2stage air comp appratus fpe001(new)

7/28/2019 2Stage Air Comp Appratus FPE001(New)

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FPE.001 TWO STAGE RECIPROCATING AIR COMPRESSOR TEST RIG

Aim of the Experiment:

To determine the volumetric efficiency and isothermal efficiencies of two stagereciprocating air compressor at various delivery pressures.

Introduction and Theory

The two stage reciprocating compressor consists of a cylinder, piston, inlet and

exit valves which is powered by a motor. Air is sucked from atmosphere and

compressed in the first cylinder (Low pressure) and passed to the second cylinder(High pressure) through an inter cooler.

In the second cylinder, air is compressed to high pressure and stored in the air

tank. During the downward motion of the piston, the pressure inside the cylinderdrops below the atmospheric pressure and the inlet valve is opened due to the

pressure difference. Air enters into the cylinder till the piston reaches the bottomdead center and as the piston starts moving upwards, the inlet valve is closed

and the pressure starts increasing continuously until the pressure inside thecylinder above the pressure of the delivery side which is connected to the receiver

tank. Then the delivery valve opens and air is delivered to the air tank till the TDCis reached. At the end of the delivery stroke a small volume of high pressure air is

left in the clearance volume. Air at high pressure in the clearance volume startsexpanding as the piston starts moving downwards up to the atmospheric pressure

and falls below as piston moves downward. Thus the cycle is repeated. Thesuction, compression and delivery of air take place in two strokes / one revolutionof the crank

Apparatus Description

The two-stage air compressor consists of two cylinders of v type. Thecompressor is driven by an AC motor. Air is first sucked into the low pressure (LP)cylinder and it is compressed and delivered at some intermediate pressure. The

compressed air is then cooled in the intercooler and the same is then sucked bythe high pressure (HP) cylinder. Compressed air is the finally discharged to the

receiver tank.

An orifice plate is mounted on one side of the air tank and which is connectedwith a manometer for the measurement of air flow rate. One side of the air tank

is attached with a flexible rubber sheet to prevent damage due to pulsating air

flow. A pressure gauge is mounted on the air tank to measure the air tankpressure. The tank pressure can be regulated by adjusting the delivery valve. A

pressure switch is mounted on the air tank to switch off the motor power supply


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automatically when the pressure inside the tank raises to the higher limit and to

avoids explosion.

Compressor Type: Two Stage Two Cylinder with finned intercooler L.P Cylinder: 76 mm bore Dia Stroke 127 mm

Motor: 3 HP; 3 phase

Max Working Pressure: 10 kg/cm2

Experimental Procedure

1. Ensure that there is sufficient oil in the crank case of the compressor2. Fill the manometer with water up to half level.

3. Keep delivery valve in closed position.4. Start the compressor and allow it to get stabilized.

5. Maintain pressure of air inside receiver constant, by adjusting delivery valve.

6. With delivery pressure constant, measure motor speed using tachometer

and note it down.7. With the same delivery pressure, note in the observation table intake

temperature, intermediate temperature, intermediate pressure, deliverytemperature, water manometer readings and delivery pressure.

8. Repeat the same procedure for the different numerical values of delivery

pressures.

Observation Table:

Sr.No. Speed(rpm) ManometerReading

hw (m)

Timefor 10

Impulse

ofEnergymeter

SuctionCondition After Stage 1

st

of Compressor AfterIntercooling DeliveryConditionP1

(kg/cm2)T1(C)

P2(kg/cm2)

T2(C)

P3(kg/cm2)

T3(C)

P4(kg/cm2)

T4(C)

CALCULATION


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1) Air Flow Rate : (Free Air Delivery)

Qa = Cd * A * V

Where, A = Area of Orifice meter (Dia 10mm) = m2

V = Velocity of Air = ( 2 g h a )Cd=Co-efficient of Discharge for given orifice meter 0.64

Now,h a = h w * w

a

hw = Diff in Water Manometer

a = 1.293 * 273 = kg/m3

(273 + T1)Since Density of Air at 273 K is 1.293 kg/m3

Qa = Cd*A* ( 2 g h w * w )a

= m3/sec

2)Volumetric Efficiency:

vol = Free Air Delivered in m3 /sec

Swept volume of Comp.

Where, Swept Volume of Comp. = *D2

*L* N4 60

= m3 / sec

Where, D = Bore Dia. 76 mm

L = Stroke Length 127 mmN = Sped of comp. in rpm

3)Isothermal Efficiency:-

= Isothermal work doneActual work done

Abs. Pressure of Before 1st stage Comp. P1 = 1.01325 * 105 N / m2

Abs. Pre. after 1st stage,P2 = _____* 9.81 *104 + 1.01325 * 105 N / m 2


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Abs. Pre. Before 2nd stage,P3 = _____* 9.81 *104 + 1.01325 * 105 N / m 2

Abs. Pre. after 2nd stage,P4 = _____* 9.81 *104 + 1.01325 * 105 N / m 2

Isothermal Work done = P1 V1 In (P4/P1)

= watts

V1 = Air Flow rate at Intake (Qa) in m3

/sec

Actual .work done :- 10 * 3.6 * 106 * 0.75

K * t

Where, K = Energy meter constant = 1600 imp/kwHt = Time for 10 impulse of Energy meter

Motor Efficiency is 0.75

4)Poly Tropic Index,(n)

For First stage, T1/T2 = (P2/ P1)n-1/n

For Second Stage, T3/T4 = (P4/P3)n-1/n

5)Compression Ratio

First Stage Compression Ratio r1 = P2/P1

Second Stage Compression Ratio r2 = P4/P3

Overall Compression Ratio r = P4/P1

Graphs:-

Plot the for

Comp. Ratio versus Vol. EfficiencyComp. Ratio versus Iso. Efficiency

Result Table:-

Sr.

No.

Delivery

Pressure

First Stage

CompressionRatio r1

Second

StageCompressionRation r2

Overall

CompressionRatio r

Volumetric

Efficiency

Isothermal

Efficiency

SAMPLE READINGS


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Observation Table:

Sr.

No.

Speed

(rpm)

Manometer

Reading

hw (m)

Time

for 10

Impulseof

Energy

meter

Suction

Condition

After Stage

1st of

Compressor

After

Intercooling

Delivery

Condition

P1(Atm)

T1(C)

P2(kg/cm2)

T2(C)

P3(kg/cm2)

T3(C)

P4(kg/cm2)

T4(C)

1 525 0.06 15 1.01325 30 1.6 94 2 56 7 94

CALCULATION

1)Air Flow Rate : (Free Air Delivery)A = Area of Orifice meter (Dia 10mm) = 3.15 x 10-5 m2

a = 1.293 * 273(273 + T1)

a = 1.293 * 273 = 1.1649 kg/m3

(273 + 30)

Now,h a = h w * w = 0 . 0 6 * 1 0 0 0 = 5 1 . 5 0 3

a 1 . 1 6 4 9

Qa = C d * A * ( 2 g h a )

Here Cd=Co-efficient of Discharge for given orifice meter 0.64

= 1.59 x 10-3 m3/sec

2)Volumetric Efficiency:

Where, Swept Volume of Comp. = *D2 *L* N4 60

= 5.04 x 10-3 m3/sec

Where, D = Bore Dia. 76 mmL = Stroke Length 127 mm


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N = Sped of comp. in rpm = 525

vol = Free Air Delivered in m3/sec = 0.3169 or 31.69%

Swept volume of Comp.

3)Isothermal Efficiency:-Abs. Pressure of Before 1st stage Comp. P1 = 1.01325 * 10

5 N / m2

Abs. Pre. after 1st stage,P2 = 1.6 * 9.81 *104 + 1.01325 * 105

= 258285 N / m 2Abs. Pre. Before 2nd stage,P3 = 2* 9.81 *10

4 + 1.01325 * 105

= 297525 N / m 2Abs. Pre. after 2nd stage,P4 = 7* 9.81 *10

4 + 1.01325 * 105

= 788025 N / m 2

Isothermal Work done = P1 V1 Ln (P4/P1)= 331.924 watts

Here V1 = Air Flow Rate = 1.59 x 10-3 m3/sec

Actual .work done :- 10 * 3.6 * 106 * 0.75

K * t

Where, K = Energy meter constant = 1600 imp/kwH

t = Time for 10 impulse of Energy meterMotor Efficiency is 0.75

Actual .work done :- 10 * 3.6 * 106 * 0.75 = 11251600 * 15

= Isothermal work done = 0.295 or 29.5%Actual work done

4)Poly Tropic Index,(n)For First stage, T1/T2 = (P2/ P1)

n-1/n

Putting Values solving Equation n = 0.83 (approx.)

For Second Stage, T3/T4 = (P4/P3)n-1/n


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Putting Values solving Equation n = 0.9 (approx.)

5)Compression Ratio

First Stage Compression Ratio r1 = P2/P1 = 2.54

Second Stage Compression Ratio r2 = P4/P3 = 2.64

Overall Compression Ratio r = P4/P1 = 7.77

Sr.No.

DeliveryPressure

First StageCompression

Ratio r1

SecondStage

Compression

Ration r2

OverallCompression

Ratio r

VolumetricEfficiency

IsothermalEfficiency

1 7 kg/cm2 2.54 2.64 7.77 31.69% 29.5%

2stage air comp appratus fpe001(new)

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