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Research Papers

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

[+] Author and Article Information
Eric C. Forrest

Primary Standards Laboratory,
Sandia National Laboratories,
Albuquerque, NM 87185
e-mail: ecforre@sandia.gov

Sarah M. Don

Department of Nuclear Science and Engineering,
Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: sarahdon@alum.mit.edu

Lin-Wen Hu

Mem. ASME
Nuclear Reactor Laboratory,
Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: lwhu@mit.edu

Jacopo Buongiorno

Mem. ASME
Department of Nuclear Science and Engineering,
Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: jacopo@mit.edu

Thomas J. McKrell

Department of Nuclear Science and Engineering,
Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: tmckrell@mit.edu

1Corresponding author.

Manuscript received July 10, 2015; final manuscript received August 18, 2015; published online February 29, 2016. Assoc. Editor: Igor Pioro.

ASME J of Nuclear Rad Sci 2(2), 021001 (Feb 29, 2016) (13 pages) Paper No: NERS-15-1159; doi: 10.1115/1.4031503 History: Received July 10, 2015; Accepted August 29, 2015

## Abstract

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.

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Sandia National Laboratories (SNL)

## Figures

Fig. 1

Hemispherical bubble model (left) and truncated sphere model (right)

Fig. 2

Exploded view of the test section, with thermocouple locations indicated by X’s

Fig. 3

Photograph of nominal plate (top) and plate following 600°C oxidation in air (bottom)

Fig. 4

Partial boiling curves based on local temperature measurements for G=750  kg/m2 s, Tbulk,in=80°C, and Pout=1.3  bar

Fig. 5

Partial forced convection boiling curve for G=3000  kg/m2 s, Tbulk,in=80°C, and Pout=1.3  bar

Fig. 6

Partitioned boiling heat flux for TC13 from the forced convection boiling curve in Fig. 4. A boiling heat flux partition of 7.5% was used to determine the ONB

Fig. 7

Measured heat flux at the ONB, determined using local temperature measurement and the partition heat flux method

Fig. 8

Comparison of the measured ONB heat flux for the oxidized and nominal surfaces as a function of mass flux. Tests shown are for an inlet temperature of 80°C, and an outlet pressure of 1.3 bar

Fig. 9

Channel pressure drop and relative standard deviation of pressure drop-time signal for G=750  kg/m2 s and Tbulk,in=90°C

Fig. 10

ONB heat flux at channel outlet as determined from pressure measurement fluctuations

Fig. 11

Active nucleation site shortly after incipience point. G=750  kg/m2 s and Tbulk,in=90°C

Fig. 12

Bubbly flow in channel. G=750  kg/m2 s and Tbulk,in=90°C

Fig. 13

Equilibrium contact angle of DI water on the nominal heater surface

Fig. 14

Static advancing contact angle (left) and static receding contact angle (right) on the nominal heater surface

Fig. 15

Equilibrium contact angle of DI water on the heavily oxidized heater surface

Fig. 16

Static advancing contact angle (left) and static receding contact angle (right) on the heavily oxidized heater surface

Fig. 17

ONB heat flux versus wall saturation superheat for all tests conducted with Tbulk,in=80°C. In this plot, the Davis–Anderson correlation is shown using the two different equilibrium contact angles measured on the nominal and oxidized surfaces

Fig. 18

Measured ONB heat flux versus that predicted using the Bergles–Rohsenow correlation along with the single-phase heat transfer correlation developed for narrow rectangular channels heated on one side (Eq. (22))

Fig. 19

Measured ONB heat flux from pressure measurement fluctuations versus that predicted at outlet conditions using the model of Bergles and Rohsenow and Eq. (22)

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