measurement equipment at the climatic chamber two plastic jacket pipes

In the climatic chamber of the FFI it is possible to measure the heat conductivity Lambda of any cylindrically symmetric pipes like district heating pipes. Test on already operating pipes can ascertain the quality of the foam as well as the remaining life time of a pipeline system. The climatic chamber is practically an adiabatic room. The walls are black in order to avoid reflective rays. Inside the climatic chamber is a constant surrounding so that the heat energy which is fed into the chamber is the only factor influencing the measurements. Temperatures are measured by contact measurement elements. These are fastened with a special paste on to the copper heat core as well as on to the PE-coating of the district heating pipe, in order to keep the heat transfer as low as possible. The copper heat core consists of copper, because of the excellent heat conductivity. The measuring tolerance of the Lambda measurements in the climatic chamber is lower than the normal values.

Equation 1:  heat loss

The loss of heat Q [W] of a distant heating pipe can be measured by the following equation 1: heat transfer coefficient k [W·m^-1·K^-1], medium temperature _i [°C], ambient temperature _a [°C] and the pipe lengths L [m]. 

The distant pipeline is ideally of a cylinder symmetric structure, which consists of several layers of different heat conductivity Lambda [W·m^-1·K^-1]. The heat flow is in this simple case defined to equation 2.

Equation 2: heat flow

Necessary characteristics:

For calculating the heat conductivity the characteristics shown in pricture 1 are necessary:

The length of the pipeline sections as well as the construction has also to be considered for calculating the heat loss.

Picture 1: Necessary characteristics for the calculation