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ISOkorsis pipe system
ISOkorsis pipes are designed for the freeflow sewerage systems and drainage in freezing soils (with a laying the depth less than the depth of seasonal freezing and permafrost conditions) when there is a risk of the pipes freezing. In the modeled system sewage water (+10 °C) occupies 2% of the pipe's crosssection. Velocity of the sewage water is 1 m/s. Sewage freeze as a result of heat exchange with the environment. It's necessary to calculate the sewage water freezing time and the maximum allowed length of the pipe.
Problem type:
Plane problems of steadystate and transient heat transfer.
Geometry:
1  insulation; 2  outer pipe; 3  inner pipe; 4  sewage water.
Given:
Initial temperature of the sewage water T_{sewage} = 10 °C;
Sewage water velocity v = 1 m/s;
Freezing depth of the soil h = 2.5 m;
Temperature of the air T_{air} = 50 °C
Task:
Determine the sewage water freezing time and the maximum allowed length of the pipe to avoid the sewage freezing.
Solution:
The solution consists of two stages:
 Initial temperature distribution in the empty tube is determined (steadystate heat transfer problem);
 Water is added to the precooled tube. Sewage water then cools down to 0 °C. Time till the beginning of the water crystallization is calculated (transient heat transfer problem).
Result:
It takes 7 seconds to cool down water from 10 °C to 0 °C. So after 7 seconds water begins to freeze. For the given flow rate of 1 m/s the maximum length of the pipe is 7 meters. If longer pipes are needed, it is necessary to use a heating system.
Download simulation files isokorsis_pipe_system.zip.
