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ISSN Online: 2377-424X

International Heat Transfer Conference 12
August, 18-23, 2002, Grenoble, France

Effect of Gravity on Flow Boiling in Narrow Ducts and Enhancement of CHF Values

Get access (open in a dialog) DOI: 10.1615/IHTC12.1600
6 pages

Resumo

Flow boiling experiments were conducted by using a transparent heating surface with coatings of temperature sensors. An unheated glass plate was located in parallel to the heating surface leaving an uniform distance from 0.7 to 10mm. Vertical upward flow was realized at constant inlet velocity regardless of gap size. It was observed the trends concerning gravity effect not expected fromthe terrestrial experiments: i)At lowmass velocity undermicrogravity conditions, the increase of inlet liquid subcooling emphasizes the trend of heat transfer deterioration when a large dry patch is extended underneath a large flattened bubble which attaches on the heating surface for a long period making a balance between the rates of evaporation and of condensation: ii) Even in an extremely narrow duct, heat transfer deterioration becomes not so serious because large dry patches are immediately re-wetted by the penetration ofbu lk liquid under the constant liquid flow rate at the inlet, and no gravity effect is observed. To increase CHF values a narrow duct structure of heating unit was developed, where liquid was supplied by fine grooves even under the conditions of vapor blanketing. CHF values were increased as much as 30% without optimization in the dimensions ofstructures or in the operating conditions.