Control of a Heat Exchanger

Control of a Heat Exchanger


  • A Temperature Indicator
  • A Flow Indicator - Orifice Meter
  • A Control Valve
  • A Temperature Controller
  • A Flow Controller


This shows a typical cascade control scheme of a heat exchanger. The aim is to keep T2 as close to the setpoint as possible.

  • Measured variables
    • flow of material inside tubes
    • temperature of material in shell
  • Manipulated variable - flow of material in tube
  • Disturbances
    • flow through shell
    • flow through tubes
    • temperature through tubes
    • change in temperature T1


An increase in T2 can be caused by

  • Increase in T1
  • Decrease in F
  • Increase in temp through tubes
  • Decrease in flow through tubes - assume that it is cooling water in tubes

To compensate the flow through the tubes should be increased. However, there is a second loop which compensates for changes in the flowrate.

The TC (Primary Loop) detects changes in the temperature brought about by changes in T1 , F or the temperature in the tubes. The FC (Secondary Loop) detects changes in the cooling water flow and hence eliminates anticipated effects on the temperature T2 .