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

Conference · Mon Jan 01 04:00:00 EST 1990

OSTI ID:5938703

Unal, C; Daw, V; Nelson, R A

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.

• Research Organization: Los Alamos National Lab., NM (USA)
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 5938703
• Report Number(s): LA-UR-90-4370; CONF-910739--3; ON: DE91005946
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
420400* -- Engineering-- Heat Transfer & Fluid Flow
640400 -- Fluid Physics
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BOILING
CRITICAL HEAT FLUX
ENERGY TRANSFER
HEAT FLUX
HEAT TRANSFER
HEATERS
NUCLEATE BOILING
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
QUENCHING
SURFACES
THERMAL CONDUCTIVITY
THERMODYNAMIC PROPERTIES