Explain Vapor Absorption System

Vapor Absorption System 

In this system refrigerant is absorbed by an absorbent on low pressure side of the system and rich
solution is pumped up on higher pressure side. Heat is released in absorption and condensation,
which is taken away by cooling water. Refrigerant is separated from absorbent in generator
where heat is supplied by steam or hot water or other heat source. Rich (or strong) solution from
absorber is pumped to generator via a heat exchanger, which serves the purpose of cooling the
weak solution on its return to absorber and heating the strong solution on way to generator. This
saves heat supplied to generator and heat removed in absorber.
Significant features and advantages

1. It is similar to standard vapor compression cycle, but it is heat operated system. Energy
source, other than electricity can be used to operate the system. Compressor is replaced
by an absorber and generator loop.

2. A secondary fluid or crystal called absorbent is used to absorb refrigerant in a vessel
called absorber. A liquid rather than a gaseous substance is pumped from low pressure
side to high pressure side which requires less work. Strong solution from absorber is
pumped to generator, where refrigerant is evaporated from absorbent by supply of
external heat to the system. Refrigerant vapor from generator is passed on to condenser
where it is condensed to liquid by removal of heat by cooling medium (air or water).
Liquid refrigerant is throttled to evaporator pressure and passed to the evaporator, where
it removes the heat from the cooled substance (called load).

3. “Performance factor” (ηp) or “COPabs” (Coefficient of Performance Absorption cycle) is
defined as:

where, qg = heat rate supplied to generator,
and qe = heat rate taken in to evaporator.

In this definition smaller quantity of mechanical work input to pumps is ignored as compared to
large quantity of heat rate sin generator and evaporator. In general, if we take into consideration
the pump work also, then the definition will be as:

[Note: In industrial practice, sometimes it may be expressed in terms of rate of steam supplied to
the system per ton of refrigeration, e.g., 20 kg / hr. ton]
Application:
1. Domestic refrigerator “Electrolux” of “Servel” company.
2. Commercial refrigeration for air conditioning in chiller plant.

Vacuum Refrigeration System

Vacuum Refrigeration System

Steam-Jet Refrigeration System

Ejector Refrigeration System

Water and steam are used as refrigerant in this system. Chilled water at 40C is achieved in the
evaporator which is kept under vacuum. Water vapor from the evaporators is pumped by steam
jet pumps (called as ejectors) to the main condenser, where vapor is condensed under vacuum.
The pressure ratio in ejector system is usually 7 to 8. The resulting water from the condenser is
pumped to atmosphere pressure. Secondary ejectors are used to pump non –condensable gasses
(air) to the atmosphere pressure. The steam used in these secondary ejectors is condensed in
inter- and after-condenses. (Refer to the figure)
Application:
1. This system is suitable for moderate refrigeration temperatures like those in air
conditioning and some industrial processes.
2. This system is economical only for large installations where steam is available for other
processes.

how to find compressor efficiency and power?

Refrigeration Compressor Efficiency

1.Volumetric Efficiency

a) Actual volumetric Efficiency

b) Clearance volumetric efficiency,

2. Compression Efficiency (or Adiabatic Efficiency), 

Mass Flow Rate of Reciprocating Compressor

 

                m=(vdis/vsuc)  x ηv/100 kg/s

Compressor Power

P = m (delta hi) kW

where, delta hi = isentropic work done on compressor per unit mass

Types and classification of Refrigeration Compressors

Types of Refrigeration Compressors

1. Reciprocating Compressors:
a) Single cylinder
b) Multi-cylinder
i. V-type
ii. W-type
iii. Radial type

2. Rotary Compressors:
a) Vane type
i. Roller type
ii. Multi-vane type (two-vane; four-vane)
b) Screw type
c) Scroll type
d) Centrifugal type

Classification of Refrigeration Compressors

1. Hermetic
2. Semi-hermetic
3. Open

Vapor compression Cycle:

In this cycle vapor is compressed then condensed to a liquid following which the pressure is

dropped so that fluid can evaporate at a low pressure.

1. Single stage cycle
2. Two stage/multi stage cycle
3. Cascade cycle

For detail of above thee systems of vapor compression see the class notes of chapter10 of
textbook by Stoecker and Jones, 2nd ed.

The Carnot Refrigeration Cycle:

The Carnot Refrigeration Cycle:

It is the most efficient cycle and valid for gases as wall a vapors i.e. It can also be realized in wet
region of the p-h or T-S diagram. These cycles approach external reversibility as T → 0. i.e
heat transfer with environment takes place with minimum possible temperature difference.
(Refer to the figure T-S diagram)
Source of irreversible losses (loss of efficiency)
· P in suction and discharge valves
· Re-expansion of gas in clearance volume
· Leakages past rings
· Leakages through discharge and suction valves
· Cylinder heating of the suction gas

Types of Refrigeration Systems:

Types of Refrigeration Systems:

1. Reversed Carnot Cycle (Ideal Refrigeration Cycle)
2. Vapor Compression Cycle
a. Single stage compression
b. Multistage compression
c. Cascade (Binary Vapor) cycle
3. Steam Jet (Or Vacuum) System
4. Vapor Absorption Cycle
5. Air Refrigeration Cycle. (Gas Refrigeration Cycle, Reversed Brayton cycle or Reversed
Gas Turbine Cycle)
6. Thermoelectric Cooling (Peltier Effect)
7. Vortex Tube Cooling
a. Counter flow vortex tube.
b. Uniflow vortex tube.
8. Cryogenic Systems
a. Linde Liquefier
b. Claude Liquefier
9. Magnetic Cooling Near Absolute Zero Temperature