SOLAR REFRIGERATION

Submitted by: Presented by:

AMIT PRAJAPATI

ABOUT REFRIGERATIONTYPES OF REFRIGERATION

ABOUT SOLAR REFRIGERATION

WORKING CYCLES

- V.C.R CYCLE

- V.A.R CYCLE

- SOLID ABSORPTION CYCLE

ADVANTAGES

APPLICATIONS

Refrigeration is the removal of heat from a space at a temperature lower than the surrounding temperature.

In other word Refrigeration is the science of providing and maintaining temperature below that of surrounding atmosphere.

There are many types of refrigeration like….1. Ice Refrigeration2. Evaporative Refrigeration3. Air Refrigeration4. Vapour Refrigeration 5. Steam-jet Refrigeration6. Solar Refrigeration7. Liquid Gases Refrigeration

In the solar refrigeration system we take a solar energy from sun and to convert solar energy into electrical energy. This Electrical energy we use in Refrigerator.

The solar energy is used for many purpose as Drying, Power Generation, Melting in Addition to Heating & Cooling.

Solar energy needs no conversion & on the other hand, it helps to conserve non renewable energy sources like oil, gas, coal and Nuclear fuels.

Solar energy may be collected either as heat or as electricity.

There are different methods of cooling using solar energy are represented on following block diagram,………

The solar energy can be used either in VAPOUR

COMPRESSION REFRIGERATION or VAPOUR

ABSORPTION REFRIGERATION system.

Solar energy could be converted directly into mechanical work for operating conventional compressor of a conventional vapour compression refrigeration system.

The shaft work to the compression was provided by a steam turbine supplied with a steam which was generated by a steam generator placed at the focus of a large parabolic mirror.

The COP of the system was found to be about 30% of the values for an idle system for the temperature values considered.

Rankine cycle conversion of solar energy into mechanical power is more complex than absorption cycle directly driven by solar heat. There fore, not much work has been done in developing the rankine cycle for the use of vapour compression system.

In this system cooling tower are not generally acceptable because of lack of water.

Air cooled condensers are an alternative but the ambient temperature rises to 50’c and therefore the condenser designed becomes critical.

COP falls considerably as high compression ratio is essential to carry out the condensation above 50’c.

The refrigerant vapours are formed using the heat collected by solar concentrators and passed through a high speed turbines which runs a centrifugal compressor of the conventional refrigeration cycle.

A small electric motor is mounted on the same shaft to provide stand by compressor power and to serve as a alternator when the compressor is idle but the sun is shining.

CIRCUIT 1.

This provides the hot water which is collected

from the solar collector. This water is used for

generating refrigerant vapour in the refrigerant

boiler. An auxiliary hot water boiler is provided

to compensate the heat required when solar

energy is not sufficient or not available due to

cloudy sun or during rains.

CIRCUIT 2.

This circuit is used to generate mechanical power which is use to run the compressor of refrigeration circuit. This power generating circuit consist of generator, turbine, condenser and a pump.

The hot water from the collector is used to vaporise the organic fluid in the refrigerant generator. The vaporised fluid drives the turbine which drives the compressor of the refrigeration cycle. The vapour coming out at lower pressure from turbine is condensed in the condenser and pumped back to the refrigerant boiler.

CIRCUIT 3.

This is conventional vapour compression refrigeration cycle which works on reversed rankine cycle. This circuit consist of compressor, condenser, expansion valve and evaporator.

An advantage of using refrigerant in the power cycle is low grad heat which can be used to generate the vapour….

But the disadvantage is thermal effinciency is very poor.

Since we can convert solar energy more

efficiently to heat than the mechanical or

electrical energy the use of absorption

refrigeration system with solar energy seem to

be the best solution at present time.

A generator contains an ammonia water mixture

with strong concentration of refrigerant.

A generator may be consider as a heat exchanger

with heat transport liquid on one side and boiling

two phase flow on the other. In the generator,

ammonia and water vapour are boiled off from

the strong mixture in the upper part of the

generator. This vapour leaving the generator

may contain from 5 to 10% of water vapour.

The vapour coming out of generator is liquefied

in the condenser and led to the refrigerant

storage. The conveying of warm condensate

from the condenser into the evaporator through

throttling valve causes a reduction in

refrigeration effect. Therefore a heat exchanger

is inserted between the storage and evaporator

to decrease the temperature of the liquid

refrigerant.there by the refrigeration effect by

recovering heat which would otherwise be lost.

The refrigerant which is at low temperature , low pressure is evaporated by absorbing the heat from the air or water which is circulated in the evaporator. This cooled air or water is further used either for refrigeration or air conditioning according to requirement.

The absorber is considered as an indirect heat exchanger with cooling water flowing on one side and weak mixture flowing from the generator on the other side.

A pressure reduction valve between the generator and absorber reduces the pressure from high generator pressure to a lower one in the absorber.

A liquid to liquid heat exchanger is used in the circuit in between absorber and generator which transfer energy from the weak hot liquid coming out from generator to the strong cooled liquid coming out of absorber.

The basic philosophy behind the development

of the cycle has been that the system should

not be dependent on energy sources other than

solar radiation and it should be simple so that

there would be virtually no need for service or

maintenance during the life time of the plant. in

addition to this, it would be also desirable if the

operation of the system is made fully

automatic.

The solid absorption cycle is the answer to all the above mentioned requirement.

The pumps and blowers are also ruled out as well as no electrical control devices are required.

An intermittent absorption cycle is very well suited to the diurnal cycle of the sun.

A solid absorption cycle with NH3 as refrigerant and calcium chloride as the absorbent came out as the best solution for the requirements.

The solid absorption cycle is based on the ability of metal halides to form complexes with certain gases, especially NH3. For refrigeration, chloride of calcium is well suited. It absorbs 8 moles of NH3 of which 6 can be driven off at temperature around 100*c.

For condensing temperature of 40*c the dotted lines to the right indicate equilibrium deabsorption temperature of 94*c & 106*c respectively.

The heats of reaction are nearly equal for the above mentioned two steps and almost twice the latent heat of vaporization. This states that the COP of the cycle can not be more than 0.5.

Another absorbent used in chloride of strontium from which 7 moles of NH3 out of 8 can be driven off which is an advantage over calcium chloride but it is very costly compared with calcium chloride.

It has no moving parts so it does not require any maintenance.

It has no problem to obtain evaporation temperature -10 to -15 oC.

The efficiency of the cycle is not very sensitive to high condensing temperature like other system.

A gravity driven evaporation/condensation loop is the only feasible solution that will lend itself easily to an automatic operation. This is only possible with this cycle.

This system is well suitabled for freezing of ice in the form of block ice or in an ice bank tank.

The former can be used in crushed form for preservation of agricultural produce, meat and fish.