Post on 10-Nov-2023
transcript
Environmental Pollution
• SOx
• NOx
• Solid waste pollutant
• Solid emission pollution
• Thermal pollutant
• Air pollution
• CO2 Pollution
SO2 Pollution & NOx
• 20 millions SO2 emitted every year
• Effects:
• Acid rain
• Photochemical smoke
• Eye irritation
• Lungs cancer
• Obstruction in breathing
• 2.5 ppm-level SO2 causes spasm to the smooth muscles of bronchus presents in the lungs
• NOx Effects:
• Acute exposure of decreases gas exchanging in blood
• Lungs cancer, pneumonia, oxygen deficiency etc
Other Pollutions
• Solid Waste Pollution
• It is formed due to the combustion of fuel
• Solid Emission Pollution
• Dust, smoke, fumes (metallic oxide), fly ash, oinder
• Thermal Pollution
• The pollution of water is regarded as thermal pollution. It is caused when the temperature of water increases and a result of that the solubility of water decreases – So the amount of oxygen decreases which leads to
• CO2 Pollution
• C18H34 + ( O2 + 3.76N2 ) → 16 CO2 + 7H2O + 3.76×24.5 N2
• If the reaction is not completed then –
• C18H34 + ( O2 + 3.76N2 ) → CO2 + CO + H2O + 3.76×24.5 N2
Pollution Prevention
• Walking/Riding bicycle → saving 60% of air
• Fluorescent lights instead of incandescent lights
• Drying clothes in a laundry line instead of clothes dryer
• Using engine limitedly
• Planting trees next to window to reduce use of AC
• Before leaving room –we should turn off light
• Sharing knowledge and ideas about pollution prevention with friends, family, neighbours and boyfriend/girlfriend
Air Pollution
• SOx
• NOx
• Disposable products – CO2
• Cooking
• Leakage of AC coolant - CFC [4800 lb of CO2 ]
• Thermostats of water heater / room heater can produce CO2
[Insulation jacket for water heater - prevention]
Definitions
• A thermodynamic system:
A thermodynamic system is defined as any quantity of matter or any region in space to which attention is directed for the purposes of analysis .
The quantity of matter or region of space must be in a prescribed boundary. This boundary maybe deformable or maybe imaginary.
• Surroundings:
Everything outside the system boundary is called surroundings. Usually the term surroundings is restricted to those things outside the system that in some way interact with the system or affect the behavior of the system
Property
• Property:
To describe and analyze a system we must know some of the quantities that are characteristic to it. These quantities are called properties.
• Intensive / Intrinsic / Qualitative property:
It is the system which is independent of the mass or total amount of the system. It is the property which have the same value for its any part of the homogeneous system. The measurement of an intensive system can be made without the knowledge of the total mass or extent.
• Extensive / Extrinsic / Quantitative property:
These properties are proportional to the mass or total amount of the system. The value of a extensive properties of a system is equal to the sum of values for the parts of the system.
Examples of PropertiesIntensive Properties
[Qualitative]
• Color
• Taste
• Odor
• Velocity
• Density
• Pressure
• Temperature
Extensive Properties
[Quantitative]
• Mass
• Weight
• Volume
• Enthalpy
• Entropy
• Energy
• Internal energy
Specific Property
• The value of an extensive property is divided by the mass of the system is called specific property.
• Example: Specific volume, specific weight, specific heat
• 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑃𝑟𝑜𝑝𝑒𝑟𝑡𝑦 =𝑉𝑎𝑙𝑢𝑒 𝑜𝑓 𝑎𝑛 𝑒𝑥𝑡𝑒𝑛𝑠𝑖𝑣𝑒 𝑝𝑟𝑜𝑝𝑒𝑟𝑡𝑦
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚
• The number of the properties needed to describe the system is depend upon the nature of the system
Process & Cycle
• Process:
The transformation of a system from one state to another is called a process
The path of a process is a series of states through which the system passes during the process
• Cycle:
A cycle or cyclic process is a process which returns the system to the state it was in before the process began.
Completion of a cycle – all properties have been restored to their initial values
∮ 𝑑𝑥 = 0
The general law for
Expansion & Compression𝑃𝑉𝑛 = 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡
• It depends upon the nature of the gas
1. when n=0, P is constant, means expansion/compression at constant
pressure process
2. n=1 , isothermal process [PV =1]
3. k>n>1 , process is polytrophic [PVn = constant]
4. n= ∞ , V = constant ; adiabatic process
The work of
A cyclic frictionless process
• Net work done = − 1
2𝑝 𝑑𝑣 −
2
3𝑝 𝑑𝑣 +
3
4𝑝 𝑑𝑣 +
4
1𝑝 𝑑𝑣
∮ 𝛿𝑊 = ∮ 𝑝𝑑𝑣 ; ∮ 𝛿𝑊 ≠ 0
• Net Heat input to the system
∮ 𝛿𝑄 = 3
4
𝑇𝑑𝑠 − 1
2
𝑇𝑑𝑠 = ∮ 𝑇𝑑𝑠 ; ∮ 𝛿𝑄 ≠ 0
Thermodynamics
Equilibrium• Thermal Equilibrium:
• Temperature will remain constant
• No temperature difference between the parts of the system
• No temperature difference between system & surroundings
• Mechanical Equilibrium:
• Pressure will remain constant
• No unbalanced force of action on any parts of the system
• Phase Equilibrium:
• Mass will remain constant
• Chemical Equilibrium:
• Chemical composition will remain constant
• No chemical reaction within the system
• No movement of any chemical constituent from 1 part to another
First Law of Thermodynamics
• When a closed system is taken through a cycle the net work delivered to the surroundings is proportional to the net heat taken from the surroundings
∮ 𝛿𝑊 = 𝐽∮ 𝛿𝑄
𝐽 ≈ 427𝑘𝑔 𝑓 𝑚
𝑘𝑐𝑎𝑙≈ 778
𝑓𝑡 𝑙𝑏𝑓
𝐵𝑡𝑢≈ 1400
𝑓𝑡 𝑙𝑏𝑓
𝐶ℎ𝑢If in the same equation heat and work are expressed in
the same units then –
∮ 𝛿𝑊 = ∮ 𝛿𝑄
⇒ ∮ 𝛿𝑄 − 𝛿𝑊 = 0
Corollary – I • There is a property of a closed system such that a change in its
value is equal to the difference between the heat supplied and work done during any change of state.
∮1−𝐴−2−𝐵−1 𝛿𝑄 − 𝛿𝑊 = 0
⇒
1−𝐴
2
𝛿𝑄 − 𝛿𝑊 +
2−𝐵
1
𝛿𝑄 − 𝛿𝑊 = 0
If C is any other path by which the system
could be restored from state 2 to state 1 then it is
likewise true that
1−𝐴
2
𝛿𝑄 − 𝛿𝑊 +
2−𝐶
1
𝛿𝑄 − 𝛿𝑊 = 0
Comparing the equations –
2−𝐵
1
𝛿𝑄 − 𝛿𝑊 =
2−𝐶
1
𝛿𝑄 − 𝛿𝑊
Internal Energy
• If the cyclic integration of any quantity is always zero then that quantity must be a property . It’s the internal energy or the stored energy
∮ 𝛿𝑄 − 𝛿𝑊 = 0∆𝐸 ≡ ∮ 𝛿𝑄 − 𝛿𝑊
• Writing Q and W as the net quantities as the heat and work crossing the boundary during the change of state
∆𝐸 = 𝑄 −𝑊
• Internal Energy:
The form of stored energy which is independent of electricity, magnetism, surface tension, motion and gravity is called internal energy.
𝑈= 𝐸 − 𝐾𝐸 − 𝑃𝐸 −𝑀𝐸 𝑚𝑎𝑔𝑛𝑒𝑡𝑖𝑐 𝑒𝑛𝑒𝑟𝑔𝑦− 𝐸𝐸 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 − 𝑆𝐸 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑒𝑛𝑒𝑟𝑔𝑦
Law of conservation of Energy
Corollary – II • The internal energy of a system is remains unchanged if the
system is isolated from its surroundings 𝑄 −𝑊 = ∆𝑈
while Q=W=0 then ∆𝑈 must be zero means the change in enthalpy is zero.
• There is no change of total quantity of energy of this system during the process
• This is the law of conservation of energy – applicable for the whole universe if the universe can be regarded as finite
Corollary - III
• A perpetual motion machine of the first kind is impossible
• A machine producing a continuous supply of work without absorbing energy from the surroundings – such a machine is called a perpetual motion machine of the first kind
• When once set in motion it would run forever
• Presence of friction makes it impossible
• Equation shows us if a net amount of heat is not supplied by the surroundings during a cycle no net amount of work can be delivered by the system
Causes of Irreversible Process• Friction
• Free expansion
• Heat transfer
• Hysteresis
• Volume
• Pressure
• Temperature
Work DoneDuring the adiabatic expansion
• According to the first law of thermodynamics- the heat absorbed or transferred
𝑞1−2 = 𝑑𝑢 + 𝑤1−2since, 𝑞1−2 = 0 , during a non-flow reversible adiabatic /
isentropic process, work done during the process-𝑤1−2 = −𝑑𝑢
⇒ 𝑤1−2 = 𝑢1 − 𝑢2• For steady flow reversible adiabatic / isentropic process –
according to steady flow energy equationℎ1 + 𝑞1−2 = ℎ2 +𝑤⇒ 𝑤1−2 = ℎ1 − ℎ2
Definitions
• Dry Air: The pure dry air is a mixture of number of gases such as nitrogen, oxygen, carbon-dioxide, hydrogen, argon, neon, helium etc. But the nitrogen and oxygen have the major portion of the combination
Moist Air &Saturated Air• Moist air: It’s a mixture of dry air and water vapour. The amount of water vapour
present in the air depends upon the absolute pressure and temperature of the
mixture.
• Saturated air: : It’s a mixture of dry air and water vapour. When the air has diffused
the maximum amount of water vapour into it.
• Degree of saturation:
Actual mass of water vapour in a unit mass of dry air : mass of water vapour in the same
mass and pressure of dry air when it is saturated
Humidity
• Humidityspecific humidity/humidity ratio :
It is the mass of water vapour present in 1kg of dry air, and generally expressed in terms
of gm per kg of dry air.
• Absolute Humidity: It is the mass of water vapour present in 1m3 dry air.
[generally expressed in terms of gm per cubic meter.or grains per cubic meter of dry air.
1kg water vapour = 15430 grains. ]
• Relative Humidity:
Actual mass of water vapour in a given volume of moist air : mass of water vapour in the
same volume of saturated air at the same temperature and pressure
BulbRelated Definitions
• Dry Bulb Temperature, td / tdb: It is the temperature of air recorded by a thermometer when it is not affected by the moisture present in the air.
• Wet Bulb Temperature, tw / twb : It is the temperature of air recorded by a thermometer when it is surrounded by a wet cloth expose to the air.
• Wet Bulb Depression: It is the difference between dry bulb temperature and wet bulb temperature at any point.
• The wet bulb depression indicates relative humidity of the air
Dew Point Temperature& Dew Point Depression• Dew Point Temperature, tdp: Its is the temperature of air
recorded by a thermometer, when the moisture present in it begins to condense
The dew point temperature is the saturation temperature corresponding to the partial pressure of water vapour
For saturated air –
tdb = twb = tdp
• Dew Point Depression: It is the difference between dry bulb temperature and dew point temperature of air
Psychrometric RelationsHumidity, W
• 𝑊 = 0.622 ×𝑝𝑣
𝑝𝑎=
0.622𝑝𝑣
𝑝𝑏 − 𝑝𝑣
• For saturated air,
𝑊𝑠 = 𝑊𝑚𝑎𝑥 = 0.622 ×𝑝𝑠
𝑝𝑏 − 𝑝𝑠
𝑝𝑣 = Partial pressure of water vapour
𝑝𝑎 = Partial pressure of dry air
𝑝𝑏= Barometric pressure
𝑝𝑠 = Partial pressure of air corresponding to saturation temperature (i.e td)
Psychrometric RelationsDegree of Saturation / Percentage Humidity 𝜇
• It also may defined as the ratio of actual specific humidity to the specific humidity of saturated air at the same dry bulb temperature.
𝜇 =𝑊
𝑊𝑠=
0.622𝑝𝑣𝑝𝑏 − 𝑝𝑣0.622𝑝𝑠𝑝𝑏 − 𝑝𝑠
=𝑝𝑣
𝑝𝑠
𝑝𝑏 − 𝑝𝑠
𝑝𝑏 − 𝑝𝑣=
𝑝𝑣
𝑝𝑠
1 −𝑝𝑠𝑝𝑏
1−𝑝𝑣𝑝𝑏
Psychrometric RelationsRelative Humidity 𝜙
• The relative humidity may also be defined as the ratio of actual partial pressure of water vapour in moist air at a given temperature to the saturation pressure of water vapour (the partial pressure of water vapour in saturated air) at the same temperature
𝜙 =𝜇
1 − 1 −𝜇𝑝𝑠𝑝𝑏
l
Psychrometric Chart
• It is a graphical representation of the various thermodynamics properties of moist air
• The psychrometric chart is normally drawn for standard atmospheric pressure of 760 mm of Hg (1.01325 bar)
• In a psychrometric chart dry bulb temperature is taken as abscissaspecific humidity moisture contents as ordinate
• Dry bulb temperature lines [vertical parallel to the ordinate]
• Specific humidity lines [parallel to the abscissa]
• Dew point temperature lines [horizontal parallel to the abscissa]
• Wet bulb temperature lines [inclined straight lines]
• Enthalpy lines [inclined straight lines]
• Specific volume lines [obliquely inclined straight lines]
• Vapour pressure lines [horizontal]
• Relative humidity lines [curved]
Psychrometric Processes
• Sensible Cooling• The cooling of air without changing its specific humidity
• Sensible Heating• The heating of air without changing its specific humidity
• Sensible Heat Factor (SHF) = 𝑆𝑒𝑛𝑠𝑖𝑏𝑙𝑒 𝐻𝑒𝑎𝑡
𝑇𝑜𝑡𝑎𝑙 𝐻𝑒𝑎𝑡
• Humidification and dehumidification• The addition of moisture to the air without changing its dry bulb
temperature
• The removal of moisture of the air without changing its dry bulb temperature
Steam Boilers
• A steam generator or boiler is a closed vessel made of steel which function is to transfer the heat produced by the combustion of fule to water and ultimately to generate steam
• Important Terms for Steam Boilers• Boiler Shell : steel plates of cylindrical form welded together
• Combustion Chamber : Space below the boiler shell meant for burning fuel
• Grate : platform upon which the fuel is burnt
• Furnace : above the grate – below the boiler shell in which fuel is actually burnt
• Mountings : fittings for boilers proper functioning
• Accessories : integral part of a boiler but not mounted on it
Essentials of a StEam Boiler
• Maximum quatity of steam with minimum fuel consumption
• Economical to install
• Rapidly meet the fluctuation of load
• Capable of quick starting
• Light in weight
• Occupy a small space
• The joints shoul be few
• Maximum fluid velocity
• Comply with safety regulation
Selection of a steam boiler
• The power required and the working pressure
• The steam generating rate
• Geographical position of the power house
• Availability of fuel and water
• The type of fuel to be used
• The probable permanency of the station
• The probable load factor
Classification of
Steam Boiler• According to The Contents in The Tube [Fire tube & Water
tube]
• According to The Position of The Furnace [Internally fired & Externally fired]
• According to The Axis of The Shell [Vertical & Horizontal]
• According to The Number of Tubes [Single & Multitubular]
• According to The Method of Circulation of Water and Steam [Natural & Forced]
• According to The Use [Stationary & Mobile]
• According to The Source of Heat
Boiler Mountings Boiler Accessories
• Water level Indicator
• Pressure Gauge
• Safety valves
• Steam stop valve
• Blow off cock
• Feed Check Valve
• Fusible Plug
Read details from R.S. Khurmi’s Book
• Feed Pump• Superheater• Economiser• Air preheater
Performance of Steam Boilers
• The performance of steam boiler is measured in terms of its evaporative capacity
• Comparable when two boilers have same• Feed water temperature
• Working pressure
• Fuel
• Final condition of steam
• The feed temperature is usually adopted is 1000 C
• Working pressure is 1.013 bar
Equivalent EvaporationE
• It is the amount of water evaporated from feed water at 1000 C and formed into dry and saturated steam at 1000 C at normal atmospheric pressure
• Equivalent evaporation “from and at 1000 C”
𝐸 =𝑇𝑜𝑡𝑎𝑙 ℎ𝑒𝑎𝑡 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝑡𝑜 𝑒𝑣𝑎𝑝𝑜𝑟𝑎𝑡𝑒 𝑓𝑒𝑒𝑑 𝑤𝑎𝑡𝑒𝑟
2257
=𝑚𝑒 ( ℎ− ℎ𝑓𝑙 )
2257• hfl = Sensible heat of feed water in KJ/kg of steam corr. to t1
0 C (from steam table)
• me = Mass of water actually evaporated / steam produced in kg/h or kg/kg of fuel burnt
• h = Enthalpy / Total heat of steam in KJ/kg of steam corresponding to a given working pressure (from steam table) = hf + x hfg [for wet steam]
= hf + hfg [for dry steam]= hg + cp (tsup – t)