The first law of thermodynamics
The first law of thermodynamics
Agenda Today ·Heat and energy The first law of thermodynamics Isothermal process,constant-volume process And constant-pressure process Adiabatic process
Agenda Today • Heat and energy • The first law of thermodynamics • Isothermal process, constant-volume process And constant-pressure process Adiabatic process
Heat: The energy transferred from one body to another due to the difference in temperature Its unit: calorie Specific heat(比热) cm△T
Heat: The energy transferred from one body to another due to the difference in temperature Its unit: calorie Specific heat(比热）
The zeroth law of thermodynamics: If bodies A and B are each in thermal equilibrium with a third body T,then they are in thermal equilibrium with each other. Or in plain word,we could use a certain property to describe the state of body in thermal equilibrium
The zeroth law of thermodynamics: If bodies A and B are each in thermal equilibrium with a third body T, then they are in thermal equilibrium with each other. Or in plain word, we could use a certain property to describe the state of body in thermal equilibrium
Temperature and temperature scales 标)： Kelvin scale: Celsius scale: Fahrenheit scale: T=T-273.15 2 +3
Temperature and temperature scales（温 标）: Kelvin scale: Celsius scale: Fahrenheit scale:
Thermal Expansion Linear Expansion: △L=LC△T a:coefficient of linear expansion Volume Expansion: △V=VB△T B coefficient of volume expansion
Thermal Expansion Linear Expansion: L LT Volume Expansion: V VT α: coefficient of linear expansion β : coefficient of volume expansion
Heat transfer of heat: H= Thermal Resistance to Conduction: R=L/k Conduction Through a Composite Slab A(TH -TL) cond ΣR
Heat transfer of heat: L T T k A t Q H H L R L/ k Thermal Resistance to Conduction: Conduction Through a Composite Slab R A T T P H L cond ( )
When only heat conduction is considered Rose will lose more heat than Jack,but she lives while Jack is dying Why? Convection: =he(Tskin -Tair), Where he is convective heat transfer coefficient per unit area
• When only heat conduction is considered , Rose will lose more heat than Jack, but she lives while Jack is dying ,Why? Convection: Where hc is convective heat transfer coefficient per unit area
For a naked person hc=10.45-w+10u0.5 in kcal/h-m2-C,for speeds between 2 m/s and 20 m/s,where again v is in m/s Find out the ratio of heat loss due to heat conduction to heat convention,under the situations in the film.Explain Jack's death
For a naked person in kcal/h-m2 -◦C, for speeds between 2 m/s and 20 m/s,where again v is in m/s Find out the ratio of heat loss due to heat conduction to heat convention, under the situations in the film. Explain Jack’s death