Flashcards in Refrigeration and Air Conditioning Deck (102)
What are refrigerants primarily classified into ?
Primary and Secondary Refrigerants
What is a primary refrigerant ?
It directly takes part in the refrigeration system
What is a secondary refrigerant ?
It is first cooled and then used
What is used to cool a secondary refrigerant ?
A primary refrigerant
What are primary refrigerants classified into ?
What are the three types of properties refrigerants are checked for before use ?
Physical, Chemical and Thermodynamic
Why should a refrigerant have a low boiling point at atmospheric pressure ?
It provides for lower refrigeration temperature
How low should it be, generally ?
Lower than the required refrigeration temperature
What should be the condensing pressure of a refrigerant at normal temperature ?
Why should a refrigerant have high critical temperature ?
Easy to provide refrigeration, even at room temperature
What is critical temperature ?
the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.
Why should refrigerants have low freezing point ?
Easy to circulate even at room temperature
What kind of a coefficient of performance (COP), is desired (high or low) ?
What is coefficient of performance (COP) ?
Ratio of refrigeration effect to work input
What is a desirable horsepower/ ton of refrigeration ?
What is ton of refrigeration ?
Amount of ice melted in 24 hours from 0 degree centigrade water
What is the required flammability of a refrigerant ?
Why should refrigerants have low water dissolvity ?
Reduces moisture chocking of expansion devices with narrow passages
What affect should refrigerants have on metals ?
They should be non corrosive to metals
How should refrigerants mix with lubricating oil ?
Should mix well
What kind of a dielectric strength in required for a refrigerant ?
Strong dielectric strength, especially for hermetically sealed units
What is the property of a hermetic seal ?
It is air tight
Why should refrigerants have high thermal conductivity ?
It increases heat transfer rates
What is the desired viscosity of a refrigerant ?
What should be the thermal capacity of a refrigerant at evaporating temperature ?
High thermal capacity at evaporating temperature
What should be the thermal capacity of a refrigerant at condensing temperature ?
Low thermal capacity at condensing temperature
What is thermal capacity ?
Measurable physical quantity equal to the ratio of the heat added to (or removed from) an object to the resulting temperature change
What are some common refrigeration systems ?
What are some special refrigeration systems ?
Steam Jet Refrigeration
Vortex tube Refrigeration