Effect of confinement geometry on pool boiling performance of gold-coated copper surfaceBahč, Gregor (Avtor) Hadžić, Armin (Avtor) Može, Matic (Avtor) Zupančič, Matevž (Avtor) Golobič, Iztok (Avtor) pool boilingconfined boilingcritical heat fluxheat transfer coefficientgap boilingPool boiling is widely employed in compact thermal management systems, but its performance can deteriorate significantly under geometric confinement. This study investigates the combined effects of vertical gap height and confinement plate diameter on pool boiling of distilled water at atmospheric pressure using gold-coated copper samples. The vertical gap between the boiling surface and an overhead plate varied from 0.1λ to 20λ, where λ = 2.5 mm is the capillary length of water, and three plate diameters were examined: 14 mm, 24 mm, and 39 mm. For large gaps ($k_{gap}≥2.5$), the critical heat flux (CHF) remained at approximately 1100 kW m$^{−2}$ and the heat transfer coefficient (HTC) was comparable to unconfined boiling. As the gap decreases below 2.5λ, both CHF and HTC decrease sharply. At the smallest gap (0.1λ), CHF and HTC were reduced by up to 78 % and 85 %, respectively, relative to the unconfined reference. In the intermediate gap range (0.5λ–2.5λ), the plate diameter had a pronounced effect, with the largest plate producing substantially lower CHF and HTC than the smallest plate for the same gap height due to more restricted radial vapor escape. High-speed visualization confirmed that strong confinement promotes bubble coalescence, vapor accumulation beneath the plate, and intermittent dryout of the boiling surface. Based on the CHF data for all gap heights and plate diameters, empirical correlations were developed using a dimensionless gap ratio and a characteristic plate-size parameter, providing a predictive framework for assessing CHF under combined vertical gap height and confinement plate diameter.20262026-01-16 14:06:32Članek v reviji178048UDK: 536.423.1:669.3ISSN pri članku: 0894-1777DOI: 10.1016/j.expthermflusci.2025.111685COBISS_ID: 265036291sl