Development and experimental validation of numerical heat transfer models for impingement jets
Industrial Collective Research (IGF), 1 January 2023 to 31 December 2024
In continuous strip lines and in chamber furnaces for the heat treatment of steel, aluminium and copper strip, nozzle systems are used to heat and cool the strips. The nozzles are directed at the strip in such a way that the resulting impingement flow ensures the highest possible and homogeneous heat transfer. The heat transfer between the strip and the gas of the nozzle flow takes place mainly convectively. To assess the heat transfer of the impingement flow, a heat transfer coefficient (HTC) α is defined and is represented dimensionlessly by the Nußelt number Nu. The heat transfer in impingement flows depends on several factors such as the nozzle exit velocity, the material values of the fluid and the geometry of the nozzle systems.
Figure of a (a) round nozzle and (b) slot nozzle system with the relevant geometric parameters h: strip distance, L: nozzle length, W: nozzle width, s: spacing
The planned project should contribute to the development of a favourable and efficient design option for nozzle systems. For this purpose, an innovative, numerical modelling approach is to be used with which the heat transfer between impact jets and the impact surface can be calculated with sufficient accuracy. At present, this is only possible with a non-economical computational effort. The validation and evaluation of the models takes place with an experimental parameter study. The turbulence structures of the impact flow can be recorded with the help of optical flow measurement methods. The local heat transfer between the impingement flow and the impingement surface can also be investigated using suitable measurement technology. Both measurement methods mentioned can be carried out simultaneously in an experimental setup at the IOB. This makes it possible to directly analyse the flow and the local Nußelt number.
Figure of the heat transfer test rig for the measurement of Nußelt numbers.
Left: Principle sketch of the test rig, bottom right: Photo of the test rig
Top right: Sample Nu distribution for combined nozzle system of round and slot nozzles
- Modification of the existing test rig for the possibility of optical flow measurement of impact jets
- Development of a numerical model for the simulation of local Nußelt numbers of nozzle fields on impact surfaces with a maximum relative error of 5%
- Development of a simplified numerical model for the simulation of mean Nußelt numbers of nozzle fields on impact surfaces with a maximum relative error of 5%
- Validation and evaluation of the numerical models
The project (project no. 22751 N) was submitted with the support of the Research Association of Industrial Furnace Manufacturers (FOGI) via the Forschungskuratorium Maschinenbau e.V. (FKM). It is funded via the German Federation of Industrial Research Associations „Otto von Guericke“ (AiF) in the program for Industrial Collective Research (IGF), initiated by the Federal Ministry for Economic Affairs and Climate Action due to a resolution of the German Bundestag.