C605.1-Explain refrigeration terms, refrigeration cycles & refrigerants.

INDUSTRIAL PROCESSES

PRESERVATION OF PERISHABLE GOODS

PROVIDING COMFORTABLE ENVIRONMENT

1. Industrial air conditioning

2. Comfort air conditioning

A heat engine is a device that absorbs heat (Q) and

uses it to do useful work (W) on the surroundings

when operating in a cycle.

In a cycle, the working substance is in the same

thermodynamic state at the end as at the start.

E

Hot Body

(source of heat)

Q1

Cold Body

(absorbs heat)

Q2

W

E

Hot Body

Q1

Cold Body

Q2

W

W

Q

work

heat

in

out

R

2

The purpose of a heat pump is to extract heat from

a old ody su h as the River Tha es a d pu p it to a hot body (such as an office building

Heat required to removed to form 1 tonne of ice at o*c within 24 hrs when initial condition of water at 0*c.

Unit is given in terms of 1 tonne of refrigeration

Taking latent heat of ice=335kj/kg

Taking mass of ice=1000

Ratio of refrigerating effect to work input to achieve refrigerating effect.

Rate at which heat observed from the body to be called is known as RE.

It is expressed in kw.

CLASSIFICATION OF REFRIGRANTS

1. Primary refrigerants.

It directly take the part in refrigeration system.

2. Secondary refrigerants.

It is not desirable to carry the heat from place, which is to be cooled directly by the refrigrantes.in this cases secondary refrigerates are used.

1. HaloCarbons

2. Azeotropic Refrigerants

3. Zeotropic Refrigerants

4. Inorganic Refrigerants

5. Hydrocarbon Refrigerants

Halocarbon Refrigerant are all synthetically produced and were developed as the Freon family of refrigerants.

Examples : CFC’s : R11, R12, R113, R114, R115

HCFC’s : R22, R123

HFC’s : R134a, R404a, R407C, R410a

Carbon Dioxide

Water

Ammonia

Air

Sulphur dioxide

A stable mixture of two or several refrigerants whose vapour and liquid phases retain identical compositions over a wide range of temperatures.

Examples : R-500 : 73.8% R12 and 26.2% R152

R-502 : 8.8% R22 and 51.2% R115

R-503 : 40.1% R23 and 59.9% R13

Many hydrocarbon gases have successfully been used as refrigerants in industrial, commercial and domestic applications.

Examples: R170, Ethane, C2H6

R290 , Propane C3H3

R600, Butane, C4H10

R600a, Isobutane, C4H10

Blends of the above Gases

- Depletion of the ozone layer in the stratosphere

- Global warming :

Refrigerants directly contributing to global warming when released to the atmosphere

Indirect contribution based on the energy consumption of among others the compressors ( CO2 produced by power stations )

Refrigerant Group Atmospheric

life

ODP GWP

R11 CFC 130 1 4000

R12 CFC 130 1 8500

R22 HCFC 15 .05 1500

R134a HFC 16 0 1300

R404a HFC 16 0 3260

R410a HFC 16 0 1720

R507 HFC 130 1 3300

R717 NH3 - 0 0

R744 CO2 - 0 1

R290 HC < 1 0 8

R600a HC < 1 0 8

Non Flammable

Non toxic

Inexpensive and widely available

Its high operating pressure provides potential for system size and weight reducing potential.

Drawbacks:

Operating pressure (high side) : 80 bars

Low efficiency

Used since the 1880’s Zero ODP and negligible GWP Good substitutes for CFC’s, HCFC’s, and HFC’s. Drop in solution Compatible with copper Miscible with mineral oil A third of original charge only is required when replacing

halocarbons refrigerant in existing equipment Energy saving : up to 20% due to lower molecular mass and

vapour pressure

Drawback : Flammable

HC refrigerants were first used in the late 1800’s/early 1900’s

They are naturally occuring

They have zero ODP and Minimal GWP

They are compatible with most lubricants

They are ‘more’ compatible with materials normally used in the industry

HC’s can reduce/eliminate acids forming

Natural production 3000 million tons/year

Production in factories 120 million tons/year

Used in refrigeration 6 million tons/year

ODP = 0

GWP = 0

Excellent thermodynamic characteristics: small molecular mass, large latent heat, large vapour density and excellent heat transfer characteristics

High critical temperature (132C) : highly efficient cycles at high condensing temperatures

Its smell causes leaks to be detected and fixed before reaching dangerous concentration

Relatively Low price

Toxic

Flammable ( 16 – 28% concentration )

Not compatible with copper

Temperature on discharge side of compressor is higher compared to other refrigerants

Most refrigerants are halogenated

hydrocarbons. The naming convention

adopted by ASHRAE is,

R(a-1)(b+1)d = CaHbClcFd c = 2(a – 1) – b - d

Example: R22 (R022)

1 0 1

1 2 1

2

2 1

2 1 1 1 2 1

a a

b b

d

c a b d

c

chlorodifluoromethane

Ozone is an isotope of oxygen with three atoms instead of normal two. It is naturally occurring gas which is created by high energy radiation from the Sun.

The greatest concentration of ozone are found from 12 km to 50 km above the earth forming a layer in the stratosphere which is called the ozone layer.

This layer, which forms a semi-permeable blanket, protects the earth by reducing the intensity of harmful ultra-violet (UV) radiation from the sun.

In the early70’s,scientists Sherwood Roland and Mario Molina at the University of California at Irvine were the first to discover the loss of ozone in stratosphere while investigating the ozone layer from highflying aircraft and spacecraft.

They postulated the theory that exceptionally stable chlorine containing fluorocarbons could, overtime, migrate to the upper reaches of the atmosphere and be broken by the intense radiation and release chlorine atoms responsible for catalytic ozone depletion.

For Humans Increase in skin cancer snow blindness cataracts Less immunity to infectious diseases malaria herpes For plants smaller size lower yield increased toxicity altered form For marine life Reduced plankton juvenile fish larval crabs and shrimps

Zero ODP & GWP

Water as refrigerant is used in absorption system .New developing technology has created space for it for use in compression cycles also.

But higher than normal working pressure in the system can be a factor in restricted use of water as refrigerant

Application HFCs used Possible Eco-friendly refrigerant

Domestic refrigeration R134a,R152a HC600a and blends

Commercial refrigeration R134a,R404A,R407C HC blends,NH3 ,CO2 **

Cold storage ,food processing

And industrial refrigeration R134a,R404A,R507A NH3 ,HCs,CO2 **

Unitary air conditioners R410A,R407C CO2 , HC s

Centralized AC (chillers) R134a,R410A,R407C NH3 ,HCs,CO2, water **

Transport refrigeration R134a,R404A CO 2,

Mobile air conditioner R134a CO2 ,HCs

Heat pumps R134a,R152a,R404A NH3 ,HCs,CO2, water **

R407C,R410A