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Applications of Thermodynamics Muhammad Umair Akram

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Industrial & Manufacturing Engineering Department, NED University of Engineering and Technology

University Road, Karachi-Sindh, Pakistan 1im079um@gmail.com

2umair.an@ymail.com

I. INTRODUCTION TO THERMODYNAMICS

Thermodynamics is a branch of physics concerned

with heat and temperature and their relation

to energy and work. It defines macroscopic variables, such

as internal energy, entropy, and pressure, which partly

describe a body of matter or radiation. It states that the

behavior of those variables is subject to general constraints,

which are common to all materials, not the peculiar properties

of particular materials. These general constraints are

expressed in the four laws of thermodynamics.

Thermodynamics describes the bulk behavior of the body, not

the microscopic behaviors of the very large numbers of its

microscopic constituents, such as molecules. Its laws are

explained by statistical mechanics, in terms of the

microscopic constituents.

Thermodynamics applies to a wide variety of topics

in science and engineering. Historically, thermodynamics

developed out of a desire to increase the efficiency and power

output of early steam engines, particularly through the work

of the French physicist Nicolas Léonard Sadi Carnot (1824)

who believed that the efficiency of heat engines was the key

that could help France win the Napoleonic Wars. The Irish-

born British physicist Lord Kelvin was the first to formulate a

concise definition of thermodynamics in 1854:

"Thermo-dynamics is the subject of the relation of heat to

forces acting between contiguous parts of bodies, and the

relation of heat to electrical agency."

Thermodynamics is actually based on some of the basics

processes which are:

Isobaric process (Pressure remains constant)

Isothermal process (Temperature remains constant)

Isochoric process (Volume remains constant)

Adiabatic process (Without transfer of heat or matter)

Isentropic process (Entropy remains constant)

Isenthalpic process (Enthalpy remains constant)

Reversible process (cycle without entropy production )

Irreversible process (Cycle with entropy production)

Table 1: Process of Thermodynamics

The combination of these processes generates different

cycles. Approximately all the applications of thermodynamic

do follow the combination these processes by arranging them

in to a specific pattern.

Heat transfer process in nature (without any device) is in

the direction of decreasing temperature, that is, from high-

temperature regions to low-temperature ones. The reverse

process (i.e. from a low-temperature region to a high-

temperature) however, does not occur by itself. Such process

requires special devices called refrigerators. Refrigerators are

cyclic devices. The working fluids used in the refrigeration

cycles are called refrigerants. Another device that transfers

heat from a low-temperature medium to a high-temperature

one is the heat pump.

Refrigerators and heat pumps are essentially the same

devices; they differ in their objectives only. The objective of a

refrigerator is to maintain the refrigerated space at a low

temperature. Discharging this heat to a higher-temperature

medium is merely a necessary part of the operation, not the

purpose. The objective of a heat pump, however, is to

maintain a heated space at a high temperature. This is

accomplished by absorbing heat from a low-temperature

source, such as well water or,

Figure 1: Refrigeration and Heat Pump cycle

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cold outside air, in winter and supplying this heat to a

warm medium such as a house.

Here in this document we are considering the refrigeration

cycle only and it applications i.e. where this cycle is being use

such as:

Refrigerator

Freezer

Air condition

Air cooler

II. REFRIGERATOR

A metal box that helps your food last longer! Have you

ever stopped to think how a “Refrigerator” keeps cool, calm,

and collected even in the blistering heat of summer? Food

goes bad because bacteria breed inside it. But bacteria grow

less quickly at lower temperatures, so the cooler you can keep

food, the longer it will last. “A refrigerator is a machine that

keeps food cool” with some very clever science. All the time

your refrigerator is humming away, liquids are turning into

gases, water is turning into ice, and your food is staying

deliciously fresh. Let's take a closer look at how a refrigerator

works!

By compressing gases, we make them hotter; by letting

them expand, we make them cooler. How can we use this

handy bit of physics to shift heat from the inside of a

refrigerator? Suppose we made a pipe that was partly inside a

refrigerator and partly outside it, and sealed so it was a

continuous loop. And suppose we filled the pipe with a gas.

Inside the refrigerator, we could make the pipe gradually get

wider, so the gas would expand and cool as it flowed through

it. Outside the refrigerator, we could have something like a

bicycle pump to compress the gas and release its heat. If the

gas flowed round and round the loop, expanding when it was

inside the refrigerator and compressing when it was outside, it

would constantly pick up heat from the inside and carry it to

the outside like a heat conveyor belt. And, surprise, this is

almost exactly how a refrigerator works.

Here's what's happening inside your refrigerator as we

speak! The left-hand side of the picture shows what's

happening inside the chiller cabinet (where you keep your

food). The dotted line and pink area show the back wall and

insulation separating the inside from the outside. The right-

hand side of the picture shows what's going around the back

of the fridge, out of sight.

1. The coolant is a liquid as it enters the expansion

valve (yellow). As it passes through, the sudden drop

in pressure makes it expand, cool, and turn into a gas

(just like a liquid aerosol turns into a cool gas when

you spray it out of a can).

2. As the coolant flows around the chiller cabinet i.e.

evaporator (usually around a pipe buried in the back

wall), it absorbs and removes heat from the food

inside.

3. The compressor squeezes the coolant, raising its

temperature and pressure. It's now a hot, high-

pressure gas.

4. The coolant flows through thin radiator pipes on

the back of the fridge, giving out its heat and cooling

back into a liquid as it does so.

5. The coolant flows back through the insulated

cabinet to the expansion valve and the cycle repeats

itself. So heat is constantly picked up from inside the

refrigerator and put down again outside it.

Figure 2: A typical Refrigerator

III. AIR CONDITIONER

Suppose you take a refrigerator and build your house

around it, so half the machine (the chiller cabinet) is inside

your home and the other half (the grid of hot fins at the back)

is outside. Now if you leave the door open, what you have in

effect is a fully fledged air conditioner. It draws in heat from

inside your home and belches it out again outside, gradually

cooling your home in the process.

The simplest air conditioner units work in almost exactly

this way, except they have fans on both sides to circulate air

more rapidly. They also have a heating element in them so

they can warm the air in a room on cold days as well as cool it

down on warm days. Machines like this are sometimes

called HVACs (heating and ventilation air conditioning

units). More elaborate air conditioners use long ducts to pipe

the warmed or cooled air throughout an entire building, but

they still work in essentially the same way.

1. Warm air from the room is sucked in through a grille

at the base of the machine

2. The air flows over some chiller pipes through which

a coolant fluid is circulating. This part of the

machine works just like the chiller cabinet in a

refrigerator. It cools down the incoming air and a

dehumidifier removes any excess moisture.

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3. The air then flows over a heating element (similar to

the one in a fan heater). On a hot day, this part of the

unit may be turned right up so the HVAC works as a

heater.

4. A fan at the top blasts the air back through another

grille into the room. If the heating element is turned

down, the air re-entering the room is much cooler, so

the room gradually cools down.

5. Meanwhile, coolant (a volatile liquid that evaporates

easily) flows through the chiller pipes. As it does so,

it picks up heat from the air blowing past the pipes

and evaporates, turning from a cool liquid into a

hotter gas. It carries this heat from inside the room to

the outside of the building, where it gives up its heat

to the outside air. How? Just like in a refrigerator, the

coolant flows through a compressor unit and some

condensing pipes, which turn it back into a cool

liquid ready to cycle round the loop again.

6. What happens to the heat? In the unit outside the

building, there are lots of metal plates that dissipate

the heat to the atmosphere. An electric fan blows air

past them to accelerate the process.

7. Over time, the heat inside the building gradually

pumps away into the outside air.

Figure 3: A typical air condition cycle

IV. AIR / EVAPORATOR COOLER

An evaporative cooler (also swamp cooler, desert

cooler and wet air cooler) is a device that cools air through the

evaporation of water. Evaporative cooling differs from

typical air conditioning systems which use vapor-

compression or absorption refrigeration cycles. Evaporative

cooling works by employing water's large enthalpy of

vaporization. The temperature of dry air can be dropped

significantly through the phase transition of liquid water to

water vapor (evaporation), which can cool air using much less

energy than refrigeration. In extremely dry climates,

evaporative cooling of air has the added benefit of

conditioning the air with more moisture for the comfort of

building occupants.

The cooling potential for evaporative cooling is dependent

on the wet bulb depression, the difference between dry-bulb

temperature and wet-bulb temperature.

Dry Bulb Temperature: This is the temperature that

we usually think of as air temperature, measured by a

regular thermometer exposed to the air stream.

Wet Bulb Temperature: This is the lowest

temperature that can be reached by the evaporation

of water only.

When considering water evaporating into air, the wet-bulb

temperature, as compared to the air's dry-bulb temperature is

a measure of the potential for evaporative cooling. The dry

and wet bulb temperature can be used to calculate the relative

humidity. Evaporation will take place when the humidity is

below 100% and the air begins to absorb water. Any given

volume of air can hold a certain amount of water vapour and

the degree of absorption will depend on the amount it is

already holding.

The term humidity describes how much water is already in

the air; relative to the amount it is capable of holding. Air is

saturated when it cannot hold any more water. Imagine it as a

sponge, if the sponge held half as much water as it was

capable of holding, it would be 50% saturated. In the case of

air, we would describe the Relative Humidity as being 50%.

Energy is required to change water from liquid to vapour.

This energy is obtained in an adiabatic process from the air

itself. Air entering an evaporative air cooler gives up heat

energy to evaporate water. During this process, the dry bulb

temperature of the air passing through the cooler is lowered.

Figure 4: Cycle of Evaporator Cooler

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Evaporative air conditioning uses evaporation to cool the

air. In an evaporative cooler, such as Breezier, a pump

circulates water from the reservoir on to a cooling pad, which

in turn becomes very wet. A fan draws air from outside the

unit through the moistened pad. As it passes through the pad

the air is cooled by evaporation. The key to effective

evaporative cooling is ensuring that each of the cooling pads

are completely saturated at all times during operation and that

the systems fan & motor are sized and designed to deliver the

appropriate airflow for the home.

V. DIFFERENCE BETWEEN AIR COOLER AND AIR CONDITIONER

Specification Cooler Air Conditioner

Definition A cooler cools the air by evaporating

the air.

An air conditioner is system designed to change the air

temperature and humidity

within an area. It can either be cold or hot

Other names Evaporative

cooler, swamp

cooler, desert cooler and wet air

cooler

AC

Process The air is pulled

through the back

of the unit and processed through

wet absorptive

pads and cooled

Warm air is run over

refrigerant-filled coils, which

absorbs heat and changes it from liquid to a gaseous state.

The air is then converted back

to liquid state and evacuated outside.

Energy-efficient More efficient

compared to AC

Less efficient compared to

coolers

Maintenance Is not costly Is costly

Cost Cost less to

purchase the unit

Costs more to purchase the

unit

Environment Friendly

More environmental

friendly

Less environmental friendly

Portability Is more portable

compared to AC

Once fixed it is not portable,

though new portable ACs are available

Advantages Less expensive to

install, Less expensive to

operate, Ease of

maintenance, air is fresher

Works in all seasons, can heat

as well as cool, can have purification benefits, cooling

can be controlled, keeps out

insects, reduces humidity

Disadvantages Humidity lowers

cooling capability,

air supplied by cooler is humid,

requires a constant

supply of water

for pads, needs

constant cleaning,

can attract mosquitoes

Less environmental friendly,

more expensive to maintain,

expensive to purchase, air is stale, uses 4x the energy of

coolers, continuous reduced

humidity can cause respiratory

problems

Table 2: Cooler vs Air Conditioner

VI. FREEZER

The basic principle behind a freezer is evaporation. When

a liquid evaporates it causes the surrounding area to cool. For

example, on a hot summer's day if you sprinkle water on your

skin it will cool your skin as you evaporate. That's an example

of refrigeration!

Water can't be used in freezer though, because it evaporates at

too high a temperature. But some liquids evaporate at very

low temperatures. For example Isobutene (becoming more

common in domestic freezers) evaporates at very low

temperatures. This ability to evaporate at very low

temperatures means that it cools surfaces which are already

very cold.

Evaporation is affected by air pressure. The higher the air

pressure, the less a liquid will evaporate.

1. The Compressor takes in the refrigerant (as gas);

raise the air pressure which converts the refrigerant gas to

liquid (compressor and light pink).

2. As the refrigerant liquid flows from the Compressor

to the Expansion Valve the high air pressure stops it

evaporating and instead it gives off heat and becomes cooler.

3. The refrigerant liquid flows through the expansion

valve (into the blue pipe) where the air pressure is much

lower. This causes the refrigerant liquid to evaporate which

cause the pipe to become very cold inside the freezer.

4. One key component of the freezer is missing from

the diagram, the thermostat. The thermostat senses the

temperature inside the freezer and when it drops below a

certain temperature it turns off the motor so the flow of the

refrigerant liquid stops. When the temperature rises above a

certain level the thermostat turns on the motor and the

refrigeration process

restarts.

Figure 5: Typical Interpretation of Freezer

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VII. TYPES OF REFRIGERATOR/ FREEZERS

A. TOP-FREEZER

Traditionally the most popular style (largely due to its

economical price), this is likely the refrigerator configuration

you grew up with. The freezer compartment is positioned atop

the fresh-foods compartment and typically claims about a

third of the unit's total volume.

Advantages: Familiar design; lower price than more feature-

rich styles.

Disadvantages: Among the least flexible configurations

(along with bottom-freezer); items in back of freezer may be

difficult to reach for children and shorter adults; requires

wide, deep space to allow doors to swing fully open.

B. BOTTOM-FREEZER

This style inverts the more traditional top-freezer

configuration, placing the freezer compartment at floor level

and raising the fresh-foods area to a more convenient height.

The freezer compartment may be accessed via a drawer or a

swinging door.

Advantages: Economically priced; offers easier access to

fresh foods than with a top-freezer refrigerator.

Disadvantages: Among the least flexible configurations

(along with top-freezer); access to frozen foods may be less

convenient (especially with a swinging door) than with top-

freezer models; requires wide, deep space to allow doors to

swing fully open.

C. SIDE-BY-SIDE

In this style, the refrigerator and freezer compartments are

more equal in size, with each taking up the full height of the

refrigerator. The compartments are narrower, as a result, so

are the doors. Adjustable shelves are a must for optimal

flexibility. Some models offer amenities like through-the-door

ice and water dispensers.

Advantages: Convenient access to both fresh and frozen

foods; abundant freezer capacity; ideal for narrow or galley-

style kitchens because less space is required for door swing

than with full-width-door models.

Disadvantages: Narrower refrigerator compartment may not

easily accommodate large platters; less overall fresh-food

space than top- and bottom-freezer designs; pricier than top-

and bottom-freezer models.

D. FRENCH DOOR

This style combines the advantages of side-by-side and

bottom-freezer configurations. The French doors at the top

open to reveal a spacious, full-width fresh-foods compartment

that easily accommodates large platters of hors drovers,

pizzas and the like. 3-door models sport a bottom-mounted

freezer compartment; 4-door models are also available that

offer dual freezer compartments, and advanced models offer a

bottom-mounted freezer and a second, counter-height drawer

that's temperature- and humidity-adjustable to accommodate

changing needs. Through-the-door ice and water dispensers

are offered on most French door refrigerators.

Advantages: Elegant aesthetic and functional design; highly

versatile to efficiently hold a wide variety of different types of

foods; narrow refrigerator doors allow more flexible

installation; advanced 4-door models deliver variable cooling

zones for optimal food freshness.

Disadvantages: Great looks and versatility come at a price.

E. COUNTER DEPTH (FULL-SIZE)

Available primarily in side-by-side and French door

styles, counter-depth refrigerators offer a shallower profile

than their standard-depth counterparts. This allows them to

blend seamlessly with kitchen cabinetry for a built-in look.

Some models are designed with wider dimensions to

compensate for their reduced depth.

VIII. MANUFACTURER OF REFRIGERATOR/ FREEZERS

IX. TYPES OF AIR COOLER AND AIR CONDITIONER

A. WINDOWS AC

These types of AC are designed to be fitted in window

sills. A single unit of Window Air Conditioner houses all the

necessary components, namely the compressor, condenser,

expansion valve or coil, evaporator and cooling coil enclosed

in a single box. Since a window AC is a single unit, it takes

less effort to install as well as for maintenance.

Advantages

Single unit air conditioner

Less effort needed for installation

Costs lesser in comparison to other varieties

B. SPLIT AC

These are kits of 2 units, one internal and another external.

The indoor unit installed inside room intakes warm air and

throws in cold air. The outdoor unit on the other hand is

installed out of the house. It contains the compressor and is

linked to the internal unit via drain pipes and electric cables.

This external unit throws out the warm air.

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Advantages

Internal unit takes up less space for installation

Usually more silent than window ACs

Minimally affect your home decor

Can be installed in room with no windows

C. TOWER AC

These are also known as floor-standing air conditioners.

Like split ACs, a tower AC set consists of 2 units- one

internal and an external. However, the indoor unit doesn’t

need wall installation. It rather occupies some space on the

floor. Tower air conditioners usually have high cooling

capacity and suitable for very large rooms.

Advantages

Suitable for high capacity cooling

Ideal for large rooms at home and in offices

Doesn't need windows or wall installation

D. CASSETTE AC

These space-saving ACs are shaped like cassettes and are

designed to be installed on ceilings. The panel of these air

conditioners is designed to blend with all kinds of home

décor. They are stylish, and are known to deliver fantastic

performances. Most cassette type air conditioners require no

ducting. They are perfect for large spaces where windows or

split AC may not reach out.

Advantages

Best at saving space

Able to cool large areas where other ACs don’t reach

out

Blends with decor

E. Cube Air Conditioner

This fairly new design introduced by Panasonic can be

mounted close to a ceiling or at the window level. Basically,

this is a smaller version of the split type air conditioner and

costs less than the former. The indoor unit features a newly

designed diagonal propeller fan for efficient and fast cooling.

Improved blade shape curvature and larger intake grill further

aid for efficient performance.

Advantages

Can be mounted close to the ceiling or at window

level

Newly designed diagonal propeller fan for fast

cooling

Improved blade shape curvature for efficient

performance

F. DIRECT AIR COOLER

Direct evaporative coolers are the most common, used to

lower the temperature of air by using latent heat of

evaporation, changing water to vapor.

G. INDIRECT AIR COOLER

Indirect evaporative cooling uses some form of

heat exchanger. The moist cooled air does not come in touch

with the environment outside.

H. TWO STAGE AIR COOLER

Two stage cooling goes through 2 stages. In the first stage

the air is precooked by heat exchanger. The precooked air in

second stage through water soaked pads. Since precooked air

goes through in the second stage, in this type of cooler the

humidity will be less

X. MANUFACTURER OF AIR COOLER AND AIR

CONDITIONER

XI. SPECIFICATIONS

Laboratory refrigerators that comply with regulations from

agencies such as the U.S. Food and Drug Administration

(FDA) are designed to provide specific levels of temperature

control and a uniform temperature throughout the chamber.

Additional standards include A-A-52150 which defines

technical and quality assurance requirements for a non-food,

explosion proof, laboratory refrigerator and BS 4376-1 for

electrically operated blood storage.

Requirements for the installation of commercial

refrigerators and freezers are included in the National

Electrical Code, ANSI/NFPA 70, and the Safety Standard for

Refrigeration Systems, ASHRAE 15.

The efficiency of central air conditioning units is governed

by U.S. law and regulated by the U.S. Department of Energy

(DOE). Every air conditioning unit is assigned an efficiency

rating known as its “seasonal energy efficiency ratio” (SEER).

The SEER is defined as the total cooling output (in British

thermal units or Btu) provided by the unit during its normal

annual usage period divided by its total energy input (in watt-

hours) during the same period.

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REFERENCES

[1] http://simple.wikipedia.org/wiki/Refrigerator

[2] http://energyquest.ca.gov/how_it_works/refrigerator.html

[3] http://www.realsimple.com/food-recipes/tools-

products/appliances/how-does-refrigerator-work

[4] http://www.ior.org.uk/ior_/fantastic_fridges_site/science/how

%20your%20fridge%20works.htm

[5] http://www.explainthatstuff.com/refrigerator.html

[6] http://www.scienceclarified.com/everyday/Real-Life-Physics-

Vol-2/Thermodynamics-Real-life-applications.html

[7] http://www.explainthatstuff.com/airconditioner.html

[8] http://www.breezair.com/me/why-evaporative/how-

evaporative-works

[9] http://www.ehow.com/how-does_5242467_do-air-coolers-

work_.html

[10] http://en.wikipedia.org/wiki/Evaporative_cooler

[11] http://www.differencebetween.info/difference-between-cooler-

and-air-conditioner

[12] http://www.cookuk.co.uk/freezer/how-work.htm

[13] http://www.guide2freezers.com/using-your-freezer/how-

freezers-work.aspx

[14] http://www.acmehowto.com/howto/appliance/freezer/overview

.php

[15] http://home.howstuffworks.com/freezer.htm

[16] http://www.globalspec.com/learnmore/labware_scientific_instr

uments/thermal_processing/laboratory_freezers_refrigerators

[17] http://ulstandards.ul.com/standard/?id=471_10

[18] http://ulstandards.ul.com/standard/?id=250_10

[19] http://www.eesi.org/papers/view/fact-sheet-air-conditioner-

efficiency-standards-seer-13-vs.-seer-12

[20] http://www.americanstandardair.com/products/heating-and-

cooling/air-conditioners.html

[21] http://energy.gov/energysaver/articles/central-air-conditioning