Download ourse 228 File

oME 228- THERMAL SCIENCES
FOR CIVIL ENGINEERING STUDENTS
LEVEL-5
PREREQUISITE- Phy 104
Number of Credits-2
GOALS- To introduce the students of civil engineering to the basic concepts of thermal engineering and
to demonstrate the application of these principles in the engineering systems.
SYALLABUS- Properties of ideal gas and liquid vapor phases of pure substance. laws of
thermodynamicsand their basic applications. Ideal, airpower, vapor power and refrigeration cycles. Basic
air conditioning processes, One dimensional steady state heat transfer.
TEXT BOOKS1-Cengel,Y.A. and Turner ,R.H., Fundamentals of Thermal- Fluid Sciences,2nd Edition, McGrawHill,2005.
2-Cengal,Y.A., Introduction to Thermodynamics and Heat Transfer,1st Edition, McGraw-Hill,1997.
3. Eastop & Mc. Conkey, Applied Thermodynamics by Longman
Course Objectives:
1.To familiarize the
students with basic
concepts, devices and
properties used in thermal
science.
3.To prepare the student to
effectively use knowledge
of thermodynamics in the
analysis of basic thermal
systems such as engines,
refrigerators and heat
pumps.
Course Outcomes:
1.be able to determine the thermodynamic properties of pure substances, ideal gases
and mixture of vapor and liquids.
2. be able to find the correct phase and remaining properties of a substance when a set
of properties is given
4 To introduce Student to
basics of air conitioning
1 understand the use of psychometric chart for the evaluation of properties of dry and
wet atmosphere.
4.To familiarize the
students with basic
concepts of heat transfer
1.understand the functioning of heat- engine , refrigerator and heat pump
2. analyze the standard ideal working cycles with regard to the properties heat and
work transfer behavior.
3. be able to calculate performance of thermal systems in terms of thermal
efficiencies and CO.P.
4.given an actual device , analyze the corresponding ideal device.
2 understand the basic air conditioning processes and their performance through the use
of psychometric chart.
1.have a basic understanding of different modes of heat transfer.
2.understand the laws that govern the different modes of heat transfer and to calculate
thermal resistances involved.
3.analyze the heat transfer by using thermal resistances and thermal circuit models.
5.To provide students with
the basic principles
required for understanding
conduction heat transfer
1. be able to determine heat transfer through plane and curved walls
2. be able to comprehend how heat transfer and thermal engineering impact the
structural design of building walls
Assessment
Method
Homework
Number/Type
Mid Terms/Final
Exams
Quizzes
Computer Tools
Used
Instructor
Assessed
TA/Grader
Assessed
X
Peer/Self
Assessed
X
X
(EES)
X
TUTORIAL SHEETS
Basics Work, Heat and Energy
(1) Classify the following processes as heat or work. Give reasons.
-Temperature rise of a gas in a cylinder when it is compressed by the piston.
-Heating of aroom when an electric iron is plugged in.
-Solar heating of a room.
-Heating of an insulated room by burning candles.
(2) Nitrogen at an initial state of 300K,150 kPa and 0.2 m3 is compressed by
isothermal process to a final pressure of 800 kPa. Find work done.
(3)What is difference between heat transfer and work transfer.
(4)Show that for a closed system under going constant pressure process
Qnet in-Wnet out=H2-H1
(5)A mass of 15kg of air in a piston cylinder deviceis heated from 250C to 770C by
passing current through a resistance heater inside the cylinder. The pressure inside the
cylinder is kept constant at 300kPa during the process and a heat transfer of 60KJ
occurs.Determine the electrical energy supplied.
(6) A piston cylinder device initially contains 0.5 m3 of a gas (Cp=1.04 kJ/kg-K,
R=297J/kg-K) at 400 kPa and 270C. An electric heater outside the cylinder is
switched on. It passes 5A current for 5minutes from a 120V source. The gas expands
at constant pressure and heat lost to the surroundings is 2800J.What is the final
temperature of the gas.
PROPERTIES OF GASES AND MIXTURES
(1) Complete the table,Fluid water
T,oC
P,kPa
u,kJ/kg
phase
400
1825
220
Saturated vapor
190
2000
4000
3040
(2) Determine specific volume of super heated water at 10 MPa and 400 oC using
(I) The ideal gas equation
(II) The generalized compressibility chart
(II)Steam table
Find the error involved in first two cases.
(3) A tank whose volume is unknown is divided into two parts by a separating partition.
One side of the tank contains 0.01 m3 of refrigerant 134a that is saturated at 0.8 MPa,
while the other side is evacuated. The partition is removed and tank fills the entire
volume of the tank. If the final state of the refrigerant is 25 oC and 200 kPa, determine the
volume of the tank.
Further Problem
1 A rigid tank contains 50 kg 0f saturated liquid at 900C.Determine pressure and volume
contained in the tank
2 Calculate specific volume, specific enthalpy and specific internal energy of steam at
150 kPa and having a dryness fraction of 0.85
3 Calculate dryness fraction of steam at 700 kPa pressure having an enthalpy of 2500
kJ/kg.
4 A rigid tank having a volume of 2.5 m3 contains 5 kg of saturated liquid vapor mixture
at 750C. It is heated slowly till it just contains saturated vapor. Find the temperature of the
steam at that time.
5 Steam at 150 bars has a specific enthalpy of 3400 kJ/kg. Calculate temperature, specific
volume, specific internal energy and quality of steam.
6 A piston cylinder device encloses 0.1 cubic meter of steam having a mass of 0.5 kg at
0.4 MPa. Heat is added to the steam at constant pressure till its temperature reaches to
3000C. Determine heat transfer and work done.
FIRST LAW FOR CLOSED SYSTEM
(1) A fluid in a rigid tank having an internal energy of 800 kJ is stirred by a paddle
wheel doing 100 kJ of work. The tank looses 500 kJ of heat to the surroundings. Find
change in internal energy.
(2) A piston cylinder device contains 25 gms of saturated water vapor at 300 kPa. An
electrical heater is placed within the device. The heater is switched on and it draws a
current of 0.5 Amperes from a source of 120 V for 10 minutes. A heat loss of 30 kJ
occurs from the device to the surroundings. Determine the final temperature of the water.
(3) A piston cylinder device initially contains 0.5 m3 of a gas (Cp=1.04 kJ/kg-K,
R=297J/kg-K) at 400 kPa and 270C. An electric heater outside the cylinder is
switched on. It passes 5A current for 5minutes from a 120V source. The gas expands
at constant pressure and heat lost to the surroundings is 2800J.What is the final
temperature of the gas
(4) A piston cylinder device initially contains 0.5 m3 of a gas (Cp=1.04 kJ/kg-K,
R=297J/kg-K) at 400 kPa and 270C. An electric heater outside the cylinder is
switched on. It passes 5A current for 5minutes from a 120V source. The gas expands
at constant pressure and heat lost to the surroundings is 2800J.What is the final
temperature of the gas.
(5) Water is being heated in a closed pan on the top of a cooking range while it is
being stirred by a paddle wheel. During this process 30 kJ of heat are added and
paddle wheel work amounts to 500N-m. If the heat loss to the surroundings from the
pan is 5 kJ find the final energy of the system if its initial energy is 10 kJ.
(6) A closed system undergoes a cycle consisting of two processes. During the first
process 40 kJ of heat are transferred to the system and system does 60 kJ of work.
During the second process 45 kJ of work are done on the system Determine the heat
transfer during the second process and calculate the net heat transfer and the work
done during cycle.
(7) A classroom of 50 students capacity is to be air-conditioned by two window units
of 5 kW rating each. The class is illuminated by 12 light bulbs of 100 W each. The
rate of heat transfer to the room from the surroundings is 15000 kJ/h. If the room
temperature is to be kept constant at 20oC, determine the minimum number of air
conditioning units needed to do the job.
FIRST LAW FOR OPEN SYSTEMS
(1) Air enters an adiabatic nozzle steadily at 300 kPa, 200oC and 30 m/s. It leaves at 100
kPa and 180 m/s. The inlet area of the nozzle is 80x10-4 m2. Find the mass flow rate
through the nozzle, temperature at the exit of the nozzle and the area of the nozzle at its
exit.
(2) Air enters a compressor at 100 kPa, 25oC and with a negligible velocity. It leaves the
compressor at 1 MPa, 347o C and at a velocity of 90 m/s. The compressor is cooled at a
rate of 1500 kJ/min and power input to the compressor is 250 kW. Determine the mass
flow rate through the compressor.
(3) 12 kg/s of steam enters steadily though a turbine at 10 MPa, 450oC and 80 m/s. The
steam leaves at 10 kPa and 50 m/s with a 92% quality. Find change in the kinetic energy,
power out put from the turbine and area of the inlet passage of the turbine.
(4) A well insulated valve is used to throttle steam from 8 Mpa and 500oC to 600oC. Find
the final temperature.
(5) A hot water stream at 80oC enters a mixing chamber with mass flow rate of 0.5 kg/s
where it mixes the cold water stream which is at 20oC. It is desired that the mixture be at
40oC. Assuming the pressure is homogenous in the mixing chamber find the flow rate of
the cold water.
(6)Steam enters an adiabatic turbine at 10Mpa, 500K, 80m/s and at a rate of 3kg/s. It
leaves at 20kPa and 50m/s. If the power output from the turbine is 2MW, determine the
temperature of the steam at the exit of the turbine.
(7) Steam at 3 MPa and 4000C enters an adiabatic nozzel steadily with a velocity of
40m/s and leaves at 2.5 MPa and 300m/s. Determine exit temperature and area ratio of
the nozzle.
(8) Refrigerant 134a is throttled from the saturated liquid state at 800 kPa to a pressure of
140 kPa. Find final temperature and specific volume.
(9) Helium is compressed from 120 kPa and 310 K to 700 kPa and 430 K. A heat loss of
20 kJ/kg occurs during compression. If the kinetic and potential energy changes are
insignificant and mass flow rate is 90 kg/min, find the power input to the compressor.
(10) Argon gas enters steadily an adiabatic turbine at 900 kPa and 450oC with a velocity
of 80 m/s. It leaves the turbine at 150 kPa with a velocity of 150 m/s. the inlet of the
turbine is 60 cm2. If the power output from the turbine is 250 kW determine the exit
temperature of the argon.
(11) Steam at 5 MPa and 500oC enters nozzle steadily with a velocity of 80 m/s and
leaves it at 2 MPa and 400oC. The inlet area of the nozzle is 50 cm2 and the heat lost from
the nozzle is 90 kJ/s. Determine the mass flow rate of steam, exit velocity of steam and
the exit area of the nozzle.
(12) Air at 80 kPa and 127oC enters an adiabatic diffuser steadily at a rate of 6000 kg/h
and leaves it at 100 kPa. The velocity of the air steam is decreased from 230 m/s to 30
m/s at it passes through the diffuser. Find the exit temperature of air and the exit area of
the diffuser.
(13) Liquid water enters at 300 kPa and 20oC a mixing chamber a rate of 1.8 kg/s where
it is mixed with superheated steam at 300 kPa and 300oC. If the mixture leaves the
mixing chamber at 60oC, determine the mass flow rate of the super heated steam.
(14) Water is heated in an insulated constant diameter tube by a 7 kW electric heater
placed inside it. If the water enters the heater at 15oC and leaves it at 70oC, find the mass
flow rate of the water.
(15) Water at 100 bar and 100 oC enters a boiler at a rate of 10 ton/hr and leaves
superheated at 400 oC. Calculate the fuel consumption rate if the boiler efficiency is 90%
and the fuel calorific value is 40 MJ/kg.
(16) Steam at 0.07 bar and 88% dryness fraction exits from a steam turbine and enters a
steam condenser at rate of 100 ton/hr. Calculate cooling water flow rate if the cooling
water temperature rise is oC.
SECOND LAW OF THERMODYNAMICS
(1) A steam power plant receives heat from a furnace at arate of 280GJ/h. Heat lost from
the steam to the surroundings is 8GJ/h and the waste heat transferred to the sink is 145
GJ/h. Determine the power output in MW and thermal efficiency of the power plant.
(2) A car engine with the power out put of 70 Kw has an efficiency of 30%.
Determine rate of fuel consumption if the heating value of the fuel is 49000 Kj/kg.
(3) A steam power plant with a power output of 200 MW consumes coal at a rate of
60000 kg/h. The heating value of the coal is 30000 Kj/kg, determine the thermal
efficiency of the power plant
(4) A 50 Kw electric car is powered by an electric motor mounted in the engine room.
If the motor has 90% efficiency calculate the heat supplied by the motor to the engine
room.
(5) A household refrigerator has a cop of 1.8. It removes heat from the refrigerated
space at a rate of 100 Kj/min. Determine the electric power consumed by its
compressor and the rate at which heat is transferred to the kitchen.
(6) 10 kg of watermelon at 200C are to be cooled to 80C by placing these in a
refrigerator of COP 2.5 and requiring a power input of 500 W. The specific heat of
watermelons is 4.2 Kj/kg-0C. Calculate the time taken for the cooling of watermelons.
(7) Determine the COP of a refrigerator that removes heat from a food compartment
at a rate of 8000 Kj/h for each Kw of power it is supplied. Also determine the rate of
heat rejection to the surroundings.
(8) An air conditioner removes heat steadily from a house at a rate of 750Kj/min
while consuming power at arate of 6 Kw. Determine the COP of the air conditioner
and the rate of heat transfer from the room.
(9) A house can be heated either by electric resistance heaters or by a heat pump. A
household consumes 1200 kWh of electric power in a month by using these electric
resistance heaters .The price of electricity is 9 Sr/kWh. Find the net saving of the
household owner if he replaces the resistance heaters by a heat pump of COP 2.5.
(10) A heat pump is used to maintain a house at aconstant temperature of 240C. The
heat lost through the walls and windows is 60000Kj/h whereas the heat generated in
the house by all means is 4000 Kj/h .For a COP of 2.5 determine the power input to
the heat pump.
(11) A Carnot engine operates between a source temperature of 1000K and asink
temperature of 300K. If the heat engine is supplied heat at a rate of 800Kj/min,
determine the thermal efficiency, and power out put of the engine.
(12) An engine designer claims to have designed an engine that receives 800 Kj of
heat from a source at 400K and produces 250 Kj of net work output while rejecting
the waste heat to a sink at 300K. Is it possible?
(13) A Carnot engine having a thermal efficiency of 55% rejects heat at a rate of 800
Kj/ min to lake at 150C. Find the power of the engine and the temperature of the
source.
(14) A Carnot refrigerator operating in aroom at 250C consumes 2 Kw of powerwhile
keeping the food in it at 30C. Determine rate of heat rejection.
(15) A building has an air conditioning load of 150 MWh when the unit cost of the
power is 50 halalas per kWh. Two air conditioners are available in the market,
Air conditioner unit (A) has COP of 3.2 and its initial cost is 22000 SR, unit (B) has
COP of 5 with an initial cost of 30000 SR. If maintenance cost and other cost are
same which unit you will choose if you wish to use the unit for 2 years and if you
wish to use it for 5 years.
(16) A Carnot engine receives heat fro a reservoir at 9000C at a rate of 800 Kj/ min
and rejects heat to the surroundings, which are at 270C. The entire work out put of the
engine is to be use to drive a carnot refrigerator whose food compartment is at -50C
and that also rejects heat to the same surroundings which are at 270C. Determine the
maximum rate of heat removal from the food compartment and the total heat that is
rejected by the heat engine and the refrigerator.
AIR-CONDITIONING
(1) A house contains air at 250C and 65% relative humidity. Will the moisture on the
inner surface of window condense when the window temperature decreases to 100C?
(2) The room temperature is 400C and it has 40% relative humidity. A man wearing glass
enters this room after a a long walk in a temperature of 80c. Will his glasses become
fogged?
(3) he dry bulb and wet bulb temperatures of atmosphere are 250C and 200C respectively.
Determine specific humidity, relative humidity and specific enthalpy of air.
(4)The dry bulb and wet bulb temperatures of atmosphere are 250C and 200C
respectively. Determine specific humidity, relative humidity and specific enthalpy of air
and dew point temperature.
(5) The air in a room is at 320C and 60% relative humidity. Determine specific humidity,
specific enthalpy, wet bulb temperature, dew point temperature, and specific volume of
air.
(6) The air in a room is at 260C and 70% relative humidity. Determine specific humidity,
specific enthalpy, wet bulb temperature, dew point temperature, and specific volume of
air.
(7) The air in a room is at 280C and 70% relative humidity. Determine specific humidity,
specific enthalpy, wet bulb temperature, dew point temperature, and specific volume of
air
(8) The dry bulb and wet bulb temperatures of atmosphere are 240C and 170C
respectively. Determine specific humidity, relative humidity and specific enthalpy of air,
specific volume and dew point temperature