Q3 An air compressor takes in air at a rate or 0.02 kg.s-1 and a specific enthalpy of 280 kJ.kg-1. The specific enthalpy at the exit of the compressor is 401 kJ.kg-1. To achieve this, the compressor requires work to be input at a rate of 2.75 kW.
A Use a control volume approach and sketch to illustrate the energy inputs and outputs of the compression process. 5 marks
B The First Law of Thermodynamics states that for a flow-through system, the total energy inputs into that system will be equal to the total energy outputs of that system. There is an imbalance in the data provided, use the First Law to propose what may be missing from the data along with a description of how the missing energy component may have been generated. 8 marks
C
The mass flow rate of the air through the compressor, measured in kg.s-1, will be constant. Is this also true of the volume flow rate, measured in m3s-1? Explain the reason for your answer 3 marks
Total 16 Marks
Q4 Hydraulic presses and hydraulic jacks both work on the same fundamental principle
A Describe the process of the hydraulic press or jack. You should include the principle of pressure transmission through a fluid and how the relative cross-sectional areas of the pistons contribute to the process 8 marks
B The area of the input piston of a hydraulic device is 50 times smaller than that of the output cylinder. If the device is to lift a mass of 1000 kg, what force must be applied to the input cylinder? 4 marks
C If the load is to be raised by 0.5 m, how far must the input cylinder be moved? 4 marks
Total 16 Marks