Transient temperature field and vapor bubble dynamics during boiling on low thermal capacitance heater with various surfaces

Bucci, Mattia (author), Zupančič, Matevž (mentor), Golobič, Iztok (comentor)

This work investigates fundamental multi-scale phenomena occurring during pool boiling on thin heat dissipators with low thermal capacitance. Experimental studies were conducted in carefully controlled boiling environments, where stable, nearly steady-state bubble life cycles at isolated nucleation sites were observed. To achieve a comprehensive visualization of boiling processes, synchronized high-speed video, infrared thermography, and micro-thermocouple measurements were employed. Artificial nucleation sites were created on the tested surfaces through a combination of laser texturing and hydrophobization techniques. The influence of the heater’s thermophysical properties on local heat transfer behavior was demonstrated, particularly during the rewetting of the bubble footprint on the wall. Their effects on the liquid rewetting temperature were clarified, providing insights into a previously unexplored aspect of the process. Furthermore, a detailed force balance analysis was performed to examine the dynamic behavior of vapor bubbles at the wall. Building upon this, the process of bubble growth was analyzed, revealing important limitations of existing models based on finite liquid thermal boundary layers. A novel correction was proposed to accurately capture the experimentally observed trend in bubble growth. The knowledge gained from the force balance approach was further utilized in the analysis of data collected aboard the International Space Station, where the dual effects of auxiliary electric fields on vapor bubble departure in microgravity were elucidated. Finally, the boiling investigations were extended to the boiling crisis, focusing on the role of the wall’s thermophysical properties in the propagation of irreversible dry spots.

• Language: English
• Keywords: boiling heat transfer, wall thermophysical properties, transient temperature fields, bubble growth dynamics, electric field, irreversible dry spot
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FS - Faculty of Mechanical Engineering
• Year: 2025
• Number of pages: XXVI, 187 str.
• PID: 20.500.12556/RUL-174504
• UDC: 536.24:532.528:544.015.2(043.2)
• COBISS.SI-ID: 251904003
• Publication date in RUL: 03.10.2025

Secondary language

• Language: Slovenian
• Title: Nestacionarno temperaturno polje in dinamika rasti parnega mehurčka pri vrenju na grelcu z majhno toplotno kapacitivnostjo in z različnimi površinami

Abstract

V doktorskem delu se osredotočamo na preučevanju fenomenov prenosa toplote pri vrenju, ki se odvijajo na različnih velikostnih nivojih pri vrenju na grelnikih z nizko toplotno kapacitivnostjo. Eksperimentalne raziskave so bile izvedene v skrbno nadzorovanih pogojih pri katerih so bili doseženi stabilni, skoraj ustaljeni življenjski cikli posameznih mehurčkov na izoliranih mestih nukleacije. Za izdelavo slednjih smo v delu združili lasersko teksturiranje s hidrofobnimi nanosi. Preko analize eksperimentalnih rezultatov je bilo pojasnjeno kako termofizikalne lastnosti grelnika vplivajo na lokalen prenos toplote pri vrenju, zlasti pri ponovnem zalivanju površine po odcepitvi mehurčka, kar omogoča vpogled v doslej neraziskan vidik procesa. Nadalje je bila izvedena analiza ravnotežja sil z namenom popisa dinamičnega obnašanja parnih mehurčkov ob steni. Na podlagi tega je bil analiziran proces rasti mehurčkov, ki razkriva omejitve obstoječih modelov, temelječih na končnih toplotnih mejnih plasteh kapljevine. Predlagana je bila korekcija za natančen popis eksperimentalno opaženega trenda rasti mehurčkov. Razvita analiza obravnave sil je bila prenesena tudi na podatke pridobljene na Mednarodni vesoljski postaji, s pomočjo česar sta bila pojasnjena dva ključna vpliva električnega polja na odcepitev mehurčkov v pogojih mikrogravitacije. Študija prenosa toplote pri vrenju je bila obravnavana vse do kritične gostote toplotnega toka s poudarkom na vplivu termofizikalnih lastnosti grelnika na širjenje izsušenih področij na površini.

• Keywords: prenos toplote pri vrenju, termofizikalne lastnosti stene, nestacionarno temperaturno polje, dinamika rasti mehurčkov, električno polje, nepovratna izsušitev površine