Lecture 2 Energy and Energy Transfer
Energy and Energy Transfer Lecture 2
Focal point of interest Temperature the measurement of heat and cold:the molecular activity Unit:oC,K,F 0°C=273.15K, T(K)=t(°C)+273.15 0C=32FT(月=32+1.8t(°C)
Focal point of interest Temperature the measurement of heat and cold : the molecular activity Unit：o C ，K, F 0 oC=273.15K, T(K)=t( oC)+273.15 0 oC=32 oF, T( o F)=32+1.8t( oC)
Energy Conservation Equation Control Volume 中年·”年… g out E t En+Eg-Eou =dEs /dt =Est The rate at which thermal and mechanical energy enters a control volume,minus that leaving out,plus the rate at which thermal energy is generated within the control volume,should equal the rate of increase of energy stored within the control volume
Energy Conservation Equation in g out st Est E E E dE dt + − == = The rate at which thermal and mechanical energy enters a control volume, minus that leaving out, plus the rate at which thermal energy is generated within the control volume, should equal the rate of increase of energy stored within the control volume. Control Volume Ein Eout E g Est
Energy inflow and outflow by conduction,convection,radiation Conduction across the surface: Rate equ. Ccond =-kAdI -Fourier's Law dx k--Thermal conductivity of the material [w/m-K]
Conduction across the surface: Rate equ. ——Fourier’s Law dT q A dx cond = − k k -- Thermal conductivity of the material [w/m·K] Energy inflow and outflow by conduction, convection, radiation
Conductivity for biological tissue: k,=0.419*(0.133+1.36mm)[wlmK)] m fraction of water mass in tissue k,(T)=k.x*[1+0.003(T-T】 Wdlch,1984
Conductivity for biological tissue: 0.419* (0.133 1.36 ) t w k m = + m w 0 , 0 ( ) *[1 0.003( )] t tT kT k T T =+ − fraction of water mass in tissue Wdlch, 1984 [w/(m·K)]