Lämmönsiirron kokeellinen määrittäminen radiaalisissa suljetuissa systeemeissä

The objective of this study was to design and conduct an easily reproducible test method to find out the thermal conductivities of different refractory materials. Another objective was to investigate the interfacial thermal resistances between the steel pipe and the refractory layer to receive better information of the total heat transfer coefficient from the outside surface of the refractory to the insides of the steel pipe. The test system consisted of an insulated cylindrical oven and a water distribution system with adjustable levels for the temperature, pressure and volume flow of the water circulating inside the test tube. Three different refractory masses were examined as they were casted on top of steel tubes and one of the masses was also used in a test tube with studs installed onto it to examine their effect onto the heat transfer. In addition to the thermal conductivity of the refractory mass the interfacial conductance between the steel pipe and the refractory was examined. After some adjustments and modifications of the equipment, the test procedures turned out to be well working and easily repeatable. The test results showed that the received thermal conductivity values were close to the estimates given by the material providers and the steel studs inside the refractory had a notable effect onto the overall heat transfer coefficient of the test tube system. Minor gap formation happened at the interface without studs, which was seen as the increase in the thermal resistance at the interface during the test runs. The obtained values for interfacial conductance cannot be used as such because they vary due to multiple things that cannot be controlled during the installation such as the contact pressure between the layers. Nevertheless, the phenomena of gap formation itself is an important thing to take into account. In conclusion, a test procedure for the testing of the thermal conductivity of a refractory in a cylindrical system was planned and executed and the procedure worked as it was planned as trustworthy and repeatable test results were obtained. Thus, the equipment can be used also in the future to examine the heat transfer of different masses or other type of cylindrical multi-layer systems