Jabatan Kejuruteraan Loji dan AutomotifFakulti Kejuruteraan Mekanikal dan PembuatanUniversiti Tun Hussein Onn Malaysia

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Tutorial 3Reciprocating Compressor

BDA 3043 Thermodynamics IIWinardi Sani

1 Air is compressed in a single-stage reciprocating compressor from 1.013 bar and15 C to 7 bar. Calculate the indicated power required for a free air delivery of0.3 m3/min, when the compression process is as follows:

(a) isentropic

(b) reversible isothermal

(c) polytropic, with n = 1.25

What is the delivery temperature at each case?(Answers: 1.31 kW; 0.98 kW; 1.20 kW; 227.3 C ; 15 C ; 150.9 C.)

2 The compressor of Question 1 is to run at 1000 rev/min. If the compressor is single-acting and has a stroke/bore ratio of 1.2/1, calculate the bore size required.(Answer: 68.3 mm)

3 A single-stage, single-acting air compressor running at 1000 rev/min delivers airat 25 bar. For this purpose the induction and free air conditions can be taken as1.013 bar and 15 C, and the FAD as 0.25 m3/min. The clearance volume is 3%of the swept volume and the stroke/bore ratio is 1.2/1. Calculate:

(a) the bore and stroke

(b) the volumetric efficiency

(c) the indicated power

(d) the isothermal efficiency

Take the index of compression and re-expansion as 1.3(Answers: 73.2 mm; 87.8 mm; 67.7%; 2kW; 67.7%)

4 The compressor of Question 3 has actual induction conditions of 1 bar and 40C, and the delivery pressure is 25 bar. Taking the bore as calculated in Question3, calculate the FAD referred to 1.013 bar and 15 C, and the indicated powerrequired. Calculate also the volumetric efficiency and compare it with that ofQuestion 3.(Answers: 0.226 m3/min; 1.98 kW; 61.2 %; 67.7 %)

5 A single-acting compressor is required to deliver air at 70 bar from an inductionpressure of 1 bar, at the rate of 2.4 m3/min measured at free air conditions of1.013 bar and 15 C. The compression is carried out in two-stages with an idealintermediate pressure and complete intercooling. The clearance volume is 3 %of the swept volume in each cylinder and the compressor speed is 750 rev/min.The index of compression and re-expansion is 1.25 for both cylinders and thetemperature at the end of the induction stroke in each cylinder is 32 C. Themechanical efficiency of the compressor is 85 %. Calculate:

2Jabatan Kejuruteraan Loji dan AutomotifFakulti Kejuruteraan Mekanikal dan PembuatanUniversiti Tun Hussein Onn Malaysia

(a) the indicated power required

(b) the saving in power over single-stage compression between the same pres-sure

(c) the swept volume of each cylinder

(d) the required power output of the drive motor.

(Answers: 22.74 kW; 5.98 kW; 0.00396 m3; 0.000474 m3; 26.75 kW)

6 Show the volumetric efficiency of an ideal single-stage reciprocating compres-sor is given by:

vol = 1 V3Vs

([p2p1

]1/n 1

)(1)

where V3 and Vs are the clearance and swept volume, respectively.