Heat transfer of liquid metal flow in a tube heated on the half of the circumference

• Applicant: Professor Dr.-Ing. Thomas Wetzel
• Subject Area: Technical Thermodynamics ; Chemical and Thermal Process Engineering
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 383514397

In the first phase of the project, the heat transfer in liquid metal cooled pipes heated over half the circumference was examined in detail experimentally. From this, a broad database was created, including thermophysical material values and values for the local and averaged heat transfer coefficients as well as locally resolved temperature distributions in the pipe wall. The results have been published. It could be shown that Nusselt correlations, which were determined for pipes heated over the full circumference, are suitable to determine circumferentially averaged Nusselt numbers for tubes heated over half the circumference also in liquid metal pipe flows. In addition, the results have shown experimentally for the first time, that in the case of liquid metal pipe flows, greater temperature differences occur in the pipe wall between the heated and unheated half than with conventional fluids. This can be explained by the significantly higher convective heat transfer coefficients in liquid metal and the greater influence of semi-circumferential heating on the local Nusselt numbers than in conventional fluids. This finding coincides with theoretical considerations from literature. It is of great relevance for the design of technical apparatus, since these higher temperature differences can also result in higher thermomechanical stresses. This is a very important aspect, especially for the desired applications with high heat flux densities and temperature levels. The value of the data developed and published is based, among other things, on the fact, that in contrast to the few literature data available to date, there is precise knowledge of the boundary conditions and measurement uncertainties. This enables a significantly more reliable design of technical equipment. In addition, the results support the validation of numerical simulations and the further development of turbulence models for liquid metal pipe flows with heat transfer. Several scientifically and technically significant open points, such as a) the systematic consideration of developing flow, b) the increasing relevance of free buoyancy flow or mixed convection at lower than the previously considered Re or Pe numbers and c) investigations, in which the material and the tube wall thickness are changed in order to systematically vary the azimuthal heat conduction in the tube wall in view of the effects described above with regard to the pronounced temperature differences between the heated and unheated tube sides, and describing them e.g. via a Biot number, are to be addressed in a second funding phase that has been applied for. The investigations would be based on the experimental methodology developed and validated in the first project phase.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Benjamin Dietrich