Heat transfer at surface contacts in preheating and heat treatment processes (“Surface Contacts II”)
Industrial Collective Research (IGF), 1 July 2021 – 31 December 2023
Surface contacts between solids occur at numerous points in thermo-processing. Surface contacts induce an additional thermal resistance due to non-ideal contact of the solids. The thermal contact resistance depends on various factors:
- the normal force or the normal stress on the contact surface
- the micro-hardness of the surface
- the thermal conductivity of the solids
- the thermal conductivity of the fluid in the interstitial space
- the temperature
Temperature distribution at a surface contact
Published studies on heat transfer between the surfaces in contact are available for low temperatures < 100 °C and low contact pressures, and in a temperature range up to 1250 °C for contact pressures above the yield stress.
In the current project, an existing test rig is further developed for investigating the temperature range relevant to thermo-processing at low contact stresses. The test rig will be used to measure the thermal resistance between surface contacts. During the measurements, the temperature, the normal force, and the atmospheric compositions can be set as parameters. The investigations include different material pairings consisting of steels, aluminium or copper alloys as well as ceramics. The results can be used to describe thermal contact resistances more accurately and to model heat transfer in thermo-processes more precisely.
Operators of thermo-processing plants thus obtain the opportunity for more precise process control of their heat treatment and heating operations. Plant manufacturers can utilize the models for the design of their plants. Suppliers of furnace manufacturers such as engineering companies for process model development and/or automation technology receive additional parameters for integration into their process models that are used to increase the energy and resource efficiency of the plants. All these companies can thus increase the quality of their products.
- Development of a method for measuring contact thermal resistances
- at sample temperatures up to 1250 °C
- at contact stresses between 0,1 MPa and 25 MPa
- in various ambient atmospheres, including pure hydrogen
- Reduction of the relative measurement error (compared to the previous project) to a maximum of 10 %
- Investigation of new material combinations
- (Further) development of models for the calculation of temperature distributions
- in steel, aluminium, and/or copper coils in heat treatment furnaces
- in steel slabs in walking beam furnaces
- in steel ladles loaded with molten metal
- (Further) development of a semi-empirical model for the analytical calculation of contact thermal resistances
The project (project no. 21803 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.