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Title: Refregeration and air conditioning system
Description: Refrigeration can be defined as a process at which cools a closed space by removing heat energy from it. And when we say removing heat energy from a space or from a body this means that there is drop in temperature so we reduce temperature from high to low .and this done by some equipment such as Air-conditioner or refrigeration, because this two equipment have same cycle for cooling and refrigeration, example about this when we cools a room at specific temperature that we want, and same thing in refrigerator.
Description: Refrigeration can be defined as a process at which cools a closed space by removing heat energy from it. And when we say removing heat energy from a space or from a body this means that there is drop in temperature so we reduce temperature from high to low .and this done by some equipment such as Air-conditioner or refrigeration, because this two equipment have same cycle for cooling and refrigeration, example about this when we cools a room at specific temperature that we want, and same thing in refrigerator.
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1
Contents
Chapter 1 :
Introduction
page 5
Types of Energy
page 8
First Law of Thermodynamics
page 10
Limitation of First law of Thermodynamics
page 13
Second Law of Thermodynamics
page 15
Chapter 2 :
Methods of Refrigeration
page 16
Introduction
page 16
Applications of Refrigeration
page 16
Applications of Nitrogen
page 17
Applications of Oxygen
page 17
Applications of Argon
page 18
Refrigeration systems
page 18
Ice Refrigeration
page 19
Evaporative Refrigeration
page 19
Chapter 3
page 21
Air Refrigeration systems
page 21
Introduction
page 21
Refrigeration Load
page 22
2
Heating Load
page 22
Concept of Heat Engine, Heat Pump, & Refrigerator
23
Heat Engine
page 23
Heat pump
page 23
Refrigerator
page 24
Air Refrigeration system
page 24
Carnot Refrigeration Cycle
page 25
Application of Aircraft system Refrigeration
page 25
External & Internal Heat Source
page 26
Methods of Air Refrigeration system
page 27
References
page 28
page
3
Preface
This a brief course was done by me Hani Tbaishat
about Refrigeration & Air Conditioning system for
Chemical & Mechanical Engineering , it was include
basis of Thermodynamic science which is the core of
Refrigeration & Air conditioning Engineering
science
...
And when we say removing
heat energy from a space or from a body this means that there is drop
in temperature so we reduce temperature from high to low
...
At begining we should remember some basic and fundamental
quantities such as :
Density, specific gravity, specific volume , mass & mass flow rate,
volume & volume flow rate, velocity and acceleration , Length, time
,current, Temperature, force & pressure, work, energy, & power,
enthalpy, specific heat, & entropy
...
And all in SI units
...
▪ Specific gravity is ratio between density of a substance to its
density in standard state , but for liquid specific gravity is ratio
between density of liquid to density of water
...
& this is vice versa with density , specific
volume=1/density
...
▪ Volume & volume flow rate :SI units for volume is Litre L,
same as mass flow rate , if unit time is in seconds then unit for
volume flow rate is L/sec
...
▪ Acceleration is a vector quantity same as velocity, its velocity
of fluid moving in unit time , acceleration unit is m/sec2
...
▪ Time can measured in min, hr , but SI units for time is sec
...
▪ Temperature is measured in kelvin
▪ Force & pressure , force is the ability to move an object with
mass in kg to accelerate it by m/sec2, while pressure is how
much force N can exerted on a unit area m2
...
▪ Enthalpy is the system energy that called internal energy U that
any fluid have + work (PV) for any fluid moving
...
▪ Entropy is randomness of particles of fluid and its unit is
kj/kg
...
Now we will discuss and make brief summary about pressure and
difference between atmospheric pressure, gauge , & absolute pressure
...
acc × height
...
Absolute pressure = atmospheric pressure + Gauge pressure
...
For each equipment that operates in refrigeration cycle has two
definitions for efficiency , first one is Coefficient of performance
( COP), & second one is Energy efficiency ratio (EER)
...
2- EER is energy efficiency ratio : its idea is same as COP , ratio
between refrigerating effect for compressor in watt to power of motor
in watt
...
The second one is outside
boundaries such as heat & work
...
▪ stored energy:
1- potential energy can be studied in two ways : microscopic &
macroscopic ways, our study on macroscopic, this potential energy is
storing inside the object or fluid in molecular configuration, and its
depend on position with relative to ground, its equal product of
gravitational force and height or distance
...
3-internal energy is the sum of kinetic energy + potential energy +
nuclear energy
...
SI unit for work is N
...
Work can be done from system to surrounding or from surrounding to
system, for example in piston cylinder device ,work can produce
from system to move piston upward, or produce into system from
surrounding to move piston downwards, and we will discuss in this
chapter the relation between work and heat & energy transfer between
system & surrounding
...
In piston cylinder device heat energy is transfer from
system to surrounding when there is work done on the system &
transfer from surrounding to system work done by the system
...
● First law of thermodynamics
First law of thermodynamics is energy conservation law and its state
that energy in any system can not be created nor be destroyed , but it
could be changed from phase to phase , examples : Heat engine,
pump, compressor , all change electrical energy to mechanical energy
...
Total energy of any system is constant, and its equal to: internal
energy + potential energy + kinetic energy
...
Note : Change in internal energy of system is equal to difference
between heat & work
...
▪ processes for ideal gases
A gas is said to undergo a process when it changing from condition to
condition or from initial state to final state , and for non flow process
is that fluid still inside boundaries not cross outside boundary, the non
flow processes are :
1- Constant volume or isochoric process ( volume=constant)
...
3- Constant temperature or isothermal process
(temperature=constant)
...
5- Polytropic process
...
1- Isochoric process (V=C): this process is done at constant
volume like rigid container, so this container volume does not
changing when physical properties such as pressure, temperature
change
...
dw = p
...
cv
...
cv
...
cv
...
2- Isobaric process (P=C) : this process is done at constant
pressure , consider piston cylinder device system, if we transfer
heat energy into the system with no change in pressure, pressure
remains constant during the process , internal energy for system
will increase, and this cause temperature rise and increase then
work done from surrounding to system to move piston upward
(frictionless)
...
dq=dw Q= ( P1
...
ln(p1/p2)
...
But here physical
prosperities pressure, temperature, volume are not constant those
are vary, in isentropic process entropy = constant
...
5-polytropic process : it can be defined by the comparison of
isothermal and adiabatic processes
...
▪ Control volume or open system is a system that it can be
transfer mass & energy from It to surrounding or from
surrounding to It, here some important equations for open
system :
Ei + (dq/dt ) = Ef + (dE/dt)cv + (dw/dt)
...
Ef : final energy in joule
...
(dE/dt) : rate of change of energy in watt
...
13
dq/dt=Q
dw/dt = W
dE/dt = 0
Ei = mi
...
(Uf + KE + PE)
Equation becomes :
mi
...
But here there is some exception that there is a device PMM1 that can
create work energy by producing or consuming without requiring any
energy, so its violates first law of thermodynamics
...
Second law of thermodynamics states that it is impossible for any
device or heat engine to convert all thermal energy that system accept
to work energy as same quantity without loss of some energy, means
efficiency for heat engine not reach 100%
...
15
Perpetual motion machine PMM2 is violates first law & kelvin
statement that it is convert all thermal energy into mechanical work
...
But there is PMM2 machine that violets clausius statement that it
could be transfer heat energy from low temperature reservoir to high
temperature reservoir without any mechanical work
...
Water is a pure
substance
...
Chapter 2 : Methods of refrigeration
● Introduction :
▪ Refrigeration is that process where is cooling of confined
(closed) space is taking place by remove heat energy from
high temperature reservoir to reduce temperature lower than
surroundings temperature , fluid that use in cooling is water,
where is using in cooling of air in air conditioning system
...
-In refrigeration system water is used to Chill to 5-7 degrees Celsius
,for air conditioning system water is using for cooling air
...
-refrigeration is using in food processing & storage units
...
B-Soft drinks , most of soft drinks are carbonated , it dissolved carbon
dioxide that cause bubbles & typical test , for each one litre of water
equal between 3
...
The solubility of
carbon dioxide in water depend on pressure & Temperature , and it is
proportional
...
C-Storage of vegetables and food products
...
-the cryogenic liquid ( Ar, N2, O2 ) are using to maintain lower than
100k
...
17
✔ Applications of Nitrogen
The main source of nitrogen gas is air, Nitrogen in puerist form is
using in cryogenic air separation technology, and its quality is
different from industry to another
...
Liquid Nitrogen (LIN) using in food frozen in few seconds &
keep its texture ,teste, colour , also keep food weigh without
reduction in weight, purity of nitrogen is reach between 95% to
98% for freezing of food
...
Nitrogen is using in freezing to destroy cancer cells in
cryosurgery technique
...
liquid Nitrogen is used in storing biological specimens
...
1
...
2
...
✔ -Applications of oxygen
Oxygen gas was the first gas that liquified on 1877, its application :
-huge quantity of oxygen gas is used in steel making industry, purity
of oxygen gas that using in conversion iron to steel reach 99
...
- oxygen used in fabrication and cutting meals using oxy-acetylene
torch
...
999% purity
...
-also used in glass manufacturing , jet aircraft , & coal gasification
...
0093% of
argon by volume
...
-decarburisation process to produce low carbon stainless steel
...
-Light bulb industry to fill argon gas inside light bulbs, to gives longer
life
...
B-Cyclic refrigeration system : this done by :
1-Air Refrigeration cycle
...
3-Vapor Absorption cycle
...
▪ Evaporative Refrigeration
This method of generating cold , but its very old & used by common
people
...
5c
...
It
20
requires about 200KJ to convert one kilogram of liquid N2 to dry
vapour
...
▪ Steam jet refrigeration
In brief words this type of refrigeration is depend on heat transfer
inside jet refrigeration system , change in pressure & temperature for
compression & cooling , with useful equation that is : energy =
mass*specific heat*temp
...
Also there is another types of refrigeration, but those are too
complicated for understand, so only I will write headlines of those:
✔ Thermoelectric Refrigeration
✔ Vortex tube
✔ Solar Refrigeration system
✔ Magnetic Refrigeration system
✔ Air Refrigeration cycle
✔ Vapour compression Refrigeration cycle
Chapter 3 – Air Refrigeration systems
21
▪ Introduction
Refrigeration is an application of thermodynamics it means transfer
heat energy from lower temperature to higher temperature region
with help with an external source (i
...
work)
...
Also vapour compression & Air Refrigeration
Cycles
...
Refrigeration cycle contains some
basic devices or equipment :
✔ Evaporator
✔ Condenser
✔ Compressor
✔ Expansion valve
✔ Temperature controller
✔ Refrigerant accumulators
For working Refrigerant :
✔ R134a : which is used in domestic refrigerators at low
temperature
✔ R22 : which is used in window air conditioning units
✔ Ammonia : which is used in large air conditioning system
✔ Air :which is used Air Refrigeration Cycles
22
Unit of refrigeration or refrigeration rate
Refrigeration means removing of heat energy , so when we want to
estimate heat energy ,it could be amount or quantity & measured in
joule, or it could be rate & measured in watt which equal (joule /
second)
...
516 watt
...
& because it is heat energy rate so units is KW( kilo watt)
or TR
...
2-convection
...
4-heat transfer from equipment such as air conditioner
...
● Heating Load
Same as refrigeration load, but here heating load is rate of heat
transfer from higher temperature to lower temperature , specially in
winter where temperature is lower than 10 c
...
,e mechanical work)
● Heat Engine
Heat Engine is a device or equipment that satisfy Second law of
Thermodynamics that say: there is no device or equipment such as
Heat Engine that consume Heat energy from source to convert all
this energy to mechanical work, there some amount of energy
produce to lower
...
To know the coefficient of performance COP , it should be know
amount of energy that heat engine received & released with also
the useful work
...
to transfer this heat energy to high temperature sink
...
Coefficient of performance COPr is ratio between heat energy rate
that transfer to houses to make room warm
...
We
will discuss now about Carnot Refrigerator
...
▪ 2nd process : Isothermal Compression Process where Air is
Compressed after 1st process from P1 to P2, but here at constant
Temperature ,so here pressure increase cause some amount of
heat energy to transfer from system to surrounding
...
▪ 4th process : Isothermal Expansion Process Where this process
same as 2nd process but here Expansion not compression at
isothermal process which temperature remains constant , work
done in piston cylinder device to move piston up ward ,this
moving of piston occur because there is release of heat energy
from the surrounding to system
...
Air us the working
substance in such air conditioning system
...
One may ask that since at high altitudes both atmospheric
temperature or pressure decrease, then why are aircraft air condition?
...
Also ,temperature of the order of -5c is needed to preserve food &
cold drinks
...
External heat source
I
...
Solar radiations enter the compartments through windows
Due to solar radiations, the outer surface of the aircraft gets
heated , therefore heat is conducted into the compartments
...
III
...
Internal heat sources
I
...
III
...
total heat dissipated would be 18 kw
...
Electrical and electronic components generate heat
throughout their use
...
Food products, Cold drinks, etc
...
II
...
IV
...
VI
...
Simple air-evaporative cooling system
Boot-Strap air cooling system
Boot-Strap air evaporative Cooling System
Reduced ambient air cooling sysrem
Regenerative air cooling system
28
References
Refrigeration and Air Conditioning , 2nd Edition , S
...
Sapali
Title: Refregeration and air conditioning system
Description: Refrigeration can be defined as a process at which cools a closed space by removing heat energy from it. And when we say removing heat energy from a space or from a body this means that there is drop in temperature so we reduce temperature from high to low .and this done by some equipment such as Air-conditioner or refrigeration, because this two equipment have same cycle for cooling and refrigeration, example about this when we cools a room at specific temperature that we want, and same thing in refrigerator.
Description: Refrigeration can be defined as a process at which cools a closed space by removing heat energy from it. And when we say removing heat energy from a space or from a body this means that there is drop in temperature so we reduce temperature from high to low .and this done by some equipment such as Air-conditioner or refrigeration, because this two equipment have same cycle for cooling and refrigeration, example about this when we cools a room at specific temperature that we want, and same thing in refrigerator.