Unit - 5

Refrigeration Equipment & Application

Q1) What do you mean by air compressor and what is the purpose in the industries?

A1)

Compressors:

Air compressors are machines with very low overall efficiency; only 10-30% of the energy supplied to the compressors reaches the point of end use.

The remaining power is converted to unusable heat energy, and to a smaller extent, is lost in friction, misuse, and noise. These factors need to be identified and minimized for optimum performance.

Air compressors are used in a variety of industries for the following purposes:

• Operating machinery like hammers, presses.
• Supplying process requirements.
• Supplying air at high pressure for chemical action

Q2) What do you mean by heat exchanger and write its functions?

A2)

• Heat exchangers are used to transfer heat. Some process like heating, cooling, condensation, boiling or evaporation.
• Different heat exchangers are named according to their application.
• For example, heat exchanger used for boiling purposes are called boilers, heat exchanger being used to condense are known as condensers.
• The condenser is a heat exchanger that usually rejects all the heat from the system.
• The condenser accepts all the hot, high-pressure refrigerant usually a super-heated gas, from the compressor.
• The condenser is usually air cooled by natural or forced convection to increase the cooling effect of the condenser.

Function:

• The purpose of the condenser in the refrigeration system is to remove heat from the refrigerant vapor leaving the compressor (or generator in case of absorption system) so that the refrigerant will condense to its liquid state.
• This liquid refrigerant will then be able to achieve the refrigerating effect in the evaporator.

Q3) What do you mean by expansion device. Write its purposes.

A3)

An expansion device is essentially a restriction offering resistance to flow so that pressure drops, resulting in throttling process.

An expansion device in a refrigeration system normally serves two purposes:

1. The thermodynamic faction of expanding the liquid refrigerant from condenser pressure to evaporator pressure.

2. The control functions which may involve the supply of liquid to the evaporator at the rate at which it is evaporated. This determines the efficiency with which evaporator surface is utilized.

Q4) What is Automatic Expansion Valve (AEV). Explain in detail.

A4)

Automatic Expansion Valve (AEV): -

The automatic expansion valve modulates the flow of the refrigerant into the evaporator to keep the evaporator pressure constant.

Unlike the capillary tube, which cannot adjust the flow of refrigerant, the automatic expansion valve opens and closes to either increase or decrease the amount of refrigerant feeding into the evaporator in response to the pressure of the refrigerant in the evaporator.

The valve operates on a “needled and seat” mechanism that changes the amount of refrigerant that is able to pass through the valve.

The position of the needle is determined by the difference between two pressures:

1. The spring pressures
2. The evaporator pressure.

The spring pressure is the pressure that opens the valve. This pressure is adjustable and is set at the desired evaporator pressure.

The higher the spring pressure, the higher the evaporator pressure will need to be for refrigerant to flow.

Q5) What is food preservation and write its advantages.

A5)

Food Preservation is the process of treating and handling food to stop or slow down food spoilage, loss of quality, edibility, or nutritional value and thus allow for longer food storage.

Preservation usually involves preventing the growth of bacteria, fungi. This means that the food treated that way will go bad (spoil from bacteria) later that if it had not been treated that way. For thousands of years, humans have used methods of preserving food, so that they can store food to eat later.

Advantages:

• Food preservation prevents the food from being spoiled by the action of enzymes and microorganisms.
• Food preservation increases the safe storage period of foodstuffs.
• It increases the availability of out of season foodstuffs.
• It increases the availability of various foodstuffs even at distant and not easily approachable places.

Q6) What is cold storage. Explain

A6)

Cold storage is a typical room with low temperature, we can maintain temperature with refrigeration and air conditioning techniques. The walls and floors of the cold storage room are insulated with low thermal conductivity materials.

In the absence of cold storage, the people want to sell there as soon after manufacturer it may affect their pricing. By cooling technologies, we may extend the life of products and slower their deterioration, beverages taste good when they are cooled.

The cold storage system is essential for extending the life of products and helps to maintain product quality. It also helps to reduce the wastage of commodities.

Control Atmosphere and cold Storage:

These kinds of cold storage systems used for long-term storage of fruits. Because the fruits need to the proper temperature, a concentration of oxygen, carbon dioxide, ethylene etc. it gets varied based upon the storage products.

These kinds of cold storage systems are used to store the dry fruits and grains, in this, the temperature is predetermined throughout the room.

Q7) What do you mean by water cooling system. Write its advantages.

A7)

Water cooling system is used for cooling the engine when the temperature of engine is high by using fresh water after boiling of sea water.

Advantages:

1. To cool down the engine.

2. Low-cost maintenance.

Disadvantages:

1. The engine cannot work properly if the engine is too cold.

2. By using seawater, it will leave the deposit and metal corrode easily.

Q8) How distribution of air through fans takers place.

A8)

The Propeller Fan:

• The propeller fan is used in exhaust-fan and condenser- fan applications.
• It will handle large volumes of air at low pressure differentials.
• The propeller fan can be cast iron, aluminum or stamped steel and is set into a housing called a venturi to encourage airflow in a straight line from one side of the fan to the other (Figure above).
• The propeller fan makes more noise than the centrifugal fan so it is normally used where noise is not a factor.

The Centrifugal Fan:

• The centrifugal fan has characteristics that make it desirable for duct work.
• It builds more pressure from the inlet to the outlet and moves more air against more pressure.
• This fan has a forward curved blade and a cutoff to shear the air spinning around the fan wheel (Figure above).
• The centrifugal fan is very quiet when properly applied.

Axial Fan:

• The axial-flow fans have blades that force air to move parallel to the shaft about which the blades rotate.
• Axial fans blow air along the axis of the fan, linearly, hence their name.
• This type of fan is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in wind tunnels
• Axial flow fans are applied for air conditioning and industrial process applications.
• Standard axial flow fans have diameters from 300-400 mm or 1800 to 2000 mm and work under pressures up to 800 Pa.

Q9) What do you mean by Comfort air conditioning and Industrial air conditioning. Write its applications.

A9)

• Comfort air conditioning: - Aim at giving max human comfort to occupants/users of conditioned space.
• Applications of Air-Conditioning to provide Comfort Air-Conditioning: - It is meant for human comfort. It provides comfortable & healthy conditions for the occupants in residences, theaters, hospitals, offices, railway coaches.
• Industrial air conditioning: - The conditioning creates, controls and maintains such an environment inside the conditioned space, that it would suit best to the needs of industry.
• Applications of Air-Conditioning to provide Industrial Air-Conditioning: - It is used for improving the quality of the manufactured materials. It increases the working efficiency of the employees in the factories.

Q10) What do you mean by evaporators? Write its function.

A10)

Evaporator:

• An evaporator is a device in a process used to turn the liquid form of a chemical substance such as water into its gaseous-form/vapor. The liquid is evaporated, or vaporized, into a gas form of the targeted substance in that process.

Function of evaporator:

• The evaporator works the opposite of the condenser, here refrigerant liquid is converted to gas, absorbing heat from the air in the compartment. When the liquid refrigerant reaches the evaporator, its pressure has been reduced, dissipating its heat content and making it much cooler than the fan air flowing around it.

Q11) Explain Refrigerates Freezers 

A11)

• A refrigerator (colloquially fridge) is a popular household appliance that consists of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room.
• Refrigeration is an essential food storage technique in developed countries.
• The lower temperature lowers the reproduction rate of bacteria, so the refrigerator reduces the rate of spoilage.
• A refrigerator maintains a temperature a few degrees above the freezing point of water. Optimum temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F).
• A similar device that maintains a temperature below the freezing point of water is called a freezer.
• The refrigerator replaced the icebox, which had been a common household appliance for almost a century and a half. For this reason, a refrigerator is sometimes referred to as an icebox in American usage.
• The Basic Components of a Freezer:

The components of a freezer are as follows:

• A compressor
• A condenser
• An evaporator
• A capillary tube
• A thermostat

• The refrigerant begins the cooling process as a vapor under low pressure. The compressor squeezes the vapor's particles, which heats it up and converts it into a high-pressure state.
• As the vapor travels through the condenser coils, it loses the heat but retains its high pressure.
• Vapor compression isn't the only way to create a super-cold food storage environment.

Q12) Write note on Ice plant.

A12)

Plant Layout:

• Air Cooled or Water Cooled or with Evaporative Condensers
• Any Environment-compatible Refrigerant (ammonia or halocarbons)
• Standard Ice Cans Square or Rectangular for 25 kg or 50 kg Blocks.

Requirements:

• Suitable Location
• Land
• Structural construction of ice plant
• Utilities
• Machineries
• Management
• Labour
• Clients

Fig. Ice plant

Q13) What do you mean Comfort and industrial air conditioning.

A13)

• Comfort air conditioning: - Aim at giving max human comfort to occupants/users of conditioned space.
• Applications of Air-Conditioning to provide Comfort Air-Conditioning: - It is meant for human comfort. It provides comfortable & healthy conditions for the occupants in residences, theaters, hospitals, offices, railway coaches.
• Industrial air conditioning: - The conditioning creates, controls and maintains such an environment inside the conditioned space that it would suit best to the needs of industry.
• Applications of Air-Conditioning to provide Industrial Air-Conditioning: - It is used for improving the quality of the manufactured materials. It increases the working efficiency of the employees in the factories.

Q14) What is cryogenic liquefaction.

A14)

• Such strategies are primarily based totally solidly in engineering thermodynamics and depend basically on a mixture of approaches which make up a cycle. A cycle includes a closed circuit in which the running fluid, for instance helium, is compressed, expanded, and warmth exchanged in such a manner as to attain cooling.
• However, actual refrigeration and liquefaction structures are made up of comparable approaches which might be normally as compared of their overall performance to that of the suitable Carnot cycle.
• In all fuelling refrigeration structures, the cooling is accomplished with the aid of using a growth method. There are basically styles of growth which might be applied. Isentropic growth is that in which the fluid does paintings and expands preserving its entropy constant (LIS= 0). This is the best approach of growth as it produces the most important temperature extrude over a given strain extrude.
• The different growth method is isenthalpic growth, in which the fluid undergoes a strain extrude without heat transfer (.dQ = 0). This approach is in not unusual place software in practical refrigeration structures for its ease of use. However, it's far of decrease thermodynamic performance due to the fact it's far an irreversible method main to no idealities.
• He thermodynamic obstacles of the liquefaction manner may be verified excellent with the aid of using attention of an excellent system, that is, a refrigeration cycle that plays at Cabot performance and therefore includes reversible isothermal and isentropic processes.
• Consider a Cabot fridge generating cooling in a low-temperature reservoir. Furthermore, not like the dialogue with inside the preceding section, expect that the fridge includes a huge wide variety of cycles working over small temperature differences.

Q15) Explain Thermo Electric refrigeration system.

A15)

• Thermoelectric refrigeration is the manner of pumping warmth electricity out of an insulated chamber on the way to lessen the temperature of the chamber under that of the encircling air.
• Thermoelectric refrigeration makes use of a precept referred to as the "PELTIER" impact to pump warmth electronically.
• The Peltier impact is known as after a French scientist who determined it in 1834.
• Special order heater ONLY variations of our insulated bins are utilized by Meals on Wheels, different senior warm meal packages, college warm meal packages and via way of means of caterers all throughout the country.
• Safety: No open flames, propane, or poisonous refrigerants used.
• Reliability: Thermoelectric have a forty 12 months confirmed song file in military, aerospace, laboratory, and now customer packages.
• Low upkeep: The best upkeep required with any Kolton unit is periodic "dusting" and Vacuuming to make sure precise warmth dissipation.
• COOLING TECHNOLOGY COMPARISON THERMOELECTRIC:
• Cooling is done electronically the usage of the "Peltier" impact - warmth is pumped with electric electricity.
• COMPRESSOR: Cooling is done via way of means of vaporizing a refrigerant (including Freon) in the fridge - warmth is absorbed via way of means of the refrigerant thru the precept of the "latent warmth of vaporization" and launched out of doors the fridge in which the vapor is condensed and compressed right into a liquid again. Uses mechanical electricity.
• In 1834 Jean Peltier mentioned that after an electrical present day is implemented throughout the junction of diverse metals, warmth is eliminated from one of the metals and transferred to the different.

Q16) Explain Steam jet refrigeration system.

A16)

• Steam jet or Ejector refrigeration machine makes use of water as refrigerant. It makes use of the simple precept of boiling of liquid at decrease temperature through lowering stress on its surface.
• This machine employs a steam ejector or booster in preference to mechanical compressor. The foremost additives as proven in determine are flash chamber or evaporator, steam nozzles, ejector and condenser.
• The flash chamber is closely insulated and is outfitted with perforated pipes which spray heat water popping out of refrigerated space. Some of this water is transformed into vapors after soaking up latent warmth from the relaxation of the water, thereby cooling it.
• Loss of water via vapors is made up from makeup water line. High stress steam from boiler is surpassed via steam nozzle thereby growing its velocity. This entrains water vapors from flash chamber and outcomes in similarly formation of vapors.
• The aggregate of steam and water vapor passes via venture-tube of ejector and receives compressed. This results in upward push in temperature and stress of the aggregate after which it's far fed to the water cooled condenser. The condensate is once more fed to boiler as feed water.

Q17) Explain Vortex tube refrigeration system.

A17)

• It is one of the non-traditional kind refrigerating structures for the manufacturing of refrigeration. The schematic diagram of vortex tube is proven with inside the Fig.
• It includes nozzle, diaphragm, valve, warm-air aspect, bloodless-air aspect. The nozzles are of converging or diverging or converging-diverging kind as in line with the layout.
• A green nozzle is designed to have better speed, more mass glide and minimal inlet losses. Chamber is a part of nozzle and centers the tangential access of excessive speed air-circulation into warm aspect.

• Generally the chambers aren't of round form, however they're steadily transformed into spiral form. Hot aspect is cylindrical in go phase and is of various lengths as in line with layout.
• Valve obstructs the glide of air via warm aspect and it additionally controls the amount of warm air via vortex tube.
• Diaphragm is a cylindrical piece of small thickness and having a small hollow of precise diameter on the center.
• Air circulation touring via the center of the new aspect is emitted via the diaphragm hollow. Cold aspect is a cylindrical component via which bloodless air is surpassed.

Q18) Explain Magnetic refrigeration system.

A18)

1. Nowadays classical vapor compression refrigeration generation is broadly used, however there are various obstacles in the usage of vapor compression device, due to the fact generation may be very power inefficient.
2. These refrigerants had been unwanted for environmental reasons. The primary disadvantage of the vapor compression device is that it calls for a compressor to compress a massive quantity of refrigerant vapor, which calls for a massive electricity for its operation.
3. In addition, it has bad COP compared with the Carnot cycle, environmental dangers restrict to the bottom temperature of the refrigeration cycle.
4. For this reason, researchers and engineers running in refrigeration have commenced to analyze new technologies for refrigeration amongst which the maximum promising is magnetic refrigeration.
5. Magnetic refrigeration is one in all such techniques, which guarantees to be of sensible importance despite the fact that the idea continues to be into research. The magnetic refrigeration device works with the aid of using making use of a magnetic subject to a magnetic fabric inflicting it to warmth up.
6. This extra warmth is eliminated from the device with the aid of using water, cooling the fabric back off to its authentic temperature.
7. The take a look at is primarily based totally on a complete and easy evaluation with info of the whole thing one wishes to recognize approximately magnetic refrigeration as an opportunity to the traditional refrigeration device.
8. In the subsequent sections, the authors will attempt to deliver complete data approximately the traditional refrigeration device and magnetic refrigeration device.