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

Journal Article · Sun Nov 01 04:00:00 EST 1992 · Journal of Heat Transfer (Transactions of the ASME (American Society of Mechanical Engineers), Series C); (United States)

DOI:https://doi.org/10.1115/1.2911909· OSTI ID:5735623

Unal, C; Daw, V; Nelson, R A ^[1]

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1. Los Alamos National Lab., NM (United States)

We investigated the hypothesis that the critical heat flux (CHF) occurs when some point on a heated surface reaches a temperature high enough that liquid can no longer maintain contact at that point, resulting in a gradual but continuous increase in the overall surface temperature for most power-controlled systems. 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 the liquid's homogeneous nucleation temperature, depending on the contact angle. The proposed hypothesis about the occurrence of the CHF is investigated through a study of the boiling mechanism of the second transition region of nucleate pool boiling of water on copper. An idealized 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 [mu]m. The radius of the dry patch varied from 15 to 23 mm (60 and 92 percent of the heater radius, respectively) for initial macrolayer thicknesses of 0 and 11 tim, respectively. The results indicated that the critical liquid-solid contact temperature at the onset of CHF (the surface temperature at the center of the dry patch) 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 on the initial dry patch liquid macrolayer thickness, varying from 180[degrees]C to 157[degrees]C for initial macrolayer thicknesses of 0 and 11 [mu]m, respectively. Independent assessment of these values shows good agreement with extrapolated contact temperature data at the onset of film boiling.

• OSTI ID: 5735623
• Journal Information: Journal of Heat Transfer (Transactions of the ASME (American Society of Mechanical Engineers), Series C); (United States), Journal Name: Journal of Heat Transfer (Transactions of the ASME (American Society of Mechanical Engineers), Series C); (United States) Vol. 114:4; ISSN 0022-1481; ISSN JHTRAO
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
420400* -- Engineering-- Heat Transfer & Fluid Flow
BOILING
CRITICAL HEAT FLUX
ENERGY TRANSFER
FILM BOILING
HEAT FLUX
HEAT TRANSFER
NUCLEATION
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
POOL BOILING
QUENCHING
THERMAL ANALYSIS
THERMAL CONDUCTIVITY
THERMODYNAMIC PROPERTIES