Natural convection in a square cavity with uniformly heated and/or insulated walls using marker-and-cell method

In this study, a numerical investigation has been performed using the computational Harlow-Welch MAC (Marker and Cell) finite difference method to analyse the unsteady state two-dimensional natural convection in lid-driven square cavity with left wall maintained at constant heat flux and remaining walls kept thermally insulated. The significant parameters in the present study are Reynolds number (Re), thermal Grashof number (Gr) and Prandtl number (Pr) and Peclét number (Pe =PrRe). The structure of thermal convection patterns is analysed via streamline, vorticity, pressure and temperature contour plots. The influence of the thermophysical parameters on these distributions is described in detail. Validation of solutions with earlier studies is included. Mesh independence is also conducted. It is observed that an increase in Prandtl number intensifies the primary circulation whereas it reduces the heat transfer rate. Increasing thermal Grashof number also decreases heat transfer rates. Furthermore the isotherms are significantly compressed towards the left (constant flux) wall with a variation in Grashof number while Peclét number is fixed. The study is relevant to solar collector heat transfer simulations and also crystal growth technologies

Deterministic Modeling of Unconfined Turbulent Diffusion Flames

An analytical model of the deterministic properties of turbulent diffusion flames is derived using a similarity analysis. Some parameters appearing in the model are quantified by experiments using porous round burners with propane as the fuel. The validity of the model is verified by experiments as well as by comparing the theory with previous experimental work. The model shows that the deterministic properties are insensitive to material properties.</jats:p

Preliminary Experiment of Magnetic Imaging Using Polarized Pulsed Neutrons at HUNS

AbstractImaging using polarized neutrons is one of the most attractive techniques in the neutron imaging field, because of its capability to visualize magnetic field inside materials or spaces by analyzing neutron polarization. An advanced method, which can quantify the magnetic field by combining the time-of-flight method with a polarization analysis of pulsed neutrons, has been developed at J-PARC. To introduce this method to the compact accelerator-driven neutron source, we have started the magnetic imaging experiments at Hokkaido University Neutron Source (HUNS). Using an experimental system consisting of a pair of magnetic super-mirrors as a polarizer and an analyzer, a spin flipper, and a two-dimensional neutron detector, we obtained the polarization of 90% at the wavelength over 6Å. The first demonstration experiments were performed for coil samples. As a result, an oscillatory behaviour of polarization depending on the wavelength due to the neutron spin's Larmor precession was clearly observed

Evaluation of Magnetic Field Vector by Polarization Analysis Using Pulsed Neutrons at HUNS for Magnetic Field Imaging

AbstractMagnetic field imaging using polarized pulsed neutrons is attractive technique because it has the capability to visualize spatial distribution of the magnetic field. Analyzing neutron polarization change due to neutron spin rotation result under a magnetic field at each position makes it possible to obtain a spatial distribution of magnetic field. As previous work, One-dimensional polarization analysis setup using pulsed neutrons was established at J-PARC MLF and HUNS. In this paper, we have established three-dimensional polarization analysis setup to deducea magnetic field strength and the directionprecisely and, quantitatively evaluated averaged magnetic field strength and the directioninside a coil by comparing ones calculated by magnetic calculation using FEM and one measured by a hall probe

Study on generation of oxygen-depleted water based on stochastically-changing solar radiation intensity

To examine the generation probability of oxygen-depleted sea water in Hakata Bay, possible 20 time-series of different hourly-solar-radiation intensities were generated stochastically, and a numerical simulation on dissolved oxygen was carried out for each time series. The results of the model calibration followed the seasonal variation of observed water quality well, and generated cumulative-frequency-distribution curves of daily solar radiation agreed well with the observed ones. The simulation results indicated that the exchange of sea water would have a great influence on the DO concentration, and that the concentration could change more than 1 mg/L in a day. This prediction method seems to be an effective way to examine a solution to minimize fishery damages when DO is depleted.</jats:p

Quantitative Evaluation of Nuclide Density Distribution in a Substance by Neutron Resonance Absorption Transmission Method

AbstractWe can non-destructively obtain an image of nuclide/isotope distribution or temperature in a substance by analyzing the dips due to the resonance absorption in a neutron transmission spectrum. The observed transmission spectra are expressed by convolution of intrinsic resonance cross section and neutron pulse shape, namely the emission time distribution of neutrons emitted from a moderator. Therefore, the pulse shape should be reproduced at arbitrary energy by a synthetic function for performing the quantitative resonance analysis. We have found that the Cole-Windsor function reproduced well the pulse shape of the instrument at J-PARC (Japan Proton Accelerator Research Complex) neutron source and succeeded in evaluating nuclide density of some samples quantitatively by analyzing transmission resonance spectra. On the other hand, the function expressing the pulse shape of a thermal neutron source at Hokkaido University has not been found. Therefore, we have calculated the pulse shape of epithermal neutrons by Monte-Carlo simulation and fitted the pulse shape using several kinds of function. We found that the Cole-Windsor function also was the best function for reproducing the pulse shape of the source. Moreover, we implemented it to the resonance analysis code and calculated the resonance transmission spectra of some nuclide to evaluate the capability for resonance analysis at Hokkaido University source