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Unformatted text preview: ChE 210: Meeting 25 March 21, 2011 Outline (F&R Sections 7.07.4) Homework Due Friday 03/25/2011
 Energy of a System 4.61 ac, 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 Nm a J
energy (Ek) translational motion of
system relative to a reference (kg/s)m2/82 Nm/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 Nm/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
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\ , 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
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‘ v 1 1 L 1K“ )\ MK {_ l" ’2 _;. i
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/
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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‘semwbm!) : 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" “TCi316: E); ._ ‘51 tﬂCéﬂ’: CLLILUH \é‘xi’uqﬂ
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.
 Spring '02
 Shanks

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