Question 2

You set out to design an automatic shower with a requirement for control of both the

flow of water and the temperature. The system specifications are as follows:

Data:

Delivered flowrate F = 15 L/min of water at 43°C by mixing hot water at 70°C with cold

water at 20°C. The system will use regulating control valves to manipulate the flows of

both the hot and cold-water streams. [Properties: pw=1000 kg/m³; Cp = 4.18 kJ/kg °C]

a) Develop a process model and determine the steady-state steam flows.

b) Calculate the respective gain elements for all pairings of controlled and

manipulated variables.

c) Calculate a relative gain array for the system (RGA) and suggest a pairing

of controlled and manipulated variables to minimise any interaction.

d) Neatly sketch your final network labelling all items using conventional

control symbols.

e) Could you suggest system modifications to make the pairing of

manipulated and controlled variables determined in part (c) more

favourable?