occur in an abrupt enlargement will therefore occur in many other pipeline fittings. A semi-empirical, mechanistic approach was used to develop a simple, one-dimensional flow model that allowed these energy loss mechanisms to be understood. The energy loss predictions from the model compared well with data available in the open literature. The model was used to generate some simple design equations. © IMechE 1998.