R&AC Lecture 24 - Lesson 24 Expansion Devices Version 1...

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Lesson 24 Expansion Devices Version 1 ME, IIT Kharagpur 1
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The specific objectives of this lecture are to: 1. Discuss the basic functions of expansion devices used in refrigeration systems and their classification ( Section 24.1 ) 2. Discuss the operating principle, concept of balance point, the effect of load variation, selection of capillary tubes using analytical and graphical methods and the advantages and disadvantages of capillary tubes ( Section 24.2 ) 3. Explain the working principle of an automatic expansion valve, its performance under varying loads and its applications ( Section 24.3 ) 4. Present a simple analysis for fluid through orifices ( Section 24.4 ) 5. Explain the working principle of a thermostatic expansion valve, its performance under varying loads, variations available such as cross-charging, external equalizer and limit charging, advantages and disadvantages of TEVs ( Section 24.5 ) 6. Explain the working principle of low-side and high-side float valves ( Section 24.6 ) 7. Explain the working principle of an electronic expansion valve ( Section 24.7 ) 8. Discuss briefly some of the practical problems with expansion devices ( Section 24.8 ) At the end of the lecture, the student should be able to: 1. Explain the basic functions of expansion devices in refrigeration systems 2. Explain the working principle and salient features of capillary tube, automatic expansion valve, thermostatic expansion valve, float type expansion valve and electronic expansion valve 3. Estimate the required length of capillary tubes using analytical and graphical methods 4. Describe advantages, disadvantages and applications of different types of expansion valves, and 5. Discuss some of the practical problems encountered in the operation of various types of expansion devices in refrigeration systems 24.1. Introduction An expansion device is another basic component of a refrigeration system. The basic functions of an expansion device used in refrigeration systems are to: 1. Reduce pressure from condenser pressure to evaporator pressure, and 2. Regulate the refrigerant flow from the high-pressure liquid line into the evaporator at a rate equal to the evaporation rate in the evaporator Under ideal conditions, the mass flow rate of refrigerant in the system should be proportional to the cooling load. Sometimes, the product to be cooled is such Version 1 ME, IIT Kharagpur 2
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that a constant evaporator temperature has to be maintained. In other cases, it is desirable that liquid refrigerant should not enter the compressor. In such a case, the mass flow rate has to be controlled in such a manner that only superheated vapour leaves the evaporator. Again, an ideal refrigeration system should have the facility to control it in such a way that the energy requirement is minimum and the required criterion of temperature and cooling load are satisfied. Some additional controls to control the capacity of compressor and the space temperature may be required in addition, so as to minimize the energy consumption.
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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.

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R&AC Lecture 24 - Lesson 24 Expansion Devices Version 1...

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