Study of free-convective onset on a horizontal wire using speckle pattern interferometry

The onset and development of heat convection from a suddenly heated thin horizontal wire in air has been studied experimentally by an optical technique, named dynamic electronic speckle pattern interferometry, which allows the acquisition of qualitative and quantitative data. Attention is focused in providing temperature field visualizations and data about the temporal behavior. The heat-rate-based Rayleigh number, Ra*, ranges from 0.069 to 0.67, a region of parameters poorly covered by previous investigations. Experimental results are compared with previous data. The extent, at which existing correlations can be used for wires of 0.2 and 0.4 mm in diameter, is outlined. A new correlation is proposed.