MECHANICAL ENGINEERING SHORT NOTES [ RAC ] ~ MECHANICAL ENGINEERING SHORT NOTES

MECHANICAL ENGINEERING SHORT NOTES

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Subject- Refrigeration And Air Conditioning

Topics covered-

Basic terms of refrigeration
Ideal Refrigeration Cycle
Pure Substance
Vapour Compression Refrigeration System (VCRS)
Vapour Absorption Refrigeration System (VARS)
Cascade Refrigeration
Refrigerant and its properties
Bell Coleman Cycle or Reversed Brayton Cycle
Psychrometry

And many important terms, key points, and concepts are there.

Working of refrigerator consist of four following process-

Evaporator
Compressor
Condensor
Expansion device

Capillary tubes are used as expansion devices.

One Ton Refrigeration-

Amount of heat required to extract from one ton of water at zero degree celsius to convert it into equivalent ice at zero degree celsius in a day.

1 Ton= 3.5 KW= 210 KJ/min

Vapour Compression Refrigeration System (VCRS)-

It has four processes-

Evaporator- Heat is taken out from storage space at constant pressure.
Compressor- Compressed working fluid from saturated state to superheated state,
Condenser- Heat is rejected at constant pressure.
Isenthalpic Expansion- Expansion takes place at constant enthalpy.

Flash Chamber-

A device used to separate out liquid particles from mixture of refrigerant and allow only liquid refrigerant to enter into the evaporator. It has no impact on COP but helps in reducing the size of the evaporator.

Vapour Absorption Refrigeration System (VARS)-

The compressor of VCRS replaces by an absorber, generator, and pump.
It works on low-grade energy
Solar absorption system works on VARS
COP of VARS is less then VCRS
Generally preferred in a remote location
Less Noisy due to the absence of moving parts like a compressor.

Bell Coleman Cycle or Reversed Brayton Cycle-

It has four following processes-

Isentropic Compression
Constant pressure heat rejection
Isentropic expansion
Constant pressure heat addition

Air is used as a working fluid because of its low weight per ton refrigeration ratio.

Desirable properties in refrigerant-

High Critical Temperature
High Enthalpy of Vaporization
High specific heat of vapour
High Thermal Conductivity
Low specific heat of liquid
Low Freezing point
Non-Toxic and Inflammable

Refrigeration and its application-

R11 - Large Centralized AC
R12 - Domestic Refrigerator and Water cooler
R22 - Window AC
NH3 - Cold Storage Plant
CO2 - Food Freezing
Brine - Milk Chilling

Psychrometry-

Moist air is an impure substance and it is in a superheated state.

For Unsaturated Air- DBT>WBT>DPT
For Saturated Air- DBT=WBT=DPT

RAC is one of the important subjects in terms of marks in different examinations. By putting some extra effort it is easily possible to solve all the problems related to it.

All important concepts and formulas are also present there. It will help you in steady quick revision and save your precious time so that you can practice more problems related to RAC.

Always refer to standard textbooks for doubt.

Here are some sample snaps for the RAC. The pdf contains a total of 11 no. of pages that cover every aspect of the RAC.

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