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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

HEAT TRANSFER ENHANCEMENT AND CRISIS PHENOMENA AT POOL BOILING ON THE SURFACES WITH STRUCTURED CAPILLARY- POROUS COATINGS

Get access (open in a dialog) DOI: 10.1615/IHTC16.bae.022936
pages 1333-1340

Resumo

The results of experimental study of heat transfer and crisis phenomena at pool boiling of water, nitrogen, refrigerants R21 with different heating conditions on the surface with structured capillary-porous coating are presented. Porous coatings with different thicknesses (400–1390 µm), morphology and high porosity (up to 60%) were obtained using the new directional plasma spraying technique. The study shows that the use of new structured capillary-porous coatings leads to significant enhancement of heat transfer at stationary heat release by up to 4 times at boiling of liquid nitrogen, refrigerants R21 and up to 3.5 times at boiling of water in the region of low heat fluxes. Based on the analysis of high-speed video, it is shown that the mechanisms of heat transfer intensification can differ substantially depending on the type of studied liquid and morphology of coatings. The enhancement factor for the developed capillary-porous coatings is compared with the results of previous studies obtained using the structured surfaces with re-entrant cavities, microchannels and coatings fabricated by the gas-thermal methods.
Structured capillary-porous coatings have also a significant influence on development of the transitional processes and crisis phenomena at stepwise heat release. There is degeneration of boiling crisis development at rapid heating on the coated surfaces in nitrogen at the heat fluxes below the value of the CHF at steady state heat release. It is also shown that at the stepwise heat release on the coated heater, fast transition to the regime of film boiling without nucleate boiling stage is not observed until heat loads, exceeding the critical heat flux at stationary heat release by the factor of 2.5.