e. industrial plant machinery - 6. refrigeration

8/2/2019 E. Industrial Plant Machinery - 6. Refrigeration

http://slidepdf.com/reader/full/e-industrial-plant-machinery-6-refrigeration 1/78

By

Engr. William R. Salazar, PME

Engr. Sid Vivas, PME

Engr. Jun Perocho, PME



What is Refrigeration?

y A process that involves the removal of heat

from an area which is desired to be kept cooland the rejection of that heat to an area whose temperature remains practically constant.

yMaintaining a space cooler than thesurrounding.



REFRIGERATION:

y-Is that branch of science which deals with the process of reducing andmaintaining the temperature of aspace or material below thetemperature of the surroundings.



KINDS OF REFRIGERATION

y1. VAPOR COMPRESSIONREFR IGERATION SYSTEM

y2.CASCADE REFR IGERATION SYSTEM

y3. A IR -CYCLE REFR IGERATION SYSTEM

y4. STEAM-JET REFR IGERATION SYSTEM



VAPOR COMPRESSION REFRIGERATION SYSTEM



CASCADE REFRIGERATION SYSTEM

CASCADE SYSTEMA cascade system combines two vapor-compression units, with the condenser of the low-temperature system discharging its heat to the

evaporator of the h igh-temperature system. Cascade systems can normally furnish refrigeration down to about -100 º C. There are two types of cascade

systems, the closed cascade condenser and the direct ± contact heat exchanger. In the closed cascade condenser fluids in the high ±pressure and low

pressure systems may be different but in the direct-contact heat exchanger the same fluid is used throughout the system. The direct-contact heat

exchanger type is most common used.



AIR CYCLE REFRIGERATION SYSTEM

-

commercial application in which a gaseous refrigerant is used throughout the cycle. Compression is

accomplished by a reciprocating or centrifugal compressor as in the vapor-compression cycle, but

condensation and evaporation are, of necessity, replaced by a sensible cooling and heating of the

gas. An air cooler is used in place of a condenser and a refrigerator in place of an evaporator. The

expansion valve is replaced by an expansion engine or turbine.



STEAM JET REFRIGERATION SYSTEM

-

Steam jet refrigeration is a type of water evaporative refrigeration where in water

is used as the refrigerant. The principle of operation is based on the fact that water will

boil or vaporize rapidly, at a relatively low temperature, if the pressure on the surface is

reduced sufficiently.

A steam jet refrigeration shown, an ejector sucks or draws water from the surface

of the in the evaporator or flash chamber, causing the pressure in the evaporator to to

drop. The ejector reduces the pressure in the evaporator to a point at which the water

will vaporize at the desired temperature. In vaporizing, it absorbs heat and cools the

remainder of the water in the evaporator. The steam pressure at the ejector nozzle



STEAM-JET REFRIGERATION SYSTEM (cont.)

The evaporation of the water in the evaporator, reduces the temperature of the water in the evaporator. This cold water, 4 º C to 21 º C, is circulated by means of pumps,

to the area to be cooled.

Steam jet systems are used extensively in air conditioning, and for cooling owater in certain chemical plants for gas absorption. The cooling temperatures

provided by the steam jet mechanism are usually between 4 º C and 21 ºC.Temperatures below 4 º C are impractical due to the danger of freezing.



STEAM JET REFRIGERATION



METHODS OF REFRIGERATION

1. ICE REFR IGERATION

2. MECHANICAL REFR IGERATION

3. ABSORPTION REFR IGERATION

4. STEAM JET REFR IGERATION

5. A IR CYCLE REFR IGERATION



What is a Refrigerant?

yRefrigerant is a chemical substance used forheat transfer in a refrigerating system.

yIt absorbs heat in the evaporator by changeof state from liquid to a gas, and gives upthis heat by condensing at a highertemperature and pressure from gas to liquidstate.



Kinds of Refrigerants

y Ammonia NH3

y

Carbon Dioxide - CO2

y Ethyl Chloride H2H5CL

y Freon 12 CCL2

y Freon 22 CHC3

y Iso Butene (CH3)3 CH

yMethyl Chloride CH3CL

y Sulfur Dioxide SO2



GOVERNMENT REGULATION

y K yoto Protocol?

MONTREAL PROTOCOL-

-This protocol on substances that deplete the

ozone layer is a multilateral environment

agreement that has been ratified by 196

countries, including the Philippines, commited to

phase out production and

consumption(importation of ODS according to an

agreed schedule. Under the protocol and our

national policies , CFCs are scheduled to be

phased out by 1January2010.



REPUBLIC ACT 6969(Toxic substances and Hazardous and

nuclear waste control act of 1990) Includesthe chemical control order for ozonedepleting substances(ODS) that covers theban, limit and/or regulation of the use,

manufacture, import, export, transport,processing, storage, possession and sale of ODS in compliance to Montreal protocol.



OZONE DEPLETING SUBSTANCES

FREONS

CFC 11

CFC 12

CFC 113HCFC 22

HALONS

Halon 1211Halon 1301

Methyl Bromide(CH3Br)

OTHERS:

HFC134aHFC23

HFC126



What is the principle of MechanicalRefrigeration?

yMechanical Refrigeration is theprocess of absorbing heat undertemperature, compression, pressure andexpansion and the working fluid known

as refrigerant.



What are the Types of Mechanical Refrigeration?

1. Absorption System of Refrigeration ability of one substance to absorb large volume amount of

vapor of another substance usually the liquidrefrigerant.2. Compression System of Refrigeration where the

refrigerant, at low pressure and temperature,enters the suction side of the compressor

through a scale trap, compression take place andrefrigerant leaves the compressor, at highpressure and temperature, passes through oilseparation which remove oil from it.



Difference between Direct and Indirect System of

Refrigeration.

yDirect expansion system the evaporation is indirect contact with the material or space

refrigerated or the refrigerant itself extracts theheat from the space to be cooled.

y Indirect expansion system the refrigerant isevaporated into the coils of the evaporator, which

are in a brine tank, thus brine secondary refrigerant is circulated to the coil of cold storagechamber to do the cooling.



What are the four processes of Mechanical

Refrigeration Cycle?(vapor compression

cycle)

1. Compression Process:a. The cold gas is withdrawn from the evaporator and

compressed to a higher temperature and discharge tothe condenser.

b. The pressure gas is changed into high pressure hotgasses.

2. Condensation Process:a. In this process, latent heat of the hot gas is removed

by passing it through the heat exchanger condensercooled by water.

b. The hot gas is changed its physical state into highpressure warm liquid.



What are the four processes of Mechanical

Refrigeration Cycle?(vapor compression cycle)

3. Expansion Process:a. In this process, the pressure of the refrigerant is reduced changing

its state into low pressure cold liquid particles.b. Refrigerant changes its state into gas picking up its latent of

evaporation thus lowering the temperature to freezing coldtemperature after it passes to the expansion control valve.

4. Evaporation Process:

In this process, the liquid refrigerant absorbs its latent of evaporationthus lowering the temperature to freezing cold temperature afterit passes to the expansion control valve.



What is refrigeration system?y An assembly of four major components

namely, the Compressor, Condenser,

Expansion Valve, and Evaporator; through which a very low boiling point substance(refrigerant) flow in cycle, and absorbs heat

from immediate surroundings, thereby producing the cooling effect (also known asrefrigerating effect).



Major Parts of Mechanical Refrigeration:

1. Compressor compresses refrigerant vapor andcauses it to flow in the system.

2. Condenser the refrigerant condenses while

rejecting heat to the cooling medium which is eitherair or water.

3. Expansion Valve reduces the pressure of therefrigerant so that low temperature will be attained;

regulates the flow of the refrigerant to theevaporator.

4. Evaporator the liquid portion of the refrigerantevaporates while absorbing heat from the

surrounding.



The Refrigeration Cycle



A basic refrigeration system



Compressor:y Function:

1. It acts as a pump , circulate therefrigerant through the system.

2. It maintain the low pressure at theevaporating unit during operation.

3. It compresses the low pressure gas to thehigher pressure and temperature thereby raising the boiling point.



Types of Compressors:

1. Reciprocating Compressor

2. Centrifugal Compressor

3. Rotary Sliding Vane Compressor

4. Helical Rotary Screw Compressor



TYPES OF COMPRESSOR



Centrifugal Compresor



Scroll Compressor



TYPES OF COMPRESSORS



TYPES OF COMPRESSOR



Typical Mounting Parts of

Reciprocating Compressor

yCylinder head

y

CrankshaftyPiston and Connecting rod

yMain bearing

yShaft sealyOil pump

ySuction Strainer



RECIPROCATING COMPRESSOR INTERNAL PARTS



Condensers:y Function:

1. Act as heat exchanger between the hot gasrefrigerant and the cooling medium.

2. Remove the heat of compression and also thelatent heat of condensation.

y Types:

1. Shell and tube condenser2. Double pipe condenser

3. Evaporative condenser

4. Air cooled Condenser



TYPES OF EVAPORATORS

TWO GENERALCATEGOR IES OFEVAPORATORS:

1. Dry -expansionevaporators

2. Flooded expansionevaporators

TYPES OF EVAPORATOR CONSTRUCTION:

1. Bare- tube evaporators

2. Plate-surface evaporator

3. Finned evaporator



REFRIGERANT DISTRIBUTOR



Types of evaporators



TYPES OF EVAPORATOR



The Compression Cycle



The Compression Cycle

Compressor Work (Power), Wc= h2 h1 k J/kg

= m(h2 h1) kw

Heat Rejected in Condenser, Qr

=h2 h3 k J/kg= m(h2 h3) kw

To find the cooling water requirement of condenser, mw:

mwCpT = m(h2 h3)

where: Cp = specific heat of water = 4.187 k J/kg-ºCT = temperature rise of the cooling water



Expansion Valve (Process)

h3 = h4h3 = (hf + x hfg)4

where: x = quality or weight of flash gas per unit weight of refrigerant

Refrigerant Effect, Qa- the rate of heat removal from the evaporator or lowtemperature space.

= h1 h4 k J/kg= m(h1 h4) kw

= m(h1 h4) Tons of Refrigeration

3.516

(1 ton of refrigeration = 3.516 kw = 200 Btu/min)

ENER G Y EFFICIENCY RATIO(EER)-is the ratio of refrigerating effect dividedby the power input and is usually expressed in Btu/hr - Watt.

EER =Refrigerating effect (Btu/Hr)

Power input (Watt)



Expansion Valve (Process)

Coefficient of Performance (COP)-the ratio of the refrigerating effect to thecompressor work.= Refrigeration Effect = Qa = h1- h4Compressor Work Wc h2 h1

Power Per Ton-the ratio compressor power in kw to the refrigerating effect.= Compressor Power , kw/ton

Tons of Refrigeration

Volume Flow at Suction, V 1= m v 1 m3/s

Volume Flow per Ton= V 1________ = ____mv 1___ , m3/secTons of Refrigeration Tons Ref ton



Standard Refrigeration Cycle:

Evaporation Temperature: 5ºF (-15ºC)

Condensing Temperature: 86ºF (30ºC)

Reversed Carnot Cycle in RefrigerationQr = heat rejected in condenser = T2(S2-S3) = T2(S1-S4)

Qa = refrigerating effect = T1(S1-S4)

W = net work = Qr Qa = T2(S2-S3) = T2(S1-S4)

COP = Qa = T1(S1-S4) = T1

W T2(S1-S4) - T1(S1-S4) Where: T1 = low absolute temperature, ºK or ºR

T2 = high absolute temperature, ºK or ºR



Refrigeration CompressorsType of Refrigeration Compressors:y 1. Reciprocating Compressor

y2. Centrifugal Compressory3. Rotary Compressor

y Vane typey Screw type



Classification of refrigeration compressors,

based on enclosure:

yOpen-Type Compressor compressor whosecrankshaft extends through the compressor

housing so that a motor can be externally coupledto the shaft.

yHermetically Sealed Compressor type in whichthe compressor and the motor are enclosed in the

same housing.y Semi-Hermetic Compressor hermetically sealedcompressor in which the cylinder head can beremoved for servicing of the valves and pistons.



TYPES OF COMPRESSOR



Performance of Reciprocating Compressor

1. Compressor work (Power)

= h2 h1 k J/kg

= m(h2 h1) kw

2. Piston Displacement, VD = D²LNC, m3/sec

4

Where: D = bore, m

L = stroke, m

N = speed, rev/s

C = number of cylinders



Performance of Reciprocating Compressor3. V 1 = volume flow at suction = m v 1

Where: v 1 = specific volume at suction, m3/kg

4. Nv = volumetric efficiency = V 1 VD

Conventional (clearance ) volumetric efficiency:Nv = 1 + c c( v 1 )

v2 where: c = clearance = Vc VD

V 1 = specific volume at suction, m3/kg V2 = specific volume at discharge, m3/kg



CONDENSERS

Types of condensers

used in refrigeration:

1. Air-cooleda. Bare tube

b. Finned tube

2. Water-cooleda. shell-and-tube

b. shell-and-coil

3. Evaporative-uses both water and air



TYPES OF CONDENSER

A IR COOLEDCONDENSERS:(Types)

1. Natural convection

2. Forced-air type

WATER -COOLEDCONDENSER:(Types)

1. Tube-in-tube or doublepipe

2. Shell-and-coil

3. Shell-and-tube



COOLING TOWER

COOLING TOWER -isused in a conjunction with the water- cooledcondenser. The coolingtower cools the warm water for recirculating itin the condenser.

Types of cooling tower:

1. Natural- draft or

atmospheric tower2. Mechanical-draft tower

a. Induced draft

b. Forced draft



COOLING TOWER



Expansion DevicesFunctions of the Expansion Device:

1. To reduce the pressure of the liquidrefrigerant from the condenser inorder to attain low temperature

2. To control the flow of the refrigerant tothe evaporator



Types of Expansion Devices:1. Capillary tube

2. Expansion Valves

a. Gate Valveb. Constant Pressure Expansion Valve

c. Thermostatic Expansion Valve

d. Thermostatic Expansion Valve withExternal Equalizer

e. Float Valve (used with flooded evaporator)



TYPES OF EXPANSION DEVICES



RefrigerantsI. Halocarbon Refrigerants

R -12 CCl2F2

DichlorodifluoromethaneR -22 CHClF2Monochlorodifluoromethane

R -40 CH3Cl Methyl Chloride

II. Inorganic Refrigrants

R -717 NH3 Ammonia

R -718 H2O Water

R -729 - Air

R -744 CO2 CarbonDioxide



Refrigerants

III. Hydrocarbon RefrigerantsR -50 CH4 Methane

R -170 C2H6 Ethane

R -290 C3H8 Propane

I V. Azeotropes

An azeotropes is a mixture of two substance in which thecomponents cannot be separated by distillation. (R -502 is amixture of 48.8% R -22 and 51.2% R -115).



DESIRABLE PROPERTIES OF A REFRIGERANT

THERMODYNAMIC PROPERTIES:

1. LOW FREEZING POINT

2. LOW CONDENSING PRESSURE3. LOW EVAPORATING PRESSURE

4. LOW POWER PER TON

5. LOW VOLUME PER TON

6. HIGH COP



DESIRABLE PROPERTIES OF A REFRIGERANT

Chemical Properties:

1. non-toxic

2. non-flammable3. non-corrosive

4. not destructive torefrigerated products.

Physical Properties:

1. low viscosity

2. high thermalconductivity

3. easy leak detection

4. miscible with oil

5. reasonable cost

REFRIGERANT LEAK DETECTION



REFRIGERANT LEAK DETECTION

1. R -12 and other systemusing halocarbonrefrigerants

Detection: Loss of coolingcapacity

Location:

a. soap sud

b. prestolite or alcohol torch

c. electronic leak detector

2. Ammonia Systems:

Detection: Toxic Odor

Location:a. soap sud

b. sulfur candle

c. litmus paper



Control Mechanism of Refrigerant into the

System:1. Hand expansion valves manually control the

refrigerant liquid f lowing to the evaporator in theevent of failure of the thermal expansion valve.

2. Suction line regulators used to control the flow of refrigerant gas from the evaporator coil.

3. Solenoid valves usually fitted in liquid suction ordischarge lines to interrupt the flow on demand

from any one of the types of temperature orpressure sensing devices.4. Check valves used to prevent the flow of gas from

the condenser back to the compressor during off cycles.



Control Mechanism of Refrigerant into the

System:

5. Hold-back valves used to limit the flow of gas tothe to the compressor to prevent surge or excessive

loads from overloading compressor motor.6. Reversing valves used in defrosting cycle or heatpump system to divert the flow of refrigerant.

7. Hot gas defrost valves fitted in modern

multiplex system for method of defrosting theentire system before the suction side of evaporatorcoil.



Electric Control Devices1. Pressure controllers control the flow in some

portion of the system, provide automatic defrosting

and transfer of liquid from the system. Three basictypes; Bellows, Diaphragm, Bourdon Type.

2. Temperature controllers control variabletemperature have similar design with basic power

elements bellows, diaphragm and bourdon tubethat are used in pressure control. Bimetalthermostat and Remote bulb thermostat.



Safety Cut outs Devices:a. High pressure cutout switch used as a safety

control on the discharge line compressor.

b. Low pressure cutout switch fitted on suction side

of compressor, opened the contact when thepressure fall below a set point.

c. Low oil pressure switch contacts are fitted into thecompressor drive motor circuit, when oil pressure

falls below the preset point.d. Water failure switch stop the compressor in casefailure of cooling water system in the condenser

e. Float switch close the circuit in response to the

rise and fall of the liquid level.



Parts of the Automatic Control Freon

Refrigeration System1. Compressor

2. Condenser

3. Liquid receiver

4. Expansion valve manual

5. Evaporator

6. Suction valve

7. Discharge valve8. Oil trap

9. Liquid/King valve

10. Charging valve

11. Dehydrator

12. Sight glass

13. Solenoid valve

14. Thermo expansion valve

15. Purging valve

16. Compound gauge

17. Cut out switch18. Discharge press gauge

19. Low oil press switch

20. Water failure switch



Instruments in Refrigeration:y Barometer instrument for measuring atmospheric

pressure, in psi or in of mercury

y

Calorimeter a device used to measure quantities of heat or determine specific heats of a substance.

yDynamometer a device for measuring poweroutput or power input of a mechanism.

yHydrometer floating instrument used to measurespecific gravity of a liquid such as refrigerants, oil.

yHygrometer instrument used to measure degree of moisture in the atmosphere.



Instruments in Refrigeration:yManometer instrument for measuring pressure

of gases and vapor.

y

Psychrometer also called wet bulb hygrometerused for measuring the relative humidity of atmospheric air.

y Pyrometer instrument used for measuring higher

temperatures.y Wet bulb a device used to measure the relative

humidity of air.



Definitions of Technical Terms:y Absolute Pressure is the pressure above a

complete vacuum, sum of gauge pressure andatmosphere pressure.

y Ambient Temperature the temperature of air in space, room temperature.

y Analyzer is a pressure vessel mounted

above the generator through which the vapors leaving the generator in absorptionsystem.



yBTU the amount of heat energy required toraise the temperature of one pound of wateror any substance , one degree Fahrenheit.

yCalorie the quantity of heat required to

raise the temperature of one gram of waterone degree Celsius

yChiller a heat exchanger in which lowpressure refrigerant boils or vaporizes thusabsorbing the heat that was remove from therefrigerated area



DEFINITION AND TERMS

REFR IGERATING EFFECT, Q- the rate of heat removalfrom the evaporator or low temperature space.

COEFFICIENT OF PERFORMANCE(COP)- the ratio of therefrigerating effect to the compressor work.



Thank you and Good Morning

e. industrial plant machinery - 6. refrigeration

Documents