Where is the power required, is the mass flow rate, is that shaft work, is the velocity of the fluid, describes the flow in the system (0.5 for laminar, 1 for turbulent), is the gravitational acceleration, is the change in height, is the constant volume PV work done, and is the force acting on the fluid. The result is the mechanical balance equation, below: To find the power outlet required by a pump to pressurize a fluid, an energy balance can be done on the system. For more information on different types of pumps, see Pumps. Pumps do work on fluids, causing them to increase in pressure at a constant volume, due to the assumption that liquids that enter pumps are mostly incompressible. It is therefore important to ensure the equipment is correctly specified to ensure accurate results. Different parameters of the pump or compressor can also be specified, such as efficiency, which will impact the results of the simulation. Typically, the inlet and outlet pressures are specified (pressure drop, or ΔP), rather than pump duty, because these variables are important to ensure process design specifications are met. There are different combinations of independent variables that will suffice and cause the model to converge. Like any piece of process equipment, it is necessary to specify a number of independent variables in order for the simulation to converge and produce unknown values.
There are many different types of modeling software for chemical processing, Aspen HYSYS, and Aspen Plus being well known. It is important however to ensure proper pressure is maintained throughout a chemical process so that blowback does not occur, and any fluids actually reach their destination as expected, at the proper conditions. Lowering the pressure of a system can also be useful however, such as to favor the products of a chemical reaction through Le Chatelier's principle. Typically, pressure changers are used mostly for increasing pressure, due to the fact that pressure losses occur within a system due to friction with pipes, pipe bends, valves, and other pieces of equipment. Pressure changers are any piece of equipment where the main goal is to increase or decrease the pressure of a stream.