Makkonen´s model: Difference between revisions
Added some text and link to LWC |
Added description of the measurements for Makkonen's model |
||
| Line 1: | Line 1: | ||
The international ISO standard Atmospheric Icing on Structures (ISO, E 2017<ref>{{Cite web| title = ISO 12494:2017 - Atmospheric icing of structures| work = iTeh Standards Store| accessdate = 2022-01-31| url = https://standards.iteh.ai/catalog/standards/iso/e35bb939-fd4b-4b3f-83cc-3d4dbb1e71ab/iso-12494-2017}}</ref>) is based on Makkonen icing model <ref>{{Cite journal| doi = 10.1098/rsta.2000.0690| volume = 358| issue = 1776| pages = 2913–2939| last1 = Poots| first1 = G.| last2 = Makkonen| first2 = Lasse| title = Models for the growth of rime, glaze, icicles and wet snow on structures| journal = Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences| accessdate = 2021-08-12| date = 2000-11-15| url = https://royalsocietypublishing.org/doi/10.1098/rsta.2000.0690}}</ref>. The icing model calculates the amount of ice accumulated over a 1 m high vertically oriented, freely rotating cylinder with a diameter of 3 cm. A threshold value of 10 g/h for the modeled icing intensity is often used <ref>{{Cite journal| doi = 10.1002/we.1998| issn = 1099-1824| volume = 20| issue = 1| pages = 171–189| last1 = Hämäläinen| first1 = Karoliina| last2 = Niemelä| first2 = Sami| title = Production of a Numerical Icing Atlas for Finland| journal = Wind Energy| accessdate = 2021-08-09| date = 2017| url = https://onlinelibrary.wiley.com/doi/abs/10.1002/we.1998}}</ref> to distinguish between icing and non-icing conditions. | |||
In Makkonen’s model icing rate can be modeled with an equation | In Makkonen’s model icing rate can be modeled with an equation | ||
Revision as of 14:20, 31 January 2022
The international ISO standard Atmospheric Icing on Structures (ISO, E 2017[1]) is based on Makkonen icing model [2]. The icing model calculates the amount of ice accumulated over a 1 m high vertically oriented, freely rotating cylinder with a diameter of 3 cm. A threshold value of 10 g/h for the modeled icing intensity is often used [3] to distinguish between icing and non-icing conditions.
In Makkonen’s model icing rate can be modeled with an equation
where 𝛼1 is collision efficiency, describing how likely a droplet hit the cylinder, and it varies between 0..1. It can be set to 1 for large droplet sizes.
𝛼2 sticking efficiency, describes how likely a droplet sticks in the cylinder when hit. It ranges from 0..1 and can be set to 1 for freezing rain
and 𝛼3 represent ice accretion efficiency, varying between 0..1
𝛼1, 𝛼2 and 𝛼3 are correction factors, and their value is between 0 and 1. Empirical data is used to determine the correction factors and they are very dependent on the icing conditions.
A is area and
v is the velocity of the particles
and ω is the mass concentration of particles, Liquid Water Content, LWC
Collision efficiency 𝛼1 is the ratio at which water droplets hit the icing surface, as some droplets, especially the smaller ones, can be directed by airflow to miss the icing object.
Sticking efficiency 𝛼2 is the measure of how much of the water droplets, or snow, that hit the surface, stick to the ice layer. Supercooled water droplets do not bounce but freeze immediately. Adversely, snow can bounce off. Snow increases the complexity of icing and therefore many icing models have a hard time modelling icing events with snowflakes.
Ice accretion efficiency 𝛼3 is a measure of how many of the particles contacting the material surface form ice on it. Some droplets do not freeze to from ice, leading to wet ice growth. The heat balance of the object surface affects the number of droplets that freeze. The surface heat balance follows equation:
where 𝑄𝑓 is latent heat of freezing,
𝑄𝑣 is frictional heating of air,
𝑄𝑐 is loss of sensible heat to air,
𝑄𝑒 is heat loss due to evaporation,
𝑄𝑙 is heat loss because of warming of supercooled water to freezing point,
and 𝑄𝑠 is heat loss due to radiation.
The ice accretion efficiency is strongly affected by how well the latent heat of freezing can leave the surface.
- ↑ "ISO 12494:2017 - Atmospheric icing of structures". iTeh Standards Store. Retrieved 2022-01-31.
- ↑ Poots, G.; Makkonen, Lasse (2000-11-15). "Models for the growth of rime, glaze, icicles and wet snow on structures". Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences. 358 (1776): 2913–2939. doi:10.1098/rsta.2000.0690. Retrieved 2021-08-12.
- ↑ Hämäläinen, Karoliina; Niemelä, Sami (2017). "Production of a Numerical Icing Atlas for Finland". Wind Energy. 20 (1): 171–189. doi:10.1002/we.1998. ISSN 1099-1824. Retrieved 2021-08-09.
- ↑ Ingvaldsen, K. (2017) Atmospheric icing in a changing climate: Impact of higher boundary temperatures on simulations of atmospheric ice accretion on structures during the 2015-2016 icing winter in West-Norway.
- ↑ Stenroos, C. (2015) Properties of icephobic surfaces in different icing conditions.
- ↑ Makkonen, L. (2000). Models for the growth of rime, glaze, icicles and wet snow on structures. Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical, and Engineering Sciences, 358(1776), 2913–2939.