Estimation of highly dynamic heat flux from surface temperature measurements using the adjoint method

2001 ◽  
Author(s):  
Tahar Loulou ◽  
Elaine Scott
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Adjoint Method ◽  
Temperature Measurements

scholarly journals Effect of Surface Oxidation on the Onset of Nucleate Boiling in a Materials Test Reactor Coolant Channel

2016 ◽  
Vol 2 (2) ◽  
Author(s):  
Eric C. Forrest ◽  
Sarah M. Don ◽  
Lin-Wen Hu ◽  
Jacopo Buongiorno ◽  
Thomas J. McKrell
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
High Speed ◽  
Surface Oxidation ◽  
Nucleate Boiling ◽  
Temperature Measurements ◽  
Native Oxide ◽  
Oxide Surface ◽  
Surface Conditions ◽  
Test Reactor

The onset of nucleate boiling (ONB) serves as the thermal-hydraulic operating limit for many research and test reactors. However, boiling incipience under forced convection has not been well-characterized in narrow channel geometries or for oxidized surface conditions. This study presents experimental data for the ONB in vertical upflow of deionized (DI) water in a simulated materials test reactor (MTR) coolant channel. The channel gap thickness and aspect ratio were 1.96 mm and 29∶1, respectively. Boiling surface conditions were carefully controlled and characterized, with both heavily oxidized and native oxide surfaces tested. Measurements were performed for mass fluxes ranging from 750 to 3000  kg/m2 s and for subcoolings ranging from 10 to 45°C. ONB was identified using a combination of high-speed visual observation, surface temperature measurements, and channel pressure drop measurements. Surface temperature measurements were found to be most reliable in identifying the ONB. For the nominal (native oxide) surface, results indicate that the correlation of Bergles and Rohsenow, when paired with the appropriate single-phase heat transfer correlation, adequately predicts the ONB heat flux. Incipience on the oxidized surface occurred at a higher heat flux and superheat than on the plain surface.

Transient Cooling of Hot Porous and Nonporous Ceramic Solids by Droplet Evaporation

1994 ◽  
Vol 116 (3) ◽  
pp. 694-701 ◽  
Author(s):  
M. Abu-Zaid ◽  
A. Atreya
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Solid Surface ◽  
Boiling Point ◽  
Droplet Diameter ◽  
Droplet Evaporation ◽  
Porous Solid ◽  
Temperature Measurements ◽  
Transient Temperature ◽  
Initial Surface

This paper presents the results of an experimental investigation into transient cooling of low-thermal-conductivity porous and nonporous ceramic solids by individual water droplets. The initial surface temperature (Ts) of both solids ranged from 75 to 200°C. Both solids were instrumented with several surface and in-depth thermocouples and had the same thermal properties. This enabled investigation into the similarities and differences in the thermal behavior of porous and nonporous solids during droplet evaporation. The measured and theoretical contact temperatures, for both solids, were found to be in good agreement until they became equal to the boiling point of water (which occurs at an initial solid surface temperature of 164°C). Further increase in the initial solid surface temperature did not change the measured contact temperature. Instead, it became roughly constant at a value slightly greater than the boiling point of water. During the droplet evaporation process, surface and in-depth temperatures for the nonporous solid remain nearly constant, whereas for the porous solid there was a continuous decrease in these temperatures. A thermocouple in the porous matrix at the same location as that of the nonporous matrix cools faster under identical conditions, indicating an energy sink in the vicinity of the thermocouple. Also, evaporation time for the nonporous solid was found to be larger than that of the porous solid for the same droplet size and under the same conditions. These observations confirm that there is both in-depth and lateral penetration of water in the porous solid. The transient temperature measurements were used to determine the following quantities: (i) the recovery time (time required by the surface to recover to its initial temperature), and (ii) the size of surface and in-depth zones affected by the droplet. The instantaneous evaporation rate, and the instantaneous average evaporative heat flux for the nonporous solid, were also determined from video measurements of the droplet diameter on the solid surface and the transient temperature measurements. It was found that the average evaporative heat flux is higher for smaller droplets because of their smaller thickness on the hot surface.

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