Rowan Deam

On Scaling Down Turbines to Millimeter Size

This article discusses how to achieve maximum theoretical effectiveness when using a viscous flow turbine such as Tesla turbine.

Methane reformation using plasma : an initial study

An initial study of the reformation of methane using a microwave induced plasma and quench has been carried out. Methane/argon mixtures at atmospheric pressure were treated experimentally. The study encompasses both experiments and modelling, to measure and predict the maximum throughput and final product mix from the reactor. Both experiments showed and theory predicted that the most important gas phase product was acetylene; however soot formation was significant. The modelling comprised both equilibrium thermodynamic and kinetic modelling. The equilibrium modelling was used to predict the throughput of the plasma reactor, because at the plasma temperature, achieved by microwaves at atmospheric pressure, equilibrium was achieved well before the plasma had time to flow through the plasma generating region of the reactor. Chemical kinetic modelling was used to predict the final products emerging from the quench and indicated that for the quench rates used in practice (about 10 000 K s−1), gas phase reactions are too slow to reach equilibrium below about 2000 K.

Mixing of liquids using obstacles in microchannels

In general, the Reynolds number is low in microfluidic channels. This means that the viscous force plays a dominant role. As a result, the flow is most likely to be laminar under normal conditions, especially for liquids. Therefore, diffusion, rather than turbulence affects the mixing. In this work, the commercial computational fluid dynamics tool for microfluidics, known as FlumeCAD, is used to study the mixing of two liquids in a Y channel and the results are presented. To improve mixing, obstacles have been placed in the channel to try to disrupt flow and reduce the lamella width. Ideally, properly designed geometric parameters, such as layout and number of obstacles, improve the mixing performance without sacrificing the pressure drop too much. In addition, various liquid properties, such as viscosity, diffusion constant, are also evaluated for their effect on mixing. The results indicate that layout of the obstacle has more effect on the mixing than the number of the obstacles. Placing obstacles or textures in the microchannels is a novel method for mixing in microfluidic devices, and the results can provide useful information in the design of these devices.

Plasma abatement of air contaminated with trichloroethene degreasing agent

Trichloroethene (TCE) is one of the volatile chlorinated hydrocarbons allowed in industrial use. TCE emissions are restricted and future regulation may require more stringent abatement of TCE discharges to air. This paper examines the environmental performance of an atmospheric pressure microwave plasma and a gas burner to treat air contaminated with TCE that is presently discharged to atmosphere. The performance of both is measured and modelled. The merits of microwave plasma verses non-thermal plasma for pollution abatement are considered, as well as the need for an increased understanding of the measures used to determine the efficiency of non-thermal plasma abatement techniques.

Investigation of capillary waves excited by a Nd : YAG laser using pyrometry

A mechanism for excitation of capillary waves on a weldpool formed by a laser is shown to be due to coupling of the weldpool height with the laser beam profile. This leads to an additional low frequency mode, which has been observed and has a frequency of about an order of magnitude lower than the classically expected capillary waves. This mechanism for wave excitation on the weldpool can only happen if the focal point of the laser beam is located above the surface of the weldpool; otherwise the waves are damped.

A Review of the Variable Frequency Microwave Technology in Material Processing

The Variable Frequency Microwave (VFM) processing technology is an emerging technique that foregoes many of the inherent problems obtained in fixed-frequency microwave processing. By sweeping through a bandwidth of frequencies, a time-averaged uniformity is obtained which can eliminate heating non-uniformities as well as catastrophic thermal excursions sometimes experienced in conventional microwave technology Primarily aimed at processing advanced materials, advantages include uniform heating, arc-free processing, a higher degree of controllability, higher coupling efficiency and the ability to choose “specific” frequency or frequency bands suitable for particular applications. The review within provides an overview of the theory behind the technique as well as an outline of the advances regarding this method in both the academic and industrial stage. Current and future applications using this emerging technology as well as numerical modeling are also discussed.

Digital universal warming

Eagerly looking forward to digital broadcasting being adopted in Australia, I rushed down to Dick Smiths – the Australian electronics chain – and bought a set-top digital box for a mere AUS

Nanometer resolution excimer laser ablat ion of thin polymer films

100 (about £40). I plugged it in and it tuned itself automatically to all the available digital radio and TV channels. So far, so good: I immediately benefited from superb picture quality and the bonus of digital-only programmes.

A correlation for predicting the kerf profile from abrasive water jet cutting

An attractive aspect of excimer laser ablation of polymers is the ability to precisely control the depth to which material is removed by controlling the number of laser pulses. Recent work by the authors has shown that greater control of layer thickness (nanometer resolution) can be achieved when ablating sub-micron thick layers of polymers. This effect of improved depth control is presented for 1 µm thick SU-8 photoresist, and n-heptylamine plasma polymers (HAPP). The ablation process of HAPP shows such control that 90nm thick films were ablated to leave a uniform film of 1.5 nm thickness on a silicon wafer substrate. In both cases the minimum feature size reliably resolved was 2 µm in width. The threshold of ablation for SU-8 and HAPP occur at 50mJ/cm2 and approximately 100mJ/cm2 respectively.A model is also presented, which shows that the observed reduction in etch rate that occurs as the polymer film thickness decreases is a result of the thermal properties of the substrate material.An attractive aspect of excimer laser ablation of polymers is the ability to precisely control the depth to which material is removed by controlling the number of laser pulses. Recent work by the authors has shown that greater control of layer thickness (nanometer resolution) can be achieved when ablating sub-micron thick layers of polymers. This effect of improved depth control is presented for 1 µm thick SU-8 photoresist, and n-heptylamine plasma polymers (HAPP). The ablation process of HAPP shows such control that 90nm thick films were ablated to leave a uniform film of 1.5 nm thickness on a silicon wafer substrate. In both cases the minimum feature size reliably resolved was 2 µm in width. The threshold of ablation for SU-8 and HAPP occur at 50mJ/cm2 and approximately 100mJ/cm2 respectively.A model is also presented, which shows that the observed reduction in etch rate that occurs as the polymer film thickness decreases is a result of the thermal properties of the substrate material.