ISBN 978-3-8439-5514-0

978-3-8439-5514-0, Reihe Thermodynamik

Björn Müller
Bewertung mikrostrukturierter Verdampferrohre hinsichtlich des Wärmeübergangs

176 Seiten, Dissertation Universität Kassel (2022), Hardcover, A5

Zusammenfassung / Abstract

The present work investigates the influence of microstructured evaporator tubes on pool boling heat transfer. Reproducible microstructures are produced on test tube surfaces in a specially developed injector blasting process using high-grade corundum. Since there are only very few investigations on evaporator surfaces made of mild steel in the literature, this work is carried out with test tubes made of mild steel. The microstructure of the respective surface is analysed with a new high-resolution optical measuring system and evaluated with roughness parameters according to the standard. A measuring system based on focus variation and a non-contact measuring system based on the near-field scanning microscopy method are used. Furthermore, a study on the wettability of fluids on microstructured surfaces is carried out. The heat transfer measurements in the area of convective boiling and in the field of pool boiling take place in a boiling apparatus equipped with new measuring technology. With this test rig, heat transfer measurements can be carried out in a wide pressure and temperature range. With constant electrical heating of the test tubes, wall superheat is measured via miniature thermocouples in the test tube and in the boiling liquid. From this, local and integral heat transfer coefficients are calculated and analysed as a function of the surface roughness. The individual boiling states are recorded and evaluated with a high-resolution, high-speed video camera. Since wettability has a significant influence on bubble formation, a comparison between roughness and wettability of the microstructured surfaces is made for all microstructured surfaces. The experimental results of the heat transfer are compared with empirical correlations from the literature and experimental literature data.