Chapter 4: Heat Capacity and Heat Transfer - · PDF fileChapter 4: Heat Capacity and Heat...
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Chapter 4: Heat Capacity and Heat Transfer Navapadol Kittiamornkul, Ph. D. Chapter 4: Heat Capacity and Heat Transfer
Transcript of Chapter 4: Heat Capacity and Heat Transfer - · PDF fileChapter 4: Heat Capacity and Heat...
Chapter 4: Heat Capacity and Heat Transfer
Navapadol Kittiamornkul, Ph. D.
Chapter 4:
Heat Capacity and Heat Transfer
Navapadol Kittiamornkul, Ph. D.
4.1 Material Structure4.2 Temperature and Material
Properties4.3 Heating and Internal Energy4.4 Heat Capacity and Latent Heat4.5 Heat Transfer
Chapter 4: Heat Capacity and Heat Transfer
4.1 Material Structure
Navapadol Kittiamornkul, Ph. D.
Atom The smallest unit of element.
Molecule The smallest unit of compound consist of many atoms
Ex. Molecule of water (H2O) consists of 2 hydrogen atom and 1 oxygen atom
Navapadol Kittiamornkul, Ph. D.
4.1 Material Structure
The Phase of Matter: Solid
Solid Molecules constructs together with strong bond.
Therefore, solid has definite volume and shape.
Navapadol Kittiamornkul, Ph. D.
4.1 Material Structure
The Phase of Matter: Liquid
Liquid Molecules can freely move, but it cannot move so far because of its bond.
Therefore, liquid has a definite volume but no definite shape.
So, it can change its shape according to it container.
Navapadol Kittiamornkul, Ph. D.
4.1 Material Structure
The Phase of Matter: Gas
Gas Molecules can freely move with long distance because it has weak bond.
Therefore, gas has neither a definite volume nor shape.
So, it can change its shape according to it container like liquid.
Navapadol Kittiamornkul, Ph. D.
4.1 Material Structure
Moving Ability of Molecules
Solid < Liquid < Gas
Kinetic Energy of Molecules
Solid < Liquid < Gas
Internal Energy of Molecules
Solid < Liquid < Gas
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
Temperature A measure of the warmth or coldness of an object which depends on internal energy (kinetic energy) of material.
High internal energy High temperature
Low internal energy Low temperature
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
Temperature Scale
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
Temperature scale in Kelvin, T(K) depends on internal energy (kinetic energy)
When T(K) is low, the molecules will move slowly until it stop at 0 K called “absolute zero”
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
Temperature measurement device called “Thermometer”
Advantage: Mercury thermometer can hold the value although it doesn’t contact patient. (User needs to flick before
measure)Mercury thermometer
Disadvantage: Mercury is toxic.
Digital thermometer
Now, mercury thermometer is replaced by Digital thermometer.
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
Material will extend when its temperature increase.
Material will shrink when its temperature decrease.
Because of kinetic energy, when kinetic energy of molecule increases, molecule velocity increase too. It causes the distance between molecules higher.
The relation between temperature change and material extending is linear
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
High temperatureLow temperature
Heat
Length difference
Referent length
Coefficient of linear expansion
Temperature difference
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
Example of coefficient of linear expansion
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
Ex. Lead has 3 cm of its length. If temperature increases from 37 ºC to 40 ºC, find the length after heating.
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
Mercury thermometer has bulbto contain liquid mercury at the terminal. Mercury will extend and flow to glass tube when temperature around its bulb increases.
Navapadol Kittiamornkul, Ph. D.
4.2 Temperature and Material Properties
To construct railway, we need to abstain around joint for extending of metal to protect the derailing.
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
The energy occurs from the difference of temperature called “Heat”.
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
In natural, heat transfers from high temperature to low temperature till equilibrium called “Thermal Equilibrium”.
Material that receives heat will increase temperature.
Material that losses heat will decrease temperature.
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
Material temperature is not only changed by heating, but it is also changed by mechanical energy and etc.
James Joule’s experiment water insulator
thermometer
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
“Heat can change material phase.”
Exothermic
Endothermic
Exothermic
Endothermic
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
If we chill watermelon and sandwich, which one can hold longer temperature?
V.S.
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
Two materials has the same mass (m), but difference heat capacity (s).
If we want to increase temperature, material that has more heat capacity (s) will need more energy (Q)
Heat Energy (Q)
If we give the same energy (Q) to two materials, material that has more heat capacity (s) will change its temperature slowly.
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
Ex. (A) Find heat energy that increases 200g water temperature for 5 degree Celsius. (Swater = 1 cal/g.C)
Ex. (B) Find heat energy that increases 200g lead temperature for 5 degree Celsius. (Slead = 0.03 cal/g.C)
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
Phase Change
Ice
Water + Ice
Give 1 cal/s of heat energy to 1 g of ice.
Water
Water + Vapor
time
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
Ice
Water + Ice
Water + Vapor
Water
time
Navapadol Kittiamornkul, Ph. D.
4.3 Heating and Internal Energy
Ice
Water + Ice
Water + Vapor
time
No temperature change
Water
Navapadol Kittiamornkul, Ph. D.
4.4 Heat Capacity and Latent Heat
Exothermic
EndothermicExothermic
Endothermic
gas
liquid
solid
condensation vaporization
fusionfreezing
Heat is used to change phase called Latent Heat.
Navapadol Kittiamornkul, Ph. D.
4.4 Heat Capacity and Latent Heat
Q v = Energy of vaporizationL v = Latent heat of vaporization
Q f = Energy of fusionL f = Latent heat of fusion
We can calculate energy that uses to change phase using the following equation.
Navapadol Kittiamornkul, Ph. D.
4.4 Heat Capacity and Latent Heat
Navapadol Kittiamornkul, Ph. D.
4.4 Heat Capacity and Latent Heat
Ex. Aluminum glass contains 800 g of water
Navapadol Kittiamornkul, Ph. D.
4.4 Heat Capacity and Latent Heat
Ex. Aluminum glass contains 800 g of water
Navapadol Kittiamornkul, Ph. D.
4.5 Heat Transfer
Heat conduction
Heat Convection
Radiation
Conduction Heat transfer of material from contact
Convection Heat transfer of material using mass movement Ex. Water in boiler boils thoroughly.
Radiation Heat transfer of light, ray, electromagnetic wave, or etc. It can be exothermic and endothermic.
Navapadol Kittiamornkul, Ph. D.
4.5 Heat Transfer
“Heat transfer occurs from collision of molecules at the contact point”
K.E. of foot molecule is higher than floor. K.E. will transfer to floor Temperature reduces
Feel Cool
Navapadol Kittiamornkul, Ph. D.
4.5 Heat Transfer
“Heat transfer occurs from collision of molecules at the contact point”
K.E. of foot molecule is lower than floor. K.E. will transfer to foot Temperature increases
Feel Hot
Navapadol Kittiamornkul, Ph. D.
4.5 Heat Transfer
Navapadol Kittiamornkul, Ph. D.
4.5 Heat Transfer
Heat Convection
In natural, heat convection occurs when object receives heat.
Although gas and liquid are not good at heat conduction, it is good at heat convection. Molecules of gas and liquid can flow for long distance, and they will bring heat energy together.
It occurs together with movement of medium.
Navapadol Kittiamornkul, Ph. D.
4.5 Heat Transfer
Radiation
Object releases electromagnetic energy called radiation
Electromagnetic wave can travel without medium. Ex. Light from the sun can travel passing space to the earth.
Navapadol Kittiamornkul, Ph. D.
4.5 Heat Transfer
In still air, heat from flame transfers with radiation process.
In flow air, heat from flame transfers with convection process.
Navapadol Kittiamornkul, Ph. D.
4.5 Heat Transfer
Heat and Human body
If human has high body temperature or low body temperature, it can cause very dangerous disease such as heat stroke and hypothermia.
How to make body temperature lower.
END OF CHAPTER 2
Navapadol Kittiamornkul, Ph. D.
END OF CHAPTER 4
Heat Capacity and Heat Transfer
