RACTest rig.docx

8/14/2019 RACTest rig.docx

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INSTRUCTION MANNUAL

OF

RECIPROCATING AIR COMPRESSOR TEST

RIG


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RECIPROCATING AIR COMPRESSOR TEST RIG

CONTENTS: Page No.

1.0 Theory 03

2.0 Specifications 04

3.0 Objectives 04

4.0 Measurements 05

5.0 Suggested Experimental work 05

6.0 Results and Discussions 05

7.0 Sample Data Sheet 07

8.0 Appendix-l: Critical data of Experimental set-up 07


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RECIPROCATING AIR COMPRESSOR TEST RIG1.0 THEORY:

The function of a compressor is to take a definite quantity of fluid (usually a gas, and most often air)

and deliver it at a required pressure. The most efficient machine is one, which will accomplish with

the minimum input of mechanical work. Both reciprocating and rotary positive displacement

machines are used for a variety of purposes. However, here we are concerned only with reciprocatingmachines.

Terminology:

1. Single acting compressors are those compressors in which suction, compression and delivery ofa gas take place on one side of the piston and we have one cycle per revolution of the crank-

shaft.

2. Double acting compressors are those compressors in which suction, compression and delivery ofair take place onboth the sides of the piston and we have two cycles per revolution of the crank-

shaft.

3. Single stage compressors are those compressors in which the compression of air from the initialpressure to the final delivery pressure is carried out in one cylinder only.

4. Multi stage compressors ire those in which the compression of air from the initial pressure to thefinal pressure is carried out in more than one cylinder. The air after compression in one cylinder

is further compressed in the second cylinder and so on.

Multistage, reciprocating air compressors are used for compressing air for very high pressures up to

1000 bar. But they have low rate of flow, limited up to 5m3/s. In a multistage air compressor, air

compressed in low-pressure cylinder is further compressed in high-pressure cylinder. For

minimum power, isothermal compressor is aimed at, inwhich case compressed air of low-pressure

stage is cooled in the intercooler to initial temperature (in perfect cooling) before it goes to high-

pressure stage.

The advantages of multistage compression are

Better volumetric efficiency. Working temperature is much lower therefore, lubrication is better and wear and tear is less. Cooling is more efficient with intercoolers and cylinder wall cooling. The cylinders are higher, only the high-pressure cylinder need be robust. They have better mechanical balance requiring smaller flywheel due to uniform torque.5. Ratio of compression is defined as the ratio of absolute discharge pressure to absolute intake

pressure.

6. Free Air is the volume delivered by the compressor measured at the pressure and temperatureof the atmosphere in which the machine is situated.

7. Displacement of compressor is the volume swept through by the first stage piston. In doubleacting compressors it is the volume swept through by the both sides of the pistons.

8. Actual capacity of a compressor is the quantity of gas actually delivered. It is expressed incubic meter of free gas per minute. The actual capacity of a compressor is always less than its

displacement.

9. The volumetric efficiency is defined as the ratio of mass of air delivered to the mass of air,which would fill the swept volume at the free air conditions of pressure and temperature. Or

it may also be defined as the volume of air delivered measured at the free air pressure and

temperature divided by the swept volume of the cylinder.


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2.0 SPECIFICATIONS:

Following are the specifications of the compressor ELGI make:

Compression Stage : Double stage

Cylinders : Two

Power : 3 H.P.

Piston Displacement : 10.69 CFM

Receiver Capacity : 220 litreWorking pressure : 12.0 kgf/C.2

Lubrication : Splash Lubrication

Diameter of LP cylinder : 70 (mm)

Diameter of H.P. cylinder SO (mm)

Stroke length 85 (mm)

Motor Speed, N 1420 (rpm)

Compressor speed 925 (rpm)

3.0 OBJECTIVE:

To determine:(i) The free air delivered by the compressor(ii) The volumetric efficiency of the compressor4.0 MEASUREMENTS:

(i) To find free air delivered by the compressor:

Free air delivered is measured with the help of a orificemeter (flow meter)

Let

M = Mass flow rate, kg/sec

Cd = Coefficient of discharge of Orificemeter

do = the diameter of smallest cross section of the flow meter, mAo = the area of smallest cross section of the flow meter, m

2

g = acceleration due to gravity

H = difference in the fluid level inthe manometer limb

Water = density of manometric fluid

Pair = density of air at the entrance to the flow meter

M =

aircorresponds to the pressure and temperature of air in the tank.

Free air delivered is given by M = PV

RT

Where P&T are the atmospheric pressure and temperature and R is the gas constant.(ii) To find volumetric efficiency of the compressor:

Volumetric efficiency = Free air delivered

Swept Volume

5.0 SUGGESTED EXPERIMENTAL WORK:

Step I: Start the compressor and allow it to run for a period of 15-20 minutes to adjust itself to the

load. Note that the delivery valve is kept open.

Step2: Record temperature T2 and pressure P2 of air after compression in the low- pressure cylinder

and temperature, T3of air after it passes through the intercooler.

Step3: Vary the opening of 'the valve, that will vary the pressure P2 and temperature T2


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6.0 RESULTS & DISCUSSIONS:

1. Collect the data carefully and till up the data sheet.2. Calculate, (i) free air delivered and (ii) volumetric efficiency at noted speed.3. Compute the index of compressor from the equation

Where,

P1= Atmospheric pressure

T1= Atmospheric temperature at the entry of the compressor

4. The temperature deference (T2-T3)indicates the cooling in the intercooler. Ideally T 3shouldbe equal to T1, but because of non-perfect cooling temperature would be higher than T3.

Comment on the temperature difference (Tg2-T3) as the flow rate decreases.


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7.0 SAMPLE DATA SHEET:

Name of Experiment: "To determine free air delivered by the compressor and volumetric

efficiency of the compressor."Name of the student:- Semester Batch Session

Cdof venturi meter =

Diameter of throat, do, m =

Throat area, Aom2 =

g, m/Sec2 =

Density of manometeric fluid, w, kg/m3 =

Density of air entering the compressor at ToC, kg/m3 =

Atmospheric temperature T1,oC =

Atmospheric pressure, P1, kg/cm2 =

Sr.

No.

Air temp

after LP

cylinder

T2

Pressure

after LP

cylinder

P2

Air Temp.

after inter

cooler T3

Mass

flow

rata M

Free air

delivered

Volumetric

efficiency

8.0 APPENDIX-1: Critical data of experiment

Cdof orifice meter = 0.62

Diameter of orifice, d0, m = 0.015

Throat area, A0m2 = 1.767

g, m/Sec2

= 9.81Density of manometeric fluid wkg/m

3 = 995-1000

Density of air entering the compressor at 27oC, kg/m3 = 1.20

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