Showing papers by "Jacopo Buongiorno published in 2013"

Separate effects of surface roughness, wettability, and porosity on the boiling critical heat flux

Abstract: The separate effects of surface wettability, porosity, and roughness on the critical heat flux (CHF) of water were examined using engineered surfaces. Values explored were 0, 5, 10, and 15 μm for Rz (roughness), 110° for static contact angle (wettability), and 0 and 50% for pore volume fraction. The porous hydrophilic surface enhanced CHF by 50%–60%, while the porous hydrophobic surface resulted in a reduction of CHF by 97%. Wettability had little effect on the smooth non-porous surface CHF. Surface roughness (Ra, Rq, Rz) had no effect on CHF within the limit of this database.

Synchronized High-Speed Video, Infrared Thermometry, and Particle Image Velocimetry Data for Validation of Interface-Tracking Simulations of Nucleate Boiling Phenomena

Abstract: Nucleation, growth, and detachment of steam bubbles during nucleate boiling of a water pool at atmospheric pressure is experimentally investigated using a combination of synchronized high-speed video, infrared thermography, and particle image velocimetry. The heater is a thin (< 1-μm), horizontal (20 × 10 mm2), resistively heated, indium-tin-oxide film, vacuum deposited on a sapphire substrate (250-μm thick), which allows for unobstructed optical access from below the boiling surface. This approach enables detailed measurement of the phase, temperature, and velocity distributions on and above the boiling surface. The database reported herein is for isolated bubbles, exhibiting nucleation temperatures 107–109°C, bubble departure diameters 3.0–3.8 mm, frequencies 4.7–15.00 Hz, and wait and growth times 52–200 ms and 15–16 ms, respectively, at average heat fluxes 29–36 kW/m2. The database is most useful for validation of modern simulations of nucleate boiling in which the phase, temperature, and velocity dis...

Pool Boiling Heat Transfer Performance of a Dielectric Fluid With Low Global Warming Potential

Abstract: Due to growing concerns over anthropogenic effects on the climate, there is increasing need to replace engineered fluids of high global warming potentials (GWPs), such as hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs), with more environmentally friendly alternatives in thermal management systems. This article presents experimental data and compares various correlations for predicting the pool boiling heat transfer coefficient of a new low-GWP fluid, FK-649. Using a pressurized boiling facility with a smooth aluminum heater, the critical heat flux (CHF) and heat transfer coefficient were measured for the pool boiling of FK-649 at various saturation conditions. The commonly used refrigerant tetrafluoroethane (R-134a) is tested in the same pressurized facility to act as a benchmark for the new fluid. While R-134a exhibited a higher heat transfer coefficient and CHF, this behavior is expected from the fluid properties. Two-phase heat transfer performance of FK-649 is expected to be similar to that of t...

Effects of Hydrophobic Surface Patterning on Boiling Heat Transfer and Critical Heat Flux of Water at Atmospheric Pressure

Abstract: The effects of hydrophilic/hydrophobic surface patterning on critical heat flux (CHF) and heat transfer coefficient (HTC) were studied using custom-engineered testing surfaces. Patterning was created over a sapphire substrate and tested in a pool boiling facility in MITs Reactor Hydraulics Laboratory. The hydrophilic and hydrophobic matrices were created using layer by layer deposition of 50 nm thick SiO2 nanoparticles and monolayer thickness fluorosilane, respectively. Ultraviolet ozone patterning was then used with chrome-printed masks to create the desired geometric features. Hexagon, ring, star, and mixed patterns were tested to determine their abilities to affect CHF and HTC through prevention of bubble pinning at high heat fluxes. During testing, an infrared camera was used to measure the surface temperature distribution as well as locate nucleation sites for data analysis. It was found that CHF values were enhanced over the bare sapphire values by approximately 90% for hexagons, 60% for stars, 65% for rings, and 50% for mixed patterns. Contrary to expectations, patterning did not seem to affect the HTC values significantly. Although patterning did improve CHF performance over bare heaters, both CHF and HTC were found to be statistically similar to those for unpatterned, uniformly hydrophilic surfaces.Copyright © 2013 by ASME

Can corrosion and CRUD actually improve safety margins in LWRs

Abstract: It is well known that boiling and quenching heat transfer depends strongly on the morphology and composition of the solid surface through which the heat transfer occurs The relevant surface features are roughness, wettability (hydrophilicity), porosity, presence of cavities, size and shape of cavities, and thermo-physical properties of the surface material Recent work at MIT has explored the separate effects of surface roughness, wettability and porosity on both Critical Heat Flux (CHF) and quenching heat transfer (Leidenfrost point temperature) Briefly, interconnected porosity within a hydrophilic matrix greatly enhances the CHF (by as much as ∼60%) and the Leidenfrost temperature (by as much as ∼150 °C) Surprisingly, surface roughness has a comparably minor effect on both CHF and quenching There are opportunities to exploit in Light Water Reactor (LWR) nuclear plants, where CHF and quenching determine the thermal margins in during loss-of-flow and loss-of-coolant accidents, respectively, and the surface of the fuel naturally develops porous hydrophilic layers because of CRUD deposition and corrosion This paper reviews the MIT experimental database generated using engineered surfaces with carefully-controlled characteristics, and discuss its applications to LWR safety, both design-basis and beyond-design-basis accidents

Effects of Hydrophobic Surface Patterning on Boiling Heat Transfer and Critical Heat Flux of Water at Atmospheric Pressure

Abstract: The effects of hydrophilic/hydrophobic surface patterning on critical heat flux (CHF) and heat transfer coefficient (HTC) were studied using custom-engineered testing surfaces. Patterning was created over a sapphire substrate and tested in a pool boiling facility in MITs Reactor Hydraulics Laboratory. The hydrophilic and hydrophobic matrices were created using layer by layer deposition of 50 nm thick SiO2 nanoparticles and monolayer thickness fluorosilane, respectively. Ultraviolet ozone patterning was then used with chrome-printed masks to create the desired geometric features. Hexagon, ring, star, and mixed patterns were tested to determine their abilities to affect CHF and HTC through prevention of bubble pinning at high heat fluxes. During testing, an infrared camera was used to measure the surface temperature distribution as well as locate nucleation sites for data analysis. It was found that CHF values were enhanced over the bare sapphire values by approximately 90% for hexagons, 60% for stars, 65% for rings, and 50% for mixed patterns. Contrary to expectations, patterning did not seem to affect the HTC values significantly. Although patterning did improve CHF performance over bare heaters, both CHF and HTC were found to be statistically similar to those for unpatterned, uniformly hydrophilic surfaces.Copyright © 2013 by ASME

Development and Application of an Integrated Fuel Performance and Subchannel Model for Analysis of Sodium Fast Reactors

Abstract: A metal fuel performance code was coupled to a subchannel analysis code to predict, in a computationally efficient way, critical phenomena that could lead to pin failure for steady-state and transi