Air movement cold chain management cold storage

mmm

1. Slide 1
Air movement and
distribution
Sunil Pareek
NIFTEM, Kundli

2. Slide 2
Air movement and distribution
-How is “air throw” definedPoints:
-Calculating air throw
-Fan types
-Draw-through or blow-through
-External pressure
-Influencing factors on air throw
-Room height & air exchange rate
-Ceiling restrictions

3. Slide 3
How is Air Throw defined
0.3 m/s
Most sources recommend a theoretical air speed of 0.3 m/s at the end of
the room. This is pure theory, however, because any airflow of less than
0.5 m/s is dispersed and becomes impractical to measure.

4. Slide 4
Calculating the range
Empirical equation:
A = Correction factor, pressure/suction
(depending on fan type and cooler design)
V
eo= Air speed at the evaporator outlet (m/s)
W
s= specific weight of the air
1.2
Air throw = A x V
eo
2
x
W
s

5. Slide 5
Fan Types
•Air is dispersed
•Good value
•High air volume
•Low additional pressure
(30 -120 Pa)
•Air is focused
•More expensive
•High air volume
•High additional pressure
(40 -400 Pa)
Propeller fans Axial fans

6. Slide 7
Influences on the correction factor (A factor)
•Outlet speed between 9 and 12
m/s:
–Propeller fan
A factor = 0.2 to 0.3
–Propeller fan + fan ring
A factor = 0.4 to 0.6
–Short cased fan
A factor between 0.4 and 0.6
–Long cased fan
A factor between 0.6 and 0.9
•Outlet speed between 2.5 and 4 m/s
–A factor = 1.5
–Range ~ 22 m
•Incl. diffuser: between 5 and 8 m/s
–A factor = 1.3
•Higher fan speeds
–A factor between 0.8 and1.3
Drawing Blowing

7. Slide 8
Air in +1 °C
Air out -1 °C
Evaporating temp.-6 °C
Surface 284 m
2
K value 24
Draw-through or blow-through air coolers
+1 °C +2 °C -1 °C +1 °C -2 °C -1 °C
Blow through Draw through
0
-1
-2
-3
-4
-5
-7
-6
-8
-9
+1
+2
Air temperature
°
C
8 K 5 KΔT
1,2=
LOG ΔT = 6.9
Capacity = m
2
x K value x LOG ΔT
= 284 x 24 x 6.9
= 47.03 kW
-1
-2
-3
-4
-5
-6
-8
-7
-9
-10
0
+1
Air temperature
°
C
7 K 4 KΔT
1,2=
LOG ΔT = 5.98
Capacity = m
2
x K value x LOG ΔT
= 284 x 24 x 5.98
= 40.89 kW

8. Slide 9
RH draw-through air coolers
Outlet -1 °C
89% relative
humidity
+1 °C
-1 °C

9. Slide 10
RH blow-through air coolers
Outlet 0 °C
98% relative
humidity
drawing: 89%)
+1 °C
-1 °C

10. Slide 11
Room height and air exchange rate
Room height < 3m
Resistance
Pressure build-up
•Room height: Rooms with low ceilings will create a certain
resistance between the two airstreams. Pressure will build up
at the end of the airstream.
•Air exchange rate: Excessively high air exchange rates
cause pressure to build up on the rear wall of the cooling cell.
•Both of these effects cause greater internal pressure loss and
adversely affect the air volume.

11. Slide 12
External pressure and air volume
600
500
400
300
200
100
0
123456789101112
Air volume (m
3
/s)
External pressure(Pa)
Air density 1.2 kg/m
3
Fan blade 22°
Air volume reduction

12. Slide 13
Average air exchange rates
•Long-term storage (frozen products)5 to 10-fold
•Apple storage, ULO rooms 35 to 40-fold
•Rapid chilling 150-fold
•Shock frosting 300-fold

13. Slide 14
Ceiling restrictions
Wrong!

14. Slide 15
Useful facts: fan laws
Speed
Dimension
Air density
•volumetric flow rate Speed
•Pressure (static, dynamic and total) Speed
2
•Required capacity Speed
3
•volumetric flow rate Fan blade
3
•Pressure (static, dynam. and total) Fan blade
2
•Required capacity Fan blade
5
•volumetric flow rate = No change
•Pressure (static, dynam. and total) Air density
•Required capacity Air density
Speed
Dimension*
Air density
Speed
Dimension
Air density
= constant
= change
= changes
* Only for geometrically similar ventilators

15. Slide 16
Useful facts: Air density
Current density = previous density x
273 + previous temp. (°C)
273 + current temp. (°C)
[kg/m
3
]
Current density = previous density x
288 -0.00649 H (m)
288
x 4.256 [kg/m
3
]
Temperature-related changes
Changes related to the installation height
(H = Height in m above sea level)
Standard air density= 1.2 kg/m
3
(at 16 °C, 100 kPa barometric pressure, and 65% relative humidity)

16. Slide 17
Useful facts: Pressure & Required Capacity
Dynamic pressure = 0.5 ρ v
2
[Pa]
ρ = air density [kg/m
3
]
v = air speed [m/s]
Required capacity =
Volumetric flow rate (m
3
/s) x total pressure (Pa)
Total efficiency x 10
[kW]
Pressure
Required capacity