Influence Of Subcooling On Pool Boiling Heat Transfer

Author : Valerie Fudurich
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (951 download)

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Download or read book Effect of Liquid Subcooling, Initial Surface Temperature, and Surface Properties on the Minimum Film Boiling Temperature written by Valerie Fudurich and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental test facility has been designed and constructed with the purpose of performing high-temperature pool boiling experiments for vertical cylinder geometry. The heat transfer regime of interest is high temperature film boiling and the transition point at the minimum film boiling temperature, Tmin. The large superheat temperature and heat flux are able to sustain a vapor blanket that prevents the bulk liquid from direct physical contact with the heated surface. Experiments focused on varying the initial rod temperature, liquid subcooling, and surface conditions through oxidation to study their influence on Tmin and the boiling curve. These initial conditions were varied for two series of quenching experiments. The first varied the rod and bath temperatures and the second held these temperatures constant for sequential tests to build an oxide layer. A stainless steel cylindrical rod fitted with embedded thermocouples was heated to a temperature well in the film boiling regime and quickly inserted in an otherwise quiescent pool of distilled water. The superheated surface is quenched when the liquid comes into contact after the collapse of the vapor film. The embedded thermocouples were connected to a data acquisition system to record temperature-time traces. Additionally, video was recorded during the quenching process for visualization of the vapor film. Quenching curves were used to calculate the heat flux and construct the boiling curve. The minimum film boiling temperature was calculated by finding the minimum heat flux associated with Tmin. Data reduction was performed by using an inverse heat conduction code (DATARH) to calculate surface temperature and heat flux. It was found that, similar to the majority of previous research, the liquid subcooling strongly influences the minimum film boiling temperature. In addition, the vapor film thickness and the behavior of the liquid-vapor boundary layer is closely linked to the liquid subcooling. The initial surface temperature had little effect on Tmin compared to the large effect of liquid subcooling. The duration of the entire quench process however, was extended when the initial surface temperature was increased. A second series of tests to investigate the effects of oxidation were also undertaken. When several tests were completed in succession without restoring the rod surface to bare conditions, Tmin changed subtly after the first oxidized test. The effect did not become more pronounced with subsequent tests. However when the rods were given multiple hours to oxidize, Tmin did not stay constant. This suggests that although stainless steel is resistant to changes to the oxide layer during short term heat cycles, extended heat influences the oxide layer. The current findings were used to observe the effectiveness of a correlation produced by Peterson and Bajorek. As the surface conditions of the oxidized rod were unable to be quantified, the basic form of the correlation was used. Most experimental data was predicted within ±10% by the correlation.