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Determination of wall thickness to prevent condensation

Boundary condition: Simbol Value DescriptionCooling air temperature: 16 °C Input value

Ambient air temperature: 35 °C Input value

Equivalent airduct diameter: 0.047 m Calculate equivalent diam.Relative humidity of ambient air: φ 70 % Input value

Allowed temperature difference: 6.3 °C From Table 3.

28.7 °C

22.35 °C

Thermal conductivity of insulation: λ 0.039 Input value

8.815

External surface coefficient: 8.5 Artboard/Recore coeff.

C´ 0.0178

Air duct wall thickness: d 10 mm Input desired thickness

APPROPRIATE THICKNESSControl calculation:

0.067 m Outside airduct diameter

0.047 m Inside airduct diameter

1.4469

0.539

29.84 °C Surface temperature

* Please fill only cells marked with red colur

ϑim

ϑa

Di

ϑse

ϑse

ϑav

Wm-1K-1

hSE Wm-2K-1

CA

De

Di

Ri mKW-1

Rie mKW-1

ϑse

SURFACE ε

aluminium, bright rolled 2.5 2.7 0.05alumnium, oxidized 3.1 3.3 0.13galvanized sheet metal, blank 4.0 4.2 0.26galvanized sheet metal, dusty 5.3 5.5 0.44austenitic steel 3.2 3.4 0.15aluminium - zinc sheet 3.4 3.6 0.18nonmetalic surfaces 8.5 8.7 0.94

Table 2 - Coefficients CA and CB for approximate calculation of total exterior thermal surface coefficient

CA CB

0.280.741.472.490.851.025.33

for approximate calculation of total exterior thermal surface coefficient

Cr x10-8 W/(m2K4)

Relative air humidities, %

30 35 40 45 50 55 60 65-20 * 10.4 9.1 8.0 7.9 6.0 5.2 4.5-15 12.3 10.8 9.6 8.3 7.3 6.4 5.4 4.6-10 12.9 11.3 9.9 8.7 7.6 6.6 5.7 4.8-5 13.4 11.7 10.3 9.0 7.9 6.8 5.8 5.00 13.9 12.2 10.7 9.3 8.1 7.1 6.0 5.12 14.3 12.6 11.0 9.7 8.5 7.4 6.4 5.44 14.7 13.0 11.4 10.1 8.9 7.7 6.7 5.86 15.1 13.4 11.8 10.4 9.2 8.1 7.0 6.18 15.6 13.8 12.2 10.8 9.6 8.4 7.3 6.2

10 16.0 14.2 12.6 11.2 10.0 8.6 7.4 6.312 16.5 14.6 13.0 11.6 10.1 8.8 7.5 6.314 16.9 15.1 13.4 11.7 10.3 8.9 7.6 6.516 17.4 15.5 13.6 11.9 10.4 9.0 7.8 6.618 17.8 15.7 13.8 12.1 10.6 9.2 7.9 6.720 18.1 15.9 14.0 12.3 10.7 9.3 8.0 6.822 18.4 16.1 14.2 12.5 10.9 9.5 8.1 6.924 18.6 16.4 14.4 12.6 11.1 9.6 8.2 7.026 18.9 16.6 14.7 12.8 11.2 9.7 8.4 7.128 19.2 16.9 14.9 13.0 11.4 9.9 8.5 7.230 19.5 17.1 15.1 13.2 11.6 10.1 8.6 7.335 20.2 17.7 15.7 13.7 12.0 10.4 9.0 7.640 20.9 18.4 16.1 14.2 12.4 10.8 9.3 7.945 21.6 19.0 16.7 14.7 12.8 11.2 9.6 8.145 22.3 19.7 17.3 15.2 13.3 11.6 9.9 8.4

Table 3 - The allowed temperature difference in °C between surface and ambient air for different relative humidities at the onset of dew formation

Ambient air temperature °C

Relative air humidities, %

70 75 80 85 90 953.7 2.9 2.3 1.7 1.1 0.53.8 3.1 2.5 1.8 1.2 0.63.9 3.2 2.5 1.8 1.2 0.64.1 3.3 2.6 1.9 1.2 0.64.2 3.5 2.7 1.9 1.3 0.74.6 3.8 3.0 2.2 1.5 0.74.9 4.0 3.1 2.3 1.5 0.75.1 4.1 3.2 2.3 1.5 0.75.1 4.2 3.2 2.3 1.5 0.85.2 4.2 3.3 2.4 1.6 0.85.3 4.3 3.3 2.4 1.6 0.85.4 4.3 3.4 2.5 1.6 0.85.4 4.4 3.5 2.5 1.7 0.85.6 4.5 3.5 2.6 1.7 0.85.6 4.6 3.6 2.6 1.7 0.85.7 4.7 3.6 2.6 1.7 0.85.8 4.7 3.7 2.7 1.8 0.85.9 4.8 3.7 2.7 1.8 0.96.0 4.9 3.8 2.8 1.8 0.96.1 5.0 3.8 2.8 1.8 0.96.3 5.1 4.0 2.9 1.9 0.96.5 5.3 4.1 3.0 2.0 1.06.8 5.5 4.3 3.1 2.1 1.07.0 5.7 4.4 3.2 2.1 1.0

°C between surface and ambient air for different relative humidities at the onset of dew formation