REFRIGERANTS

The refrigerant is a heat carrying medium which during the cycle in the refrigeration system absorbs heat from a low temperature system and rejects the heat to a higher temperature system.

Refrigerant Classification

Refrigerants are working substances or heat- carrying medium in refrigeration system, during a refrigeration cycle heat is absorbed from a low temperature system and rejects the heat to a high temperature system.

Refrigerants can be classified as follows:

• On the basis of working principle:

(A) Primary refrigerants and (B) Secondary refrigerants

(A) Primary refrigerants

The refrigerant which directly participate in the refrigeration system and cools the products or substances are called Primary refrigerants. These refrigerants undergo change of phase during heat absorption or heat rejection in the evaporator and condenser.

(B) Secondary refrigerants

This refrigerant does not directly participate in the refrigeration cycle, but is used only as a medium for cooling. This refrigerant first cooled by primary refrigerants and then cools the substance which is to be maintained at lower temperatures.

Examples are H2O, Brine and calcium chloride solutions.

Qualities of secondary refrigerants:

• Remain liquid state under all working conditions
• Non corrosive when in contact with metal
• High specific heat and
• Undergo no change when in contact with refrigerants or other
• On the basis of nature of the refrigerants:

(A) Natural Refrigerants and (B) Artificial or synthetic refrigerants

• On the basis of safety:

(A) Safety refrigerants and (B) Flammable refrigerants

• On the basis of chemical composition (A)Halocarbon refrigerants, (B) Hydrocarbon refrigerants, (C)Inorganic refrigerants and (D) Azetropic refrigerants

1. R-11,Trichloro-monofluoro-methane (CCl3F) -The R-11 ia a synthetic chemical product which can be used as a It is stable, non-flammable and non-toxic. It is considered to be a low-pressure refrigerant. Due to its low operating pressure, this refrigerant is used in large centrifugal compressor system of 200 TR and above..
2. R-12,Dichloro-difluoro-methane (CCl2F2)- The R-12 is a colourless, odourless liquid with boiling point of – 290C at atmospheric It is non-toxic, non-corrosive, non-irritating and non-flammable. Itazze iw Dell 152 which is an advantage in small refrigerating mastices. The izoztu ziza will permit the use of less sensitive and more positive opening and naring teams operates at a low but positive head and back pressure and a winners BV refrigerant is used in many different types of industrial concer refrigerators, freezers, water coolers, room and windon osoite on rice is found in reciprocating and rotary compressors. but is use is a compresi commercial air-conditioning is increasing
3. R-13,Monochloro-trifluoro-methane (CClF3)- The R-13 has a boiling temperature of – 4°C at atmospheric pressure and a critical temperature of + 28.8°C. This refrigerant is used for the low-temperature side of cascade systems. It is suitable with reciprocating compressors.
4. R-14,Carbontetrafluoride (CF4) -The R-14 has a boiling temperature of – 128°C at atmospheric pressure and critical temperature of – 5°C. It serves as an ultra-low temperature refrigerant for use in cascade systems.
5. R-21,Dichloro-monofluoro-methane (CHCI2F)- The R-21 has a boiling temperature of +9°C at atmospheric pressure. It is used in centrifugal compressor systems .
6. R-22,Monochloro-difluoro-methane (CHCIF2)- The R-22 is a man-made refrigerant developed for refrigeration installations that need a low evaporating It is used with reciprocating and centrifugal compressors.

Methane Series:

CHFC ——————R22 ——————————-Monochlore difluoro methane

HFC ——————R32 ——————————Difluoro methane

Ethane Series:

CHFC——————-R123 (CHCL2 – CF3) ————-Dichloro trifluro ethane

HFC ——————-R125 (CHF2 –CF3) —————-Pentafluoro ethane

HFC———————R134a (CH2F-CF3) —————-Tetrafluoro ethane

HFC ——————–R143a (CH3 –CF3) ——————Trifluro ehane

HFC———————R152a (CH3-CHF2) —————–Difluro ethane

 

 

Propane Series:

HFC——————–R245fa (C3H3F3) ——————Pentafluoro propane

HC————————-R290 (C3H8) ——————Propane

Butane Series:

HC ————————–R600a—- (C4H10) ————–Isobutane

Zeotropic Blends:

HFC ————————R407A [R125/143a/134a (44/52/4)]

HFC ————————R407C [R32/125/134a (23/25/52)]

HFC ————————-R410A [R32/125(50/50)]

Azeotropic Blends:

HFC ————————R507A [R125/143a (50/50)]

Inorganic refrigerants:

(NH3) ———————–R717—————————-Ammonia

(H2O) ———————–R718—————————-Water

(CO2) ———————- R744————————— Carbon dioxide.

 

Properties of Refrigerants

An ideal refrigerant should give a good coefficient of performance and also safe to use while operating between the pressures. There is no ideal refrigerant which can be used under all operating conditions. The characteristics of some refrigerants make them suitable for use with reciprocating compressor and other refrigerants are best suited to centrifugal compressor or rotary compressor. Therefore in order to select a correct refrigerant, it is necessary that it should satisfy those properties which make it ideal to use for the particular application. The properties of refrigerants are essential in determining its use for a particular application.

 

There are three groups of properties,

(I). Thermodynamic properties of refrigerants, (II). Chemical properties of refrigerants and (III). Physical properties of refrigerants

(I) Thermodynamic properties of refrigerants:

1. Boiling point temperature:
   • Low boiling temperature at atmospheric pressure is It increases the capacity of plant

2. Freezing point temperature:
   • The freezing point should be low to prevent the refrigerant which will leads to choking of valves

 

 

3. Evaporator and condenser pressures:
   • The evaporative pressure and condenser pressure should be positive e., above the atmospheric pressure in order to avoid air leakage into the system.
4. Critical temperature and pressure:
   • Critical temperature for a refrigerant should be high to prevent excessive power consumption
   • Critical pressure should be low so as to give low pressure
5. Latent heat of vaporisation:
   • Latent heat of vaporization should be large to minimize the quantity of refrigerant
6. Coefficient of performance:
   • High COP is desirable to reduce the running cost
7. Specific volume:
   • Low specific volume reduces the size of the compressor
8. Power requirement:
   • Power require should be low as possible
   • Increases the system coefficient of

(II) Chemical properties of refrigerants:

• • Non flammable and non-explosive
  • Non-poisonous, non-toxic and no effecting food stuffs
  • Should not have any disagreeable odor
  • Should not have any corrosion action on the parts of the system

(C)  Physical properties of refrigerants:

1. Stability and inertness:
   • An ideal refrigerant should not decompose at any temperature of refrigeration
   • It should not form higher boiling point liquids or solid substance through polymerization
2. Corrosive property:
   • An ideal refrigerant should not corrode with metals
3. Viscosity:
   • Low viscosity is desirable for better heat transfer and low pumping Power
4. Leakage tendency:
   • Leakage tendency of a refrigerant should be low to prevent loss of Refrigerant
5. Dielectric strength:
   • Dielectric strength for a refrigerant is desirable to prevent electric motor directly exposed to the refrigerant
6. Thermal conductivity:
   • High thermal conductivity of a refrigerant is desirable because it reduces the flow rate of refrigerant for a given capacity
7. Cost:
   • The cost of the refrigerant should be low
   • It vary depending upon the capacity of refrigerating system

The characteristics of some refrigerants make them suitable for use with reciprocating compressor and other refrigerants are best suited to rotary or centrifugal compressor. Therefore in order to select a correct refrigerant, it is necessary that it should satisfy those properties which

make it ideal to be used for the particular application. High flammable refrigerants have bigger risk, the refrigerant R-410A, Non-Flammable refrigerant and R-32.

Designation System for Refrigerants:

The refrigerants are internationally designated as ‘R’ followed by certain numbers such as

• 11, R-12. R-114 A refrigerant followed by a two-digit number indicates that a refrigerant is derived from methane base while three-digit number respresents ethane base. The first digit on the right is the number of fluorine (F) atoms in the refrigerant. The second digit from the right is one more than the number of hydrogen (H) atoms present. The third digit from the right is one less than the number of carbon (C) atoms, but when this digit is zero, it is omitted. The general chemical formulafor the refrigerant, either for methane or ethane base, is given as CmHnCIpFq in which n+p+q= 2m + 2

 

where

m = Number of carbon atoms. n= Number of hydrogen atoms,

p= Number of chlorine atoms, and q= Number of fluorine atoms.

the number of the refrigerant is given by R (m-1)(n+1) (q).

Let us consider the following refrigerants to find its chemical formula and the number.

1. Dichloro-difluoro-methane

In this refrigerant Number of chlorine atoms, p = 2

Number of fluorine atoms, q=2 and number of hydrogen atoms. n=0

n+p+q = 2m +2

0+2+2 = 2m +2

or

m=1

Number of carbon atoms =1 Thus the chemical formula for dichloro-difluoro-methane becomes CCI2F2, and the number of refrigerant becomes R (1-1) (0+1)(2) or R-012 i.e R-12

2. Dichloro-tetrafluoro-ethane

In this refrigerant

Number of chlorine atoms, p=2 Number of fluorine atoms, q=4 and number of hydrogen atoms, n=0 We know that n + p + q =2m+2 0+2+4=2m +2

or m=2

Number of carbon atoms 2

Thus the chemical formula for dichloro-tetrafluoro ethane becomes C2Cl2,F4, and the number of refrigerant becomes R(2-1) (0+1) (4) or R-114.

3. Dichlore-trifluoro-ethane

 

In this refrigerant

Number of chlorine atoms, p=2 Number of fluorine atoms, q=3

and number of hydrogen atoms, n=1 We know that n + p + q =2m+2 1+2+3=2m +2

or m=2

Number of carbon atoms 2

Thus the chemical formula for dichloro triflouro-ethane becomes CHCI2CF3, and the number of refrigerant becomes R(2-1)(1+1)(3) or R-123

 

Substitutes for Chloro-fluoro-Carbon (CFC) Refrigerants:

The most commonly used halo-carbon or organic refrigerants are the chloro-fluoro derivatives of methane (CH4) and ethane( C2H6.). The fully halogenated refrigerants with chlorine (CI) atom in their molecules are referred to as chloro-fluoro-carbon (CFC) refrigerants. The refrigerants such as R-11, R-12, R-13, R-113, R-114 and R-115 are CFC refrigerants

.The refrigerants which contain hydrogen (H) atoms in their molecule along with chlorine (CI) and fluorine (F) atoms are referred to as hydro-chloro-fluoro-carbon (HCFC) refrigerants. The refrigerants such as R-22, R-123 are HCFC refrigerants.

The refrigerants which contain no chlorine atom in their molecules are referred to as hydro fluoro carbon (HFC) refrigerants. The refrigerants such as R-134a, R-152a are HFC refrigerants. The refrigerants which contain no chlorine and fluorine atoms in their molecule are referred to as hydrocarbon (HC) refrigerants. The refrigerants such as R-290, R-600a are HC refrigerants.

The fluorine (F) atom in the molecule of the refrigerants makes them physiologically more favourable. The chlorine (CI) atom in the molecule of the refrigerants is considered to be responsible for the depletion of ozone layer in the upper atmosphere which allows harmful ultra- violet rays from the sun to penetrate through the atmosphere and reach the earth’s surface causing skin cancer.

At present, the following substitutes are available

1. The HCFC refrigerant R-123a (CF3CHCl2)in place of R-11 (CCl3F)
2. The HFC refrigerant R-134a (CF3CH2F)and R-152a (CH3CHF2)  in place of R12

 

• The HFC refrigerant R-143a (CH3CF3)and R-125 (CHF2CF3) in place of R-502 (a mixture of R-22 and R-115)

 

• The HC refrigerants propane R–290 (C3,H8)and isobutene R-600a (C4H10) in place of R-12

 

Applications of refrigeration

cold storage: The storages which are used for short-term storage purposes are known as cold storages.

• The period of short term cold storages ranges from one to two days or to a
• The maximum period of long term cold storages ranges from seven to ten days for some sensitive products.
• Most of the foods for short-term storages are stored at a temperature slightly above the freezing point and the relative humidity and air motion should be controlled to prevent excessive loss of moisture from fruits and
• When different types of food products are stored , then it is called mixed storage to minimise the chances of damaging the more sensitive
• The condition of the products at the time of entering the storage is one of the important factors for determining storage life of a refrigerated

dairy  refrigeration:  Pasteurization  method  is  used  on  large  scale  to  protect  milk against bacterial infection.

• The milk used for the preparation of milk products like cheese, butter and ice cream is
• Refrigeration is the most important utility  required for dairy plants for  low temperature storage of different food and dairy It is also very essential for cold chain of handling of milk and other perishable food products.
• ammonia based vapour compression refrigeration systems are the most preferred mode for cooling in milk processing Ammonia based systems are low pressure systems with very less sophistication. They have good heat transfer properties, low cost and high efficiency.

Ice plant:

• The function of an ice plant or ice factory is to make or form ice in large quantity and in large size . An ice plant which is a huge commercial factory, it uses separate ice making or ice freezing The cold is produced in one circuit and it is transferred to the water cans by another circuit.
• Ammonia: It is the primary refrigerant which takes heat from This ammonia changes phase while moving in the circuit and Brine: It is the secondary refrigerant which takes heat from the water and produces ice.
• There are three main circuits of working medium in ice plant:

 

1. Refrigeration circuit: Ammonia as working medium which actually produces the cold by changes its phase at different location
2. Cooling water circuit: Cooling water as working medium to remove the heat  of condenser
3. Brine circuit: Brine solution as working medium which transfers the cold from ammonia to water filled cans where ice is to be

water cooler:

There are two types of Water Cooler as follows:

1. Storage type water
2. Instantaneous type water

 

1. Storage type water cooler: In this type of water cooler, the basic cycle is vapour compression cycle consisting of compressor, condenser, fan with motor, expansion device, filter or strainer, thermostatic switch and evaporator

• Temperature is control by thermostatic switch as per our desired
• Compressor compresses the Refrigerant R12 vapour to high temperature high pressure vapour is then condensed in condenser by fan motor High pressure high temperature vapour converted into High pressure high temperature liquid in condenser.
• Liquid refrigerant passes through strainer or filter which removes moisture and impurities
• The liquid refrigerant is throttled through expansion device (generally capillary tube). In throttling pressure and temperature of liquid drops This low-pressure low temperature refrigerant then extracts heat of water from the evaporator. By taking heat  from  water  refrigerant  evaporates  and  this  vapour  refrigerant  sucked  by compressor and process continues.

 

2. Instantaneous type water cooler:

• This storage type cooler has evaporated coils solders on the wall of storage The tank is either of stainless steel or galvanized steel.
• The Evaporator in instantaneous type consist of two separate coils made of either copper or stainless Copper pipe carries R12 while stainless steel pipe carries water. The two pipe or coils are bound together by soldering.
• Thermostatic filler bulb is clamped on the water coil just at outlet end in case of instantaneous type, while in storage type it is emerged in the water in the

 

Frost free refrigerator:

A frost-free freezer has three basic parts:

• A timer
• A heating coil
• A temperature sensor

 

• After every six hours or so, the timer turns on the heating The heating coil is wrapped among the freezer coils. The heater melts the ice frosted on it and after a certain level of heat, the temperature sensor senses the rise in temperature above 32 degrees F (0 degrees C) and turns off the heater.
• Because of the frost-free refrigeration, it is much easier to see the food packaging and keeps the food fresh for up to 14 days with minimal effort and more
• the power consumption will not
• Heating the coils every six hours takes energy, and it also cycles the food in the freezer through temperature the food lasts longer and the freezer uses less power. Due to constant air circulation in frost-free refrigerators, the probability of experiencing bad odours in the fridge remains less.
• The frost-free freezer offers uniform cooling any time, delivers a more precise temperature control to help reduce internal