Unifying the controlling mechanisms for the critical heat flux and quenching: The ability of liquid to contact the hot surface

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We investigate the hypothesis that the critical heat flux (CHF) occurs when some point on a heated surface reaches a temperature high enough so that liquid can no longer maintain contact at that point, resulting in a gradual but continuous increase in the overall surface temperature. This hypothesis unifies the occurrence of the CHF with the quenching of hot surfaces by relating them to the same concept: the ability of a liquid to contact a hot surface, generally defined as some fraction of liquid's homogenous nucleation temperature, depending upon the contact angle. The proposed hypothesis about the occurrence of the ... continued below

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Pages: (44 p)

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Unal, C.; Daw, V. & Nelson, R.A. January 1, 1990.

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Description

We investigate the hypothesis that the critical heat flux (CHF) occurs when some point on a heated surface reaches a temperature high enough so that liquid can no longer maintain contact at that point, resulting in a gradual but continuous increase in the overall surface temperature. This hypothesis unifies the occurrence of the CHF with the quenching of hot surfaces by relating them to the same concept: the ability of a liquid to contact a hot surface, generally defined as some fraction of liquid's homogenous nucleation temperature, depending upon the contact angle. The proposed hypothesis about the occurrence of the CHF is investigated through study of the boiling mechanism of the second transition region of nucleate pool boiling. A two-dimensional transient conduction heat-transfer model was developed to investigate the heat-transfer mechanism. The initial macrolayer thickness on the dry portion of the heater, in the second transition region, was found to be bounded between 0 and 11 microns for a copper heater. The results indicated that the critical liquid-solid contact temperature at the onset of CHF must be lower than the homogeneous nucleation temperature of the liquid for the pool boiling of water on a clean horizontal surface. The liquid-solid contact temperature was dependent upon the initial liquid macrolayer thickness, varying from 180{degree}C to 157{degree}C for initial macrolayer thicknesses of 0 and 11 microns, respectively. These values are in good agreement with extrapolated contact temperature data at the onset of film boiling. This indicates that the mechanism for the occurrence of the CHF could be similar to the mechanism generally accepted for the quenching of the hot surfaces.

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Pages: (44 p)

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OSTI; NTIS; GPO Dep.

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  • ASME/AIChE/ANS national heat transfer conference, Minneapolis, MN (USA), 26-31 Jul 1991

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  • Other: DE91005946
  • Report No.: LA-UR-90-4370
  • Report No.: CONF-910739--3
  • Grant Number: W-7405-ENG-36
  • Office of Scientific & Technical Information Report Number: 5938703
  • Archival Resource Key: ark:/67531/metadc1096838

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  • January 1, 1990

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  • Feb. 18, 2018, 3:59 p.m.

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  • March 2, 2018, 5:19 p.m.

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Unal, C.; Daw, V. & Nelson, R.A. Unifying the controlling mechanisms for the critical heat flux and quenching: The ability of liquid to contact the hot surface, article, January 1, 1990; United States. (digital.library.unt.edu/ark:/67531/metadc1096838/: accessed April 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.