2013-3-6 Review:Energy Rate Balance for CS The energy balance can be written in differential form as dE 60-8W The time rate form of the closed system energy balance is dE =Q-币 dt The rate form expressed in words is et rate contained withi transferred in the syste 4-19 Energy Rate Balance for CV, Comparina a control volume to a clos ed system: also ha ve energy that is carried in and out by the mass crossing its boundary ime rate of nge et rate at which net rate of energy of the en d ou the control volume by heat transfer by wo mass floving For one-inlet one-exit CV with one dir nsional flow =Q-巾+m,(+ g=i)-ite(ue+ +g）E4e) nergy o 102013-3-6 10 ►The rate form expressed in words is time rate of change of the energy contained within the system at time t net rate at which energy is being transferred in by heat transfer at time t net rate at which energy is being transferred out by work at time t ►The time rate form of the closed system energy balance is Q W dt dE & & = − 4-19 Review: Energy Rate Balance for CS ►The energy balance can be written in differential form as Energy Rate Balance for CV 4-20 ) 2 V ) ( 2 V ( 2 2 cv e e i e e i Q W mi ui gz m u gz dt dE = − + & + + − & + + & & (Eq. 4e) time rate of change of the energy contained within the control volume at time t net rate at which energy is being transferred in by heat transfer at time t net rate at which energy is being transferred out by work at time t net rate of energy transfer into the control volume accompanying mass flow ►Comparing a control volume to a closed system: we also have energy that is carried in and out by the mass crossing its boundary ►For one-inlet one-exit CV with one dimensional flow Rate of transfer of internal, kinetic and potential energy of entering/exiting streams