2013-3-6 Entropy Balance for Closed Systems That o has a value of zero when there are no internal irreversibilities and is positive when irreversibilities are present within the system leads to the interpretation that o accounts for entropy produced(or generated)within the system by action of irreversibilities. Expressed in words,the entropy balance is within the system across the system boundar the system during some time inte Entropy Balance for Closed Systems Example:One kg of water vapor contained within a piston-cylinder assembly,initially at 5 bar,400C,undergoes an adiabatic expansion to a state where pressure is 1 bar Water and the temperature is (a)200C,(b)100C. Using the entropy balance,determine the Boundary nature of the process in each case. Since the expansion occurs adiabatically,Eq.6.24 reduces to give --Aa一ma-=。0 where m=1 kg and Table A-4 gives s =7.7938 k./kg-K. 92013-3-6 9 Entropy Balance for Closed Systems ►That σ has a value of zero when there are no internal irreversibilities and is positive when irreversibilities are present within the system leads to the interpretation that σ accounts for entropy produced (or generated) within the system by action of irreversibilities. ►Expressed in words, the entropy balance is change in the amount of entropy contained within the system during some time interval net amount of entropy transferred in across the system boundary accompanying heat transfer during some time interval amount of entropy produced within the system during some time interval + Entropy Balance for Closed Systems ►Since the expansion occurs adiabatically, Eq. 6.24 reduces to give Example: One kg of water vapor contained within a piston-cylinder assembly, initially at 5 bar, 400oC, undergoes an adiabatic expansion to a state where pressure is 1 bar and the temperature is (a) 200oC, (b) 100oC. Using the entropy balance, determine the nature of the process in each case. σ δ ⎟ + ⎠ ⎞ ⎜ ⎝ ⎛ − = ∫ b 2 1 T Q S S 1 2 0 → m(s2 – s1) = σ (1) where m = 1 kg and Table A-4 gives s1 = 7.7938 kJ/kg·K. Boundary