Lecture25 - ChE 210: Meeting 25 March 21, 2011 Outline...

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Unformatted text preview: ChE 210: Meeting 25 March 21, 2011 Outline (F&R Sections 7.0-7.4) Homework Due Friday 03/25/2011 - Energy of a System 4.61 a-c, 4.78, 6.59, 7.1, 7.4, 7.11, - Transfer of Energy between 7.14 System and Surroundings - Energy Balances on Closed Systems - Energy Balances on Open Systems Energy of a System Total energy of a system has 3 components: Natural Units Derived Units Kinetic Energy due to kg—mzls2 N-m a J energy (Ek) translational motion of system relative to a reference (kg/s)-m2/82 N-m/s a J/s E W Potential Energy due to position of kg-(m/sz)-m energy (Ep) a system in a potential field (e.g., gravity) (kg/s)—(m/sz)-m N-m/s E J/s E w Internal energy (U) All other energy possessed by a system - Motion of molecules - Rotational or vibrational motion - Electromagnetic interactions - Interactions of atomic or subatomic constituents 1/6 ChE 210: Meeting 25 March 21, 2011 1St Law of Thermodynamics: Energy cannot be created nor destroyed **Energy CAN be converted between from one type of energy to another” Transfer of Energy between System and Surroundings Heat (Q) 2 energy that flows as a result of T difference - Positive TO system FROM surroundings Work (W) 5 energy that flows as a result of something other than T difference - Force, torque, voltage - Positive when work done ON system BY surroundings Types of work: - Shaft work (W8) — work done by a process fluid on a moving part (e.g., a pump rotor) - Flow work (We) — work done by a fluid at the outlet minus the work done by a fluid at the inlet Fluid entering has W done ON it by fluid directly behind it: Fluid exiting DOES W on fluid in front of it: Wf=Wf,out—Wf,in = E u . ‘ 2/6 ii ,: ChE 210: Meeting 25 March 21, 2011 Enthalpy is the combination of internal energy and flow work: A A A H a U + PV Energy Balances on Closed Systems Closed system a No mass flows across boundaries General Balance Equation: In + Generation — CUt — Consumption = Accumulation 3r. Accumulation a Final System Energy — Initial System Energy \ l ‘3'“ r “' V. ‘ i‘ , " " i Simplifying the energy; *bé‘ié‘ribei 1. Q = 0 if the system and surroundings have the same T or the system is perfectly insulated (adiabatic) 2. W = 0 if no moving parts, electrical currents, radiation 3. AEk = 0 if system is not accelerating 4. AEp = 0 if system does not rise or fall 5. AU = 0 if no AT, no phase change, no reaction 3/6 ChE 210: Meeting 25 Example Problem 7.9 1'==25<: “W x \ L. “34L _—9 . I 2; If 1 T v I! ' 1 RA 1 T — "i ., :’ —20C - Wm v. water as»: W; )1 m3“ unbuéi‘y v ‘ x s”:- U ' r. ‘ ,»‘ X J. “WU: «m N y. 3 g 5; (,9 / , .ms««__:‘.a u m ‘ , .. ‘7 Rxn . ; v r J r' 1‘ if ‘7 1 w 3‘ N ' V I 4/6 March 21, 2011 . r . .. «5 J ‘ <' y A y K' a 7 f f, \ , L7. ChE 210: Meeting 25 March 21, 2011 Energy Balances on Open Systems Open system a Mass flows across boundaries General Balance Equation: 1 All yrj‘la‘tgi ““ 1x‘u’liiirsfl in + Generation — dut — Consumption = Accumulation \ K i if“ - k 4"»: 111‘: i i i, 1 “x \ » — y X k a ‘\ \JV.‘ 12‘ 7‘ L 1‘ L\ '1 1» ‘ji 1 I 1 I ‘ »' J a $7.311: ,‘ A »— M- \ I} 1% 1‘1» ‘1 1/14, i \. x i, ‘ v 1 1 L 1K“ )\ MK {_ l" ’2 _;. i I . / E i ‘ i ’ i i“ L i, W i x a , g I 1, 5/6 ChE 210: Meeting 25 March 21, 2011 Examgle Problem 7.25 fuel Q: (O.65)(813 kW) air Water (L) Saturated Steam T=25C P=20barabs “1’1de : m, a) gain . N ‘ [Vt/“f ! W): M] E r-, ' Fl - A '§l\(;.¥"«'~. \"3 ‘ ,1 ’ ~._\ _ r1 /, . : "-‘ m , ~ ’ .- v tfl ,l mutt < «“kfl‘t,)(fl.\ .lxwtx H \) _ (fl) ‘ \V A V L (7 r H 9‘— (l‘ll'J' {INKMRCHX {'JL'J‘ 1 u If 7“ m 7' twin mt 11 w. rather«1L , i if \I\ kill“) {"K‘ 5.1 * 1 l.‘ \(Atpfk‘fldm BE; a" 6“ y NMM‘” L3?) L.) 2 my?" N f V‘s-emwbm!) : awa mm fit’WLfiE (ftmt‘udfld biref‘q‘r‘) (Ubifi be («1' '7‘: 52x19. ~+“( = 14:35. ~36 K % \ S :M‘U\\ were \lnydLUZ—‘L d; U36" “TC-i316: E); ._ ‘51 tflCéfl’: CLLILUH \é‘xi’uq-fl 6/6 +0 UV"; “Wt ("(133 ...
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This note was uploaded on 07/31/2011 for the course CHEM E 210 taught by Professor Shanks during the Spring '02 term at Iowa State.

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Lecture25 - ChE 210: Meeting 25 March 21, 2011 Outline...

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