Application of a Differential Interferometer to the Measurement of Heat Transfer Coefficients

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Abstract
The basic components and principles of operation of a differential interferometer are discussed. This type of interferometer is inexpensive, relatively insensitive to vibration, and does not require extensive alignment adjustments. For free convection to an ideal gas the differential interferometer produces a fringe shift that is a function of the temperature gradient. The interferometer described is capable of producing an infinite fringe pattern in which fringe lines correspond to lines of constant index of refraction gradient. These facts make the differential interferometer useful for the measurement of convective heat transfer coefficients and flow visualization, particularly in dynamic systems and in cases where there are rapid fluctuation in the flow structure. A derivation of an expression for the free convection heat transfer coefficient is presented as a function of fringe shift. Several interferograms are included.