Engineering topics

Brooks, Paul

Publications and source records attributed to Brooks, Paul.

3 records

DOE OSTI2020

Enhanced flow boiling heat transfer on chromium coated zircaloy-4 using cold spray technique for accident tolerant fuel (ATF) materials

Flow boiling heat transfer tests were conducted to evaluate the Critical Heat Flux (CHF) and Heat Transfer Coefficient (HTC) of conventional and accident tolerant fuel (ATF) cladding materials, i.e., bare Zircaloy-4 (Zr4), and Zircaloy-4 coated with Chromium using physical vapor deposition (PVD) (Zr4-Cr-PVD) and cold spray process (Zr4-Cr-CS), respectively. The tests were performed on a single heater rod with a uniform heat flux profile, at the atmospheric pressure, inlet temperature (24 °C) and mass flow rate (750 kg/m 2 s). HTC’s were increased by 5.2% and 3.3% on Zr4-Cr-CS compared to bare Zr4 and Zr4-Cr-PVD. Improved HTCwas attributed to the increased void fraction and high roughness (Ra = 532 nm) of the Zr4-Cr-CS. In detail, the micro-cavities, which act as bubble seeds, were entirely distributed on the Zr4-Cr-CS, and these micro-cavities generated smaller and faster bubbles, thus the void fraction increased by 10.9% compared to bare Zr4. HTC is improved by these smaller and faster bubbles which can remove heat from the heater rod surface more efficiently. To identify the exact location of CHF, the surface temperature profile was measured using advanced fiber-optic sensors which have high temporal/spatial resolution (distance between point to point: ~2.5 mm, frequency ~100 Hz). CHF occurred at 80–95% along the heated length and showed an 11.6% reduction on Zr4-Cr-CS compared to bare Zr4. We hypothesize the CHF reduction was caused by the lower wettability of the Zr4-Cr-CS which reduces the liquid supply to the surface, and vigorous bubble accumulation owing to high void fraction near the outlet, which results in early formation of the vapor film. During the post-CHF quenching phase, the rougher Zr4-Cr-CS showed larger cooling rates compared to the bare Zr4 and Zr4-Cr-PVD, preventing of oxidation by chromium layer. In conclusion, we demonstrate that the high roughness on the Zr4-Cr-CS increased the number of micro-cavities on the surface, resulting in 5.2% increase in HTC and improvement in the quenching heat transfer performance whereas CHF was 11.6% reduced compared to bare Zr4. Overall statistically there is little effect in the coating with regards to CHF and slight improvement in HTC.

42 ENGINEERING↗

DOE OSTI2019

Hillslope Hydrology in Global Change Research and Earth System Modeling

Earth System Models (ESMs) are essential tools for understanding and predicting global change, but they cannot explicitly resolve hillslope-scale terrain structures that have been long recognized by hydrologists as the fundamental organizers of water, energy, and biogeochemical stores and fluxes. Here, we bring together hydrologists, Critical Zone scientists and ESM developers, to explore how hillslope structures may modulate ESM grid-level water, energy and biogeochemical fluxes. In contrast to the traditional one-dimensional (1D), vertical, 2-3m deep, and free-draining soil hydrology in current ESM land models, we argue that 3D, lateral ridge-to-valley flow through shallow and deep paths, and insolation contrasts between sunny and shady slopes, are the top two basic, long-acknowledged, and readily quantifiable organizers of water and energy (and hence vegetation) within an ESM grid cell. We argue that these two processes will be most consequential where (and when) water and/or energy are limiting. We further hypothesize that if they are implemented in ESM land models, they will increase continental water storage and residence time, buffering land ecosystems against seasonal and interannual droughts. We explore efficient ways to capture these mechanisms in ESMs and identify critical knowledge gaps preventing us from scaling up hillslope to global processes. One such gap is our extremely limited view of the subsurface, where water is stored to support vegetation and released to stream baseflow and aquatic ecosystems. We conclude with a call for global syntheses activities and model experiments to assess the impact of hillslope hydrology on global change predictions.

Fan, Ying↗

DOE OSTI2019

Natural circulation FLiBe loop overview

A new large natural circulation FLiBe loop has operated for the first time in 40 years. Reaching temperatures above 700 C with stable flow rates around 5 cm/s, the loop exhibits a range of flow phenomena pertinent to high temperature natural circulation safety systems for nuclear reactors. This paper discusses the system and several operating conditions spanning a wide range of behavior to aid the development of other systems, simulation benchmarks, or system-codes. Analysis of heat transport phenomena indicates that standard Nusselt number correlations apply to a first approximation. More accurate salt-freezing models may be necessary for air-cooled salt-systems due to the insulating affect of the low thermal-conductivity frozen salt layer on the cold pipe walls.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗