R&AC Lecture 26 - Lesson 26 Refrigerants Version 1...

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Version 1 ME, IIT Kharagpur 1 Lesson 26 Refrigerants
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2 The specific objectives of this lecture are to: 1. Discuss the importance of selection of suitable refrigerant in a refrigeration system ( Section 26.1 ) 2. Classify refrigerants into primary and secondary, and discuss the important differences between primary and secondary refrigerants ( Section 26.2 ) 3. Discuss refrigerant selection criteria based on thermodynamic, thermophysical, environmental and economic properties ( Section 26.3 ) 4. Describe the numbering system used for designating refrigerants ( Section 26.4 ) 5. Present a comparison between different refrigerants ( Section 26.5 ) At the end of the lecture, the student should be able to: 1. Explain the importance of refrigerant selection 2. Differentiate between primary and secondary refrigerants 3. List the criteria used in selecting refrigerants 4. List important thermodynamic and environmental properties influencing refrigerant selection 5. Write the chemical formula of a refrigerant from its number 6. Compare different refrigerants and suggest replacements for CFCs and HCFCs 26.1. Introduction: The thermodynamic efficiency of a refrigeration system depends mainly on its operating temperatures. However, important practical issues such as the system design, size, initial and operating costs, safety, reliability, and serviceability etc. depend very much on the type of refrigerant selected for a given application. Due to several environmental issues such as ozone layer depletion and global warming and their relation to the various refrigerants used, the selection of suitable refrigerant has become one of the most important issues in recent times. Replacement of an existing refrigerant by a completely new refrigerant, for whatever reason, is an expensive proposition as it may call for several changes in the design and manufacturing of refrigeration systems. Hence it is very important to understand the issues related to the selection and use of refrigerants. In principle, any fluid can be used as a refrigerant. Air used in an air cycle refrigeration system can also be considered as a refrigerant. However, in this lecture the attention is mainly focused on those fluids that can be used as refrigerants in vapour compression refrigeration systems only. 26.2. Primary and secondary refrigerants: Fluids suitable for refrigeration purposes can be classified into primary and secondary refrigerants. Primary refrigerants are those fluids, which are used directly as working fluids, for example in vapour compression and vapour absorption refrigeration systems. When used in compression or absorption systems, these fluids provide refrigeration by undergoing a phase change process in the evaporator. As the name implies, secondary refrigerants are those liquids, which are used for transporting thermal energy from one location to other. Secondary refrigerants are also known under the name brines or antifreezes. Of
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R&AC Lecture 26 - Lesson 26 Refrigerants Version 1...

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