Term Examination - Part 2

A fan delivers 4.7 m³/s at a static pressure of 5.08 cm of water when operating at a speed of 400 rpm. The power input required is 2.963 kW. If 7.05 m³/s are desired in the same fan and installation, find the pressure in cm of water.

• 7.62 cm
• 17.14 cm
• 11.43 cm
• 5.03 cm

A fan described in a manufacturer’s table is rated to deliver 500 m³/min at a static pressure gage of 254 cm of water when running at 250 rpm and requiring 3.6 kW. If the fan speed is changed to 305 rpm and the air handled were at 65°C instead of standard 21 °C, find the power in kW.

• 3.82 kW
• 5.08 kW
• 4.66 kW
• 5.68 kW

It is proposed to design a homologous model for a centrifugal pump. The prototype pump is to run at 600 rpm and develop 30 m head the flow rate being 1 m³/s. The model of 1/4 scale is to run at 1450 rpm. Determine the head developed discharge and power required for the model. Overall efficiency = 80%.

• 0.03776 m³/s, 09.95 m and 4.07 kW
• 0.03776 m³/s, 10.95 m and 5.07 kW
• 0.61 m³/s, 37.27 m and 6.07 kW
• 0.61 m³/s, 12.95 m and 7.07 kW

A centrifugal pump has been designed to run at 950 rpm delivering 0.4 m /s against a head of 16 m. If the pump is to be coupled to a motor of rated speed 1450 rpm. Calculate the discharge, head and power input. Assume that the overall efficiency is 0.82 remains constant.

• 0.03776 m³/s, 09.95 m and 252 kW
• 0.03776 m³/s, 10.95 m and 262 kW
• 0.61 m³/s, 37.27 m and 272 kW
• 0.61 m³/s, 12.95 m and 282 kW

An air compressor is to compress 8.5 m³ per min from 98.56 kPa to 985.6 kPa. Assuming conditions ideal, and with n = 1.3, what will be the saving in work due to two staging?

• 4.6 kW
• zero
• 5.6 kW
• 3.5 kW

A 2-stage air compressor operates between constant pressure limits of 98.6 kPa and 1.103 MPa. The swept volume of the low pressure piston is 0.142 cu. meter. Due to failure of the cooling water supply to the intercooler, air is passed to the high pressure cylinder without reduction in temperature. Using PV^1.2 = C, determine the percentage increase in power.

• 26
• 21
• 11
• 16

A compressor of a compressed air system displaces air at 25 cubic meters per minute when the intake pressure is 101.4 kPa. Compute the time required to pump up a 9-cubic meter receiver from 550 kPa to 828 kPa if the average volumetric efficiency of the compressor is 70%.

• 1.95 minutes
• 2.84 minutes
• 1.41 minutes
• 1.82 minutes

Air is compressed in reversible compressor at an initial temperature and pressure of 28 deg. C and 95 kPa, respectively. Air leaves the compressor at 650 kPa. Compute the compressor work per unit mass.

• -221.34 kJ/kg
• -228.34 kJ/kg
• -234.34 kJ/kg
• -324.34 kJ/kg

A 12 x 14-in double-acting air compressor with 5.5% clearance operates at 150 rpm, drawing air at 14.5 psia and 85 deg. F and discharging it at 62 psia, the compression and expansion processes are polytropic with n = 1.34. Determine the volume of free air handled per minute, if atmospheric conditions are 82 deg. F and 14.7 psia.

• 210.6 cfm
• 220.6 cfm
• 230.6 cfm
• 240.6 cfm

An ideal single stage air compressor without clearance takes in air at 100 kPa with a temperature of 16 deg. C and delivered it at 413 kPa after isentropic compression. What is the discharge work done by the compressor in kJ/kg?

• -59.22
• -118.44
• -72.5
• -145