Small Hole Patterns Research Articles

Impact of H2-enriched natural gas on pollutant emissions from domestic condensing boilers: numerical simulations of the combustion chamber

The addition of green hydrogen to the gas mixture feeding domestic boilers may help the ecological transition of the residential sector. However, there are concerns about the combustion process as hydrogen shows power density and reactivity that are much different than those of natural gas. In this work, we perform three-dimensional simulations with detailed kinetics to describe and comprehend the combustion process in a real modern boiler, equipped with a perforated premixed burner (presenting a pattern of small holes and slits), with the purpose also to evaluate the impact of green hydrogen. The flame structure is complex and characterized by the interaction of flames exiting from neighbor holes and slits; these flames may merge and lead to very intense flames, especially at high flow rates. The presence of a flow distributor, upstream of the burner, induces different velocities at the holes and slits, ultimately affecting the morphology, propagation and interactions of the flames. This behavior is observed for all investigated H2 concentrations, i.e., up to 50% by vol. The model is validated against available measurements of carbon monoxide and nitric oxides in flue gases, which both indicate very satisfactory predictions. More specifically, the addition of green H2 has a beneficial effect on both CO and NO emissions. More specifically the CO emissions at the nominal power are observed to diminish from 154 to 18 ppm when shifting from 0 to 50% H2 in the fuel mixture, while NO emissions decrease from 20 to only 5 ppm. This latter reduction is a surprising and encouraging result; the reason is due to the fact that the addition of hydrogen in the fuel mixture leads naturally to more dilute operating conditions in a condensing boiler. We believe that the proposed model represents a valid tool to explore strategies to improve the combustion process with alternative fuels.

Numerical Analysis and Modelling of Heat Transfer Processes through Perforated Clay Brick Masonry Walls

The aim of this study is to analyse the thermal behaviour of walls corresponding to perforated clay brick masonry layers. The complexity of this work relies on the effect of all heat transfer mechanisms simultaneously; therefore, apart from conduction through the solid material, the propagation of heat depends on convection and radiation mechanisms in the region of the air cavities (pattern of small holes). Evidently, the geometry of perforated bricks and mortar joints of the brickwork, as well as the thermophysical properties of building materials, can modify significantly the evolution of the heat wave under specific boundary conditions at both external/internal sides of the examined layer (ambience). Furthermore, the dynamics of the actual heat flow are affected by the values of thermal-emissivity at the exposed surfaces of the brick holes. In this study, several of these issues are analysed in order to expose their influence on the thermal response of perforated clay brick masonry walls. The transient thermal analysis was carried out by employing the finite element method and by adopting a well-known CFD program focused on heat transfer processes. Secondly, the investigation has been extended to determine the corresponding thermophysical properties of an analogous solid layer (same thickness) that can produce an equivalent heat wave excitation at its interior surface. The resulting values can be useful to promote the building design and diminish the uncertainties regarding the heat flows through building envelopes; besides, assessing precisely the thermal behaviour of building configurations is essential, since the calculation of energy requirements through buildings has become of increasing importance lately.

Deployment and evaluation of a dual-sensor autofocusing method for on-machine measurement of patterns of small holes on freeform surfaces.

This paper presents and evaluates an active dual-sensor autofocusing system that combines an optical vision sensor and a tactile probe for autofocusing on arrays of small holes on freeform surfaces. The system has been tested on a two-axis test rig and then integrated onto a three-axis computer numerical control (CNC) milling machine, where the aim is to rapidly and controllably measure the hole position errors while the part is still on the machine. The principle of operation is for the tactile probe to locate the nominal positions of holes, and the optical vision sensor follows to focus and capture the images of the holes. The images are then processed to provide hole position measurement. In this paper, the autofocusing deviations are analyzed. First, the deviations caused by the geometric errors of the axes on which the dual-sensor unit is deployed are estimated to be 11 μm when deployed on a test rig and 7 μm on the CNC machine tool. Subsequently, the autofocusing deviations caused by the interaction of the tactile probe, surface, and small hole are mathematically analyzed and evaluated. The deviations are a result of the tactile probe radius, the curvatures at the positions where small holes are drilled on the freeform surface, and the effect of the position error of the hole on focusing. An example case study is provided for the measurement of a pattern of small holes on an elliptical cylinder on the two machines. The absolute sum of the autofocusing deviations is 118 μm on the test rig and 144 μm on the machine tool. This is much less than the 500 μm depth of field of the optical microscope. Therefore, the method is capable of capturing a group of clear images of the small holes on this workpiece for either implementation.

Preparation of Ge-doped SbTe Material Thin Film for Phase Change Random Access Memory by Magnetron Sputtering on Small Hole Patterns

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Further developments and beam tests of the gas electron multiplier (GEM)

We describe the development and operation of the Gas Electron Multiplier (GEM), a thin insulating foil metal-clad on both sides and perforated by a regular pattern of small holes. The mesh can be incorporated into the gas volume of an active detector to provide a first amplification channel for electrons, or used as stand alone. We report on the basic properties of GEMs manufactured with different geometries and operated in several gas mixtures as well as on their long-term stability after accumulation of charge equivalent to several years of operation in high-luminosity experiments. Optimized GEMs reach gains close to 10 000 at safe operating voltages, permitting the detection of ionizing tracks, without other amplifying elements, on a simple Printed Circuit Board (PCB), opening new possibilities for detector design.

0.2 µm Hole Pattern Generation by Critical Dimension Biassing Using Resin Overcoat

A method of generating very small hole patterns by introduction of transfer bias into a resist pattern after original resist pattern generation has been developed and evaluated. Introduction of transfer bias was carried out using a resin overcoating and strippig process and a novolak resist pattern was used as the original hole pattern. The overcoating resin used was polymethylmethacrylate (PMMA) and transfer bias was introduced by intermixing of novolak resin and PMMA during the PMMA baking step. From scanning electron microscope (SEM) observation, it appeared that 0.20 µ m hole pattern generation was possible by i-line lithography. The amount of undersize was controllable by PMMA bake temperature, and 0.06-0.15 µ m undersize could be achieved by using a bake temperature range of 60-120° C. From results of etching SiO2 substrate using overcoat treated hole pattern, it appeared that the mixinglayer functioned as an etching mask for oxide film.