Circumferential Overlap Research Articles

Investigation into the effect of overlap factors and process parameters on surface roughness and machined depth during micro-turning process with Nd:YAG laser

Abstract One of the emerging laser material processing technologies to process cylindrical shaped materials is the laser micro-turning process. This process is used to machine micro-turned groove or surface on the difficult-to-process materials for a specific length of turn along its axis. The present experimental study investigates the laser micro-turning operation of a cylindrical shaped aluminum oxide (Al2O3) ceramic to explore the effect of successive spot overlap and circumferential overlap on the surface roughness (Ra) criterion. Moreover, depth of machining has also been studied by varying various process parameters such as pulse frequency, workpiece rotating speed and laser beam average power. Various amounts of spot overlap have been accomplished by different combined settings of related parameters i.e. workpiece rotating speed and pulse frequency. In contrast, various circumferential overlap between successive rotational scan widths have been achieved by varying the rotational speed and also axial feed rate of the workpiece. Surface roughness (Ra) and machined depth have been measured as output response for machining at various parametric combinations. Analyses have been made through different plots of surface roughness (Ra) and machined depth to study the influence of these overlaps and different process parameters. The experimental results revealed that surface roughness decreases with the increase of both the overlap factors. It is observed from the results that with the increase in circumferential overlap, roughness of the machined surface decreases for each workpiece rotating speed setting. Further, wide spot crater is achieved at a higher value of average power. Minimum surface roughness is achieved as 5.25 µm at average power 10 W, pulse frequency 3000 Hz, workpiece rotating speed 400 rpm and Y feed rate 0.3 mm/s. The achieved machined depth is high at a low speed of rotation and pulse frequency settings. With the increase of average power of laser beam, the machined depth is found to increase linearly. The maximum micro-turning depth is achieved as 0.146 mm at parametric combination of average power of 10 W, pulse frequency of 3000 Hz, workpiece rotating speed of 400 rpm and Y feed rate of 0.3 mm/s.

Numerical Investigation on Circumferential Overlap Trisection Helical Baffle Heat Exchanger

The circumferential overlap trisection helical baffle shell-and-tube heat exchanger (cothSTHX) is a modification one based on the quadrant helical baffle one to improve the heat transfer performance. The model of cothSTHX has 34 tubes and 3 rods with tube layout of equilateral triangle and a baffle inclined angle of 20°, and the numerical simulation of flow and thermal performances was conducted using the commercial CFD software FLUENT. The distributions of temperature, pressure and velocity, and temperature, pressure or velocity nephograms with superimposed velocity vectors for special slices can provide access to important implicit information in the simulation results. The Dean vortex secondary flow, which is one of the key mechanisms of enhancing heat transfer in heat exchangers, is clearly depicted, and it shows that the fluid in spiral channel flows outward under the centrifugal force, then flows back to the axis under radial differential pressure, thus a single vortex is formed in each baffle pitch cycle. The unfolded concentric hexagonal slices are designed to make up for the defect that the shortcut leakage flow in the V-notch zone of the adjacent baffles could not be depicted along the longitudinal slices. Moreover, the shortcut leakage flow is restricted with the damper effect of the structure that a row of tubes in the circumferential overlap area of adjacent baffles.

Numerical simulation on flow field in circumferential overlap trisection helical baffle heat exchanger

A novel helical heat exchanger structure consisting of circumferential-overlap trisection helical baffle shell-and-tube heat exchangers (cothSTHXs) is proposed as a means of overcoming the limitations imposed by non-uniformity of the quadrant baffle sectors with natural intervals used in helical baffle heat exchangers with equilateral triangle tube layouts. The cothSTHXs also exhibit anti-shortcut protection by using one row of tubes in each gap between adjacent circumferential overlap baffles to damp the shortcut leakage. A numerical model was used to determine the flow field in a cothSTHX of the same geometric size as the test exchanger. A figure showing the pressure nephogram with superimposed velocity vectors is presented. The Dean vortex secondary flow field, which is one of the key mechanisms of enhancing heat transfer in heat exchangers, is clearly depicted. The unfolded concentric hexagonal section charts demonstrate that the shortcut leakage flow is restricted and that the flow pattern in the cothSTHX is very nearly “plug flow”.

Open, Intraperitoneal, Ventral Hernia Repair

Recent literature suggests that laparoscopic repair of ventral hernias may have very low recurrence rates. However, laparoscopy may not be feasible in certain situations. We describe an open technique that uses the tension-free retrofascial principles of laparoscopic repair without the need for subcutaneous flaps. Through an incision in the hernia, the peritoneum is entered and adhesions are taken down. A piece of DualMesh (W.L. Gore & Associates, Inc, Newark, Del) is trimmed to fit with a 5-cm circumferential overlap. A vertical incision is made in the mid portion of the mesh. The mesh is fixed in an intraperitoneal retrofascial position using GORE-TEX sutures (W.L. Gore & Associates, Inc). The sutures are brought through the abdominal wall using a laparoscopic suture passer and tied into place on one side of the mesh. That side is then tacked to the posterior fascia with a spiral tacking device. The other side is sutured into place in a similar fashion and then tacked to the fascia by passing the spiral tacking device through the incision in the mesh. The mesh incision is closed with a running GORE-TEX suture. The overlying tissues are closed in layers.

Dynamic changes of the microtubule system corresponding to the unequal and spiral cleavage modes in the embryo of the zebra mussel, Dreissena polymorpha (Mollusca, Bivalvia).

Unequal cleavage requires a highly organised cytoskeleton. We investigated the localisation of both tubulins and microtubular arrays in Dreissena eggs during and after fertilisation using confocal laser scanning microscopy. Freshly spawned eggs are arrested in metaphase I. A maternal pool of gamma-tubulin is found mainly in the centre of the asters of the meiotic spindle. The paternal pool of gamma-tubulin, present in the fertilising sperm, could not be traced within the egg, but a microtubule-organising centre forms near the male pronucleus at anaphase II. Male and female pronuclei grow as they migrate in the wake of their aster and rendezvous. First cleavage is unequal and starts without pronuclear fusion. At metaphase the two equal-sized asters span the entire egg in a symmetrical arrangement. At late metaphase the spindle shifts along its longitudinal axis into an eccentric position and the peripheral aster takes on an umbrella-like appearance, whereas the central aster remains spherical. The cleavage furrow becomes determined in the circumferential overlap of the asters. The inequality at second cleavage, however, is due to the unequal size of the asters. The third cleavage spindle also has asymmetrical asters and spindle shift was only observed in the D-cell. The spiral character is a result of an asymmetrical organisation of the larger, vegetal aster. Our results show that the arrangement of the gamma-tubulin clusters and of microtubules changes and develops during early development of Dreissena in a way that can explain the axis-generating asymmetries in cell pattern and the spiral sense of cleavage. The major cytological characters expected to direct pattern formation in this phase of development are: size, position, and symmetry or asymmetry of both spindle and asters.