Eric C. Forrest

Nanofluids for Enhanced Economics and Safety of Nuclear Reactors: An Evaluation of the Potential Features, Issues, and Research Gaps

Nanofluids are engineered colloidal suspensions of nanoparticles in water and exhibit a very significant enhancement (up to 200%) of the boiling critical heat flux (CHF) at modest nanoparticle concentrations (

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

0.1% by volume). Since CHF is the upper limit of nucleate boiling, such enhancement offers the potential for major performance improvement in many practical applications that use nucleate boiling as their prevalent heat transfer mode. The Massachusetts Institute of Technology is exploring the nuclear applications of nanofluids, specifically the following three: 1. main reactor coolant for pressurized water reactors (PWRs)2. coolant for the emergency core cooling system (ECCS) of both PWRs and boiling water reactors3. coolant for in-vessel retention of the molten core during severe accidents in high-power-density light water reactors. The main features and potential issues of these applications are discussed. The first application could enable significant power uprates in current and future PWRs, thus enhancing their economic performance. Specifically, the use of nanofluids with at least 32% higher CHF could enable a 20% power density uprate in current plants without changing the fuel assembly design and without reducing the margin to CHF. The nanoparticles would not alter the neutronic performance of the system significantly. A RELAP5 analysis of the large-break loss-of-coolant accident in PWRs has shown that the use of a nanofluid in the ECCS accumulators and safety injection can increase the peak-cladding-temperature margins (in the nominal-power core) or maintain them in uprated cores if the nanofluid has a higher post-CHF heat transfer rate. The third application can increase the margin to vessel breach by 40% during severe accidents in high-power density systems such as Westinghouse AP1000 and the Korean APR1400. In summary, the use of nanofluids in nuclear systems seems promising; however, several significant gaps are evident, including, most notably, demonstration of the nanofluid thermal-hydraulic performance at prototypical reactor conditions and the compatibility of the nanofluid chemistry with the reactor materials. These gaps must be closed before any of the aforementioned applications can be implemented in a nuclear power plant.

Pressure effects on the pool boiling of the fluorinated ketone C 2 F 5 C(O)CF(CF 3 ) 2

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/m2s 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. Furthermore, incipience on the oxidized surface occurred at a higher heat flux and superheat than on the plain surface.

Modeling physical vapor deposition of energetic materials

A low global warming potential dielectric fluid is under investigation for use in two-phase electronic cooling systems. The fluorinated ketone C2F5C(O)CF(CF3)2, sufficient for either indirect cooling or direct immersion cooling, may be an environmentally friendly alternative for the cooling of power electronics and other high power density devices. This study examines pressure effects on the pool boiling heat transfer coefficient and critical heat flux of the fluorinated ketone. Using a pressurized boiling facility, an aluminum substrate is heated by conduction with a cartridge heater. By measuring the surface temperature and surface heat flux, the nucleate boiling heat transfer coefficient and critical heat flux are obtained for the fluorinated ketone under saturated conditions at various system pressures. Results are compared to the pool boiling of tetrafluoroethane (R-134a) in the same pressurized facility. Data are fitted using the Rohsenow correlation and surface-fluids parameters for R-134a and the fluorinated ketone are determined. Data indicate that the CHF and nucleate boiling heat transfer coefficient of the fluorinated ketone may be increased with only modest increases in the system pressure.

Convective heat transfer in a high aspect ratio minichannel heated on one side

Morphology and microstructure of organic explosive films formed using physical vapor deposition (PVD) processes strongly depends on local surface temperature during deposition. Currently, there is no accurate means of quantifying the local surface temperature during PVD processes in the deposition chambers. This work focuses on using a multiphysics computational fluid dynamics tool, STARCCM+, to simulate pentaerythritol tetranitrate (PETN) deposition. The PETN vapor and solid phase were simulated using the volume of fluid method and its deposition in the vacuum chamber on spinning silicon wafers was modeled. The model also included the spinning copper cooling block where the wafers are placed along with the chiller operating with forced convection refrigerant. Implicit time-dependent simulations in two- and three-dimensional were performed to derive insights in the governing physics for PETN thin film formation. PETN is deposited at the rate of 14 nm/s at 142.9 °C on a wafer with an initial temperature of...

Augmentation of nucleate boiling heat transfer and critical heat flux using nanoparticle thin-film coatings

United States. National Nuclear Security Administration. Global Threat Reduction Initiative (Argonne National Laboratory. Contract 25-30101-0004 A)