Thermal Properties - gsnu.ac.krma.gsnu.ac.kr/course/ms/16_Thermal.pdf · 2020-05-07 · Thermal...
Transcript of Thermal Properties - gsnu.ac.krma.gsnu.ac.kr/course/ms/16_Thermal.pdf · 2020-05-07 · Thermal...
Thermal properties
Material science
© Su-Jin Kim, GNU
Thermal Properties(열적성질)
Professor Su-Jin Kim
Gyeongsang National University
Thermal properties
Material science
© Su-Jin Kim, GNU
OCW
Motion of molecule (TED 5min) Temperature, Radiation
https://youtu.be/b0IbXG0hnOk
Thermal conductivity
https://youtu.be/TmeJFYJcdaw
Thermal properties
Material science
© Su-Jin Kim, GNU
KOCW
재료의열적성질
http://www.kocw.net/home/cview.do?lid=a5a36e3b7fdebee6
Thermal properties
Material science
© Su-Jin Kim, GNU
Melting point (녹는점)• Depends on the energy required to separate its atoms.
• Plastic < Lead < Al < Cu < Fe < Ti < Ceramic < Tungsten
Thermal properties
Material science
© Su-Jin Kim, GNU
Energy & Atomic vibration
• Energy is stored as atomic vibrations.
• Energy storage and thermal expansion.
Interatomic distance
Vib
rati
on
en
ergy
Automic Vibration
Thermal properties
Material science
© Su-Jin Kim, GNU
• Heat capacity(열용량) is the ability of a material to absorb heat.• The energy required to increase the temperature of the material.
dQ = C dT
Specific heat (비열)
• Specific heat(비열) has typical units of (J/kgK)energy required to increase a unit mass by a unit T.Energy input(J) = Specific heat(J/kgK) x Mass(kg) x Temperature change (K)
dQ = c m dT
Thermal properties
Material science
© Su-Jin Kim, GNU
Specific heatMaterial cp (J/kgK)
Liquid Water 4186
Oil 2300
Polymers
1600
Polypropylene 1925
Polyethylene 1850
Polystyrene 1170
Teflon 1050
Ceramics
800
Magnesia(MgO) 940
Alumina(Al2O3) 775
Glass 840
Metals
400
Aluminum 900
Steel 486
Tungsten 138
Gold 128
Thermal properties
Material science
© Su-Jin Kim, GNU
Energy cost, Excel
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Air Water Aluminum Iron Plastic Alumina
Cost $ Volume Temperature change Energy cost
V(m3) dT(ºC) ($/kWh) $/kJ
1 25 0.2 5.55556E-05
Density Mass Specific Heat Energy input Cost
Material ρ(kg/m3) m(kg) c(J/kgºC) dQ(kJ) $
Air 1.225 1.225 1000 31 0.0
Water 1000 1000 4200 105000 5.8
Aluminum 2700 2700 900 60750 3.4
Iron 7874 7874 448 88189 4.9
Plastic 920 920 1800 41400 2.3
Alumina 3950 3950 775 76531 4.3
m = ρ V dQ = c m dT
Thermal properties
Material science
© Su-Jin Kim, GNU
Thermal Expansion (열팽창)
• Materials expand upon heating and contract when cooled.
• Thermal expansion coefficient α(K-1)
∆l = α l0 ∆T
Linear extension (m/m)
Temperature increase (K)
l0 ∆l∆T
Thermal properties
Material science
© Su-Jin Kim, GNU
Thermal Expansion Coefficient
Material α(10-6/K)
Polymers
100
Polypropylene 145-180
Polyethylene 106-198
Polystyrene 90-150
Teflon 126-216
Metals
10
Aluminum 23.6
Steel 12
Tungsten 4.5
Gold 14.2
Ceramics
5
Magnesia(MgO) 13.5
Alumina(Al2O3) 7.6
Soda-lime Glass 9
Silica (cryst. SiO2) 0.4
Thermal properties
Material science
© Su-Jin Kim, GNU
Thermal Conductivity (열전도율)
• The ability of a material to transfer heat.
• Thermal conductivity, k (W/mK)
Q = -k A (Th-Tl) / x
Q: Thermal Conduction (W) (Th-Tl) / x : Temperature gradient (K/m)
x
Th
Q
Tl k
A
Thermal properties
Material science
© Su-Jin Kim, GNU
Thermal Conductivity
Material k (W/mK)
Metals
100
Aluminum 247
Steel 52
Tungsten 178
Gold 315
Ceramics
20
Magnesia(MgO) 38
Alumina(Al2O3) 39
Soda-lime Glass 1.7
Silica (cryst. SiO2) 1.4
Polymers
0.2
Polypropylene 0.12
Polyethylene 0.48
Polystyrene 0.13
Teflon 0.25
Thermal properties
Material science
© Su-Jin Kim, GNU
Thermal Stress (열응력)
• Thermal stress occurs due to uneven heating & cooling and mismatch in thermal expansion.
Thermal stress (MPa)
Modulus of elasticity (GPa)
Thermal expansion coefficient (K-1)
Temperature increase (K)
∆T
σ = E α ∆T
Thermal properties
Material science
© Su-Jin Kim, GNU
Thermal Shock (열충격)
• Thermal shock occurs due to uneven heating & cooling.
• Assume top thin layer is rapidly cooled ∆T
• Tension stress at the surface :
• Quench rate : dq/dx = k ∆T
TE
∆Tqdx
• Thermal shock resistance is the ability of a material to be rapidly cooled and not crack. Maximize
E
kf
1500℃