The lithium-bromide absorption refrigeration system uses a solution of lithium bromide in water. In this system, the *water is being used as a refrigerant whereas lithium bromide, which is a highly hydroscopic salt, as an absorbent. The lithium bromide solution has a strong affinity for water vapour because of its very low vapour pressure. Since lithium bromide solution is corrosive, therefore inhibitors should be added in order to protect the metal parts of the system against corrosion. for air conditioning in which low refrigeration temperatures (not below 00 C)** are required.
Fig.
3.4 shows a lithium bromide vapour absorption system. In this system. the absorber and the evaporator are placed in one shell which operates at the
same low pressure of the system. The generator and condenser are placed in another
shell which operates at the same high pressure of the system. The principle of
operation of this system is discussed below :
The water for air-conditioning coils or process requirements is chilled as it
is pumped through the chilled-water tubes in.the evaporator by giving up heat to
the refrigerant water sprayed over the tubes. Since the pressure inside the
evaporator is maintained very low, therefore, the refrigerant water evaporates. The water
vapours thus formed will be absorbed by the strong lithium-bromide solution which is sprayed in the absorber. In absorbing the water vapour, the lithium bromide
solution helps in maintaining very low pressure (high vacuum) needed in the evaporator,
and the solution becomes weak. This weak solution is pumped by a pump to the
generator where it is heated up by using steam or hot water in the heating coils. A
portion of water is evaporated by the heat and the solution now becomes more strong. This strong solution is passed through the heat exchanger and then sprayed in the
absorber as discussed above. The weak solution of lithium bromide from the absorber to
the generator is also passed through the heat exchanger. This weak solution gets
heat
from the strong solution in the heat exchanger, thus reducing the quantity of
steam required to heat the weak solution in the generator.
Lithium-Bromide absorption refrigeration system.
The refrigerant water vapours formed in the generator due to heating of
solution are passed to the condenser where they are cooled and condensed by the cooling water flowing through the condenser water tubes. The cooling water for condensing is pumped from the cooling water pond or tower. This cooling water
first enters the absorber where it takes away the heat of condensation and dilution.
The condensate from the condenser is supplied to the evaporator to compensate the
water vapour formed in the evaporator. The pressure reducing valve reduces the
pressure of condensate from the condenser pressure to the evaporator pressure. The cooled
water from the evaporator is pumped and sprayed in the evaporator in order to cool
the water for air conditioning flowing through the chilled tubes. This completes
the cycle.
Note: The pressure difference between the generator and the absorber and
the gravity due to the height difference of the two shells is utilised to
create the pressure for the spray.
Refrigeration & air conditioning, Book
★ABOUT THE BOOK:
The respected text delivers a comprehensive introduction to the principles and practice of refrigeration. Clear and straightforward, it is designed for students (NVQ/vocational level) and professional HVAC engineers, including those on short or CPD courses. Inexperienced readers are provided with a comprehensive introduction to the fundamentals of the technology. With its concise style yet broad sweep the book covers most of the applications professionals will encounter, enabling them to understand, specify, commission, use and maintain these systems. Many readers will appreciate the clarity with which the book covers the subject without swamping them with detailed technical or product specific information. New material in this edition includes the latest developments in refrigerants and lubricants, together with updated information on compressors, heat exchanges, liquid chillers, electronic expansion valves, controls and cold storage.
“A Textbook of Refrigeration and Air Conditioning” is an aptly written textbooks for the students of Mechanical Engineering while also a must-read for anyone with an interest in the subject.
For 30 years, topics such as Air Refrigeration Cycles and Systems, Vapour Compression Refrigeration Systems (Simple and Compound), Refrigerants (incl. Compressors), Psychrometry and Applications of Refrigeration and Air Conditioning have been included and updated for students to conceptualise the subject in a complete manner. The chapters consist of various exercises, examples, and multiple illustrations that aid in understanding the subject better.
Key Features:
- Every concept has been treated individually and then linked within the chapter to provide not only information but also insight.
- Close to 800 examples, figures, tables and pictorial depictions aid to the concepts explained.
- More than 500 chapter-end (objective and subjective) and exercise questions add to the practice of the students.
Table of Content :
- Introduction
- Air Refrigeration Cycles
- Air Refrigeration Systems
- Simple Vapour Compression Refrigeration Systems
- Compound Vapour Compression Refrigeration Systems
- Multiple Evaporator and Compressor Systems
- Vapour Absorption Refrigeration Systems
- Refrigerants
- Refrigerant Compressors
- Condensers
- Evaporators
- Expansion Devices
- Food Preservation
- Low Temperature Refrigeration (Cryogenics)
- Steam Jet Refrigeration System
- Psychrometry
- Comfort Conditions
- Air Conditioning Systems
- Cooling Load Estimation
- Ducts
- Fans
- Applications of Refrigeration and Air Conditioning
Unit installation Absorption Refrigeration steam jet Refrigeration cascade Refrigeration systems ; low temperature Refrigeration thermal insulation Psychrometry building survey ; heat load estimate applied Psychrometry (advanced) human comfort evaporative air Conditioning moisture transfer pressure losses and duct sizing ventilation systems air-conditioning systems ; applications all air-systems
fans food preservation indoor air quality refrigerant tables ; charts.
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