Unit Operation of Food Engineering

1
1304 231 Unit Operations in Momentum Transfer
Dr. Supatpong Mattaraj Instructor Department of
Chemical Engineering Faculty of Engineering Ubon
Ratchathani University
Presented to Chemical Engineering Students,
Ubon Ratchathani University Semester 2/2546
2
Specific weight and specific gravity
??????????????????? (?) ?????????????????????????
?????????? ?????????????????????????????? 62.4
lb/ft3 ??????????? 9.79 kN/m3
???????????????????????????? ( ? 1/v)
???????????????????? ?????? v
???????????????????????? T ??????????????? R
?????????????????????? P ?????????????? ?
?????????????????? ??? g ???????????????????
9.81 m/s2 ?????????????????????????????????????
??????????????????????????????????????????????????
???? ?????????????????????????????? 0.75
???????????????????? (0.75)(62.4 lb/ft3)
46.8 lb/ft3
3
Example
?????????????????????? 6 ????????????????????? 47
?????????? ???????????????????????? (?)
??????????? (?) ?????????????????
4
Viscosity of a Fluid
???????? (viscosity) (?) ?????????????????????????
????????????????? ????????????????????????????????
?????????????????
F
5
Newtonian fluid
????????????? Newtonian (slope ?)
?????????????????????????????? ?
??????????????????????? Newtonian fluid
?????????????????????????????????????????????? ?
???? ??? ?????? ??????????????? ???????
6
Example
??????????????????? ?????????????????????????????
0.001 kg/m.s (0.001 Pa.s) ?????????????????????
0.913 ?????????????????????????????? (velocity
gradient) ??????????? ???????????? V
15y (m/s) dV/dy 15 s-1
7
Example
??????????????????? ?????????????????????????????
0.001 kg/m.s (0.001 Pa.s) ????????????????????????
?????? (velocity gradient) ??????????? ???
????????? V 45 - 5(3-y)2 dV/dy
10(3-y)
8
Viscosity of gas and liquid at 1 atm
(Newtonian fluids)
At higher pressure (for gases), the viscosity
of gases (newtonian fluids) increases with
temperature. For liquid, the viscosity
decreases with increasing temperature.
9
Kinematic viscosity
Kinematic viscosity (?) ?????????????????????????
????????? (absolute viscosity, ?) ??????????????
(?)
10
Surface tension
?????????? (surface tension) ?????????????????????
??????????????????????????????????????????????????
??????????????????????????????? ?????????
????????????????????????? 0.0756 N/m ??? 0
????????????
11
Capillarity
??????????????????????????????????? capillary
tube ?????????????????????????????????????????????
?????? capillary tube ????????????????????????????
???????????????????????????? 3/8 ???? (10 mm)
?????????????????????????? 1/2 ???? (12 mm) ?????
capillarity ?????????
12
Example 4
??????????????????????????? capillary tube
??????????????????? 0.003 ????
??????????????????????? 0.0727 N/m
13
Fluid statics
??????????????????????????????????????????????????
??? ???????????????????????????????
?????????????????????????????????????????? ?????
?????? lb/in2 (psi) ?????????? (Pa ???? N/m2)
???????????????????????????????????????
??????????????????????? ?????????????????????????
???????????????????????????????????????????? ????
?? ? ?????????????????????????????? ??? h2-h1
??????????????????????? ?????????????????????????
?????? h ?????????????????????????
14
Vacuum/atmospheric/gage pressure
Vacuum pressure ??????????????????????????????????
???????? (atmospheric pressure)
??????????????????????????????????
????????????????????????????????????????????
(standard atmospheric pressure) ???????????? 14.7
lb/in2 (psi) ????????????????????????????????????
?????????? 10 psi ????????????????????????????????
???????????????????? 14.7-10 psi ???? 4.7
psi Absolute and gage pressure
???????????????????? (absolute pressure)
??????????????????????????????????????????????????
??? (101.3 kPa ???? 1 atm ???? 14.7 psi)
?????????????????????????????????? 5.5 kPa
????????????????????????????? 101.3 kPa 5.5 kPa
??????? 106.8 kPa ??????????????????????????
??????? ????? psia ??????????????????????????????
????????????????? psig ????????????????
15
Example

• 1. ??????????????????????????????? 6
  ????????????????????
• 2. ??????????????????????????????????????????? 9
  ???? ????????????????????? 0.75
• 3. ??????????????? (Absolute pressure)
  ???????????????? 6 ????????????????????
  ???????????? Barometer ??????? 0.1
  ????????????????????????????????????????????????
  13.57

16
Pressure in a Fluid
???????????? ? ??????? ? ????????????
?????????????????????????
17
Pressure in a Fluid
????????????????????????????????????????????
???????????????????????????????????????? ?????????
????????????
18
Example

• 4. ???????????????????????? ????????? 2 ????
  ????????????????? glycerin ??????? 1.26
• 5.
• 2. ??????????????????????????????????????????? 9
  ???? ????????????????????? 0.75

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Example

• 5. a. ???????????????????????????? A b.
  ?????????????????? A c. ?????????????????? B
  d. ??????????????????????????

20
Example

• 6. ???????????????????????????????????????
  ????????????????? ????????????????????????????????
  ??? ??????? 13.6

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Example
????????????????????? P1 ????????????????????????
? P2 ????????????? ???????????????? ????????????
?????? 917 kg/m3 ???????????????????? 3
????????????? ?????????????????????? ????????????
?? 0.5 ???? ???????????????????? P1
??????????????? P2 ???????????????????????
22
Example
???????????? P2 ???????????
???????????????????????
23
Pressure measurement in a vessel
??????????????????? pA
??????????????????????? 2
??????????????????????? 1
??????????????????????? pA ?????? p1 p2
24
Head of a Fluid
???????????????????????????????????? 4 oc
?????????????????????????????? 1.01325?105 atm
????????????????????????????????????? 0 oc
?????????????????????????????? 1.01325?105 atm