Absorption Refrigeration Systems Overview
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Questions and Answers

What is the primary function of the generator in the LiBr absorption refrigeration system?

  • To expand the refrigerant before it enters the evaporator.
  • To absorb heat from the solution.
  • To cool the refrigerant after condensation.
  • To raise the pressure of the refrigerant vapour. (correct)

    • At what pressure is the R-718 refrigerant in the generator?

  • $5 kPa$
  • $20 kPa$
  • $10 kPa$ (correct)
  • $15 kPa$

    • What happens to the refrigerant after it is boiled from the weak solution in the generator?

  • It raises the pressure and is then condensed in the condenser. (correct)
  • It evaporates and cools the chilled water.
  • It is directly used in the absorber.
  • It is stored in a tank for later use.

    • Which component in the absorption refrigeration system is responsible for the cooling of the refrigerant?

    <p>Condenser</p> Signup and view all the answers

    What is the temperature of R-718 at the pressure of $10 kPa$?

    <p>46°C</p> Signup and view all the answers

    What role does the expansion orifice play in the refrigeration cycle?

    <p>It restricts the flow of refrigerant into the evaporator.</p> Signup and view all the answers

    What process occurs in the absorber of the LiBr absorption refrigeration system?

    <p>Heat is released during absorption reaction.</p> Signup and view all the answers

    What is the primary purpose of adding octyl alcohol to the lithium bromide solution?

    <p>To enhance the absorption of water vapor</p> Signup and view all the answers

    Which component is directly involved in transferring heat from the concentrated to the weak solution?

    <p>Heat Exchanger</p> Signup and view all the answers

    How often should the strength of the anti-corrosion agent in the chilled water be checked?

    <p>Monthly</p> Signup and view all the answers

    What should be done to check for bacterial growth in the cooling system?

    <p>Add biocide to control bacterial growth</p> Signup and view all the answers

    When servicing the control system of an absorption refrigeration unit, what is recommended for operators?

    <p>Call a service company for assistance</p> Signup and view all the answers

    What is the function of log sheets or computer printouts in an absorption refrigeration unit?

    <p>To track periodic readings for performance diagnosis</p> Signup and view all the answers

    What is the correct procedure for adding octyl alcohol to the system?

    <p>Fill a tube with distilled water first</p> Signup and view all the answers

    What should operators do if they notice a gradual change in the absorption unit's performance?

    <p>Analyze log sheets for trends and diagnose issues</p> Signup and view all the answers

    What is a common mistake to avoid when dealing with malfunctions in control systems?

    <p>Attempting to tinker with the controls</p> Signup and view all the answers

    What occurs when a saturated salt solution is heated?

    <p>It becomes unsaturated and can hold more salt.</p> Signup and view all the answers

    What happens to a saturated solution when it is cooled?

    <p>Salt crystals will precipitate out of the solution.</p> Signup and view all the answers

    What is the consequence of crystallization in a lithium bromide system?

    <p>Crystals may block circulation.</p> Signup and view all the answers

    What is the relationship between the solubility of a solid and temperature?

    <p>Higher temperatures generally increase solubility.</p> Signup and view all the answers

    What occurs in the lithium bromide absorption refrigeration unit due to the low-pressure section?

    <p>Vapor pressure decreases due to high concentration.</p> Signup and view all the answers

    At what point is a solution classified as saturated?

    <p>When no additional salt can dissolve in it.</p> Signup and view all the answers

    What is crystallization?

    <p>The formation of salt crystals when a solution is cooled.</p> Signup and view all the answers

    What impact does the temperature have on vapor pressures in a lithium bromide unit?

    <p>Vapor pressure is affected by both temperature and concentration.</p> Signup and view all the answers

    What is the primary purpose of the bypass in the Lithium Bromide Absorption Unit?

    <p>To control the concentration of the solution</p> Signup and view all the answers

    At what temperature does the condenser operate in the system?

    <p>45°C</p> Signup and view all the answers

    Which component is used to cool the water entering the system?

    <p>Chilled Water System</p> Signup and view all the answers

    In the Lithium Bromide Absorption Unit, what pressure does the flash chamber operate at?

    <p>6.3 mm Hg</p> Signup and view all the answers

    What is the purpose of the economizer in the absorption unit?

    <p>To preheat the dilute solution before absorption</p> Signup and view all the answers

    What is the maximum temperature the evaporator reaches in the system?

    <p>99°C</p> Signup and view all the answers

    Which part of the system is responsible for pumping the concentrated solution?

    <p>Concentrator Pump</p> Signup and view all the answers

    What is a primary advantage of absorption refrigeration systems over compression systems?

    <p>They do not require compressors.</p> Signup and view all the answers

    What is the temperature difference between cooling water in and cooling water out?

    <p>7°C</p> Signup and view all the answers

    Why are lithium bromide systems only used in HVAC service?

    <p>They cannot achieve low temperatures.</p> Signup and view all the answers

    What is the refrigerant used in lithium bromide absorption systems?

    <p>R-718 (water)</p> Signup and view all the answers

    Which temperature represents the cooling water entering the absorption unit?

    <p>35°C</p> Signup and view all the answers

    What must be closely controlled to prevent crystallization in lithium bromide systems?

    <p>Temperature and pressure</p> Signup and view all the answers

    What does the absorber do in the Lithium Bromide Absorption Unit?

    <p>Increases concentration of lithium bromide</p> Signup and view all the answers

    What procedure must be followed during system shutdown to prevent crystallization?

    <p>Implement special shutdown procedures.</p> Signup and view all the answers

    What is a common issue that may arise with lithium bromide systems due to their salt solution?

    <p>Precipitation of lithium bromide salt crystals</p> Signup and view all the answers

    What is necessary to keep air out of lithium bromide absorption systems?

    <p>Hermetically sealed pumps and vessels</p> Signup and view all the answers

    What happens to the chilled water flow switch if there is improper operation?

    <p>It opens and needs resetting.</p> Signup and view all the answers

    What is the first action taken to initiate the purge process in the absorption refrigeration system?

    <p>Close the purge return valve</p> Signup and view all the answers

    Why is the purge exhaust valve cracked open during the purge process?

    <p>To allow for the observation of escaping gases</p> Signup and view all the answers

    What happens after all gases have been purged from the system?

    <p>The purge return valve is opened to start a new cycle</p> Signup and view all the answers

    What is the typical environmental setup for observing the gases during purging?

    <p>A water-filled container</p> Signup and view all the answers

    How does the solution supply affect the storage chamber during purging?

    <p>It compresses non-condensable gases above atmospheric pressure</p> Signup and view all the answers

    What role does automated control play in the start-up sequence of an absorption refrigeration system?

    <p>It dictates the order of each step in the sequence</p> Signup and view all the answers

    What is the primary function of the purge return valve?

    <p>To initiate the purge cycle</p> Signup and view all the answers

    What happens to the gases trapped in the upper part of the storage chamber during the purge?

    <p>They are vented to atmosphere</p> Signup and view all the answers

    Study Notes

    Absorption Refrigeration Systems

    • Absorption refrigeration systems use heat energy instead of mechanical energy, using low-cost sources like waste heat
    • They do not require compressors, thus reducing electrical energy consumption
    • Two common types of absorption systems are ammonia and lithium bromide systems
    • Ammonia systems are used in industrial settings, while lithium bromide systems are used in large HVAC chillers
    • Absorption systems use natural refrigerants (R-717 and R-718) which reduces global warming potential, and are not ozone-depleting
    • Absorption systems require a condenser, liquid receiver, expansion valve, and an evaporator, unlike compression systems which use a compressor
    • Compared to compression systems, absorption systems require more cooling water
    • Typical problems with absorption systems can include non-condensable gases, faulty purging (in the system), and issues with cooling water supply
    • Maintenance procedures include checking pulleys, belts, oil in vacuum pumps, cleaning strainers and traps, and checking pump oil levels and lubrication

    Learning Objectives

    • Describe basic absorption systems, comparing them to compression systems
    • Explain the operation of ammonia and lithium bromide absorption refrigeration systems
    • Describe the components of an absorption system, including heat exchangers and bypass, pump motor lubrication, and purging systems
    • Describe startup and shutdown procedures for absorption refrigeration systems
    • Explain typical problems and resolutions related to these systems
    • Understand crystallization and dilution in absorption refrigeration systems

    Chapter Introduction

    • Absorption refrigeration systems use heat energy instead of mechanical energy
    • This reduces electrical energy consumption, permitting the use of low-cost heat sources
    • Ammonia and lithium bromide systems are the two primary types

    Objective 1

    • Basic absorption systems differ from compression systems, as they do not include a compressor.
    • Absorption systems use a liquid absorbent that removes refrigerant vapor, a high-pressure generator to evaporate the refrigerant, and a pump to move the concentrated absorption solution
    • The factors involved in choosing an absorption system include waste heat availability, and the economics of the cooling requirement

    Objective 2

    • In ammonia absorption systems, water acts as the absorbent
    • The system circulates refrigerant (ammonia) through an evaporator, absorber, condenser & generator
    • Heat from a high-pressure source (steam, hot water) boils off the ammonia, leaving a weak solution

    Objective 3

    • Lithium bromide (LiBr) absorption systems use water as the refrigerant, and a lithium bromide solution as the absorbent
    • These systems maintain an evaporator temperature of 4°C to 7°C (40°F to 45°F)

    Objective 4

    • The solubility of a salt in water depends on its temperature; a higher temperature can dissolve more salt
    • This principle is crucial in preventing crystallization, where the amount of dissolved salt exceeds solubility limits at a lower temperature

    Objective 5

    • The major parts and systems of an absorption system include heat exchangers, bypass systems, and pump motor lubrication and cooling, as well as purging systems
    • Understanding the functions of the heat exchanger bypass and purging system is vital

    Objective 6

    • Describing the steps involved in the startup and shutdown procedures of absorption systems
    • This will involve understanding the actions of various pumps, valves, and cooling and steam systems
    • Following manufacturer's guidelines is essential

    Objective 7

    • Maintenance is critical to keep the system running smoothly
    • Cleaning and regular checks are essential
    • This includes verifying mechanical components, pumps, valves, etc for proper operation and to prevent leaks
    • Preventive maintenance includes pulley and belt checks, cleaning, ensuring proper oil levels and lubrication, and cleaning of critical mechanical parts
    • Regular cleaning of strainers and trap elements is essential
    • Checking refrigerant levels and adding octyl alcohol at intervals as required is essential

    Objective 8

    • Troubleshooting includes identifying potential causes, like non-condensable gases, issues with cooling water, or insufficient concentrations of chemical compounds (like octyl alcohol)
    • Potential problems in absorption units include decreased capacity, crystallization, issues involving the startup, and operational problems with crystallization at shutdown, safety interlocks and malfunctions
    • Correct resolutions for each of these potential causes are outlined

    Chapter Summary

    • Advantages of absorption refrigeration systems versus compression systems, focusing on cost-effective heat sources and environmental impact
    • Describing how ammonia and lithium bromide systems differ and explain their specific uses

    Knowledge Exercises (Questions and Answers)

    • These provide specific exercises for students to practice identifying components, understanding the processes, and diagnosing maintenance issues.

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    Absorption Refrigeration Systems PDF - 4th Class Edition PDF

    Description

    Explore the fundamentals of absorption refrigeration systems, which leverage heat energy instead of mechanical energy, making them more sustainable and cost-effective. This quiz covers the types of systems, their components, advantages, and common maintenance challenges. Discover how these systems play a critical role in reducing environmental impact through natural refrigerants.

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