Heat Engines and Thermal Efficiency| Grade 9 Science Quarter 4 Week 7
Summary
TLDRThis video lesson from a YouTube channel focuses on the principles of heat engines and thermal efficiency. It begins by explaining the concept of heat transfer, which is the movement of energy from a high-temperature object to a low-temperature one, and how it can be used to perform work. The video then delves into the three methods of heat transfer: conduction, convection, and radiation. It introduces heat engines as devices that convert thermal energy into mechanical work, with examples such as geothermal power plants. The lesson also covers the workings of combustion engines, including the four-stroke cycle in gasoline engines. Thermal efficiency is discussed, highlighting that not all thermal energy can be converted into useful work due to waste heat. The video presents the Carnot efficiency formula, which shows that the efficiency of an ideal heat engine depends on the temperature difference between the hot and cold reservoirs. Finally, it works through sample problems to illustrate how to calculate the efficiency of heat engines, providing a clear understanding of the topic.
Takeaways
- 🔥 **Heat Transfer**: Heat transfer occurs when there's a temperature change, moving from a high-temperature object to a low-temperature one, and can happen through conduction, convection, and radiation.
- 🚀 **Heat Engines**: A heat engine is a device that uses thermal energy or heat to perform work, taking in heat from a high-temperature source and releasing some as waste heat to a low-temperature sink.
- 🔩 **Engine Cycles**: Heat engines operate in cycles where heat is added, some is used to do work, and the rest is removed at a lower temperature, exemplified by geothermal power plants and combustion engines.
- 🏎️ **Combustion Engines**: There are two types of combustion engines: external (like steam engines) and internal (like gasoline or diesel engines), with the latter being common in vehicles.
- 🔬 **Thermal Efficiency**: The efficiency of a heat engine is the ratio of useful work done to the heat input, with a maximum theoretical limit set by the temperatures of the hot and cold reservoirs.
- 📉 **Waste Heat**: Not all absorbed heat can be converted into useful work; the rest is lost as waste heat, which is inevitable and limits engine efficiency.
- 💯 **Efficiency Calculation**: Efficiency is calculated as the work done divided by the input heat, minus the exhaust heat, and can also be determined by temperature measurements of the hot and cold reservoirs.
- ⚙️ **Four Stroke Cycle**: In a gasoline engine, the four strokes are intake, compression, power, and exhaust, which define the operation of the engine.
- 🔢 **Sample Problem**: The script provides a method to calculate the efficiency of a heat engine using given values of energy input and waste heat.
- 📐 **Carnot Efficiency**: According to Carnot, the efficiency of an ideal heat engine depends only on the temperature difference between the hot and cold reservoirs.
- 🌡️ **Temperature Scale**: Efficiency calculations use absolute temperatures, measured on the Kelvin scale.
- 🎓 **Educational Content**: The script is educational, aimed at teaching students about heat engines, their operation, and the principles of thermal efficiency.
Q & A
What is the main topic of the week 7 science lesson for grade 9?
-The main topic of the week 7 science lesson for grade 9 is heat engines and thermal efficiency.
How is heat transfer related to work?
-Heat transfer is related to work because it involves the release of heat that can be used to perform work, such as in heat engines like geothermal power plants.
What are the three methods of heat transfer?
-The three methods of heat transfer are conduction, convection, and radiation.
How does a heat engine work?
-A heat engine works by taking in heat from a high-temperature reservoir, using the absorbed energy to perform useful work, and then releasing waste heat to a low-temperature reservoir.
What is the difference between an external and internal combustion engine?
-An external combustion engine burns fuel outside the engine, such as in a steam engine, while an internal combustion engine burns fuel inside the engine, like in gasoline or diesel engines.
What are the four strokes of a four-stroke gasoline engine?
-The four strokes of a four-stroke gasoline engine are the intake stroke, compression stroke, power stroke, and exhaust stroke.
Why can't a heat engine be 100% efficient?
-A heat engine can't be 100% efficient because some of the thermal energy is inevitably lost as waste heat due to interactions like friction, and not all heat can be converted into useful work.
What is the formula for calculating the efficiency of a heat engine?
-The efficiency of a heat engine is calculated as efficiency equals (input heat - exhaust heat) divided by input heat times 100 percent.
How does the temperature difference between the hot and cold reservoirs affect the efficiency of a heat engine?
-According to Carnot's principle, a heat engine operating between two reservoirs with a higher temperature difference is more efficient than one operating between reservoirs with nearly the same temperatures.
What is the maximum efficiency of a steam engine that receives steam at 600 Kelvin and exhausts to a condenser at 350 Kelvin?
-The maximum efficiency of this steam engine is 41.67%, calculated using the formula efficiency = 1 - (Tc/Th) * 100%, where Tc is the temperature of the cold reservoir and Th is the temperature of the hot reservoir.
What is the efficiency of a gasoline engine that receives 193 joules of energy from combustion and loses 125 joules by heat to exhaust during one cycle?
-The efficiency of the gasoline engine is 35.23%, calculated using the formula efficiency = 1 - (Qc/Qh) * 100%, where Qc is the energy removed by heat and Qh is the energy added by heat.
Outlines
🔥 Introduction to Heat Engines and Thermal Efficiency
This paragraph introduces the topic of heat engines and thermal efficiency. It explains the relationship between heat and temperature, and how heat transfer can lead to energy transfer. The focus is on how heat can be converted into work, with examples from everyday life like boiling water. Three methods of heat transfer are discussed: conduction, convection, and radiation. The concept of a heat engine is introduced, which is a device that uses thermal energy to perform work. The limitations of heat engines are also mentioned, with an explanation of waste heat and the efficiency of converting heat into useful work. The paragraph concludes with an introduction to geothermal power plants as an example of heat engines.
🚗 Combustion Engines and Their Efficiency
The second paragraph delves into the specifics of combustion engines, which are a type of heat engine. It differentiates between external and internal combustion engines, providing examples of each. The four-stroke cycle of a gasoline engine is described in detail, including the intake, compression, power, and exhaust strokes. The concept of thermal efficiency is further explored, emphasizing that not all thermal energy can be converted into useful work, with the remainder being waste heat. The inefficiency of car engines is highlighted, noting that they are only about 30% efficient. The paragraph also discusses the theoretical maximum efficiency of heat engines based on the temperature difference between the hot and cold reservoirs, as postulated by Sadi Carnot. An equation for calculating efficiency is provided, and a sample problem is solved to illustrate the concept.
🧮 Calculating Thermal Efficiency with Sample Problems
The final paragraph provides a step-by-step guide to calculating the thermal efficiency of heat engines using sample problems. The first sample problem involves a gasoline engine with given values for energy input from combustion and heat loss to exhaust, using the previously introduced efficiency formula. The second sample problem concerns a steam engine operating between two temperature reservoirs, and it demonstrates how to calculate the maximum efficiency using temperature measurements. The paragraph concludes with a reminder to round off final answers and an encouragement to apply the knowledge gained to solve similar problems. The video ends with a prompt for viewers to like, share, subscribe, and engage with the content, and a thank you note to the viewers for their support.
Mindmap
Keywords
💡Heat Engines
💡Thermal Efficiency
💡Heat Transfer
💡Conduction
💡Convection
💡Radiation
💡Combustion Engine
💡Waste Heat
💡Temperature Reservoirs
💡Carnot Efficiency
💡Sample Problem
Highlights
Heat transfer can be used to do work, involving the release of heat
Heat transfer and energy transformation make heat engines like geothermal power plants work
Heat is related to temperature and heat transfer may change an object's temperature
Heat transfer occurs when there is a temperature change, transferring energy from high to low temperature objects
Three methods of heat transfer: conduction, convection, and radiation
A heat engine is a device that converts thermal energy into mechanical work
Not all heat absorbed by a heat engine can be converted into useful work - some is lost as waste heat
The energy converted into useful mechanical work is the difference between heat input and heat output
Examples of heat engines include power plants like geothermal
A combustion engine produces heat using a combustion process with fuel and an oxidizer
There are two classes of combustion engines: external (e.g. steam engine) and internal (e.g. gasoline or diesel)
In a four-stroke gasoline engine, the piston undergoes intake, compression, power, and exhaust strokes
Thermal efficiency is the ratio of useful work output to the thermal energy input
Not all thermal energy can be converted into useful work - some is lost as waste heat
Car engines are only around 30% efficient, with 70% of thermal energy lost as waste heat
It's impossible to construct a 100% efficient heat engine that fully converts all heat into useful work
The efficiency of ideal heat engines depends only on the temperature difference between the hot and cold reservoirs
Efficiency can be calculated as (work done / input heat) x 100% or using temperature measurements
Sample problem: Calculate the efficiency of a gasoline engine given energy input and heat loss to exhaust
Sample problem: Calculate the maximum efficiency of a steam engine given temperatures of hot and cold reservoirs
Transcripts
good day students welcome back to my
strong techie youtube channel we are now
in week 7 of grade 9 science quarter 4
lesson if you haven't watched our
previous lesson for the past weeks pause
the video and check the links in the
description box below this week's lesson
is all about heat engines and thermal
efficiency interesting right now let's
check out our learning objectives infer
that heat transfer can be used to do
work and that work involves the release
of heat explain how heat transfer and
energy transformation make heat engines
like geothermal power plants work
if you want to know more about this
lesson please keep on watching
[Music]
in your grade 7 science you have learned
that heat is related to temperature heat
transfer may change one's temperature
this change in temperature either a
decrease or an increase means that there
is an energy transfer in the form of
heat this video focuses on heat and work
and how heat can be turned into work and
how work involves the release of heat in
our everyday life heat transfer is
always evident many times we experience
heat transfer when we do majority of our
household chores and even when we go on
sports but what exactly is heat transfer
whenever there is a temperature change
heat transfer takes place it is the
transfer of energy from a high
temperature object to a low temperature
object an example of heat transfer is
boiling of water the hot stove heats the
pot and the pot heats the water inside
once transfer it can no longer be called
heat it becomes the internal energy of
the body transfer of energy from hot
objects to cool objects stops when the
two attain the same temperature the
objects are said to be in thermal
equilibrium so many processes involve
heat transfer it is hard to imagine a
situation where no heat transfer occurs
there are three methods of heat transfer
the first one is the conduction it is
the transfer of heat due to direct
contact between two objects or materials
with different temperatures the process
of heat transfer in solids is called
conduction one example is the rod on
firewood second method of heat transfer
is convection it is the transfer of heat
from one location to the other by the
movement of fluids examples are boiling
of waters and the steam the third method
of heat transfer is what we call
radiation it is the transfer of heat by
electromagnetic
wave and another example is the
microwave oven
now let us talk about engines
one such object that allows us to
produce mechanical work from type of
energy is called an engine if the energy
that was used to perform work was
thermal energy or heat then the engine
is called a heat engine to perform work
heat is taken in by the engine from a
heat source also called the high
temperature reservoir the energy
absorbed by the heat engine is used to
perform useful work however not all the
heat absorbed by the engine can be
converted into useful work
there will always be a portion of heat
that will be lost as a result of other
interactions like friction this lost
heat is called a waste heat this waste
heat goes to the low temperature
reservoir or the heat sink of that heat
engine the energy converted as useful
mechanical work is equal to the
difference in the heat input from high
temperature super server and the heat
output that was received by the low
temperature reservoir so work is equal
to heat input minus heat output again
class heat engine is a device which
converts thermal energy to mechanical
energy examples of heat engine are power
plants such as geothermal there are
three things that happen in the full
cycle of a heat engine first one
heat is added it is an input heat which
is relatively high temperature second
some of that energy from that input heat
is used to do work and third the rest of
the heat is removed at a relatively cold
temperature furthermore class a common
type of heat engine is called combustion
engine in a combustion engine heat is
produced using a combustion process
which in turn makes use of a fuel and an
oxidizer for that fuel-like air there
are two classes of combustion engines
the first one is external combustion
engine burning a fuel takes place
outside the engine examples are steam
and the piston engine that is shown in
your screen right now the second one is
the internal combustion engine burning a
fuel takes place inside the cylinder or
turbine engine examples are gasoline or
diesel engine most automobiles make use
of either a d cell or a gasoline engine
in the case of gasoline engines most
have four cylinders each containing a
piston each piston undergoes a series of
four movements or strokes as shown in
your screen right now is a four stroke
cycle in a gasoline engine the first
stroke is the intake stroke the intake
valve opens allowing the cylinder to
receive the fuel air mixture as the
piston moves downward the second one is
the compression stroke the piston moves
up compressing the fuel air mixture the
third one is the power stroke the spark
plug at the top of the cylinder causes
the mixture to ignite and combust making
its temperature high and the last one is
the exhaust stroke the combusted gases
are pushed out of the open exhaust bulb
through an upward motion on the piston
now let us talk about thermal efficiency
the thermal energy produced from the
combustion of fuel air mixture is
transformed into mechanical energy which
moves the car however not all thermal
energy is converted into useful work
this thermal energy which is not
converted to useful work is called waste
heat these heat losses are unavoidable
and greatly limit the efficiency of heat
engine for example the engines of cars
are only 30 percent efficient this means
that for every 100 joules of thermal
energy produced by a combustion of
gasoline only 30 joules are used to
actually move the car therefore it is
impossible to construct a heat engine
that is 100 efficient which can fully
convert all the heat into a useful work
an engine that converts energy into more
work and less weight is said to be more
efficient however according to sadi
carnot he found out that while it is
true that we can express efficiency in
terms of work the efficiency of ideal
heat engines depends only on the
temperatures of the hot and cold
reservoir according to him an engine
operating between two reservoirs of
higher temperature difference is more
efficient than an engine operating
between reservoirs of nearly the same
temperatures now let us have the
equation for efficiency it is calculated
as efficiency equals work done divided
by input heat times a hundred percent
but since work is just the input heat
minus the exhaust heat the equation
becomes efficiency equals the input heat
minus the exhaust heat divided by the
input heat times a hundred percent
simplifying this equation we have input
heat divided by input heat that is one
and we have the remaining minus exhaust
heat divided by input heat times a
hundred percent where q sub c is the
energy removed by heat or energy in cold
reservoir and q sub h is the energy
added by heat or energy in hot reservoir
the equation for efficiency can also be
modified to use temperature measurement
instead of the energy values therefore
we can say that efficiency is equal to 1
minus p sub c where t sub c is the
absolute temperature in cold reservoir
divided by t sub h where it is the
absolute temperature in hot reservoir
times a hundred percent take note class
the temperatures are the absolute
temperatures on the kelvin scale now let
us have a sample problem sample problem
number one what is the efficiency of a
gasoline engine that receives 193 joules
of energy from combustion
and lose 125 joules by heat to exhaust
during one cycle the given are q sub c
or the energy removed by heat which is
125 joules q sub h which is the energy
added by the heat and that is 193 joules
and we are looking for its efficiency we
are going to use this formula the one
that we had a while ago now let us
substitute our given to our formula and
we have one minus we have q sub c
divided by q sub h times a hundred
percent following the pemdas rule we
need first to calculate the numbers
inside the parentheses and do the
division first before the subtraction
125 joules divided by
193 joules we have
0.6476 and so on next subtract 1 minus
0.6476
we have
0.3523 and so on do not forget to
multiply it to 100
the product is 35.23
do not forget to round off your final
answer now let us have sample problem
number two suppose a steam engine
receives steam at 600 kelvin the engine
uses a part of these thermal energy for
work it exhausts the rest to a condenser
at the temperature of 350 kelvin what is
the maximum efficiency of this steam
engine our given we have the temperature
in cold reservoir which is 350 kelvin
and the absolute temperature in the hot
reservoir which is 600 kelvin and we are
looking for its efficiency our formula
the one that we had a while ago now let
us substitute our given to our formula
efficiency is equal to 1 minus 350
kelvin divided by 600 kelvin times
hundred percent again we need to follow
the pemdas rule divide first 350 divided
by 600 and this is the quotient next one
minus
0.583 and so on we have the difference
of
zero point four one six six and so on
then multiply it to one hundred percent
we have the product of forty one point
sixty seven percent do not forget to
round off your final answer and that is
how you are going to solve problems
involving thermal efficiency and that's
it for our lesson this week i hope you
learned something new again if this
video helped you please do like share
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keep you updated for my future videos
comment now for a shout out
shout out to gerlain bailon
john paul imessolania riya solomon
raniel de vera again from the bottom of
my heart thank you all so much for
watching you may also subscribe to lady
alchemist youtube channel for more
advanced chemistry lessons and to kcmctv
youtube channel for some inspirational
spoken poetry videos bye class and see
you on my next video
[Music]
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