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Refrigeration equipments

FILL IN THE BLANKS-REFRIGERATION EVAPORATORS

Posted on April 7, 2018 7:28 am by admin

 

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FILL IN THE BLANKS-REFRIGERATION EVAPORATORS

Fill in the blanks will improve the deep understanding of a evaporator used in refrigeration. Evaporators are the cooling unit in a refrigeration unit. Both dry and flooded evaporators produce cooling using latent heat. Fill in the blanks for evaporators in refrigeration further increases practical knowledge.

  1. Evaporator used in the domestic units is called ————-evaporator.
  2. Commercial refrigeration uses an evaporator which is called ————-evaporator.
  3. Industrial refrigeration uses an evaporator which is called ————-evaporator.
  4. The evaporator is fitted between —————- and —————-.
  5.  Degree of super heat in dry evaporators is ————–.
  6. But flooded evaporator require   ————–degree of super heat.
  7. Standard degree of super heat  is ————–.
  8.  In actual practice, degree of super heat is ————–.
  9. Refrigerant evaporates in the evaporator by taking ——–heat in the evaporator.
  10. Evaporation of refrigerant is by taking heat from the ——–to be cooled in the evaporator.
  11.  Other name of evaporator is  ——unit.
  12. Pressure of the refrigerant is ——in the evaporator.
  13. Temperature of the refrigerant is ——in the evaporator.
  14. State of the refrigerant at the inlet of the evaporator is mostly————.
  15. At the outlet of the dry evaporator, state of the refrigerant  is ————-vapor.
  16. Name of the unit between the flooded evaporator and compressor is ————.
  17.  Expansion valve used with dry evaporators is ————-.
  18. The expansion valve used with flooded evaporators is ——-side float
  19. Evaporation temperature in the evaporator depends upon the ————in the evaporator.
  20.  Evaporator pressure is linked to the ——boiling point of the refrigerant.
  21.  Most of the evaporators have pressure  ———- atmospheric pressure.
  22.  Outlet of the flooded evaporator has refrigerant as  ——–and————.
  23. Material of the evaporator tubes is ————–with ammonia as refrigerant.
  24. Tubes of evaporator are made of  ————–with refrigerant R-134a.
  25.  COP of a refrigeration unit———–with the decrease of evaporation temperature.
  26. Power input increases as evaporator temperature ————.

ANS:

  1. Dry, 2. Dry, 3. Flooded, 4. Expansion vale, compressor, 5.zero, 6.zero, 7.50C, 8. Variable, 9.latent, 10. Products, 11. Cooling, 12. Low, 13. Low, 14. Liquid, 15.saturated, 16. Accumulator, 17. Capillary tube, 18.Low, 19. Pressure, 20. Normal, 21. Above, 22. Liquid, vapor, 23. Steel, 24. Copper, 25. Decreases, 26. decreases


FILL IN THE BLANKS REFRIGEATION CONDENSERS

Posted on April 2, 2018 3:40 pm by admin

https://www.mesubjects.net/wp-admin/post.php?post=7356&action=edit         Refrigeration Filling blanks Expansion valves

https://www.mesubjects.net/wp-admin/post.php?post=6742&action=edit        Q. A. Vapor Compression Refrigeration-3

https://www.mesubjects.net/wp-admin/post.php?post=6740&action=edit         Refrigeration Compressors

FILL IN THE BLANKS REFRIGEATION CONDENSERS

Fill in the blanks for condensers in refrigeration increase the understanding. Thus, more fill in the blanks on condensers be tried to further increase the knowledge.

  1. Condenser removes ——— and ——— heat.
  2.  Vapors change into liquid in the condenser at the  ———— temperature.
  3.   In the condenser, vapors change into liquid at a  ———temperature.
  4. During change of vapors into liquid in the condenser ———-remains constant.
  5. Air cooled condensers are used with ————— refrigeration plants.
  6. Water cooled condensers are used with ————–capacity refrigeration plants.
  7. Evaporation cooled condensers are used with —————capacity refrigeration plants.
  8. Hot water in the condenser is cooled by ———–for reusing in the condenser.
  9. Blower used for cooling in the cooling tower causes ——– draft.
  10. ———- pump is used to circulate water in the cooling tower.
  11. Receiver stores the ———pressure liquid refrigerant.
  12. The installation of the receiver is between the condenser and the————-cum filter.
  13. While refrigerant in the receiver is to be collected, its ——— valve is closed.
  14. A fine metallic ———– is used in the drier cum filter.
  15. ————- is filled in the drier cum filter for removing water from the—————.
  16. Drier cum filter removes —————–particles and————–.
  17. Drier cum filter can be refillable or —————— type.
  18. The location of the Drier cum filter is after the —————– in the refrigeration circuit.
  19. In refrigeration, receiver is used with —————capacity refrigeration unit.
  20. ————- cooled condensers are used in small refrigeration units.
  21.  Evaporating condenser uses  water and ——– for condensing the refrigerant.
  22.  Outlet of the drier cum filter is connected to the ————-device.
  23. Cooling towers have natural, forced and ———— type drafts.
  24. Use of cooling tower is necessary when the space is —————.
  25. One can use cooling pond i when the space is —————.
  26. There is ——- difference in the aim of the cooling tower and the cooling —————.

ANSWERS

  1. Super heat and latent heat, 2. Saturation, 3.constant, 4. Pressure, 5. Domestic units, 6.medium, 7. Large, 8. Cooling tower, 9. Forced, 10. Centrifugal, 11. High, 12. Drier, 13. Outlet, 14.sieve, 15. Silica gel, 16. Solid, moisture, 17. Replaceable, 18. Receiver, 19. Large, 20. Air, 21. Air, 22. Expansion, 23. Balanced, 24. Limited, 25. Unlimited, 26.no, pond


FILL IN BLANKS-COMPRESSOR

Posted on April 2, 2018 4:52 am by admin

FILL IN BLANKS-COMPRESSOR

Fill in the blanks makes the understanding of a refrigeration compressor deep and clear. Thus, more fill in the blanks will further increase the knowledge.

  1.  Compressor using a belt drive in a refrigeration system is called—————.
  2.  In a refrigeration system, compressor  is called the ———–of the system.
  3. The function of the compressor is to ————–low temperature and low pressure vapors.
  4. State of the refrigerant after compression is ——-pressure and ———–temperature.
  5. Pressure is increased by the compressor  because of decrease in—————.
  6. Type of Compressor used in the domestic unit is called the—————–unit.
  7. Most commonly used compressors in refrigeration are————, rotary and———.
  8. Reciprocating compressors are used for high———difference and low—————.
  9. Rotary compressors are used for medium pressure difference and ——–volume.
  10. Centrifugal compressors are used for ———pressure difference and high —–.
  11.  Refrigerants used with reciprocating compressors are R-22 and ——.
  12.  ——is the refrigerant used with rotary compressor.
  13. Various refrigerants used with centrifugal compressors are R-114 and R————-.
  14.  Boiling point of the refrigerant to be used with reciprocating compressor should be much——— 00 C
  15.  With rotary compressors, the normal boiling point of the refrigerant  should ——— 00 C
  16.  Normal boiling point of the refrigerant to be used with centrifugal compressor should be much——— 00 C.
  17.  Material of construction of the compressor dome is—————.
  18. Connecting rod  material of construction  is—————.
  19. Piston’s  material of construction is—————.
  20.  Ammonia compressors are always ————- cooled.
  21.  Freon compressors are always ——– cooled.
  22. ————is used for stopping the leakage around the valve stem of a service valve.
  23. Single acting compressor completes one cycle in —————-revolutions.
  24. ————–cooling in between the compressors improves the COP.
  25. When piston reaches the bottom of the cylinder, it is called the ———dead center.
  26. Refrigerating capacity of the Compressor increases with the ———————of the compressor.
  27. Volumetric efficiency increases with the ————of the compressor.
  28. ——and————–are enclosed in the hermetically sealed unit.
  29. Speed of the compressor can be ————-by the use of a bigger pulley.
  30. Oil separator is used to separate ——-oil from the ———–.
  31. Motor and compressor speed is ————– in a hermetically sealed unit.
  32. Using a hermetically sealed unit, the speed of the compressor ———be changed easily.
  33. Domestic unit uses ———– is used as an expansion valve.
  34. Generally —————– valves are not used in a hermetically sealed unit.
  35. There are absolutely no chances of refrigerant —————-in a hermetically sealed unit.

 

ANS:

1.Open unit, 2.Heart, 3. Compress, 4.high, high, 5.volume, 6. hermetically sealed unit, 7. reciprocating, centrifugal, 8. pressure, volume, 9. Medium, 10. low, volume, 11. Ammonia, 12. Iso-butane,13. R-11, 14. Below, 15. Around, 16. above above, 17. Cast iron, 18. Cast iron, 19. Cast iron, 20. Water, 21. Air, 22. Gland packing, 23.two, 24. Inter, 25. bottom, 26. speed, 27. decrease, 28. Compressor, motor  29. decreases, 30. lubricating, refrigerant, 31.same, 32. Cannot, 33.capillary tube, 34. Service, 35. leakage



REFRIGERATION RECIPROCATING COMPRESSORS

Posted on December 12, 2017 1:32 pm by admin

 

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https://www.mesubjects.net/wp-admin/post.php?post=6714&action=edit         Vapor Compression Refrigeration

REFRIGERATION RECIPROCATING COMPRESSORS

Three types of compressors are used. These are

  1. Reciprocating compressor
  2. Rotary compressor
  3. Centrifugal compressor

 Reciprocating compressors used with respect to the type of drive 

These are of three types.

  1. Hermetically sealed compressor–when compressor and motor has the same shaft or coupled shaft and this assembly is sealed in a single housing.
  2. Semi-open unit–The housing for motor and compressor are different. These are directly coupled and have the same speed.
  3. Open unit–Compressor and motor are coupled by a belt drive and hence their speeds are different.

Definition a reciprocating compressor

In this, piston moves to and fro in a straight line. It sucks the low pressure low temperature from the evaporator and increases its pressure and temperature by compression. Thus creates the flow of refrigerant too.

 Reciprocating compressors

The types of reciprocating compressors is based on their construction, orientation and working.

  1. As per number of cylinders, namely single cylinder, double cylinder and multi-cylinder
  2. According to the orientation of the cylinders, namely horizontal, vertical. Vertical cylinder type is more commonly used
  3.  Positioning of the working vapor or gas with the piston, namely single acting or double acting. Double acting is of horizontal type. These are more common in steam engines.
  4. With respect to the times of compression, namely single compression (single stage compression) and multi-stage compression.
  5. On the basis of the cooling medium used for cooling the head of the compressor, namely air cooled (more common) and water cooled (Ammonia compressors )
  6.  Arrangement of pistons, namely V arrangement and W arrangement.

 Main parts of a reciprocating compressor

The main parts are

  • Valve plate ad valves
  • Cylinder
  • Piston and piston rings
  • Gudgeon pin
  • Connecting rod
  • Service valves
  • Shaft
  • Shaft seal
  • Flywheel

 Shaft seal and  its types.

Shaft seal is one which prevents the leakage from where it is coming out of the compressor and is then connected to the flywheel. As shaft has to rotate leakage can Easily occur from the crankcase which is under pressure. These shaft seals are of two types, namely Bellows type and rotary type.

(a) Bellows type shaft seal

The various parts of the seal are

  1. Bronze bellows
  2. Spring
  3. Seal ring has a rubber ring surrounded by a steel ring
  4. Seal plate
  5. Gasket

When this assembly is made in the compressor around the shaft, the seal ring is pressed against the d provides a leak proof joint. Further, bellows also provides a high degree flexibility to keep the seal ring in perfect contact with the shaft. The seal flange is clamped against the lead gasket by the seal plate.

(b) Rotary type shaft seal

The parts of a rotary seal are

  1. Seal Plate
  2. Spring
  3. Seal ring

It differs from the bellows type that it does has a bellows but clamped against the lead gasket by a seal plate.

 



REFRIGERATION EQUIPMENTS-2

Posted on November 27, 2015 10:33 am by admin

 

 

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https://www.mesubjects.net/wp-admin/post.php?post=5065&action=edit      Refrigeration equipment-1

https://www.mesubjects.net/wp-admin/post.php?post=4198&action=edit      MCQ Vapor Compression Refrigeration

https://www.mesubjects.net/wp-admin/post.php?post=4194&action=edit       MCQ non-conventional refrigeration

REFRIGERATION EQUIPMENTS-2

Dry evaporators are used in domestic units. Flooded evaporators are in commercial and industrial units. Liquid suction heat exchanger ensures super heated vapor to compressor and sub-cooled refrigerant to the expansion valve. Refrigeration equipment includes compressors, condensers, evaporators, expansion valves, piping and various controls.

TYPES OF EVAPORATORS

Dry expansion type and flooded type

In dry expansion type evaporator, the refrigerant is fully dry before the exit of evaporator. It is used in refrigerators, window air conditioners, water coolers, deep freezers.

Flooded evaporators

Evaporators contain liquid and vapor till its outlet. There is a separator called  accumulator to send only vapors to the compressor. The remaining liquid is sent back to the evaporator inlet. These are used in large capacity refrigeration plants.

Oil separator

Oil separator is a cylindrical vessel. It is placed the just after the compressor. This separator has baffles in it. It separates the lubricating oil from the refrigerant. If the oil is not separated, oil will flow to the condenser and the evaporator. This will decrease the rate of heat transfer. Thus cooling capacity of the refrigerating unit will decrease. Oil collected at the bottom is sent back to the compressor sump. Oil separator allows effectively oil free refrigerant to the condenser.

Muffler

A cylinder after the compressor to reduce the velocity of refrigerant and also reduces the noise in the unit.

Liquid suction heat exchanger (LSHE)

LSHE sub-cools liquid refrigerant going to the throttle valve. It also super heats the vapors coming from the evaporator. It increases the refrigerating effect and hence increases the COP.

Drier cum Filter

Drier cum filter is placed just before the expansion valve. It filters the refrigerant from impurities. It also removes any moisture present in the refrigerant.

Suction accumulator

Used in flooded evaporators. It separates vapor refrigerant going to the compressor. It,also, sends liquid refrigerant back to the evaporator.

Sight glass

Sight glass  is a glass window. It is fitted after the condenser. It helps to see the state of refrigerant and the type of flow.

Moisture indicator

Moisture  indicator tells the moisture present in the air. Necessary steps can be taken to insure the correct amount of moisture in the conditioned air.

Solenoid valve

This valve is placed in liquid line. It has only two positions either fully open or fully closed. It is electrically operated. When power is off, it is in closed position.

Check valve

A valve which allows flow only in one direction.

Evaporator back pressure regulating valve (BPRV)

Hand operated valve which controls rate of refrigerant flow and pressure in evaporator. In this, there are two outlets. Through one pipe refrigerant goes to the compressor. Through the other pipe, refrigerant goes to the outlet of evaporator for the pressure adjustments.

 Relief valve

This is provided in the receiver to release excess pressure. It is a safety valve like a one in a pressure cooker.

Fusible plug

Fusible plug is a plug which can melt (fuse) due to excessive heat. It is there in a pressure cooker or in a boiler.

Pipes/Tubes in Refrigeration

Copper  and copper alloys are often used in heating, air conditioning, refrigeration, and water supply installations because of their inherent resistance to corrosion and also ease of installation. There are two principal classes of copper tubes. Copper tubes of Types K, L, and M are used with Freon refrigerants. These are normally annealed (soft) copper tubing (without threading). Copper tubing is joined with soldered or brazed. Small size copper tubes are joined by FLARE or compression fittings.

 PIPE MATERIAL WITH AMMONIA

Mild steel pipe is used with ammonia refrigerant since ammonia is highly corrosive to copper.

 



REFRIGERATION EQUIPMENTS-1

Posted on November 27, 2015 10:28 am by admin

 

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https://www.mesubjects.net/wp-admin/post.php?post=5067&action=edit      Refrigeration equipment-2

https://www.mesubjects.net/wp-admin/post.php?post=4198&action=edit      MCQ Vapor Compression Refrigeration

https://www.mesubjects.net/wp-admin/post.php?post=4194&action=edit       MCQ non-conventional refrigeration

REFRIGERATION EQUIPMENTS-1

Reciprocating, rotary and centrifugal compressors are used for refrigerants having lower, medium and high boiling points. Air, water and evaporative condensers are used in domestic, commercial and industrial plants. Cooling tower cools the hot water from the condenser for its reuse.

COMPRESSORS:(i)  Reciprocating compressors: used with

(a) lower boiling temperature (much below 00C) refrigerants

(ii)  low specific volume at – 150C,

(c) (pcond – –pevap) > 3.5 atm (  R-22, NH3, etc.).

Reciprocating compressors are of three types.

(a) Hermetically sealed units: Has both compressor and motor in one housing, used in refrigerators, water coolers, window air conditioners, display cabinets

(b) Semi-open units: There is a separate housing for compressor and motor, directly coupled having same RPM, used in units of 100 TR capacity refrigeration plants

© Open units: It has a separate housing for motor and compressor, connected by belt/gear drive, different RPM, used in large capacity refrigeration plants

(ii) Rotary compressors: This is used for

(a) medium boiling point ( between +2 and -20C) refrigerants,

(b) medium specific volume at -150C

(c) (pcond – –pevap) > 1.5 atm and <3.5 atm  (isobutene)

(iii) Centrifugal compressors: It is used with

(a) higher boiling point ( much > 00C) refrigerants

(b) large specific volume at -150C

(c) (pcond – –pevap) < 1.5 atm such as R-113

L/D RATIO FOR VARIOUS RECIPROCATING COMPRESSORS

Type of unit                                                     L/D

Vacuum pumps                                               0.5

High speed air compressors                         0.5

Reciprocating Freon Compressors              0.8

Ammonia Reciprocating  Compressors      1.0

High pressure compressors                           4.0

( To keep piston force per unit inertia small, diameter is kept small for high pressure compressors)

DIFFERENT TYPES OF CONDENSERS:

(a)Finned tube type

(b) Double tube type

(c)  Coil shell type

(d) Shell and tube type

Q. Give the brief description of Shell and Tube Condenser.

The refrigerant passes through the shell (Cylinder) and the water passes through the tubes. There are number of straight tubes and hence there are no bends to reduce the pressure drops. It is also easy to clean the tubes when the scale is formed in the tubes. Hot water coming out of the condenser is cooled in the cooling tower for reuse,

THREE TYPES OF COOLING ARRANGEMENT IN CONDENSERS

 AIR COOLED: Finned tube type: natural Air cooled  in refrigerators,  forced air cooled in water coolers, window air conditioners and deep freezers.

WATER COOLED: Shell and tube type: water in tubes and refrigerant in shell. These are used in medium capacity plants in libraries, cinema halls.

EVAPORATIVE COOLED (Simultaneously Air as well as water cooled ): bare tube type: used in large cooling plants in cold storage’s, ice plants, wine industries, milk plants and refineries.

Cooling Tower: It is a heat exchanger where hot water from condenser outlet is cooled by atmospheric air. This cooled water is reused in the condenser. Thus, it makes the cooling in the condenser economical. There is an accumulator to send only vapors to the compressor and remaining liquid to the evaporator inlet. These are used in large capacity refrigeration plants.

EXPANSION VALVES: Five types: Capillary tube, Automatic expansion valve (AEV), Thermostatic expansion valve(TEV), Low Side float valve(LSFV) and high side float valve(HSFV).

Capillary tube:  Used in small capacity plants like refrigerators, window air conditioners, water coolers, display cabinets, and deep freezers.

Automatic expansion valve(A E V): It is used with constant cooling requirements: not very common as it has disadvantages like supply of more refrigerant on decrease of cooling requirement and reduced supply of refrigerant on increase of cooling requirements.

Thermostatic Expansion Valve (T E V): It maintains a constant degree of super heat at the outlet of the evaporator under all conditions of cooling load. It increases the flow of refrigerant on increase of cooling requirements. It decreases the flow on decreasing cooling requirements. There is a feeler bulb containing a different refrigerant than the one circulating in the refrigerating machine. This feeler bulb feels the degree of super heat at the outlet of the evaporator. In case of increase of degree of super heat it increases the flow rate. When degree of super heat decreases the flow rate of refrigerant.

Low Side Float valve (L S F V): A float valve is located in the evaporator itself. If cooling requirement increase causing increase in evaporation. Due to this, the level goes down and the float permits more quantity of refrigerant. When cooling requirement decreases, there is less rate of evaporation. Hence, float goes down by lesser height and refrigerant flow decreases.

High Side Float Valve (H S F V): Float valve is located in the receiver itself. More cooling requirements increase the pressure in the evaporator. This increased pressure lifts the float and increases the supply of refrigerant in the evaporator and vice versa.  On less cooling requirement, pressure decreases and there is lesser flow of refrigerant.



EVAPORATORS

Posted on May 12, 2015 10:57 am by admin

EVAPORATORS

It is cooling coil in a refrigeration system. Normally its temperature is much lower than 0 o C. The liquid refrigerant enters into the evaporator and is converted into vapor by taking latent from the items to be cooled. The items to be cooled surround the evaporator. The evaporator inlet is connected to the outlet of the expansion valve. The evaporator outlet is connected to the inlet of the compressor.

Types of Evaporators

The classification is based on vapor condition, frost formation, construction and secondary refrigerant used.

(a) Vapor Condition- These evaporators are on vapor condition at the inlet of compressor. These are of two types.

(i) Dry evaporators

These are used in small (≤ 3 tons) and medium refrigeration plants (≥ 3 and ≤ 50 tons). These are used with hermetic sealed compressors and commercial refrigeration units. In these refrigerant becomes dry saturated vapor just before the outlet of the evaporator and super heated vapors enters the compressor. The cooling effect is contributed mainly by latent heat. These are used in fridges, window air conditioners, water coolers, cinema houses, hospitals etc. This type of evaporator uses expansion valve capillary tube in domestic units and thermostatic expansion valve in commercial units.

(ii) Flooded Evaporators

These are used with large cooling capacity industrial refrigeration units (≥50 tons). In these, refrigerant remains in liquid and vapor state at the just outlet of the evaporator. This liquid vapor mixture enter into a cylindrical unit called the accumulator which sends only the vapors to the compressor and liquid is sent back at the inlet of the evaporator. In this type, entire evaporator is used more effectively for causing cooling effect by the latent heat only. These are used in big industries and refineries having large cooling requirements. This type of evaporator uses low side and high side float valves as expansion devices.

(b) Based on Frost – These are frosting, defrosting type and non frosting types.

(i) Frosting type—Used in frozen food cabinets

(ii) Defrosting type – Used in fridges. Defrosting was manual in earlier days. Presently it is automatic by using a heater in the evaporator with a timer. Say after every 24 hours, compressors becomes off and heater is on for a fixed period (say ten minutes). The heater goes off and compressor automatically restarts. The evaporator becomes frost free.

(iii) Non frosting type – when the evaporator is working above freezing point of water i.e. in water coolers.

(c)  Evaporators based on shape of construction

(i) Bare tube type –Used in ice plants for cooling of the brine solution.

(ii) Plate and tube type – Used in fridges

(iii) Finned tube type – Used in window air conditioners and water coolers

(iv) Shell and Tube type – Used for getting chilled water (between 5-90C) in central air conditioning plants. Chilled water is sent to the various rooms. Each room is having a fan coil unit. In this, chilled water flows through the coil and air is blown over it with a blower. The cooled air cools the room. The hot water returns back to the shell and tube type evaporator. Refrigerant flows through the tubes and water is there in the shell. This type of evaporator is also called WATER CHILLER.

(v) Shell and coil Type — Used in ice plants for the cooling of the brine solution much below 00C.  Sodium chloride solution does not freeze till -290C and calcium chloride brine solution do not freeze till -550C. These solutions are called antifreeze solutions. There are many more anti-freeze solutions. Any one of these can be used as a secondary refrigerant in the ice plant.

(d) On the basis of secondary refrigerant

(i)  Direct system- Cools air which further cools the products placed in contact with air as in case of a fridge or window air conditioner.

(ii) Indirect System-Cooling coil cools water or brine. . This cooled brine cools the products as in case of ice plants. Chilled water is used in central air conditioning plants.



OPEN AND HERMETICALLY SEALED COMPRESSOR UNITS

Posted on May 10, 2015 9:40 am by admin

 

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https://www.mesubjects.net/wp-admin/post.php?post=5065&action=edit      Refrigeration equipment-1

https://www.mesubjects.net/wp-admin/post.php?post=4198&action=edit      MCQ Vapor Compression Refrigeration

https://www.mesubjects.net/wp-admin/post.php?post=4194&action=edit       MCQ non-conventional refrigeration

OPEN AND HERMETICALLY SEALED COMPRESSOR UNITS

Sr. No. Open Unit Hermetic Sealed Unit
1. Compressor and motor are connected with a V- belt Compressor and motor have the same shaft and are placed in a welded dome.
2.  Prime mover can be an AC/DC motor or an IC engine Prime mover is a single phase induction AC motor.
3. Speed of the compressor can be varied by using a stepped pulley. Speed of the compressor is fixed.
4. RPM of motor and compressor are different. RPM of motor and compressor are same.
5. A shaft seal is used for preventing the leakage around the shaft of the compressor. No shaft seal is required.
6. Compressor is mounted vertically and the motor is mounted horizontally. Compressor and motor can be mounted in any orientation.
7. Expansion valve is thermostatic/Low side float valve/high side float valve Expansion valve used is the capillary tube.
8. Uses suction and discharge service valves Only  a charging tube is used.
9. Charging of refrigerant is done from the high pressure side. Charging of refrigerant is done from the low  pressure side.
10.  It occupies more space. It is a compact unit.
11. It is costly. It is cheap.
12. It is noisy. It is quiet.
13. It is used for high cooling requirements i.e. for commercial units like cold storage, ice plants and industries. It is used for domestic units like refrigerator, window air conditioner,  water cooler and display unit in a confectionary shop.
14. Servicing is easy and less costly. Servicing is difficult and costly.
15. Chances of refrigerant leakage are more. Chances of refrigerant leakage are remote.
16. A receiver unit is used for storing of liquid refrigerant to supply  more  or less refrigerant during increased or decreased cooling requirements. This receiver is installed just after the condenser No receiver unit is  as large change in cooling requirements is not applicable.

 



COOLING TOWERS-NATURAL AND FORCED DRAFT

Posted on May 10, 2015 5:22 am by admin

COOLING TOWERS-NATURAL AND FORCED DRAFT 

Function

Cooling towers cool the hot water from the condenser so that same water can be reused time and again to reduce the cost of water used in condenser. Water is used in the condenser for condensing refrigerant for medium cooling plants having up to 100 tons of refrigeration cooling capacity. It is a  special type of heat exchanger. In this, hot water and atmospheric air are brought into direct physical contact. Air gets heated up and water gets cooled. Thus, some amount of water also gets evaporated and goes away with air. This evaporation is the main cause for the cooling of water. The cooling towers are one of main component of refrigeration units having water cooled condensers. Thus, these are used in  power plants, chemical processing industries and steel mills. Further, these are used to provide comfort cooling in hotels, hospitals and airports.

Types of Cooling Towers

There are four types of cooling towers mentioned below.

(i) Natural draft cooling tower–No blower is used.

(ii) Forced draft cooling tower – When a blower from below introduces air into the cooling tower.

(iii) Induced draft cooling tower – When a blower is placed at the top of the cooling tower and sucks air into it.

(iv) Balanced cooling tower – When induced and forced blowers are placed in the tower.

Out of these cooling towers, natural and forced cooling towers are more common in refrigeration and air conditioning.

 Advantages of a cooling tower

(i) There is a Significant reduction in the cost of water used in the condenser.

(ii) Compact – Does not need any extra space as it is mounted on the roof of a building or in the vertical orientation.

Difference between Natural Draft and Forced Draft Cooling Towers

Sr.No. Natural Draft Cooling Tower Forced Draft Cooling Tower
1. Hot water from condenser is cooled by natural air using free convection. Hot water from condenser is cooled by moving air using a blower.
2. It is widely open on sides. It is less open on sides.
3. It occupies more space. It occupies less space and hence is compact.
4. It is less efficient. It is more efficient.
5. It is cheap. It is costly.
6. It is installed in the open space where natural air is freely available. It is installed at the roof of the building.
7. Used for less refrigeration requirements. Used for large refrigeration requirements.


MCQ-CONDENSERS AND EVAPORATORS

Posted on April 8, 2015 4:29 am by admin

MCQ-CONDENSERS AND EVAPORATORS 

Dry evaporators are used in domestic units. These ensure that only super heated vapor goes to the compressor for its safety. Flooded evaporators are in commercial and industrial applications, These improve the COP of the plant.
 

 Evaporators

 Dry evaporator is used in A.C. Units of capacity
(a) < 3 tons
(b) < 10 tons
(c) >10 tons
(d) None
(Ans:a)

Flooded evaporator is used in A.C. Units of capacity
(a) < 3 tons
(b) < 10 tons
(c) >10 tons
(d) None

(Ans:c)

In a dry evaporator, refrigerant at the outlet is

(a) in the wet state

(b) saturated state

(c) super heated state

(d) None

(Ans: c)

In a flooded evaporator, refrigerant at the outlet is

(a) in the wet state

(b) saturated state

(c) super heated state

(d) None

(Ans: a)

Flooded evaporator needs at the outlet a

(a) Flash chamber

(b) Accumulator

(c) Inter cooler

(d) None

(Ans: b)

Finned tube evaporators are used in a

(a) Fridge

(b) Window air conditioner

(c) Water cooler

(d) None

(Ans: b)

Bare tube evaporator is used in a
(a) Cold storage plant

(b) ice plant

(c) milk Plant

(d) None

(Ans:b)

Evaporator in a refrigeration plant is fitted

(a) Before the condenser

(B) After the condenser

(c) After the compressor

(d) None

(Ans: d)

Evaporator in a refrigeration plant is fitted

(a) Before the condenser

(B) Before the expansion valve

(c) Before the compressor

(d) None

(Ans: c)

Condenser in a real refrigeration system does
(a) De-super heating and condensation
(b) Sub-cooling and condensation only
(c) De-super heating, condensation and sub-cooling
(d) None
(Ans:c)

Condenser in a refrigeration system decreases
(a) Temperature only
(b) Pressure only
(c) Temperature and pressure
(d) None
(Ans:a)

Condenser is air cooled when tons of refrigeration required is
(a) < 3
(b) <50
(c) > 100
(d) None
(Ans:a)

Condenser is water cooled when tons of refrigeration required is
(a) < 3
(b) <50
(c) > 100
(d) None
(Ans:b)

Which is the type of condenser used for ≤ 3 Tons cooling capacity of a refrigeration unit?
(a) Shell and tube type
(b) Finned tube type
(c) Bare tube type
(d) None
(Ans:b)

Which is the type of condenser used for 10- 50 Tons cooling capacity of a refrigeration unit?
(a) Shell and tube type
(b) Finned tube type
(c) Bare tube type
(d) None
(Ans:a)

Which is the type of condenser used for ≤ 3 Tons cooling capacity of a refrigeration unit?
(a) Water cooled
(b) Air cooled
(c) Water and air cooled
(d) None
(Ans:b)

Which is the type of condenser used for ≥ 3 ≤50 Tons cooling capacity of a refrigeration unit?
(a) Water cooled
(b) Air cooled
(c) Water and air cooled
(d) None
(Ans:a)

Which is the type of condenser used for > 50 Tons cooling capacity of a refrigeration unit?
(a) Water cooled
(b) Air cooled
(c) Water and air cooled
(d) None
(Ans:c)
Forced air cooled condenser in refrigeration unit has a
(a) Counter flow
(b) Parallel flow
(c) Cross flow
(d) None
(Ans:c)

Water cooled condenser in refrigeration unit has a
Counter flow
Parallel flow
Cross flow
None
(Ans:a)

Heat lost in the condenser is

(a) <(N+W)

(b) = (N+W)

(c) >(N+W)

(d) None

(Ans:b)

Heat lost in the condenser is due 

(a) Decrease in the degree of super heat

(b) Decrease in the degree of sub cooling

(c) Decrease in degree of super heat +Latent heat + Increase of degree of sub-cooling

(d) None

(Ans: c)




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