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EGR 334 Thermodynamics
Chapter 4: Section 1-3
Lecture 12:
Control Volumes and
Conseration o! "ass#ui$ Today%
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Today&s main concepts:
'e a(le to e)plain *hat a control olume is 'e a(le to *rite mass (alance and mass rate (alance e+uations
!or a control olume,
'e a(le to e)plain the continuity o! mass !lo* e+uation,
E)plain the di!!erence (et*een mass !lo* rate and olumetric!lo* rate,
'e a(le to set up pro(lems inolin mass (alance
Readin .ssinment:
/ome*or0 .ssinment:
Read Chap 4: Sections 4-
rom Chap 4: 1 11 22
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So !ar *e hae loo0ed at closed systems
5nly Qand Wpass the (oundary
Enery 'alance
3Sec 4,1: Conseration o! "ass
6o* moe to open system
mass can also pass the (oundary,
add the mass (alance,
E *ithin
the system
net #
input
net 7
output8 9 8 9;
8 9
rom Chapter 2: Enery 'alance
m *ithin
the system
net m
input
net m
output8 98 9;8 9
"ass 'alance
# and 7
"ass
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4Sec 4,1: Conseration o! "ass
m *ithin
the system
net m
input
net m
output
8 9
8 9;
8 9
"ass 'alance
CV control olume
i inlet e e)it
General !orm !or multiple inlets
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Sec 4,1,2: "ass lo* Rate
"ass lu)
*here = density
Vn normal elocity component
. cross sectional area V olume
Continuity >rinciple:
mass !lo* is steady and continuous
"ass !lo* rate:
!or constant .rea
!or aria(le .rea
(V )nm
V tA = =
Vn
A
m dA= &
Vn=
Vn
dmm A
dt= =&
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Sec 4,2 "ass Rate 'alance
5ne-?imensional lo* @Continuity E+uationA
lo* is normal to the (oundary
The !luid is homoeneous @intensie propertiesare uni!orm *ith positionA,
where: = mass flow rate = density
= volumetric flow rate V = velocity
v= specific volume A = area
General !orm !or multiple inlets
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B
E)ample: @4,1A .mmonia enters a control olume operatin at steady state at
p. 14 (ar T. 2oC *ith a mass !lo* rate o! D, 0
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Sec 4,3 : .pplications o! the "ass Rate 'alance
p. 14 (ar
T. 2oC
m.D, 0
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ISec 4,3 : .pplications o! the "ass Rate 'alance
Saturated
li+uid
state Inlet A Exit B Exit C
> @(arA 14 4 4
T @CA 2 -1,ID -1,ID
@m3
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1DSec 4,3 : .pplications o! the "ass Rate 'alance
Saturated
li+uid
state Inlet A Exit B Exit C
> @(arA 14 4 4
T @CA 2 -1,ID -1,ID
@m3
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11Sec 4,3 : .pplications o! the "ass Rate 'alance
Saturated
li+uid
state Inlet A Exit B Exit C
> @(arA 14 4 4
T @CA 2 -1,ID -1,ID
@m3
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state Inlet A Exit B Exit C
V 8!t
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13Sec 4,3 : .pplications o! the "ass Rate 'alance
state Inlet A Exit B Exit C
V 8!t
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14Sec 4,3 : .pplications o! the "ass Rate 'alance
state Inlet A Exit B Exit C
V 8!t
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1
inally the olumetric !lo* rate o! the inlet may (e !ound:
Sec 4,3 : .pplications o! the "ass Rate 'alance
state Inlet A Exit B Exit C
V 8!t
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End o! slides !or Lecture 12
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