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Main >> Applications >> Sample problems

ISOkorsis pipe system - QuickField simulation example

This example is a courtesy of Cheboksary pipe factory.

ISOkorsis pipes are designed for the free-flow 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 cross-section. 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.

Engineering question

How to find thermal insulation performance of isokorsis pipe systems?

Answer
Set up a plane-parallel QuickField Steady-state Heat Transfer problem for an ISOkorsis pipe system and evaluate thermal insulation performance from computed field results.

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Typical applications
insulated sewer pipelines, underground insulated pipes, freeze-protected pipelines

ISOkorsis pipe system

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Simulation problem

Problem Type
Plane problems of steady-state and transient heat transfer.

Geometry

1 - insulation; 2 - outer pipe; 3 - inner pipe; 4 - sewage water.

Given
Initial temperature of the sewage water Tsewage = 10 °C;
Sewage water velocity v = 1 m/s;
Freezing depth of the soil h = 2.5 m;
Temperature of the air Tair = -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:

  1. Initial temperature distribution in the empty tube is determined (steady-state heat transfer problem);
  2. Water is added to the pre-cooled 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.

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