AN INTERFEROMETRIC STUDY OF COUPLED CONVECTIVE HEAT TRANSFER IN A HORIZONTAL FLAT PLATE ENCLOSUR

A long path Mach-Zehnder interferometer was combined with a low speed wind tunnel in order to study the coupling effect between natural heat convection inside the enclosure of a simulated solar collector and external natural and forced convection. This technique permitted qualitative as well as quantitative temperature field visualization of the fluid layers within the enclosure between the hot bottom plate and cold top plate boundaries of the collector, and the coupling effect of natural and forced convection on the cold plate.;The horizontal rectangular enclosure of the simulated solar collector was heated isothermally at the bottom surface and cooled at the top surface. Both plates had a dimension of 45.72 cm by 44.96 cm, and the height of the enclosure was adjustable.;Horizontal and vertical temperature profiles, as well as local and overall heat transfer coefficients were determined for Reynolds number from 0.0 to 6.6 x 10('4), Rayleigh number from 10('3) to 4.0 x 10('5), and aspect ratio (length/height) from 8.85 to 35.40.;A technique was developed by which finite and infinite fringe field interferograms with the same boundary conditions could be produced on the same film negative. The finite fringe field interferogram made possible the calculation of the temperature fields, while the isotherm patterns of the infinite fringe field interferograms allowed the study of convective heat transfer, the vertical structure of the convection cell and the circulation pattern.;For low Rayleigh number in the enclosure (Ra < 1717) conduction was the predominant mode of heat transfer. As Rayleigh number was increased, the Benard cell height-to-width ratio was decreased. This increase in Rayleigh number resulted in an observation of convection heat transfer in the central region and conduction heat transfer near the horizontal boundaries. A reversal of the temperature profile occurred for Ra (GREATERTHEQ) 12,000.;The heat transfer coefficient in the enclosure was found to be strongly dependent on the heating rate and the Rayleigh number, and moderately dependent on the external forced convection. The magnitudes of the local and average Nusselt numbers near the horizontal boundaries in the enclosure were determined, and the results presented in the form of heat transfer correlations for natural convection within the enclosure and external forced convection. These results were found to have close agreement with those of previous investigators.