The onset of manifest convection from suddenly heated horizontal cylinders

Experimental data are presented for the onset of manifest convection in water around a heated horizontal cylinder. Thin nickel coatings were applied to three plexiglass cylinders of different diameters. The nickel surface was used as a heater and observations were made by a holographic interferometer. Initially, conduction prevailed within the system, in agreement with other time-dependent investigations of heating or cooling from a surface. After a period of time the manifest convection was detected around the cylinder. The critical Rayleigh number which defines the onset of convection was 20–30 for cylinders with 15, 25 and 40 mm diameters.