29 Questions
What did Carrier present in an ASME meeting?
Rational Psychrometric Formulae
When did air conditioning for comfort start in motion-picture theatres?
1922 in Chicago
Can moist air be considered a pure substance?
No, it is never a pure substance
Which part of moist air is considered the fixed part?
Dry air
Why can perfect gas laws be applied to dry air and water vapor?
Given their low pressures in the atmosphere
What properties can be established using Gibbs-Dalton laws?
Properties of dry air only
What is a key similarity between vapour absorption refrigeration and vapour compression refrigeration?
Both systems remove heat from a low temperature source
What advantage do vapour-compression refrigeration cycles have over other refrigeration cycles?
They have an isothermal nature during vaporization
What happens to the compressed gas in a vapour compression system when it is allowed to expand?
It gets hotter than the source of cooling
What role does the large thermal energy required to change a liquid to a vapor play in vapour compression refrigeration?
It allows for faster heat transfer out of the air-conditioned space
Why is an isothermal process beneficial in vapour compression refrigeration?
It enables the fastest rate of heat transfer
What is the primary method used to provide mechanical cooling according to the text?
Vapour-compression refrigeration
What is the main reason the Carnot vapor refrigeration cycle is not suitable for refrigeration systems?
Low efficiency at high cost
In a vapor absorption system, what function does the generator perform?
Compression and discharge
Why does the absorbent solution need to be heated in the generator in a vapor absorption system?
For regeneration of the refrigerant
Which component replaces the compressor in a vapor absorption system?
Absorber
What distinguishes ammonia absorbent systems from lithium bromide absorption systems?
Different refrigerants and absorbents used
Who is known as the 'Father of Air Conditioning'?
Carrier
What purpose does a shell and tube heat exchanger serve in a vapor absorption system?
Regeneration of refrigerant
Why does the refrigerant operating temperature in a lithium bromide absorption system's evaporator have to be above 0°C?
To enable evaporation of water as the refrigerant
What role does the absorbent play in an absorber of a vapor absorption system?
Draws refrigerant vapors to maintain low pressure in evaporator
What does an expansion valve do in a refrigeration system?
Throttles refrigerant from saturated liquid to liquid-vapor mixture
Which component of a vapor compression system is responsible for raising the pressure of the refrigerant?
Compressor
In a vapor compression system, what is the function of the expansion valve?
Control the flow of condensed refrigerant
What happens during the throttling process in a vapor compression system?
An irreversible process
In a Carnot vapor compression system, what is the primary issue with achieving isothermal compression?
It is impossible to achieve in practice
What is the main drawback of wet compression in a vapor compression system?
Liquid droplets react with lubricant
Why is the Carnot vapor compression cycle not suitable for practical refrigeration systems?
Dry vs. wet compression issues
Which component of a vapor compression system functions by absorbing heat while evaporating the refrigerant?
Evaporator
Study Notes
Vapour Absorption Systems vs. Vapour Compression Systems
- Vapour absorption refrigeration is a heat-operated system similar to vapour compression systems.
- Both systems have evaporators and condensers, but the method of creating pressure levels and refrigerant circulation differs.
Vapour Compression Systems
- The primary method of providing mechanical cooling.
- Takes advantage of the idea that highly compressed fluids will tend to get colder when expanded.
- Exploits the thermal energy required to change a liquid to a vapour, allowing for efficient heat removal.
- Has two additional advantages:
- The isothermal nature of vaporization allows for fast heat transfer without raising the working fluid temperature.
- Large thermal energy is required to change a liquid to a vapour, enabling efficient heat removal.
Limitations of Carnot Vapour Compression Systems
- Although the Carnot vapour compression cycle has the highest COP, it is not suitable for practical refrigeration systems.
- Isothermal compression from state 2 to state 3 is virtually impossible to achieve in a finite time interval.
- Dry compression is desirable, but wet compression is highly undesirable due to the presence of liquid droplets.
Vapour Compression Cycle
- Consists of four basic components: evaporator, condenser, compressor, and expansion valve.
- The evaporator and condenser are heat exchangers that evaporate and condense the refrigerant while absorbing and rejecting heat.
- The compressor raises the pressure sufficiently for the vapour to condense in the condenser.
- The expansion device controls the flow of condensed refrigerant back into the evaporator.
Air Refrigeration Introduction
- The art of air conditioning developed gradually from the predecessor arts of cooling, cleaning, heating, and ventilating.
- W.H. Carrier is known as the "Father of Air Conditioning" for his contributions to the field.
- The first year-round air-conditioning system provided for the four major functions of heating, cooling, humidifying, and dehumidifying.
Working Substance in Air Conditioning
- The working substance in air conditioning is moist air, a mixture of two gases: dry air and water vapour.
- Moist air is not a pure substance, as it consists of two parts with different properties.
- Dry air is a mixture of permanent gases, while water vapour can be considered as a perfect gas.
- Gibbs-Dalton laws for non-reactive mixtures of gases can be applied to the dry air part to obtain its properties as a single pure substance.
Explore the differences between vapour absorption and vapour compression refrigeration systems in this quiz. Learn about the heat operations and challenges involved in each system.
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