An experimental technique, using liquid crystals and the transient method, was developed to measure in-tube condensing local heat transfer coefficients. Measurements wilh R-l2 inside a horizontal, smooth circular tube is presented. This article describes the experimental procedures used to achieve a step change in the surface temperature with a special valve. The test section consists of a transparent glass tube obserued from outside. The inside surface transient temperature response is measured by a thin layer of choksteric liquid crystals. The color distribution oflhe liquid crysIIJIs is then translated Ihrough a digital color image processing unit into a surface temperature distribution. The local condensing heat transfer coefficients are obtained using a transient heal conduction analysis. Results for stratified flow regime are compared wilh results from the literature. This experimental technique provides a new tool for the measurement of lhe condensing local heal transfer.The technique is applicabk 10 measurements of condensing local heal transfer coefficients inside noncircular passages with plain or enhanced surfaces, which are commonly employed in state-of-me-an and advanced phase-change heal exchangers.
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