1. Introduction to Food Engineering
Unit 2
Fluid Flow in Food Processing

2. Liquid Transport Systems
Pipelines for Processing Plants

3. Types of Pumps

4. 2. Properties of Liquids
1. Role of Stress in Fluid Flow
Stress = force / unit area, normal stress = pressure
Shear stress --> flow

5. Fig. 2.7 Illustration of drag generated on underlying cards as the top card in a deck is moved. This is analogous to the movement of the top layer of a fluid.

6. Density Mass per unit volume, kg/m3 Depend on temperature
Measured by hydrometer compared with water

7. Resistance to shear force
Viscosity
Resistance to shear force
(2.1)
(2.2)
(2.3)

8. Viscosity du/dy = shear rate  = coefficient of viscosity
Newtonian liquid
unit
 = N/m2 = Pa
 = Pa.s

9. Example
Determine shear stress for water at ambient temperature when exposed to a shear rate of 100 s-1
Given viscosity of water at ambient temp = 10-3 Pa.s
 =  du/dy = (10-3 Pa.s)(100 s-1)
= 0.1 Pa

10. Measurement of Viscosity
Capillary Tube Viscometer

11. (2.4)
(2.5)
(2.6)

12. (2.7)
 = 0 at center of tube, r = R at wall
(2.8)
(2.9)

13. (2.10)
(2.11)
(2.12)
Cross sectional area of a shell in tube

14. Vol flow rate = u . dA .
(2.13) .
(2.14) .
(2.15)

15. (2.16) . See example Tube length L, radius R
Measure Vol flow rate at pressure P
See example

16. Example
Measure viscosity of honey at 30 C. Tube radium 2.5 cm, length 25 cm.
P (Pa)
V (cm3/s)
 (Pa.s) 10
1.25
4.909
12.5
1.55
4.948
15.0
1.80
5.113
17.5
2.05
5.238
20.0
2.55
4.812

17. (2.17) (2.18) If allow gravitational force to provide P for flow
(P = F/A, F = ma)

18. (2.19)
Since V = R2L, m = V
(2.20)
Measure time of liquid mass, m flow in tube length, L

19. Rotational Viscometer

20. Rotational Viscometer
torque
(2.21)
Shear rate,   Angular velocity, 
(2.22)

21.  =
Integrate between outer & inner cylinders
(2.24)
(2.25)

22. (2.26)
N = revolution per sec
(2.27)
 Measurement of  at given N

23. (2.28) Outer radius Ro ->  Single-cylinder viscometer
Assuming container wall has no influence on shear stress
(2.28)

24. Single-cylinder viscometer 1 cm radius 6 cm length
N (rpm)
 (x 10-3 N.cm)
 (Pa.s) 3
1.2
0.507 6
2.3
0.485 9
3.7
0.521 12
5.0
0.528

25. N = 3 rpm = 3/60 rev/sec = 0.05 rev/s
L = 0.06 m
Ri = 0.01 m
= 1.2 x 10-3 N.cm = 1.2 x 10-5 N.m
 = Pa.s

26. Influence of Temperature on Viscosity
(2.29)
BA = Arrhenium constant
Ea = activation energy constant
Rg = gas constant