Numerical investigation into the influence of air curtain discharge - - PowerPoint PPT Presentation

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

RCUK Centre for Sustainable Energy Use in Food Chains

Paphos, Cyprus

Numerical investigation into the influence of air curtain discharge angles in refrigerated trucks

Ashika Rai, Jining Sun, Savvas Tassou

RCUK Centre for Sustainable Energy Use in Food Chains (CSEF)

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

2

Air curtain- effective technology to prevent infiltration

Infiltration can account for more than half of the overall refrigeration load!

• Use of diesel powered auxTRUs .
• Most-effective

protective technology against infiltration of warm air during door opening.

• Energy savings of up to 35% .
• Majority of air curtain not used in
• ptimum condition.
• How

can we further improve the energy efficiency of an air curtain?

Main engine Aux engine

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

3

Influence of discharge jet velocity and angle

• Adjustment of discharge velocity and discharge angle.
• Discharge velocity to improve the strength of air barrier.
• Discharge angle to prevent the air leakage losses.

Discharge velocity at 1-5 m/s

CFD model

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

4

𝐹𝑠 = 𝑁𝑏𝑗𝑠𝐷𝑞𝑏𝑗𝑠 𝑈𝑏𝑗𝑠 − 𝑈𝑗𝑜𝑢 + 𝑁𝑞𝑠𝑝𝑒𝐷𝑞𝑞𝑠𝑝𝑒 𝑈𝑞𝑠𝑝𝑒 − 𝑈𝑗𝑜𝑗

Recovery energy

Set T = 0°C T increase = 15°C Pulldown T = 0°C Energy required to pulldown the temperature of internal air and food products back to set temperature.

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

5 Figure: Recovery energy for angle 0° and 10°

• At 1 m/s: angles 0° and 10° have similar performance.
• 1 m/s to 3 m/s: angle 10° account for less recovery energy in comparison to angle 0°.
• 3 m/s to 4 m/s: angle 10° has same recovery energy whereas angle 0°’s increases

swiftly.

• 4 m/s to 4.5 m/s: the recovery energy decreases in 0° case and increases in 10° case.
• Beyond 5 m/s: the recovery energy of both the cases, 0° and 10°, increases.

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

6

Performance at low air curtain velocity 2 m/s

0° 10°

• Weak discharge jet.
• Dominant natural convection.
• The effect of discharge angle is very minimal.

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

7

Performance at mid air curtain velocity 3 m/s

0° 10°

• In both cases, the discharge jet reaches the floor.
• Prevents natural infiltration.
• Boundary flow effect and core flow effect.
• Bending angle of 10° < bending angle of 0°.
• Two streams at impingement, forced infiltration and
• utflow.

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

8

Performance at air curtain velocity 4 m/s

0° 10°

• Air curtain jet velocity much stronger.
• Prevents

the deflection created by natural convection thoroughly.

• Larger share of discharge jet comes in contact with the

floor, ‘attachment angle’.

• Smaller attachment angle = higher forced infiltration.

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

9

Performance at air curtain velocity 5 m/s

• Strong forced infiltration.
• For 10° case, discharge jet flow outwards, small

impingement.

• Forced infiltration in 0°<10°.
• Higher discharge velocity, lower boundary flow effect.

0° 10°

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

10

Conclusion

• Adjusting

angle decreases core flow and boundary flow effect.

• At low discharge velocity, the jet is

weak and so would be the effect of discharge angle.

• At velocity explicitly, the bending

effect is high and so would be the effect

• f

discharge jet, energy savings of 17.6%.

• At high discharge velocity, not as

much jet deflection, energy savings

• f 5.6%.

Energy savings

• f 35%

+17.6%