Discharge pressure of the compressor
Course:- Mechanical Engineering
Reference No.:- EM13346

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Question 1

A compressor installed at a whalf (for loading container ships) is able to provide 6 bar gpressure into the pressure reciever. The compressor is moved to a site that is 5000 ft above sea level (atmospheric pressure 0.85 bar.a) in the mountains. What is the discharge revised discharge pressure (guage pressure) of the compressor ?

Assume there is no change in temperature.

Part (a)

Is the assumption of change in temperature valid for calculating the discharge pressure of the compressor ?

Part (b)
The temperature at the whalf is 35 oC and in the mountains is 19oC, what is the reduction in volumetic output from the compressor ?

Question 2

The system on site is a pressure sand filter, with a service curve. The filter is backwashed using the feed pump, at a higher flow rate, shown as backwash curve.

Service duty point : 3 m3/h
Backwash duty point : 9 m3/h

Part (a)

What is the speed of the pump to achieve the service and backwash flow rates ?

Part (b)

What would be the best way to control the speed of the pump? Why ?

Part (C)

The pump is set up as a fixed speed constant pressure system (pump runs once system pressure reaches 550 kPa, turns off, when pressure drops to 450 kPa plant re-starts) to maintain a system pressure of 500 kPa at the discharge of the pump. What would be the service and backwash rates from the pump ?

Question 3

We have a reciprocating compressor operating at 800 rpm. Suction pressure and discharge pressure are held constant by other systems that have nothing to do with the compressor. We increase the speed from 800 to 840 rpm (a 5% increase).

• Part a what is the change in flow rate through the compressor Flow increases by (840/800) or 1.05, or 5% increase.
• Part b what is the change in pressure rise through the compressor.
• Part c what is the change in power that must be delivered to the compressor

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