Session: 07-04: Experiments and Analyses - III

Paper Number: 135141

135141 - Experimental Investigation of Heat Transfer to Supercritical Pressure R134a in Artifially Roughened Tubes 

Abstract: 

The environment in supercritical water cooled reactors (SCWR) is highly corrosive. This is very challenging for the fuel rod cladding materials used in such a reactor type. With increasing time of operation, an oxide layer grows on the surfaces of the fuel rod cladding. This oxide layer increases the roughness of the surface of the fuel rod cladding. The aim of this study is the investigation of the influence of the roughness due to corrosion on the heat transfer to a fluid at supercritical pressure conditions. The heat transfer to a fluid at supercritical pressure conditions is a very complex phenomenon, especially, when the pseudo critical temperature is within the operation conditions. Here, drastic variations in the thermophysical properties can lead to a deterioration or an enhancement of the heat transfer. In particular the correct prediction of the heat transfer deterioration, which can cause sharp temperature peaks on the fuel rod cladding is a big challenge. Until the current day, the vast majority of experimental investigations consider hydraulically smooth heat transfer surfaces. In the present investigation, the effect of the surface roughness is investigated systematically with experiments, using R134a as working fluid. In a first step, heat transfer experiments are conducted in a hydraulically smooth directly heated tube, covering a wide range of operating conditions. In a second step, the experiments where repeated, using a tube with rough inner surface. The surface of the rough tube was roughened by sand paper which was mounted on a drilling machine. Detailed measurements of the surface roughness, using contact and non-contact profilometer are presented in this paper. From this data, the equivalent sand grain roughness is estimated. Based on the different sand grain roughness of the two test tubes, the effect of the surface roughness on heat transfer is evaluated by comparison of the experimental results. Three different effects can be observed: Uniform enhancement of the heat transfer coefficient due to the roughness, for experimental cases where the variation of the thermophysical properties is small, suppressed heat transfer deterioration due to the rough surface, when the mass flux is comparably small and a roughness induced degradation of the onset heat flux for heat transfer deterioration at comparably large mass fluxes. A literature review on the existing heat transfer correlations, which consider the effect of the surface roughness is performed and the existing correlations are assessed with the newly generated experimental database for heat transfer to supercritical pressure fluid at a rough surface.

Presenting Author: Fabian Wiltschko Karlsruhe Institute of Technology

Presenting Author Biography: - 2017: Bachelor of Science, Mechanical Engineering, University of Stuttgart, Germany
- 2019: Master of Science, Mechanical Engineering, University of Stuttgart, Germany,
- 2019-2020: Research Assistant at Karlsruhe Institute of Technology (KIT) (CFD Simulation of Liquid Heavy Metal Flows)
- since 2020: PhD. Student at KIT, Experimental Investigation of Heat Transfer to Supercritical Pressure R134a at rough surface

Authors:

Fabian Wiltschko Karlsruhe Institute of Technology
Monika Sipova Centrum Výzkumu Řež
Jan Vit Centrum Výzkumu Řež
Xu Cheng Karlsruhe Institute of Technology