![Heat capacity
Heat capacity is a material’s ability to absorb heat from the
external surroundings; it represents the amount of energy
needed to increase the temperature of a substance 1 degree, so
the units are J / oC. In mathematical terms, the heat capacity C
is expressed as follows: C = ΔQ/ΔT = dQ/dT [J/deg] Where
dQ is the energy required to produce a dT temperature change.
Ordinarily, heat capacity is specified per mole of material (e.g.,
J/mol-K, or cal/mol-K). Table below give the heat capacity of
some materials. When the temperature is increased, the kinetic
energy of the particles in the material changes. 7](https://image.slidesharecdn.com/presentation1-230809121735-94e3ab1e/85/Presentation1-pptx-7-320.jpg)
![Relation between Different Scales of
Temperatures
Specific Heat
The amount of heat required to raise the temperature of unit
mass the substance through 1°C is called its specific heat.
It is denoted by c or s.
Its SI unit is joule/kilogram-°C'(J/kg-°C).
Its dimensions are [L2T-2θ-1].
The specific heat of water is 4200 J kg-1°C-1 or 1 cal. g-1
C-1, which high compared with most other substances.
12](https://image.slidesharecdn.com/presentation1-230809121735-94e3ab1e/85/Presentation1-pptx-12-320.jpg)
Presentation1.pptx
- 1. Ethiopian Institute of Technology-Mekelle Mekelle University, Ethiopia December, 2019 School of Mechanical and Industrial Engineering Manufacturing Engineering Chair Department of material science Advanced engineering materials and processing Heat capacity, thermal properties, expansions, conductivity and stress 1
- 2. introduction Thermal Properties. Thermal ... linear and volume coefficients of thermal expansion ... Heat capacity is a measure of the ability of the material to .... Thermal conductivity: heat is transferred from high to low .... At what temperature does the stress reach -172 MPa? T. 0 2
- 3. How heat creates on materials Light, electrical, mechanical, chemical, nuclear, sound and thermal energy itself can each cause a substance to heat up by increasing the speed of its molecules. So, put energy into a system and it heats up, take energy away and it cools. ... So, when you heat something up, you are just making its molecules move faster. 3
- 4. Heat Heat is a form of energy called thermal energy which flows from a higher temperature body to a lower temperature body when they are placed in contact. Heat or thermal energy of a body is the sum of kinetic energies of all its constituent particles, on account of translational, vibrational and rotational motion. 4
- 5. Cont. The SI unit of heat energy is joule (J). The practical unit of heat energy is calorie. 1 cal. = 4.18 J 1 calorie is the quantity of heat required to raise the temperature of 1 g of water by 1°C. Mechanical energy or work (W) can be converted into heat (Q) by 1 W = JQ 5
- 6. 6 J = Joule’s mechanical equivalent of heat. J is a conversion factor (not a physical quantity) and its value is 4.186 J/cal. Cont. where
- 7. Heat capacity Heat capacity is a material’s ability to absorb heat from the external surroundings; it represents the amount of energy needed to increase the temperature of a substance 1 degree, so the units are J / oC. In mathematical terms, the heat capacity C is expressed as follows: C = ΔQ/ΔT = dQ/dT [J/deg] Where dQ is the energy required to produce a dT temperature change. Ordinarily, heat capacity is specified per mole of material (e.g., J/mol-K, or cal/mol-K). Table below give the heat capacity of some materials. When the temperature is increased, the kinetic energy of the particles in the material changes. 7
- 8. Heat capacity of various materials (at RT) 8
- 9. Cont.……. 9
- 10. Temperature Temperature of a body is the degree of hotness or coldness of the body. A device which is used to measure the temperature is called a thermometer. Branch of Physics dealing with production and measurement temperature close to 0 K is known as cryogenics, while that deaf with the measurement of very high temperature is called pyromet NTP or STP implies 273.15 K (0°C = 32°F). 10
- 11. Different Scale of Temperatures 1. Celsius Scale in this scale of temperature, the melting point ice is taken as 0°C and the boiling point of water as 100°C 2. Fahrenheit Scale in this scale of temperature, the melt point of ice is taken as 32°F and the boiling point of water as 211 3. Kelvin Scale in this scale of temperature, the melting pouxl ice is taken as 273 K and the boiling point of water as 373 K 11
- 12. Relation between Different Scales of Temperatures Specific Heat The amount of heat required to raise the temperature of unit mass the substance through 1°C is called its specific heat. It is denoted by c or s. Its SI unit is joule/kilogram-°C'(J/kg-°C). Its dimensions are [L2T-2θ-1]. The specific heat of water is 4200 J kg-1°C-1 or 1 cal. g-1 C-1, which high compared with most other substances. 12
- 13. Gases have two types of specific heat i. The specific heat capacity at constant volume (Cv). ii. The specific heat capacity at constant pressure (Cr). Specific heat at constant pressure (Cp) is greater than specific heat constant volume(CV), i.e., Cp > CV. For molar specific heats Cp – CV = R where R = gas constant and this relation is called Mayer’s formula. The ratio of two principal specific heats of a gas is represented by γ. The value of depends on atomicity of the gas. Amount γ of heat energy required to change the temperature of any substance is given by Q = mcΔt 13
- 14. Cont. where, m = mass of the substance = specific heat of the substance and Δt = change in temperature. Thermal Expansion Is a process which increases the size material by heating is called thermal expansion. There are three types of thermal expansion. Expansion of solids Expansion of liquids Expansion of gases Expansion of Solids Three types of expansion -takes place in solid. these are 1. Linear Expansion, 2. Superficial Expansion and 3. Cubical Expansion 14
- 15. Linear Expansion Linear Expansion is an expansion in length material by heating is called linear expansion. And the mathematical expression of a linear expansion Increase in length are L2 = L1(1 + α Δt) where, • L1 and L2 are initial and final lengths, • Δt = change in temperature and • α = coefficient of linear expansion. Coefficient of linear expansion expressed as α = (Δl/l * Δt) where 1= real length and Δl = change in length and Δt= change in temperature 15
- 16. Superficial Expansion Superficial Expansion is an Expansion in area on heating is called superficial expansion. Increase in area A2 = A1(1 + β Δt) where, • A1 and A2 are initial and final areas and • β is a coefficient of superficial expansion. • Coefficient of superficial expansion β = (ΔA/A * Δt) where. • A = area, • ΔA = change in area and • Δt = change in temperature 16
- 17. Cubical Expansion Cubical Expansion is an expansion in volume on heating is called cubical expansion. Increase in volume V2 = V1(1 + γ Δ t) where • V1 and V2 are initial and final volumes and • γ is a coefficient of cubical expansion. Coefficient of cubical expansion where • V = real volume, • ΔV =change in volume and • Δ t = change in temperature. 17
- 18. Cont.. 18 Relation between coefficients of linear, superficial and cubical expansions β = 2α and γ = 3α or α: β: γ = 1:2:3
- 19. Expansion of Liquids Expansion of Liquids In liquids only expansion in volume takes place on heating. 1. Apparent Expansion of Liquids When expansion of the container containing liquid, on heating is not taken into account then observed expansion is called apparent expansion of liquids. Coefficient of apparent expansion of a liquid 1. Real Expansion of Liquids When expansion of the container, containing liquid, on heating is also taken into account, then observed expansion is called real expansion of liquids. 19
- 20. Cont.… Coefficient of real expansion of a liquid Both, yr, and ya are measured in °C-1. We can show that yr = ya + yg where, • yr, and ya are coefficient of real and apparent expansion of liquids and • yg is coefficient of cubical expansion of the container Anomalous Expansion of Water When temperature of water is increased from 0°C, then its vol. decreases up to 4°C, becomes minimum at 4°C and then increases. behavior of water around 4°C is called, anomalous expansion water. 20
- 21. Expansion of Gases Expansion of Gases There are two types of coefficient of expansion in gases Volume Coefficient (γv) At constant pressure, the change in volume per unit volume per degree Celsius is called volume coefficient. where V0, V1, and V2 are volumes of the gas at 0°C, t1°C and t2°C. Pressure Coefficient (γp) At constant volume, the change in pressure per unit pressure per degree Celsius is called pressure coefficient. where P0, P1 and P2 are pressure of the gas at 0°C, t1°C and t2°C. 21
- 22. Thermal Conductivity. Thermal conductivity refers to the amount/speed of heat transmitted through a material. Heat transfer occurs at a higher rate across materials of high thermal conductivity than those of low thermal conductivity. ... Thermal conductivity of materials is temperature dependent. 22
- 23. Resistances of thermal conductivity materials These phenolic resin insulation materials have characteristic flame resistance, low smoke generation, low thermal conductivity, and high temperature resistance. Phenolic resin foams are good heat insulators up to 120°C, whereas glass wool and rock wool are good insulators up to 260°C and 385 °C, respectively. 23
- 24. Thermal stresses Thermal stress is stress caused by differences in temperature or by differences in thermal expansion. A crack formed as a result of thermal stress produced by rapid cooling from a high temperature. Because the section of rail was fixed at both ends it experienced a thermal stress when the ambient temperature increased. 24
- 25. Effects of thermal stresses on materials Thermal stress is stress created by any change in temperature to a material. These stresses can lead to fracture or plastic deformation depending on the other variables of heating, which include material types and constraints. 25
- 26. Protections of thermal stress Thermal protection system (TPS) materials are used to manufacture the heat shield that protects the structure, the aerodynamic surfaces, and the payload of missiles and warheads from the severe heating encountered during the entry flight through a planetary 26
- 27. conclusions In generally the thermal properties Heat capacity Thermal expansion Thermal conductivity& Thermal stresses of materials are under thermodynamics engineering's 27