IcingWiki - User contributions [en]

Atmospheric Icing

2021-09-24T13:52:16Z

WorkshopUser9:

Atmospheric Icing is icing happening in the air, when water droplets freeze on objects. The water droplets can be in form of [[Mist]], [[Fog]], [[Cloud]] or rain. Sometimes also water vapour can cause icing directly without the presence of liquid water.

The ice is often classified as follows:
* [[Clear ice]]
* [[Hard Rime]] ice
* [[Soft Rime]] ice
* [[Frost]]

[[Freezing rain]] causes [[Clear ice]] or [[Hard Rime]] ice. Freezing [[Fog]], clouds or [[Mist]] cause [[Soft Rime]] and cold water vapour may cause [[Frost]].

The international ISO standard Atmospheric Icing on Structures (ISO, E 2017) is based on Makkonen icing model. The icing model calculates the amount of ice accumulated over a 1m high vertically oriented, freely rotating cylinder with a diameter of 3 cm. A threshold value of 10 g/h for the modelled icing intensity is often used (Hämäläinen and Niemelä 2017; Kjeller Vindteknikk 2020) to distinguish between icing and non-icing conditions. Production of a Numerical Icing Atlas for Finland

The equation 3.1 describes the rime ice rate [g/h] over the standard cylinder, taking into account also melting

<math>\frac{\mathrm{d} M}{\mathrm{d} t}=\alpha_1 \cdot \alpha_2 \cdot \alpha_3 \cdot \rho_{LW} \cdot A \cdot v -Q_m,</math>

where dM/dt is the rate of accretion [g/s], The collision (α1), sticking (α2 ) and accretion (α3) are unitless coefficients and they describe the interactions between the cylinder and cloud water droplets. The ρLW is the liquid water content [g/m3], A is the surface area of the cylinder [m2] and v is the wind speed [m/s]. Liquid water content, ρLW depends on cloud type. In clean air ρLW=0, and in different kinds of clouds it varies ρLW = [0.03-3.0] g/cm3. The only relevant cloud type in our case is fog, when ρLW = 0.06 g/cm3. Another

Atmospheric Icing

2021-09-24T13:32:54Z

WorkshopUser9: Description of amostpheric icing

Atmospheric Icing is icing happening in the air, when water droplets freeze on objects. The water droplets can be in form of [[Mist]], [[Fog]], [[Cloud]] or rain. Sometimes also water vapour can cause icing directly without the presence of liquid water.

The ice is often classified as follows:
* [[Clear ice]]
* [[Hard Rime]] ice
* [[Soft Rime]] ice
* [[Frost]]

[[Freezing rain]] causes [[Clear ice]] or [[Hard Rime]] ice. Freezing [[Fog]], clouds or [[Mist]] cause [[Soft Rime]] and cold water vapour may cause [[Frost]].

The international ISO standard Atmospheric Icing on Structures (ISO, E 2017) is based on Makkonen icing model. The icing model calculates the amount of ice accumulated over a 1m high vertically oriented, freely rotating cylinder with a diameter of 3 cm. A threshold value of 10 g/h for the modelled icing intensity is often used (Hämäläinen and Niemelä 2017; Kjeller Vindteknikk 2020) to distinguish between icing and non-icing conditions. Production of a Numerical Icing Atlas for Finland

The equation 3.1 describes the rime ice rate [g/h] over the standard cylinder, taking into account also melting

<math>\frac{\mathrm{d} M}{\mathrm{d} t}=\alpha_1 \cdot \alpha_2 \cdot \alpha_3 \cdot
\rho_{LW} \cdot A \cdot v -Q_m,</math>

where dM/dt is the rate of accretion [g/s], The collision (α1), sticking (α2 ) and accretion (α3) are unitless coefficients and they describe the interactions between the cylinder and cloud water droplets. The ρLW is the liquid water content [g/m3], A is the surface area of the cylinder [m2] and v is the wind speed [m/s]. Liquid water content, ρLW depends on cloud type. In clean air ρLW=0, and in different kinds of clouds it varies ρLW = [0.03-3.0] g/cm3. The only relevant cloud type in our case is fog, when ρLW = 0.06 g/cm3. Another