西南交通大学：《大学物理》课程教学资源（讲稿，双语）CHAPTER 13 Temperature Heat Transfer and First Lawl Thermodynamics

UNIVERSITY PHYSICS I CHAPTER 13 Chapter 13 temperature, heat transfer, and first law of thermodynamics Thermodynamics study the thermal energy(often Universe just after called the internal energy) of systems Highest laboratory The central concept of Center of the Sun thermodynamics is temperature Surface of the sun Temperature is one of the% Water freezes seven SI base quantities. Universe today What is temperature? Sense of hot and cold is not/ log/ always reliable 109H--Record low ter

1 Chapter 13 temperature, heat transfer, and first law of thermodynamics Thermodynamics study the thermal energy (often called the internal energy) of systems. The central concept of thermodynamics is temperature. Temperature is one of the seven SI base quantities. What is temperature? Sense of hot and cold is not always reliable

s13.1 Some important concepts 1. The simple thermodynamic system A thermodynamic system is defined as a collection of many particles such as atoms and/or molecules A simple thermodynamic system is a system that is macroscopic, homogeneous, isotropic, uncharged, chemically inert, and experiences no change in its total mechanical energy. The system is sufficiently large that surface effects can be neglect. No electric or magnetic fields are present, and gravitational fields are irrelevant 813.1 Some important concepts 2. Thermal equilibrium Put two system in thermal contact, after long enough time, if their properties(for instance the temperature)do not change, they are in thermal equilibrium. 3. The zeroth law of thermodynamics

2 §13.1 Some important concepts 1. The simple thermodynamic system A thermodynamic system is defined as a collection of many particles such as atoms and/or molecules. A simple thermodynamic system is a system that is macroscopic, homogeneous, isotropic, uncharged, chemically inert, and experiences no change in its total mechanical energy. The system is sufficiently large that surface effects can be neglect. No electric or magnetic fields are present, and gravitational fields are irrelevant. 2. Thermal equilibrium Put two system in thermal contact, after long enough time, if their properties (for instance: the temperature) do not change, they are in thermal equilibrium. 3. The zeroth law of thermodynamics §13.1 Some important concepts

813.1 Some important concepts If body a and b are each in thermal equilibrium with a third body t, then they are in thermal equilibrium with each other. Every body has a property called temperature. When two bodies are in thermal equilibrium we say that they have same temperature And vice versa 4. Temperature There exists a scalar quantity called temperature, which is a property of all thermodynamics systems in equilibrium. Two systems are in thermal equilibrium if and only if their temperatures are equal 813.1 Some important concepts Measuring temperature: ① types of thermometer thermometric property that change with er- By using some physical properties of matte temperature Scale Volume of mercury--common household and laboratory thermometers Constant volume gas thermometer: as shown in Figure

3 If body A and B are each in thermal equilibrium with a third body T, then they are in thermal equilibrium with each other. Every body has a property called temperature. When two bodies are in thermal equilibrium, we say that they have same temperature. And vice versa. 4. Temperature There exists a scalar quantity called temperature, which is a property of all thermodynamics systems in equilibrium. Two systems are in thermal equilibrium if and only if their temperatures are equal. §13.1 Some important concepts Measuring temperature: 1types of thermometer By using some physical properties of matter— thermometric property that change with temperature. Volume of mercury—common household and laboratory thermometers. Constant volume gas thermometer: as shown in Figure §13.1 Some important concepts

813.1 Some important concepts Platinum resistance thermometers--electrical resistance as a thermometric property Thermocouple-different thermal properties of two kind of metal Brass Pointer Helical bimetal 813.1 Some important concepts @Calibrating thermometers (X)=100X-X)(Y)=I 100(Y-Y0 X-X r(X0)=t(X0)=0Ct(X100)=t(X10)=100°C AY)

4 Platinum resistance thermometers—electrical resistance as a thermometric property Thermocouple—different thermal properties of two kind of metal §13.1 Some important concepts 2Calibrating thermometers t X t Y C t X t Y C Y Y Y Y t Y X X X X t X o o ( ) ( ) 0 ( ) ( ) 100 100( ) ( ) 100( ) ( ) 0 0 100 100 100 0 0 100 0 0 = = = = − − = − − = §13.1 Some important concepts

813.1 Some important concepts 3 Ideal gas temperature scale(Kelvin scale) How to avoid the dependence of the particular means or substance? The triple point of water: 0.01C, 1=0K R. Boyle: PV=cons tant J Gay-Lussac: V=vo(1+a,t) J.A. C. Charles: P=Po(1+apt) When P0 a,=ap=a=l/To T=273.l5C s13.1 Some important concepts Experiments: Po oc m P=P(1+apt The intercept of the line on the axis t is 1/ap For all kind of gas, when m is decrease, Po0 a,=a=a=1/T Seale T=273.15°C Gas 1 Gas 3

5 3 Ideal gas temperature scale (Kelvin scale) How to avoid the dependence of the particular means or substance? The triple point of water: t=0.01ºC, T=0K R. Boyle: PV = constant L. J. Gay-Lussac: (1 ) 0 V V t = +α V J. A. C. Charles: (1 ) 0 P P t = +α P When P0Æ0 273.15 C 1/ 0 0 o = = = = T α V α P α T §13.1 Some important concepts For all kind of gas, when m is decrease, P0Æ0. 273.15 C 1/ 0 0 o = = = = T α V α P α T (1 ) 0 P P t P0 ∝ m = +α P The intercept of the line on the axis t is . α P 1/ §13.1 Some important concepts Experiments: 0 100 o t / C P −T0 Gas 1 Gas 2 Gas 3 P0

813.1 Some important concepts 1=0K is called absolute zero One Kelvin is defined to be 1273.16 of the temperature of the triple point of water. Ideal gas temperature scale: T=273.16K(lim +0P T=telsius +273.15 (K) 813.2 Heat transfer and calorimetry 1. Heat and heat transfer Heat is energy that flow between a system and its environment simply because of the difference of temperature between them Characteristic: Othe process of heat transfer continues until the both systems reach to thermal equilibrium (have same temperature); @heat transfer occurs from the hotter system to the cooler system; Cheat transfer is essentially a microscopic atom-to-atom transfer of energy, it is distinctly different from macroscopic wok 6

6 T=0K is called absolute zero. One Kelvin is defined to be 1/273.16 of the temperature of the triple point of water. Ideal gas temperature scale: 273.16K( lim ) 3 gas 0 P P T → = 273.15 (K) T = tcelsius + §13.1 Some important concepts §13.2 Heat transfer, and calorimetry 1. Heat and heat transfer Heat is energy that flow between a system and its environment simply because of the difference of temperature between them. Characteristic: 1the process of heat transfer continues until the both systems reach to thermal equilibrium (have same temperature); 2heat transfer occurs from the hotter system to the cooler system; 3heat transfer is essentially a microscopic atom-to-atom transfer of energy, it is distinctly different from macroscopic wok

813.2 Heat transfer and calorimetry Environment T Environment T Environment 1>7 0, heat transfer to a system 2. Temperature change and specific heat do Experiment:dT∝ do= cmdT I do specific heat J/kg. KI m dT 813.2 Heat transfer and calorimetry do= cmdT= ncmolar dT I do molar=---molar specific heat J/molK n dT Molar specific heat is the heat transfer to one mole of the material needed to raise it temperature by one Kelvin do do For gases: Cy m dT dT Molars do do n dT molar p dT

7 Q 0, heat transfer to a system. 2. Temperature change and specific heat Experiment: m Q T d d ∝ dQ = cmdT T Q m c d 1 d = --specific heat [J/kg·K] §13.2 Heat transfer, and calorimetry dQ = cmdT = ncmolardT T Q n c d 1 d molar = --molar specific heat[J/mol·K] Molar specific heat is the heat transfer to one mole of the material needed to raise it temperature by one Kelvin. V V T Q m c ) d d ( 1 For gases: = P P T Q m c ) d d ( 1 = V T Q n c ) d d ( 1 molar V = P T Q n c ) d d ( 1 molar P = §13.2 Heat transfer, and calorimetry

813.2 Heat transfer and calorimetry Notice: @the specific heat of a substance usually varies with the temperature @in this text, we consider the specific heat to be independent of temperature. 3. Changes of phase and latent heat Latent heat-the heat transfer needed to change the phase of a substance Ofirst-order phase transitions The phase transitions involved latent heats are called first-order phase transitions. For instance: converting water at 100C to steam at100°C 813.2 Heat transfer and calorimetry @second-order phase transitions The phase transitions that have zero latent heats are called second-order phase transitions latent heat(heat of fusion and heat of vaporization) 0=mL or Q=n Example: P605 13.12 8

8 Notice: 1the specific heat of a substance usually varies with the temperature; 2in this text , we consider the specific heat to be independent of temperature. 3. Changes of phase and latent heat 1first-order phase transitions The phase transitions involved latent heats are called first-order phase transitions. For instance: converting water at 100ºC to steam at 100ºC. §13.2 Heat transfer, and calorimetry Latent heat—the heat transfer needed to change the phase of a substance. 2second-order phase transitions The phase transitions that have zero latent heats are called second-order phase transitions. 3latent heat (heat of fusion and heat of vaporization) molar Q = mL or Q = nL Example: P605 13.12 §13.2 Heat transfer, and calorimetry

$13.3 mechanisms of heat transfer 1. reservoirs Reservoir is a special thermodynamics system. When a system in thermal Insulation contact with a reservoir experiences heat transfer t or from the system until it has the same temperature as the reservoir. The temperature of the reservoir does not change 90 ∵Q=cm△T∴A7Q ifcm> e then△r→0mca、s $13.3 mechanisms of heat transfer 2. Mechanisms of heat transfer ① conduction Heat transfer by conduction depends on critically on the material bridging or connecting the warmer and cooler regions Heat flow: dg_-ka dr dt k--thermal conductivity A-the the area of thermal contact dT --Temperature gradient dx

9 §13.3 mechanisms of heat transfer 1. reservoirs Reservoir is a special thermodynamics system. When a system in thermal contact with a reservoir experiences heat transfer to or from the system until it has the same temperature as the reservoir. The temperature of the reservoir does not change. if >> then ∆ → 0 = ∆ ∴∆ = cm Q T cm Q Q Q cm T T 2. Mechanisms of heat transfer 1conduction Heat transfer by conduction depends on critically on the material bridging or connecting the warmer and cooler regions. Heat flow: x T kA t Q d d d d = − k—thermal conductivity x T d d --Temperature gradient A—the the area of thermal contact §13.3 mechanisms of heat transfer

$13.3 mechanisms of heat transfer For a steady state dT =-s= constant d dT=l-sdx d T-TT-t Hot reservoir Cold reservoir =kA-HC=A dt d R k-thermal resistance 13.3 mechanisms of heat transfer For material in series: de TH-Ic R R Rm=R1+R2+…+RN Hot reservoir Cold reservoir/ T 7 ndoors ka A 10

10 For a steady state: = −s = x T d d constant d ∫ ∫ = − T x T T s x H 0 d d d T T x T T s H H − C = − = R T T A d T T kA t Q H C H − C = − = d d k d R = --thermal resistance §13.3 mechanisms of heat transfer For material in series: d 1 2 total d R T T A R R T T A t Q H C H − C = + − = Rtotal = R1 + R2 +L+ RN d2 d1 §13.3 mechanisms of heat transfer