Lecture 3 Apply Energy Conservation Equation
Lecture 3 Apply Energy Conservation Equation
Energy Conservation Equation Control Volume out E st En+E。-Eom=dEu/dt=Et 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
Procedure: Define appropriate control volume with the control surface ldentify appropriate time basis Identify relevant energy processes Write conservation equation
Procedure: • Define appropriate control volume with the control surface • Identify appropriate time basis • Identify relevant energy processes • Write conservation equation
Surface Energy Balance Surroundings Tsur 9gaa qcond Fluid qconv ↓ T uoo,To Control surfaces Energy balance for conservation of energy at the surface of a medium
Surface Energy Balance T1 T2 T x T ∞ Control surfaces Fluid Energy balance for conservation of energy at the surface of a medium
Ein-Eout =0 Conduction from the medium to the control surface Qcond Convection from the surface to a fluid qconv Net radiation exchange from the surface to the surroundings qrad Energy Balance: qcond -qconv -qrad =0