With saturated steam, temperature and pressure are strictly related therefore controlling the steam pressure easily regulates the temperature.Ĭonsider an application where steam at 10 bar g is supplied to a control valve, and a given mass flow of steam passes through the valve to a heat exchanger. To achieve this heat output, a certain saturated steam temperature will be required at the heat transfer surface (such as the inside of a heating coil in a shell and tube heat exchanger). Saturated steam flow through a control valveĪ heat exchanger manufacturer will design equipment to give a certain heat output. ΔTm is reduced, then the heat transfer from the steam to the secondary fluid is also reduced. The overall heat transfer coefficient (U) does not change very much during the process, and the area (A) is fixed, so if the mean temperature difference This means that a smaller difference in temperature exists between the steam and the process, so the rate of heat transfer is reduced, in accordance with Equation 2.5.3.
The steam pressure falls in the steam space and so too the steam temperature.
Steam passes through the control valve and into the steam space of the equipment where it comes into contact with the heat transfer surfaces.Steam is supplied at a specific pressure to the upstream side of the control valve through which it passes to a heat exchanger, also operating at a specific pressure.Before discussing the sizing of control valves for steam systems, it is useful to review the characteristics of steam in a heat transfer application.