《多尺度生物传输》课程教学资源（讲稿）传热基本原理

ContentsThermal energyThree modes of heat transferHeat transfer processDiscussion

◆ Thermal energy ◆ Three modes of heat transfer ◆ Heat transfer process ◆ Discussion Contents

Thermal EnergyEnergyElectricMechanicalMagneticSound waveWindenergyChemicalThermalSolarenergy> In physics, energy is the property that must be transferred to anobject in order to perform work on, or to heat, the object

Thermal Energy ➢ In physics, energy is the property that must be transferred to an object in order to perform work on, or to heat, the object. Energy Mechanical Electric Magnetic Sound wave Solar energy Wind energy Chemical Thermal

Thermal EnergyEnergytransformationNew energy vehiclesNatureHydroelectricityThermodynamics> First law of thermodynamics: The internal energy of an isolatedsystemis constant

Thermodynamics ➢ First law of thermodynamics: The internal energy of an isolated system is constant. Energy transformation Nature Hydroelectricity New energy vehicles Thermal Energy

Thermal EnergyThermalenergyCHILL OUT,IT'S ONLYALITTLESNOw....VThermal energy refers to the internal energy present in a system duetoitstemperature.布朗通動Thermal energy is the statistical sum of the kinetic energy of the particles

➢ Thermal energy is the statistical sum of the kinetic energy of the particles ➢ Thermal energy refers to the internal energy present in a system due to its temperature. Thermal energy Thermal Energy

Thermal EnergyHeat transferEvaporationConvection30%27%RadiatiorSouthInnerRadi40%wallAirsurfaceSolarConductionmotionh,T-1h2TaConvectionConductionOuterConductionsurface3%XLFloorThermodynamicsThe second law of thermodynamics: heat spontaneously flowsfrom a body of higher temperature to one at lower temperature

Heat transfer Thermal Energy Thermodynamics ➢ The second law of thermodynamics: heat spontaneously flows from a body of higher temperature to one at lower temperature

> Heat transfer is the science which seeks to predict the energytransferwhich may take place between material bodies due to temperaturedifference.Driving force:temperature differenceThermalEquilibrium> Thermal equilibrium:two systems are said to be inthermalequilibrium when their temperatures are equal.Ineguilibrium,therearenoheatflows.> The steady state: In steady state, temperatures do not changewithtime

Thermal Equilibrium ➢ Thermal equilibrium: two systems are said to be in thermal equilibrium when their temperatures are equal. In equilibrium, there are no heat flows. ➢ The steady state: In steady state, temperatures do not change with time. ➢ Heat transfer is the science which seeks to predict the energy transfer which may take place between material bodies due to temperature difference. ➢ Driving force: temperature difference

Thermal EnergyEnergyconservationInOutGenRate ofRate ofRate ofRateof+EnergyInEnergyOutEnergyGenerationEnergy StorageThefirstlaw of thermodynamics: energy is conserved> Total energy of the system plus surroundings remain constant.> Different forms of energy can inter-convert but their sumremains constant

Energy conservation The first law of thermodynamics: energy is conserved ➢ Total energy of the system plus surroundings remain constant. ➢ Different forms of energy can inter-convert but their sum remains constant. Thermal Energy

Thermal EnergyEnergy conservation5g-10℃Q = mc4T2.1 J/g°℃m: massc: specific heat capacity△T: temperature difference5g10°℃4.2J/g°CEnergy Inm1Cp(Ti -0)=0EnergyOut=0EnergyGeneration=ChangeinEnergy Storage(m1Cpl +m2Cp2)(T -0) -m2Cp2(T2 - 0)finalinitial

Energy conservation m: mass c: specific heat capacity 𝛥𝑇: temperature difference 𝑄 = 𝑚𝑐𝛥𝑇 Thermal Energy oC oC

Thermal EnergySpecific heat capacity (c)> The quantity of heat required to raise the temperature of a substanceper gram by one degree Celsius is called the specific heat capacity ofthe substance.Unit: J/(g°C) or J/(gK)食用油c: water is 4.18 J/(g°C)oil is 1.97 J/(gC)

➢ The quantity of heat required to raise the temperature of a substance per gram by one degree Celsius is called the specific heat capacity of the substance. Unit: J/(g oC) or J/(gK) c: water is 4.18 J/(g oC) oil is 1.97 J/(g oC) Specific heat capacity (c) Thermal Energy

Thermal EnergyRate ofRateofRate ofRateof+EnergyOutEnergyGenerationEnergyStorageEnergyIn5g-10℃2.1J/gm1Cpl(Ti-0)=(m1Cpl+m2Cp2)(T-0)-m2Cp2(T2-0)5g10℃4.2 J/g5(2.1)(-10- 0) = (5(2.1) + 5(4.2))(T - 0) -5(4.2)(10 - 0)The final temperature T = 3.33°C.Thus, using energy conservation, we can find the final orequilibrium temperature or the final state of the system

The final temperature T = 3.33℃. Thus, using energy conservation, we can find the final or equilibrium temperature or the final state of the system. Thermal Energy