DEPARTMENT OF MECHANICAL ENGINEERING

FACULTY OF ENGINEERING

NATIONAL DEFENCE UNIVERSITY OF MALAYSIA

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Muhamad & Rizal – Thermodynamic Laboratory – Sep 20111

EML 3822LABORATORY III

VARIATION OF PERFORMANCE OF A RECIPROCATING AIR COMPRESSOR WITH PRESSURE

THERMODYNAMICS LABORATORY

Marks:

/100

1.0 TITLE

Variation of Performance of a Reciprocating Air Compressor with Pressure

2.0 OBJECTIVE

To investigate the effect of delivery pressure on the performance of a reciprocating air compressor.

3.0 INTRODUCTION

Air is an expensive substance and dangerous when used at high pressures. For this reason, most applications are confined to things requiring low pressures (10 bar or lower) but there are industrial uses for high pressure air up to 100 bar. The common source of the air is the compressor. Its function is to draw in air from the atmosphere and produce air at pressures substantially higher. This laboratory is mainly about reciprocating compressor which is probably the most versatile of all types of compressors, mainly for high pressures.

4.0 APPARATUS AND METHOD

Set up Cussons P9050 Two-Stage Reciprocating Air Compressor as a single stage air compressor operating into both air receivers by removing the drive belt from the second stage compressor, opening the bypass valves to bypass the second stage compressor, closing the bypass around the water cooler and opening the interconnecting valve to the second air receiver.

For a quick test close the discharge valve, operate the compressor at constant speed ND and take readings whilst the air receivers charge. At increments of air receiver pressure of 0.5 bar, record the following:

Air compressor discharge pressure Pc

Inlet air flow orifice manometer reading hDynamometer load LD

When the air receiver pressure reaches the value pre-set on the off-loading valve, both inlet values will be held open and compressor delivery will cease. A reading of the dynamometer load in this condition can then be used as a measure of the drive belt and cylinder friction power which can then be deducted from the measurement of dynamometer power output to give a measure of the compressor air power input W C.

Muhamad & Rizal – Thermodynamic Laboratory – Sep 20112

5.0 RESULTS

Calculate and tabulate each set of results (referring to the working equations) of the following parameters:-

Absolute pressure P2

Inlet air flow QC

Volumetric efficiency ηvol

Dynamometer power output W D

Compressor power input W C

Ideal isothermal power input W T

Ideal isentropic power input W S

Isothermal thermal efficiency ηT

Isentropic thermal efficiency ηS

6.0 ANALYSIS

Plot graphs of the discharge pressure P2 against the inlet air flow QC, and plot P2 against the power outputs W C, W D, W S and W T, finally plot the efficiencies ηvol, ηS

and ηT also against P2.

Comment on what do you understand from each of the graphs plotted.

7.0 DISCUSSIONS

a. Why is the isothermal power input lower than the isentropic power input?

b. Suggest how to increase the compressor (Isothermal thermal) efficiency, ηT.

c. Comment on your experimental results.

8.0 CONCLUSION

List major lessons learnt from the experiment. .

Muhamad & Rizal – Thermodynamic Laboratory – Sep 20113