Fraunhofer ISC, Center for High Temperature Materials and Design HTL, BayreuthFor industrial heat treatment, a range of very different types of furnaces are used, e.g.: Pusher plate furnaces, tunnel furnaces, belt furnaces, roller furnaces, ring furnaces or chamber furnaces. The mode of operation (continuous / lot by lot), the required furnace atmosphere, the maximum temperature, the throughput, the firing as well as the support and the transport of the material to be heated in the furnace are decisive for the choice of the furnace type. Depending on the requirements of the furnace operator, furnace systems must be designed very flexibly for a range of different products and production lots, or for constant high throughput of large series.
With the finite element (FE), fluid dynamics (CFD) and kinetic models used at Fraunhofer-Center HTL, thermal processes can be designed and optimized. They include drying, debinding, pyrolysis, sintering, recrystallization or crystal growth and diffusion processes. One special feature is the possibility of Simulating the heating process from the point of view of the material to be heated (see Thermal processes), which ensures a high product quality. At the same time, the energy efficiency of the process is optimized.
For successful heat management, exact input data for the FE simulation is required. This data is not well known for many refractory materials. The Application properties of furnace materials are determined under operating conditions with the ThermoOptical measurement systems (TOM) developed at Fraunhofer-Center HTL (see High temperature characterization). FE simulation can then be used, for example, to design the frequently multi-layered structure of a furnace insulation (see App for heat transfer calculation) and to select the best material in terms of price and performance. The Heat management in the effective volume can be managed more easily using FE and CFD methods (see Furnace simulation). Setting patterns can be optimized with regard to minimum temperature gradients. If required, mechanical and thermomechanical material properties of the furnace materials are also measured at Fraunhofer-Center HTL and considered in the design. For large furnace components, specific tests are developed at Fraunhofer-Center HTL to investigate the component behavior under operating conditions. On customer’s request, the HTL will undertake firing tests on one of its 40 own furnaces.
Industrial furnaces that are already installed can be examined directly on site with the mobile furnace measuring system (see Furnace analysis) developed at Fraunhofer-Center HTL as well as with autonomous sensor modules. For this purpose, the furnace operation does not have to be interrupted.
Fraunhofer-Center HTL develops furnace components. These can be moving components such as fans (see heat exchangers), hot gas flaps of lift gates (see Nöth, A.; Rüdinger, A.; Pritzkow, W.: Oxide Ceramic Matrix Composites – Manufacturing, Machining, Properties and Industrial Applications) or components, which are exposed to particularly high temperature gradients, thermal shocks or corrosive stress such as, for example, burner components (see Vogt, J.; von Issendorf, F.: High-temperature and corrosion-resistant perforated boards for porous burner flame traps by gelcasting), heat exchangers or sensors. Furthermore, foam ceramics (see Vogt, J.: Cost-Efficient Directly Foamed Ceramics for High-Temperature Thermal Insulation) are developed as high temperature insulation. In addition to the material selection, the Fraunhofer-Center HTL undertakes component design and optimization by simulating application behavior. As high temperature materials, monolithic ceramics, ceramic protection coatings or fiber reinforced ceramics (CMC) are used.