RAC Lecture 10 - Lesson 10 Vapour Compression Refrigeration...

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Lesson 10 Vapour Compression Refrigeration Systems Version 1 ME, IIT Kharagpur 1
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The specific objectives of the lesson: This lesson discusses the most commonly used refrigeration system, i.e. Vapour compression refrigeration system. The following things are emphasized in detail: 1. The Carnot refrigeration cycle & its practical limitations ( Section 10.3 ) 2. The Standard Vapour compression Refrigeration System ( Section 10.4 ) 3. Analysis of Standard Vapour compression Refrigeration System ( Section 10.5 ) At the end of the lesson the student should be able to: 1. Analyze and perform cyclic calculations for Carnot refrigeration cycle ( Section 10.3 ) 2. State the difficulties with Carnot refrigeration cycle ( Section 10.3 ) 3. Analyze and perform cyclic calculations for standard vapour compression refrigeration systems ( Section 10.4 ) 4. Perform various cycle calculations for different types of refrigerants ( Section 10.4 ) 10.1. Comparison between gas cycles and vapor cycles Thermodynamic cycles can be categorized into gas cycles and vapour cycles. As mentioned in the previous chapter, in a typical gas cycle, the working fluid (a gas) does not undergo phase change, consequently the operating cycle will be away from the vapour dome. In gas cycles, heat rejection and refrigeration take place as the gas undergoes sensible cooling and heating. In a vapour cycle the working fluid undergoes phase change and refrigeration effect is due to the vaporization of refrigerant liquid. If the refrigerant is a pure substance then its temperature remains constant during the phase change processes. However, if a zeotropic mixture is used as a refrigerant, then there will be a temperature glide during vaporization and condensation. Since the refrigeration effect is produced during phase change, large amount of heat (latent heat) can be transferred per kilogram of refrigerant at a near constant temperature. Hence, the required mass flow rates for a given refrigeration capacity will be much smaller compared to a gas cycle. Vapour cycles can be subdivided into vapour compression systems, vapour absorption systems, vapour jet systems etc. Among these the vapour compression refrigeration systems are predominant. 10.2. Vapour Compression Refrigeration Systems As mentioned, vapour compression refrigeration systems are the most commonly used among all refrigeration systems. As the name implies, these systems belong to the general class of vapour cycles, wherein the working fluid (refrigerant) undergoes phase change at least during one process. In a vapour compression refrigeration system, refrigeration is obtained as the refrigerant evaporates at low temperatures. The input to the system is in the form of mechanical energy required to run the compressor. Hence these systems are also called as mechanical refrigeration systems. Vapour compression refrigeration Version 1 ME, IIT Kharagpur 2
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systems are available to suit almost all applications with the refrigeration capacities ranging from few Watts to few megawatts. A wide variety of refrigerants can be used in these systems to suit different applications, capacities etc. The actual vapour compression
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This note was uploaded on 12/04/2010 for the course ME N/A taught by Professor N/a during the Spring '10 term at Indian Institute of Technology, Kharagpur.

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RAC Lecture 10 - Lesson 10 Vapour Compression Refrigeration...

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