<p> The homogeneous partial oxidation of ortho-xylene vapour by air in a 316 s.s. flow reactor was studied in this work, which was conducted in connection with, and preceding an investigation of the kinetics of catalytic vapour-phase partial oxidation of a-xylene. The main purpose of the present work was to make an exploratory study of the contribution of the homogeneous reaction, if any, in as much as it would affect the catalytic oxidation to be studied on the same experimental set-up. This would permit the correction for the rate of homogeneous reaction during the catalytic reaction under a range of experimental conditions, or, reveal conditions under which the catalytic reaction could be conducted with minimum contribution by the homogeneous reaction. </p> <p> The three variables studied and the range of conditions for each are as follows : 1. Air: o-xylene molar ratio: ,124 to J78 2. Residence time: 0.443 sec. to 0.539 sec. 3. Temperature: 430° C to 490° c </p> <p>The reaction product stream was analyzed mainly by Gas Chromatography, both qualitatively and quantitatively. Qualitative analyses of liquid samples of the reactor condensate were also conducted using a Nuclear Magnetic Resonance Spectrometer, Mass Spectrometer, Infrared Spectrophotometer and also by conventional chemical techniques. </p> <p> Product analysis indicated a-xylene oxide as the reaction product at the lmv conversions studied. An empirical correlation obtained by statistical analysis of the experimental data, relating the conversions obtained and the variables studied, has been proposed to calculate the extent of the homogeneous reaction under the conditions of a catalytic reaction study. The results obtained in this work are consistent with the suggested kinetics and mechanism for this reaction. </p> / Thesis / Master of Engineering (MEngr)

<p> The radiation balance at a ship station in the eastern tropical Atlantic Ocean is calculated using a term-by-term approach. Irradiances are calculated using upper air data from four daily radiosonde ascents and hourly surface weather observations made at the Canadian vessel 'Quadra' during GATE Phase 1 (June- July, 1974).</p> <p> Global irradiance is calculated by a cloud layer model similar to that used by Davies et al in Southern Ontario, Canada. The model considers first, cloudless sky attenuation of solar irradiance by water vapour, ozone and Rayleigh scattering. Second, cloud effects are added by considering contributions from three cloud layers - high, middle and low and secondary radiation from cloud base of reflected surface radiation. Reflected solar irradiance is calculated using a mean sea-surface albedo of 6% suggested by Payne for that part of the Atlantic Ocean.</p> <p> Estimates of incoming longwave irradiance are made first, from a numerical flux emissivity model which uses radiosonde ascent data and cloud amount at three heights and second, from a simple model which uses surface temperature and total cloud amount.</p> <p> Outgoing longwave emittance is evaluated using surface temperature and an emissivity of 0.98. The radiation balance is then obtained as the algebraic sum of the four components.</p> <p> The estimated values are compared with values measured at 'Quadra'. In 70% of the cases, calculated and measured solar irradiance agree to within 20%. Model performance for cloud amount > 5/10 is least satisfactory.</p> <p> In all cases, model and measured values of daily incoming longwave irradiance agree to within 5%. In 60% of the cases, measured and calculated radiation balance agree to within 20%.</p> / Thesis / Master of Science (MSc)

No abstract provided. / Thesis / Master of Engineering (MEngr)

Yes / The major concern of the physical and chemical instability of effervescent products during manufacturing and storage is addressed through a co-crystallization strategy. Citric acid (CA) and sodium bicarbonate (SBC) are the essential components of effervescent products. CA is hygroscopic and led to an uncontrollable autocatalytic chain reaction with SBC in the presence of a small amount of moisture, causing product instability. The acid···amide dimer bond and layered structure of the citric acid-nicotinamide co-crystal restricts interaction of moisture with CA, making it nonhygroscopic, and improves the stability of effervescent products. The comparative study of effervescent products containing CA in its free form and as a co-crystal suggests a significant advantage of the use of co-crystal in effervescent products. This finding is supported by the mechanistic understanding developed through GAB and Y&N models obtained from moisture sorption data along with the computational investigations into moisture interactions with different crystal surfaces.

Yes / A simulation was conducted using Aspen HYSYS® software for an industrial scale condensate stabilization unit and the results of the product composition from the simulation were compared with the plant data. The results were also compared to the results obtained using PRO/II software. It was found that the simulation is closely matched with the plant data and in particular for medium range hydrocarbons. The effects of four process conditions, i.e. feed flow rate, temperature, pressure and reboiler temperature on the product Reid Vapour Pressure (RVP) and sulphur content were also studied. The operating conditions which gave rise to the production of off-specification condensate were found. It was found that at a column pressure of 8.5 barg and reboiler temperature of 180°C, the condensate is successfully stabilised to a RVP of 60.6 kPa (8.78 psia). It is also found that as compared to the other parameters the reboiler temperature is the most influential parameter control the product properties. Among the all sulphur contents in the feed, nP-Mercaptan played a dominant role for the finishing product in terms of sulphur contents.

Yes / In this paper, local meteorological data for a period of 35 years (from 1979 to 2013) from Kuujuaq station have been used to calculate the surface refractivity, N and to estimate the vertical refractivity gradient, dN1, in the lowest atmospheric layer above the ground. Monthly and yearly variations of the mean of N and dN1 are provided. The values obtained are compared with the corresponding values from the ITU maps. The long-term trend of the surface refractivity is also investigated. The data demonstrate that the indices N and dN1 are subject to an evolution which may have significance in the context of climate change (CC). Monthly means of N show an increasing departure from ITU-R values since 1990. Yearly mean values of the dN1 show a progressive decrease over the period of study. Seasonal means of dN1 show a decrease over time, especially for summer. Such a trend may increase the occurrence of super-refraction. However, currently available ITU-R recommendations for microwave link design assume a stationary climate, so there is a need for a new modelling approach.

Copper vapour laser (CVL) pumped high repetition rate narrow bandwidth dye laser is an important source of tunable radiation. It finds numerous applications in spectroscopic investigations and selective material processing like atomic vapour laser isotope separation (AVLIS). Being wavelength selective in these applications stability of the output wavelength and bandwidth are extremely important. The stability of these parameters depend upon the refractive index fluctuation of the dye medium, due to pump beam induced temperature gradients, dye solution flow, and mechanical stability of optical components. Precise measurement of wavelength and bandwidth of a dye laser and control over parameters governing the variations are important for any stable dye laser system. In this thesis, details of investigations carried out on a Rhodamine 6G dye laser for obtaining stable wavelength and output power are presented. Parameters that affect the stability were identified, monitored and put on close loop control to achieve the desired stability. Pump beam i.e. CVL optical power, dye flow rate and dye solution temperature are mainly these parameters. CVL power is mainly a function of input electrical power and pressure of the buffer gas inside the tube. To monitor and regulate these parameters, different sensors and actuators were selected and interfaced with a master slave topology based data acquisition and control system. The DAQ and control system is designed around a micro controller card based on advanced CPU P80552 and has on chip 8 channel 10 bit multiplexed analog input, 16 TTL digital inputs and 16 digital outputs. It works as slave and PC as master. Following closed loops were designed and incorporated to maintain a stable output: a. Average output of CVL was maintained constant by regulating the electric input power through closed loop control. b. The buffer gas pressure was monitored with a semiconductor pressure sensor and was regulated using pulse width modulation. c. Temperature of the dye solution was monitored with PT100 and was controlled using proportional controller. d. Flow rate of dye solution was controlled using a variable frequency drive (VFD) for the dye circulation pump. e. The dye laser wavelength was monitored by using a high resolution spectrograph and pixel position of the peak from CCD image obtained from spectrograph is used for feedback correction using a pico motor. In the present work with application of the above-mentioned input power and pressure loops, a stable output of CVL, is achieved. Variations in power and pulse width of CVL are got limited to within 2%, from 10% when CVL system was working unregulated. This control system does the line regulations and corrects the input electrical power if variations in discharge current occur due to pressure variation. Every dye cell has limits on flow rate because of its geometry. With flow and temperature control dye cell was characterized to work with lower linewidth. VFD (variable frequency drive) is used for flow regulation. Finally active control on set wavelength was also achieved with resolution of 0.01nm accuracy. Measurement of wavelength was done with 0.3 m, 0.054 nm resolution spectrograph. Closed loop pico motor with 30 nm per step linear resolution was used for wavelength control. The thesis is organized in four chapters. First chapter presents a brief introduction to high repetition rate CVL pumped dye laser, operation of a CVL and parameters affecting the dye laser stability and their control schemes. Literature survey in this chapter is focused on different control mechanisms used with such lasers. Second chapter describes the laser system and interfacing of data acquisition system used for experimental setup. Closed loop controls for different parameters are described in this chapter. It also describes the software algorithms developed for this work. Third chapter presents experimental results and analysis with discussion on performance of the control loops. Finally the conclusion is given and few suggestions are made for further work.

Please read the abstract in the section, 00front of this document / Dissertation (MEng (Environmental Engineering))--University of Pretoria, 2008. / Chemical Engineering / MEng / Unrestricted

Increase in demand for uniform ceramic coatings on larger industrial components have led to a need for a PP-MOCVD coating system scale up. The objective of this thesis is to develop a fully functional coating system operating in the PP-MOCVD regime that is able to deposit thin film ceramic coatings on commercial or industrial components with complex 3D geometries. This can be achieved by applying engineering and vacuum science theories, coupled with the established fundamentals of PP-MOCVD. A larger system was designed and assembled around the boundaries set by the dimensions and geometry of a stainless steel water pump impellor acting as the base substrate. Most of the components were sourced off the shelf from vacuum and fluid specialists. Components which were unavailable for various reasons were designed, and machined in-house by the departmental workshop. Initial test depositions were conducted using small stainless steel disk substrates, heated using a resistive heater similar to the one utilised on the research scale system. The test depositions were performed with the heater and substrate combination placed in strategic locations. This is to test the overall uniformity of precursor flux in the chamber volume. The resulting coating uniformity on the disk surfaces were fair but problems such as the large collection of unreacted precursor on the chamber viewport and valve timing issues had to be addressed. Before making any improvements to the system, each of the process areas leading to a successful deposition needed to be understood. Five process areas were developed: ‘Liquid Delivery’, ‘Atomization’, ‘Evaporation’, ‘Transport and Reactor Geometry’, and ‘Droplet Management’. Each of the process areas were analysed individually and changes were made to push for a maximum evaporation efficiency. xviii The improved system provided opportunities to perform depositions that were once not possible for PP-MOCVD. Two sets of deposition tests were designed and conducted. Firstly, the improvements were justified with a series of depositions using flat stainless steel plates with dimensions 65x65x5mm. The other set of 3D case study depositions involve observing the effects of the operational parameters of PP-MOCVD on the uniformity and penetration depths of the coatings into different sized macro blind trenches. Five geometric setup conditions were used to justify the improvements made to the system. These are: ‘Substrate positioned in the direct line of spray’, ‘Use of an unheated receptor’, ‘Use of a heated receptor’, ‘Use of an unheated receptor with a non-axial substrate setup’, and “Choked Flow’. As expected, the uniformity of the coatings on both sides of the plate varied significantly when the substrate is placed over the line of sight of the precursor spray. Similarly, the coating produced under the induced choked flow condition resulted in low conformality. The introduction of an unheated receptor plate resulted in an increase in uniformity on both sides of the plate. Further prove that PP-MOCVD is geometry independent is provided by the deposition made with the non-axial substrate placement resulting in a coating of similar result to the unheated receptor. The use of a heated receptor provided a source for a secondary evaporation of the larger precursor droplets collected resulting in an increase in coating thickness while maintaining good conformality. The effects of temperature, pressure, injection volume, and concentration were explored in the final case study. With maximum depths of 50mm, the macro blind trenches has an aspect ratio of 1:1 and cross-sectional areas of 3x3mm, 9x9mm, and 15x15mm. The final results show that as the temperature rises, the depth penetrated into the trench decreases. This could be due to the change in rate limiting steps as homogeneous reactions begin to increase at higher temperatures. Similar trends were observed with increasing pressure. As the pressure difference between the volume of the trenches and the rest of the chamber decreases, the push needed to xix force the precursor down the trench also decreases, resulting in less depth penetration. The effects of injection volume and concentration observed, can be explained by how much precursor molecules are present during one pulse cycle. The more that is available at any given time, the more likely a reaction will occur and deeper the penetration will get. Of course a ceiling or a limit exists where the molecules in the chamber will get evacuated without being reacted. The future work made possible as a result of the scaled up system are proposed. These include a scale up of the operational parameters to suit any given substrate geometry, improvements to the heating source to achieve greater thermal uniformity, further improvements to the overall system accessibility, and performing other depositions using different substrate materials and precursor types.

Växthus används för att ge ett bättre odlingsklimat åt grödor och växter. För ytterligare förbättring av förhållandena används växthusvävar som exempelvis kan reglera temperatur, fuktighet och ljustillförsel. Väven som behandlas i denna rapport är en så kallad energiväv som främst har till uppgift att minska energiåtgången vid uppvärmning.När väven är fördragen nattetid, ökar luftfuktigheten då grödorna avger fukt dygnet runt. Fukten kan kondenseras mot energiväven, vilket gör att det bildas droppar på väven som kan falla ned på växtligheten. Den höga luftfuktigheten kan medföra svampsjukdomar och i övrigt också bidra till att tillväxten avstannar. Ludvig Svensson AB i Kinna som tillverkar växthusvävar vill undersöka hur struktur och materialval påverkar energivävens fuktgenomsläpplighet. Detta skall göras genom framtagning av ett antal olika provmaterial, där modifieringar av energiväven görs. Provmaterialens fukttransmission mäts med fyra metoder, saltmetoden (EN ISO 15 496:2004), kanadensiska burkmetoden (CAN2-4.2-metod 49:1977), hudmodellen (ISO 11 092:1993 (E)) och Permatran-W som baseras på ASTM E96/E96M-05. De två förstnämnda metoderna utfördes på Swerea IVF AB i Mölndal. Ett antal förändringar gjordes på väven, däribland byte av material, ändring av masklängd och bindningstyp. Resultaten visade att en modifiering av plastsorten i väven gav störst förändring av fuktgenomsläppligheten. De flesta provmaterialen påvisade en mindre fukttransmission än hos den ursprungliga energiväven, dessa värden kan i sig ge användbar data inför framtida produktutveckling. / <p>Greenhouses are used for the improvement of the cultivation climate for crops and plants. For further improvement of the environment, climate screens can be used, they control for example the temperature, humidity and brightness. The screen which is treated in this report is an energy saving screen that lowers the energy consumption.</p><p></p><p>When the greenhouse is covered at night, the humidity increases, since the crops transpire round the clock. The moisture can condense on the cold screen which contributes to the forming of drops that fall down on the vegetation. This effect and the high humidity level in the greenhouse could lead to fungus disease and a decrease in the growth of the cultivation.</p><p></p><p>Ludvig Svensson AB in Kinna who produces different climate screens, would like to investigate how structure and choice of material affects the energy saving screens water vapour transmission. This should be done by modifying the existing climate screen. The modified materials will be tested with four water vapour transmission methods, ISO 15496:2004, the cup method (CAN2-4.2-method 49:1977), the sweating hotplate method (ISO 11092:1993 (E)) and Permatran-W (based on ASTM - E 96/E 96M -05). The first two methods will be executed at Swerea IVF in Mölndal.</p><p></p><p>A few changes were made on the original screen, for example an exchange of materials, a change of looplenght and a change of binding. The results showed that a modification of the plastic band in the screen gave the largest vapour transmission. The most of the modified materials showed a lower humidity transport then the now existing screen. The given results can still offer useful information for future product development.</p><p>Program: Textilingenjörsutbildningen</p>