R&AC Lecture 20 - Lesson 20 Rotary, Positive...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Lesson 20 Rotary, Positive Displacement Type Compressors Version 1 ME, IIT Kharagpur 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The specific objectives of this lecture are to: 1. Discuss working principle and characteristics of a fixed vane, rolling piston type compressor ( Section 20.1 ) 2. Discuss working principle and characteristics of a multiple vane, rotary compressor ( Section 20.2, 20.3 ) 3. Discuss working principle and characteristics of a twin-screw type compressor ( Section 20.4.1 ) 4. Discuss working principle and characteristics of a single-screw type compressor ( Section 20.4.2 ) 5. Discuss working principle, characteristics and specific advantages of a scroll compressor ( Section 20.5 ) At the end of the lecture, the student should be able to 1. Explain with schematics the working principles of rotary fixed and multiple vane type compressors, single- and twin-screw type compressors and scroll compressors. 2. Explain the performance characteristics, advantages and applications of rotary, positive displacement type compressors. 20.1. Rolling piston (fixed vane) type compressors: Rolling piston or fixed vane type compressors are used in small refrigeration systems (upto 2 kW capacity) such as domestic refrigerators or air conditioners. These compressors belong to the class of positive displacement type as compression is achieved by reducing the volume of the refrigerant. In this type of compressors, the rotating shaft of the roller has its axis of rotation that matches with the centerline of the cylinder, however, it is eccentric with respect to the roller (Figure 20.1). This eccentricity of the shaft with respect to the roller creates suction and compression of the refrigerant as shown in Fig.20.1. A single vane or blade is positioned in the non-rotating cylindrical block. The rotating motion of the roller causes a reciprocating motion of the single vane. Version 1 ME, IIT Kharagpur 2
Background image of page 2
Cylinder block Roller suction discharge Discharge valve Fig.20.1 : Working principle of a rolling piston type compressor As shown in Fig.20.1, this type of compressor does not require a suction valve but requires a discharge valve. The sealing between the high and low pressure sides has to be provided: - Along the line of contact between roller and cylinder block - Along the line of contact between vane and roller, and - between the roller and end-pates The leakage is controlled through hydrodynamic sealing and matching between the mating components. The effectiveness of the sealing depends on the clearance, compressor speed, surface finish and oil viscosity. Close tolerances and good surface finishing is required to minimize internal leakage. Unlike in reciprocating compressors, the small clearance volume filled with high-pressure refrigerant does not expand, but simply mixes with the suction refrigerant in the suction space. As a result, the volumetric efficiency does not reduce drastically with increasing pressure ratio, indicating small re-expansion losses. The compressor runs smoothly and is relatively quiet as the refrigerant flow is continuous. Version 1 ME, IIT Kharagpur
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/29/2012 for the course CHEMICAL 302 taught by Professor Nptel during the Spring '12 term at Birla Institute of Technology & Science.

Page1 / 15

R&AC Lecture 20 - Lesson 20 Rotary, Positive...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online