3.The size and geometry of a fan with backward facing blades is shown in figure Q3.The fan runs at 1500 rev/min. The inlet air pressure is 1 bar and inlet

temperature is 20°C and the flow through the fan can be considered to be incompressible. At the ideal fan speed the air enters the fan without shock (the flow is smooth onto the blades) and with zero inlet whirl velocity. Slip occurs in the fan such that the ratio of actual to ideal exit whirl velocity is 0.85. You may assume that the blades have negligible thickness. a) Sketch the inlet and exit velocity diagrams. b) Calculate the ideal volume flow rate, the power required to drive the fan and the total air pressure rise (in mm H2O).[9 marks] c) It is planned to use the same fan in a pressurised heating process where the air inlet pressure and temperature at inlet will be 1.5 bar and 120°C and the fan volume flow rate needs to be 20% less than that calculated in b). The manufacturer says that can be achieved by reducing the speed of the fan.What should be the new speed of the fan and how will this affect the powe rrequired and the total pressure rise?[6 marks] d) Briefly describe what other options or modifications are there for reducing the flow rate of this fan as required in c)?[5 marks]