R&AC Lecture 25 - Lesson 25 Analysis Of Complete...

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Lesson 25 Analysis Of Complete Vapour Compression Refrigeration Systems Version 1 ME, IIT Kharagpur 1
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The specific objectives of this lecture are to: 1. Importance of complete vapour compression refrigeration system analysis and the methods used ( Section 25.1 ) 2. Performance characteristics of reciprocating compressors ( Section 25.2 ) 3. Performance characteristics of reciprocating condensers ( Section 25.3 ) 4. Performance characteristics of evaporators ( Section 25.4 ) 5. Performance characteristics of expansion valves ( Section 25.5 ) 6. Performance characteristics of condensing unit ( Section 25.6 ) 7. Performance characteristics of complete system by matching characteristics of evaporator and condensing unit ( Section 25.7 ) 8. Effect of expansion valve on complete system performance ( Section 25.8 ) 9. Meaning of sensitivity analysis ( Section 25.9 ) At the end of the lecture, the student should be able to: 1. Explain the concept of complete system analysis and the characteristics of graphical and analytical methods 2. Express or plot the performance characteristics of individual components such as compressors, condensers and evaporators and enumerate the influence of operating parameters such as cooling water and brine flow rates, inlet temperatures etc. 3. Obtain balance point for a condensing unit by matching the characteristics of compressors and condensers 4. Obtain the balance point and characteristics curves for a complete system assuming an ideal expansion valve 5. Explain the effect of expansion device on system performance 6. Explain the meaning of sensitivity analysis and its importance in system design and optimization Version 1 ME, IIT Kharagpur 2
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25.1. Introduction A basic vapour compression refrigeration system consists of four essential components, namely compressor, condenser, expansion valve and evaporator. The individual performance characteristics of these components have been discussed in earlier lectures. However, in an actual system these components work in unison. The performance of a complete system is a result of the balance between these four components. For example, when the heat sink temperature varies, it affects the performance of the condenser, which in turn, affects the performance of the expansion device, evaporator and the compressor. It is seen in Chapter 24 that expansion valve and compressor work in such a manner that the mass flow rate through the two components is the same at steady state. The balance point at steady state was obtained by equating the mass flow rates through these components. This is an example of balancing two components. Similar procedure can be extended to include the other two components also, so that a balance point for the entire system can be obtained by taking into account the individual characteristics. In principle, the balance point for the system can be obtained either by a graphical method or by an analytical method. In graphical method, the performance of two interdependent components
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R&AC Lecture 25 - Lesson 25 Analysis Of Complete...

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