Effect of aspect ratio on thermal convection in open and closed systems

Internally heated fluids are found across the nuclear fuel cycle. In certain situations the motion of the fluid is driven by the decay heat (i.e. corium melt pools in severe accidents, the shutdown of liquid metal reactors, molten salt and the passive control of light water reactors) as well as normal operation (i.e. intermediate waste storage and generation IV reactor designs). This can in the long-term affect reactor vessel integrity or lead to localized hot spots and accumulation of solid wastes that may prompt local increases in activity. Two approaches to the modeling of internally heated convection are presented here. These are based on numerical analysis using codes developed in-house and simulations using widely available computational fluid dynamics solvers. Open and closed fluid layers at around the transition between conduction and convection of various aspect ratios are considered. We determine optimum domain aspect ratio (1:7:7 up to 1:24:24 for open systems and 5:5:1, 1:10:10 and 1:20:20 for closed systems), mesh resolutions and turbulence models required to accurately and efficiently capture the convection structures that evolve when perturbing the conductive state of the fluid layer. Note that the open and closed fluid layers we study here are bounded by a conducting surface over an insulating surface. Conclusions will be drawn on the influence of the periodic boundary conditions on the flow patterns observed. We have also examined the stability of the nonlinear solutions that we found with the aim of identifying the bifurcation sequence of these solutions en route to turbulence.

Effect of oscillatory flow on nucleation kinetics of butyl paraben

More than 165 induction times of butyl paraben-ethanol solution in a batch moving fluid oscillation baffled crystallizer with various amplitudes (1-9 mm) and frequencies (1.0-9.0 Hz) have been determined to study the effect of COBR operating conditions on nucleation. The induction time decreases with increasing amplitude and frequency at power density below about 500 W/m3; however, a further increase of the frequency and amplitude leads to an increase of the induction time. The interfacial energies and pre-exponential factors in both homogeneous and heterogeneous nucleation are determined by classical nucleation theory at oscillatory frequency 2.0 Hz and amplitudes of 3 or 5 mm both with and without net flow. To capture the shear rate conditions in oscillatory flow crystallizers, a large eddy simulation approach in a computational fluid dynamics framework is applied. Under ideal conditions the shear rate distribution shows spatial and temporal periodicity and radial symmetry. The spatial distributions of the shear rate indicate an increase of average and maximum values of the shear rate with increasing amplitude and frequency. In continuous operation, net flow enhances the shear rate at most time points, promoting nucleation. The mechanism of the shear rate influence on nucleation is discussed.

Using an Infra-red sensor to measure the dynamic behaviour of N2O gas escaping through different sized holes

An anastomosis is a surgical procedure that consists of the connection of two parts of an organ and is commonly required in cases of colorectal cancer. About 80% of the patients diagnosed with this problem require surgery. The malignant tissue located on the gastrointestinal track must be resected and the most common procedure adopted is the anastomosis. Therefore, an anastomotic leak represents a significant problem and increases the duration of hospital stay, which is associated with remedial treatment and recovery, causing, as a result, a negative financial impact. A number of techniques to treat, prevent and even detect an anastomotic leakage are under investigation. However, studies show that these techniques are not always able to prevent an anastomotic leak from occurring. This paper discusses the monitoring of leakage through differently sized and differently positioned leak holes in phantom colons, using physical experiments and a Computational Fluid Dynamics package called FloWorks. © 2011 Taylor & Francis Group.

Time scale analysis for fluidizedbedmeltgranulation-II: binder spreading rate

The spreading time of liquid binder droplet on the surface a primary particle is analyzed for Fluidized Bed Melt Granulation (FBMG). As discussed in the first paper of this series (Chua et al., in press) the droplet spreading rate has been identified as one of the important parameters affecting the probability of particles aggregation in FBMG. In this paper, the binder droplet spreading time has been estimated using Computational Fluid Dynamic modeling (CFD) based on Volume of Fluid approach (VOF). A simplified analytical solution has been developed and tested to explore its validity for predicting the spreading time. For the purpose of models validation, the droplet spreading evolution was recorded using a high speed video camera. Based on the validated model, a generalized correlative equation for binder spreading time is proposed. For the operating conditions considered here, the spreading time for Polyethylene Glycol (PEG1500) binder was found to fall within the range of 10-2 to 10-5 s. The study also included a number of other common binders used in FBMG. The results obtained here will be further used in paper III, where the binder solidification rate is discussed.

Pattern competition in homogeneously heated fluid layers

Simulations examining pattern competition have been performed on a horizontal homogeneously heated layer that is bounded by an isothermal plane above an adiabatic plane. Several different circulation patterns arose as the heating regime applied to the horizontal layer was modified. The sequence of the patterns formed as the Grashof number was increased had the following order: laminar layer, rolls, squares, hexagons and pentagons, and then two square modes of differing orientations. Fourier analysis was used to determine how the key modes interact with each pattern.