RAC Lecture 15 - Lesson 15 Vapour Absorption Refrigeration...

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Lesson 15 Vapour Absorption Refrigeration Systems Based On Water- Lithium Bromide Pair Version 1 ME, IIT Kharagpur 1
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The objectives of this lesson are to: 1. Introduce vapour absorption refrigeration systems based on water-lithium bromide ( Section 15.1 ) 2. Discuss properties of water-lithium bromide solution and describe pressure- temperature-concentration (p-T- ξ ) and enthalpy–temperature-concentration (h-T- ξ ) charts ( Section 15.2 ) 3. Present steady-flow analysis of a single stage, water-lithium bromide system ( Section 15.3 ) 4. Discuss practical problems in actual water-lithium bromide systems ( Section 15.4 ) 5. Describe commercial water-lithium bromide systems ( Section 15.5 ) 6. Discuss heat sources for water-lithium bromide systems ( Section 15.6 ) 7. Discuss typical application data for water-lithium bromide systems ( Section 15.7 ) 8. Discuss briefly the methods of capacity control in water-lithium bromide systems ( Section 15.8 ) At the end of the lecture, the student should be able to: 1. Draw the schematic of the water-lithium bromide system and explain its working principle 2. Evaluate the properties of water-lithium bromide solution using p-T- ξ and h-T- ξ charts 3. Evaluate the steady-state performance of a single stage water-lithium bromide system using the input data and fluid properties 4. Describe commercial water-lithium bromide systems and list practical problems in these systems 5. List typical operating temperatures and performance aspects of water-lithium bromide systems 6. Compare various capacity control methods in water-lithium bromide systems 15.1. Introduction Vapour absorption refrigeration systems using water-lithium bromide pair are extensively used in large capacity air conditioning systems. In these systems water is used as refrigerant and a solution of lithium bromide in water is used as absorbent. Since water is used as refrigerant, using these systems it is not possible to provide refrigeration at sub-zero temperatures. Hence it is used only in applications requiring refrigeration at temperatures above 0 o C. Hence these systems are used for air conditioning applications. The analysis of this system is relatively easy as the vapour generated in the generator is almost pure refrigerant (water), unlike ammonia-water systems where both ammonia and water vapour are generated in the generator. Version 1 ME, IIT Kharagpur 2
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15.2. Properties of water-lithium bromide solutions 15.2.1. Composition: The composition of water-lithium bromide solutions can be expressed either in mass fraction ( ξ ) or mole fraction (x). For water-lithium bromide solutions, the mass fraction ξ is defined as the ratio of mass of anhydrous lithium bromide to the total mass of solution, i.e., W L L m m m + = ξ (15.1) where m L and m W are the mass of anhydrous lithium bromide and water in solution, respectively. The composition can also be expressed in terms of mole fraction of lithium
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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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RAC Lecture 15 - Lesson 15 Vapour Absorption Refrigeration...

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