CUTTING IMPROVEMENTS BY ADDING DILATANTS FLUID
Effect of addition of viscoelastic additive on the stability and precision enhancement of the abrasive waterjet is studied. Cornstarch is chosen to be added to the mixture of water and abrasive for it is readily available in large quantities at low cost. Yet it shows major nonlinear properties valuable for waterjet machining. It is shown that the normal stresses developed in the nonlinear viscoelastic cornstarch remain substantially unchanged throughout effective jet length resulting in an almost completely prismatic jet, most desirable for precision and straight machining. Furthermore, the jet becomes more stable upon increasing the cornstarch percentage. The additive also causes the jet to produce less friction with the surrounding air avoiding possible jet disintegration. Clearly, due to the increase of elastic as well as viscous effects, there is restriction to the pump delivery upon adding the dilatant cornstarch. Different percentages of the additive are therefore examined. It is found that, a 22% additive results in the best performance based on the precision, available pump power and stability of the jet. The experiment was carried out on three products; marble, aluminum and glass. In all cases, kerf angle was reduced significantly. Simulation of the problem is in good agreement with the experimental observations.
Review of stability of liquid jets and the influence of nozzle design
Abstract An attempt has been made to form a qualitative correlation between the nozzle shape and issuing jet shape. The following points can be made: 1. (i) The major requirement of a nozzle is the efficient conversion of potential energy to kinetic energy. This is best achieved by a sudden, smooth contraction of the flow area from the supply line to the desired nozzle diameter. 2. (ii) The question of the angle of convergence appears uncertain. There would seem to be an optimum somewhere between 15° and 100°. It is possible that this optimum value might be a function of system dynamics and fluid properties. 3. (iii) The nozzle aspect ratio L/d has a highly significant effect on the initial jet velocity profile and subsequent jet surface shape up to L/d values where the shear stress and static pressure gradient are fully developed. In fact, the variability of L/d offers a means of control of the jet surface roughness over a considerable range. 4. (iv) There is some evidence favouring the rounding and polishing of the nozzle internal surfaces in order to achieve maximum performance. 5. (v) The theoretical hydrodynamic approach, involving numerical methods, should provide reasonable plug flow nozzles for systems where the liquid viscosity is low, viz. “water-like”.
Numerical tools applied to power reactor noise analysis
In order to be able to calculate the space- and frequency-dependent neutron noise in real inhomogeneous systems in two-group theory, a code was developed for the calculation of the Green's function (dynamic transfer function) of such systems. This paper reports on the development as well as the test and application of the numerical tools employed. The code that was developed yields the space-dependence of the fluctuations of the neutron flux induced by fluctuating properties of the medium in the two-group diffusion approximation and in a two-dimensional representation of heterogeneous systems, for both critical systems and non-critical systems with an external source. Some applications of these tools to power reactor noise analysis are then described, including the unfolding of the parameters of the noise source from the induced neutron noise, measured at a few discrete locations throughout the core. Other concrete applications concern the study of the space-dependence of the Decay Ratio in Boiling Water Reactors, the noise-based estimation of the Moderator Temperature Coefficient of reactivity in Pressurized Water Reactors, the modeling of the beam- and shell-mode core-barrel vibrations in Pressurized Water Reactors, and the investigation of the validity of the point-kinetic approximation in subcritical systems driven by an external source. In most of these applications, calculations performed using the code are compared with at-power plant measurements. Power reactor noise analysis applications of the above type, i.e. core monitoring without disturbing plant operation, is of particular interest in the framework of the extensive program of power uprates worldwide.