An Experimental Investigation of Forced Convective Heat Transfer to a Fluid in the Region of its Critical Point

Citation

Hauptmann, Edward Gerald (1966) An Experimental Investigation of Forced Convective Heat Transfer to a Fluid in the Region of its Critical Point. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8KYC-F077. https://resolver.caltech.edu/CaltechETD:etd-09182002-110836

Abstract

Experimental results are presented for forced convective heat transfer from a heated flat plate in carbon dioxide near the thermodynamic critical point. The heated plate was in a horizontal position and most measurements were made in the fully turbulent downstream portion, with the heated surface facing both up and down. The bulk conditions of the carbon dioxide were varied from below the pseudocritical temperature ("liquid-like" region) to above the pseudocritical temperature ("vapor-like" region), and in some instances the bulk and wall temperatures were on either side of the pseudocritical temperature. Some limited observations on the effect of free stream velocity were made, and experiments were also conducted below the critical pressure in order to obtain a comparison with boiling. One of the principal objectives was to observe the nature of the heated boundary layer. High speed movie films were taken using a color schlieren apparatus, modified to obtain semi-focusing effects. Although the experimentally determined heat transfer coefficient became high whenever the wall temperature approached the pseudocritical, no significant change in the gross nature of the flow field could be observed. A few exploratory hot wire measurements of the velocity fluctuations near the plate were also made, and they confirmed that no significant increase in turbulence was associated with the regions of high heat transfer coefficients. On the basis of the results it is concluded that the high heat transfer coefficients observed were due to the large values of thermodynamic and transport properties occurring near the critical point, and not because of the occurrence of a "pseudo-boiling" phenomena. It is further concluded that the "pseudo-boiling" phenomena does not occur with this particular heater geometry or in the range of parameters investigated, although it may in others. Because of the similarity of fully turbulent boundary layers to turbulent pipe flow, it is felt these conclusion may be extended to cover the latter case as well. Photographic materials on pages 171-175 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.

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