ISBN 9783843944243

978-3-8439-4424-3, Reihe Thermodynamik

Anika Steurer
Application of the Transient Heat Transfer Measurement Technique Using Thermochromic Liquid Crystals in Networks of Intersecting Circular Passages

190 Seiten, Dissertation Universität Stuttgart (2019), Softcover, A5

Zusammenfassung / Abstract

Results of a combined experimental and numerical investigation of networks of intersecting circular passages are presented. The three examined networks share the same passage diameter and intersection angle but vary in the number of cooling passages and intersection levels, and the passage pitch. A steady-state 3D CFD study revealed that the overall mass flow is not equally distributed between the passages within a network. A different local pressure drop in each passage due to the irregular set-up of the networks causes mixing and redistribution of passage mass flows in each intersection, along with strong temperature gradients. To receive heat transfer information on the entire network surface, the transient TLC technique was used. Due to the temperature gradients within the passages, the required reference temperature information could not be gained experimentally. Therefore, a new evaluation method was developed that uses local bulk temperatures from steady-state CFD. The missing information on temporal evolution of local fluid temperatures is extracted from thermocouple measurements and transferred to the CFD bulk temperature courses to receive quantitative local heat transfer results. Local heat transfer rates were seen to be dependent on network-specific flow conditions. To overcome this dependency and replicate periodic flow conditions in a regular network, one network was equipped with exchangeable apertures, forcing a similar degree of local pressure drop in each passage. An irregular network design results in increased localized as well as overall network heat transfer rates. A more uniform heat transfer performance is reached with a regular network. Using the regular set-up, a comparison of heat transfer rates gained with the new evaluation method and results from steady-state CFD revealed that the performed computations are capable of displaying heat transfer characteristics and the overall heat transfer level in networks.