OBSERVATIONS OF PATTERN EVOLUTION IN THERMAL-CONVECTION WITH HIGH-RESOLUTION QUANTITATIVE SCHLIEREN IMAGING

High-resolution measurements of the mean temperature gradient field of a fluid undergoing thermal convection in a vertical slot were made. The detection method employs schlieren optics with a linear photodiode array detector. With proper calibration the schlieren signals permit quantitative reconstruction of the varying temperature field along one dimension in the fluid, with a relative temperature resolution of +/- 0.02 K. The critical applied temperature difference, DELTA-T(b,c), is determined by extrapolation of the measured convection pattern amplitudes. The measurements permit detailed monitoring of the wave number distribution and its development in time as well as harmonic analysis of the temperature waveform. The stability limits of convective patterns are investigated as a function of forcing and wave number and the observed limits are compared to theoretical predictions. The details of the transitions from conduction to convection and from one convective spatial pattern to another are observed and analyzed as the degree of forcing is varied. The creation and destruction of convective roll cells is observed as is the propagation of convective flow across the slot.