I have a dilemma. I do a simple heat transfer analysis and I wonder about the results. I have small plate (40x40x1 mm) of aluminum sheet. In centre I apply 1W heat load and the Free Convection to Environment defined on that plate. My brain (and also a simple measurement) says that the plate should have lower temperature if it is in vertical position (convection defined as inclined plate) than in case of horizontal position. But the results of my simulation are different - vertical position shows higher temperature than in horizontal position.
It depends. For tubulent cases a heated horizontal plate facing upwards will have a higher convection coefficient than a vertical plate. Check Holman 9th edition table 7.2. This is also confirmed by the thermal web thermal wizard at this URL: