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COMPARISON OF ROTARY AND RECIPROCATING COMPRESSORS
The comparison of rotary and reciprocating compressors is given in Table 13.1. Table 13.1 Comparison of rotary and reciprocating compressors Example 13.3 Free air of 30 m3/min is compressed from 101.3 kPa to 2.23 bar in roots blower. Determine the power required and the isentropic efficiency. Solution The p − V diagrams for roots blower is shown in Fig.…
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Example 13.2
A rotary vanes blower works between the pressure limits of 1 bar and 1.8 bar, and gives 5 m3/min of free air delivered when running at 240 rpm. Determine the power required to drive the blower when (a) ports are so placed that there is no internal compression and (b) when the ports are so…
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Example 13.1
Free air of 25 m3/min is compressed from 1 bar to 2.5 bar. Calculate the indicated power required if the compression is carried out in (a) roots blower and (b) vanes blower. Assume that there is 20% reduction in volume before the backflow occurs. Also, calculate the isentropic efficiency in each case. Solution The p−V diagrams for…
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WORKING PRINCIPLE OF DIFFERENT ROTARY COMPRESSORS
In positive displacement type rotary compressors, the air is compressed by entrapping it between the reduced space of two sets of engaging surfaces. The pressure rise is either by backflow of air, as in the case of roots blower, or by both squeezing action and backflow of air, as in the case of vane type.…
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INTRODUCTION
In a rotary compressor, the compression of air is achieved due to the rotating blades fitted in a rotor. It requires less starting torque as compared to reciprocating compressors because of direct coupling with the prime over. Usually, rotary compressors operate at high speed and supplies higher quantity of air than reciprocating compressors. Rotary compressors…
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CONTROL OF COMPRESSOR
In order to balance the demand and supply of air, it is necessary to incorporate devices for the compressor control. The common methods of control are as follows: Example 12.1 A single-stage reciprocating air compressor is required to compress 72 m3 of air per minute from 15°C and 1.0 bar to 8 bar pressure. Find the…
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HEAT REJECTED
If the air is cooled to the initial temperature, then there is no change in internal energy per kg mass of air, and all the work done is rejected to the cooling medium party during the compression process and the remaining after compression at constant pressure. Now, q1–2 = du + w1–2 However, du = 0 For a single-stage compressor, the heat…
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INDICATOR DIAGRAM
The theoretical of p − V diagram for the single-stage reciprocating compressor is represented by 1–2–3–4–1 in Fig. 12.17. The actual indicator diagram is 1–2′–3–4′–1. The difference between the actual and theoretical indicator diagrams is due to the intake and discharge losses. The intake losses include the friction losses in pipe, friction loss in inlet valve, and valve inertia loss.…
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AIR MOTORS
The working of an air motor is similar to that of air compressor. High pressure air is admitted to the motor cylinder through a mechanically operated inlet valve and drives the piston in the forward direction. After a part of the stroke of the piston has been performed, the air supply is cut-off and the…
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INDICATED POWER OF A COMPRESSOR
where A = area of the cylinder, m2 L = length of stroke, m N = rpm of compressor crank pm = mean effective pressure of air, Pa (N/m2) Theoretically, m.e.p. for a single-acting, single-stage compressor is, where ηv = volumetric efficiency of compressor Using indicator card, the m.e.p. is:
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