Effect of Surface Conditions on Pool Boiling Critical Heat Fluxes in Saturated and Subcooled Liquid Nitrogen at Various Pressures
Critical heat fluxes (CHFs) in the fully developed nucleate boiling (FDNB) regime were measured for a 1.2 mm diameter horizontal cylinder with commercial or rough surface (CS or RS) in a pool of liquid nitrogen for subcooling covering a range from 0 K to about 40 K at pressures ranging from 0.3 to 2 MPa, The CHFs for the cylinders with the two different surfaces were compared under the same experimental conditions. Measured all data of the CHFs for both surface conditions were well explained by the two different CHF mechanisms; one is due to the hydrodynamic instability (HI), and another is due to the heterogeneous spontaneous nucleation in originally flooded cavities. The CHFs due to the HI obtained for both surface condition agree well with the values derived from the saturated and subcooled CHF correlations : the former was given by Kutateladze and the latter was given by the authors, respectively. It was clarified that the CHFs due to the HI are independent of the surface conditions. Little effect of the surface condition tested here was observed on the CHFs due to the HSN except the CHFs at a pressure of 2047 kPa for low subcooling near saturated conditions. An empirical correlation for the CHFs due to the HSN is presented.
KeywordsSurface Condition Critical Heat Flux Cylinder Surface Boiling Heat Transfer Hydrodynamic Instability
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