Range Of Present Conditions Research Articles

Experimental study on melt-jet behavior during SFR core disruptive accidents using simulant materials

Investigations on melt-jet behavior during Core Disruptive Accidents (CDAs) of Sodium-cooled Fast Reactors (SFR) are crucial to the design of In-Vessel Retention (IVR) strategy. In present work, aimed to achieve a comprehensive understanding on this behavior, a number of simulated experiments are conducted by discharging a molten low-melting-point alloy jet into a water pool. Different experimental parameters such as melt temperature, water temperature, melt penetration velocity, nozzle diameter and water pool depth are taken. Based on visual observation as well as the quantified particle and debris-bed properties measured (e.g. average size and size distribution of fragments, particle sphericity and bed porosity), the effect of different releasing conditions on the melt-jet behavior mode, particle characteristics and debris-bed morphology are clarified. Dominant factors that influence the melt-jet breakup phenomenon are identified over present range of conditions. The performed analyses also suggest that the fragment mass median diameter can be reasonably interpreted by the Kelvin-Helmholtz instability model which integrates solidification effect and the Weber number theory. Besides, map diagrams distinguishing hydrodynamic effect and thermal effect with regard to melt-jet behavior mode, debris bed morphology (porosity) and particle morphology (sphericity) are explored. Insight and experimental data obtained in this work will be utilized for the future improved validations of fast reactor safety analysis codes in China, such as the thermal–hydraulic models for the prediction of fragmentation and debris formation phenomena.

Mass transfer inside spiral coils under laminar flow and possible applications

ABSTRACT Rates of mass transfer in a spiral coil were measured by a technique involving the diffusion-controlled dissolution of copper in acidified dichromate. The variables studied were solution velocity, spiral tube pitch, and physical properties of the solution. The data were correlated by the equation For a given set of conditions, the mass transfer coefficient predicted from the above equation was found to be much higher than that of the straight tube. Comparison of the ratio between the mass transfer coefficient and pressure drop for spiral tubes and straight tubes has revealed that for spiral tubes is much higher than that of a straight tube under the present range of conditions. The possibility of using the above equation in predicting the rate of diffusion-controlled corrosion and the corrosion allowance needed to design a spiral tube heat exchanger was noted. Other possible applications in heterogeneous reactor design and membrane processes are reported.

Experimental investigation on TiO2 nanoparticle migration from refrigerant–oil mixture to lubricating oil during refrigerant dryout

The application of nanorefrigerant–oil mixture in refrigeration system requires continuous circulation of nanoparticles; however, only a small part of nanoparticles circulate by migration from the mixture to vapor within refrigerant dryout process. This study points out a more important nanoparticle circulation way by migration from bulk refrigerant–oil mixture to oil excess layer, and quantitatively evaluate the mixture-to-oil migration ratio affected by oil mass fraction, nanoparticle mass fraction and heat flux. The nanorefrigerant–oil mixture is TiO2/R141b/NM56; experimental conditions cover oil mass fraction of 5%–20%, nanoparticle mass fraction of 0.2%–1.0%, and heat flux of 10–100 kW m−2; the mixture-to-oil migration ratio is measured by absorbance method. The results show that mixture-to-oil migration ratio ranges within 0.388–0.969, and increases averagely by 51.8%, 28.3% and 8.0% with increasing oil mass fraction, reducing nanoparticle mass fraction and lowering heat flux over the whole range of present conditions, respectively.

Momentum and heat transfer characteristics from heated spheroids in water based nanofluids

In this work, the governing field equations describing the momentum and forced convection heat transfer from heated spheroids, including the limiting case of a sphere, in water based nanofluids have been solved numerically in the steady and axisymmetric flow regime over the following ranges of conditions: Reynolds number, 1⩽Re⩽100; nanoparticle volume fraction, 0⩽ϕ⩽0.06 and aspect ratio, 0.2⩽e⩽5 for two sizes (dp), namely, 30nm and 100nm, of CuO and Al2O3 nanoparticles. Over the present range of conditions, a qualitative similar behavior is observed for both CuO and Al2O3 nanofluids. The detailed structure of the flow and temperature fields in the vicinity of the spheroid is analyzed in terms of streamline patterns and isotherm contours, respectively. The value of the total drag coefficient for all configurations of the spheroid is always seen to increase with the increasing value of ϕ for all values of Re,dp and e. All else being equal, the flow detaches early from the spheroid in nanofluids comprised of 100nm nanoparticles, whereas the flow separation delays in nanofluids containing 30nm nanoparticles with reference to that seen in clear water. The rate of heat transfer is seen to be monotonic with ϕ for nanofluids containing 100nm nanoparticles, whereas it is seen to be non-monotonic for nanofluids having nanoparticles of 30nm in size. Finally, the present values of the total drag coefficient and average Nusselt number are correlated using simple analytical forms which facilitate the interpolation of the present results for the intermediate values of the governing parameters.

Intensification of the rate of electropolishing and diffusion controlled electrochemical machining by workpiece oscillation

The effect of electrode oscillation on the rate of diffusion-controlled anodic processes such as electropolishing and electrochemical machining was studied by measuring the limiting current of the anodic dissolution of a vertical copper cylinder in phosphoric acid. Parameters studied were frequency and amplitude of oscillation, and phosphoric acid concentration. Within the present range of conditions, electrode oscillation was found to enhance the rate of anodic dissolution up to a maximum of 7.17 depending on the operating conditions. The mass transfer coefficient of the dissolution of the oscillating vertical copper cylinder in H3PO4 was correlated to other parameters by the equation: Sh=0.316Sc0.33Rev0.64.The importance of the present study for increasing the rate of production in electropolishing and electrochemical machining, and other electrometallurgical processes limited by anode passivity due to salt formation such as electrorefining of metals was highlighted.

An Experimental Study of Natural Convection in Vertical, Open-Ended, Concentric, and Eccentric Annular Channels

The effects of eccentricity on the natural convection heat transfer from a vertical open-ended cylindrical annulus with diameter ratio of 1.63 and aspect ratio of 18:1 have been investigated experimentally. Within the range of present conditions, and with the possible exclusion of the highest eccentricities, it was found that the flow was thermally fully developed in a considerable section of the apparatus, as indicated by the linear variation of wall temperature with height. This made it possible to estimate the mass flow rate from the wall temperature gradient in the mid-section of the annulus, and use it to calculate the bulk Reynolds number, which was found to be weakly sensitive to eccentricity for a constant wall heat flux and to increase with increased wall heat flux. With the exception of the very low eccentricity range in which it was insensitive to eccentricity, the overall heat transfer rate diminished monotonically with increasing eccentricity. Plots of the local azimuthal variation of the Nusselt number showed that, at low eccentricities, the heat transfer rate increased near the wider gap but decreased near the narrower gap. The average Nusselt number was found to decrease measurably with increasing eccentricity and to increase slightly with increasing heat flux within the examined range. In contrast, the Grashof number was found to be much more sensitive to changes in heat flux and only had a weak dependence on eccentricity.

Turbulence-chemistry interactions in the intermediate regime of premixed combustion

A numerical model for the partially stirred reactor (PaSR) is developed, and the effects of turbulence on NO, CO, and other quantities are computed. Turbulent mixing is accounted for by the “Interaction-by-Exchange-with-the-Mean” submodel. The PaSR is described by a system of (2 N s+1) × N p first-order coupled o.d.e.'s in time, where N s ≡ number of species, and N p ≡ number of particles. Combustion of a 50% CO 50% H 2 (by vol.) fuel premixed with air is considered, represented by 18 species and 43 reactions. In the limit of mixing frequency ω becoming small, the solutions tend to those of the plug flow as expected. NO and CO increase with mixing frequency. In the range of time scales relevant to turbulent combustion, say, 10 −4 s < 1 ω < 10 −2 s, NO increases by a factor of about 2 as the mixing time becomes small enough to affect the concentration of oxyhydrogen radicals while CO increases by over an order of magnitude. These variations agree qualitatively with experimental data from turbulent combustors. In-combustor stirring clearly plays a large role even in premixed combustion. The algorithm converges to the perfectly stirred reactor solution at large mixing frequencies. The partial equilibrium model is found to be reasonable for CO H 2 fuels in the present range of conditions, and effects a computational speedup by a factor on the order of 100. Besides providing a useful combustion model, the PaSR provides a test-bed for mixing models, for simplified chemical schemes, and for algorithms intended for particle-tracking pdf transport models.