Ångbubbelbildning

Ångbubbelbildning, also known as vapor bubble nucleation, is the process by which vapor bubbles form within a liquid. This phenomenon is critical in various boiling processes, from household kettles to industrial heat exchangers. Nucleation typically occurs at specific sites on a heated surface, known as nucleation sites. These sites are often imperfections or irregularities on the surface, such as microscopic scratches, pits, or trapped gas.

The formation of a vapor bubble begins when the liquid at a nucleation site reaches its saturation temperature. The small amount of vapor or gas trapped at the site then expands due to the heat, forming a embryonic bubble. This bubble grows by evaporation from the surrounding superheated liquid. As the bubble grows, it detaches from the nucleation site and rises through the liquid, carrying heat with it.

The density and distribution of nucleation sites significantly influence the boiling process. A surface with many active nucleation sites will exhibit more vigorous boiling at a lower temperature difference between the surface and the liquid. Conversely, a very smooth surface with few nucleation sites might require a higher temperature difference to initiate boiling, leading to a phenomenon known as superheating. Understanding and controlling ångbubbelbildning is essential for efficient heat transfer and preventing issues like burnout in thermal systems.