A presentation on

lithium bromide absorption refrigeration system

ByRohan Sharma

• Vapour compression refrigeration system

• Lithium bromide • Vapour absorption refrigeration system• Working• Advantages• Disadvantages• Future scope

Table of contents

At present vapor compression system is widely being use for refrigeration purpose. The major disadvantages of this system is that Use of refrigerant increases the cost and has environmental impact.

Vapour compression refrigeration system

Being a salt, lithium bromide does not exert any pressure and does not boil off when heated. Thus there is no need of rectifier to separate out the absorbent vapor from the refrigerant vapor.

The rate of absorption of water vapor comes down as temperature of the solution increases. The concentration of a solution does not change with temperature, its concentration comes down. This is because the weight of the total solution has increased on absorbing water, but salt content has not changed. A stronger solution can absorb more water vapor than a solution of lower concentration

Lithium bromide

Vapour absorption refrigeration systems using water-lithium bromide pair are extensively used in large capacity air conditioning systems. In these systems water is used as refrigerant and a solution of lithium bromide in water is used as absorbent.

it is used only in applications requiring refrigeration at temperatures above 0oC Since water is used as refrigerant, using these systems it is not possible to provide refrigeration at sub-zero temperatures.

The analysis of this system is relatively easy as the Vapour generated in the generator is almost pure refrigerant (water), unlike ammonia-water systems where both ammonia and water Vapour are generated in the generator.

Vapour absorption refrigeration system

IN ABSORBER AND GENERATOR The evaporator and absorber are inter-

connected. So the refrigerant vapor formed in the evaporator is absorbed by the absorbent in the absorber thereby maintaining the refrigerant vapor pressure in the evaporator at the low level required for continuous vaporization of liquid refrigerator to obtain refrigeration. To recover the refrigerant from the absorbent it is pumped from the absorber to the generator, where it is heated using steam or hot water.

working

Contd.

On getting heated the absorbent releases the refrigerant vapor as a high temperature/pressure vapor. It passes to the comparatively cooler condenser where it is condensed. The liquid refrigerant then passes on to the evaporator thus completing the refrigerant cycle. The absorbent flows back from the generator to the absorber

Here the condenser is replaced by the radiator of the vehicle . When the air cooler is not switched on the hot coolant water flows into it, when the AC is switched on it acts as a condenser for the unit

Contd.In condensor and evaporator

Schematic representation of refrigeration system

Operating conditions

Generator solution temperature = 990C

• Generator solution strength= 63.3%• Generator solution vapor

pressure=76.2mmHg abs• Condensing temperature=460C• Condensing pressure of

refrigerant=76.2mmHg abs• Absorber solution temperature=38.30C• Absorber solution strength=59.5%• Absorber solution vapor

pressure=6.35mmHg• Evaporator temperature=4.440C• Evaporator refrigerant vapor

pressure=6.35mm(0.25”)Hg abs

except for two small centrifugal pumps, there are no moving parts so less number of moving parts

step less capacity control down to 0%capacity which is not possible with reciprocating machines and centrifugal

No Freon used no recharging cost of refrigerant ,which will be

quite substantial and inevitable in vapor compression cycle

low working pressure

advantages

low COP high heat rejection factor, so

requirement of higher cooling tower and pump capacities

corrosive nature of lithium bromide corrodes the heat exchanger

disadvantages

Condensed liquid refrigerant from the condenser can be used for refrigeration by passing the same through capillary tube and then to evaporator

All the accessories of a vehicle can be made to run with the power obtained from refrigerant turbine, so as to reduce the energy loss of 2.2%

Future scope

Thank you