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Reaction calorimetry applied to kinetic problems. The design and construction of an isothermal calorimeter with heat compensation by the Peltier effect, and the application of the calorimeter in the study of reaction kinetics in solvent/water mixtures.
No full textAn isothermal calorimeter controlled by the
Peltier effect has been designed and constructed
in order to investigate reaction rates in solventwater mixtures. Because a thermal method was used
a constant temperature environment was essential
and this was achieved by using a water bath
controlled to + 0.0010C.
This callorinieter has been used to study the
alkaline hydrolysis of methyl acetate in
dimethylsulphoxide, and tetrahydrofuran - water mixtures at 15, 25 and 35 [degrees]C.
The results of other investigations on similar
reactions have been reviewed and an attempt has
been made to correlate the electrostatic theories
of Laidler and Eyring, and Amis and jaffe with
these results.
Finally, because it appears that specific
solvent interactions play a major part in the
reaction rates the role of water in the reaction
mechanism has been examined. A mechanistic
explanation has been proposed in order to correlate
the rate of reaction with the composition of water-solvent
mixtures which justifies the Laidler and
Eyring treatment of solvent effects on ion-molecule
reactions.Bradford Universit
Gas purification by short cycle pressure swing adsorption. Experimental and theoretical studies of a fixed bed adsorption process for the separation of carbon dioxide from air at ambient temperatures using molecular sieve 5A and activated charcoal adsorbents.
No full textAn experimental pressure swing adsorption unit has been
constructed and used to investigate the separation of carbon dioxide
from carbon dioxide enriched air using both an activated carbon and
a type 5A molecular sieve adsorbent. Continuous, cyclic operation
was achievedusing a pair of fixed bed adsorbers. At any one time
the feed gas entered one bed at a high pressure and part of the
purified gas was returned to the other bed at a reduced pressure
to provide countercurrent regeneration of the adsorbent.
The beds of adsorbent used were each nominally 0.165m diameter
and Im. deep. Separations were carried out at approximately ambient
temperature using air flow rates in the range 0.15 to 0.95 kg/m2s and inlet carbon dioxide concentrations'in the range 0.1 to 1.5% v/v.
Adsorption pressures of 2 to 6.4 bar were examined, the desorption
pressure being maintained throughout at essentially 1.0 bar. The
period time was varied from 30 to 900 seconds and the revert ratio
(i. e. the ratio of the product gas returned for desorption to the
total feed rate to the unit) was varied from 0 to 1.0.
The carbon dioxide separation efficiency was found to increase
markedly as the adsorption pressure and the revert ratio were
increased whereas it was relatively insensitive to variations in feed
rate and, more particularly, feed concentration. The performance of
the molecular sieve adsorbent was found to be very sensitive to the
presence of moisture in the feed gas. In contrast the carbon dioxide
efficiencies observed with Lhe activated carbon were unaffected by the
presence of small amounts (circa 100 ppm) of moisture in the feed.
A theoretical model has been proposed for predicting the
performance of pressure swing adsorption systems of the type
investigated and approximate analytical equations and more precise
numerical techniques have been established to represent its solution.
The approximate analytical solutions were found to give close agreement
with the more precise methods examined under conditions corresponding
to low values of a dimensionless period time parameter. The proposed
theoretical model incorporates an effective irean mass transfer
coefficient to represent the diffusion process within the adsorbent
particles. Methods for estimation of the value of this coefficient
based on the limiting conditions of a periodic constant surface flux
or a periodic constant surface concentration are presented.
The experimental performance data were analysed in terms of the
proposed analytical solution to give values of the apparent solid phase
mass transfer coefficient for comparison with those predicted theoretically.
In general the apparent experimental values were consistently
less than the predicted values. In addition the relationship between
the experimental and predicted coefficients was found to be dependent
on both the nature of the adsorbent and a parameter formed by the
product of the revert ratio and the adsorption to desorption pressure
ratio. Empirical correlating equations which incorporate this
dependence are presented
Mixing of particles of different size has been studied and a method devised for predicting the quality of mixtures from a measurement of the segregating tendency of the components
No full textThis thesis is an account of research into the mixing and segregation of particulate solids of different particle size.
The main aim of the work was to develop a simple laboratory test ifor the measurement of the segregation tendency of the mix components, the results of which could be used in the selection of a suitable mixer for a particular duty. Binary test mixtures of different diameter ratios prepared from narrowly sieved fractions of the same material were used in segregation tests to establish a standard test procedure for the measurement of the segregation tendency of the components. Segregation in test mixtures was measured by three different methods and a segregation index i.e. coefficient of segregation, which is based on the difference in the composition in the two halves of the sample was used to measure the degree of segregation. The inclined rotating drum was found to be most suitable and simple apparatus and a standard testing procedure was established.
The effects of the diameter ratio and mean diameter of the components and the effect of moisture content in sand mixtures, on the coefficient of segregation were studied and it was found that the segregation increases with the diameter ratio between particles up to a value of 4.3 but for higher diameter ratios, the coefficient of segregation is not affected. At a constant diameter ratio the coefficient of segregation was found to decrease when the mean diameter of the components was reduced below 500 microns. Segregation in sand mixtures of various diameter ratios was found to decrease markedly as water was added, falling to a very small value with the addition of 1% of water by weight, and an equation was developed to calculate the amount of water required for adhesion between equally sized particles.
The ’thief' probe sampling technique was critically examined and a new sampling technique was developed which causes very little disturbance in mixtures in comparison with the ’thief' probe sampling which is very widely used.
The performance of three different types of mixers was investigated by measuring the degree of mixing of different sized components having different segregation tendency. It was found that the degree of mixing in a Nauta mixer was much better than that in a tumbling mixer. For higher diameter ratio mixtures the performance of the Nauta mixer was unchanged whereas the performance of a Ribbon blender was slightly reduced. In tumbling V-mixers the degree of mixing was very markedly reduced with an increase in the diameter ratio between components up to a value of about 2.4 ; at higher diameter ratios the quality of mixing was slightly improved.
The effect of the change of sample volume on the quality of mixing in a tumbling V-mixer was studied and it was found that the standard deviation is not affected when the volume of sample is changed from 1.42 cubic cm to 6.28 cubic cm.
From the mixing and segregation tests it was found that the segregation tendency of the mix components determined in the inclined rotating drum can be used to evaluate the ultimate degree of mixing in a mixer in which the segregation is predominantly due to the percolation as the segregation mechanisms prevailing in the inclined rotating drum is similar to that occurring in the mixer.University of Bradford and
Ministry of Technolog
Bubble sizes in cylindrical equipment are satisfactorily predicted from theory and from two-dimensional studies. The distribution of gas between dense and bubble phases is calculated from bed expansion data
No full textGas fluidized beds have provided fascinating and infuriating problems for both the academic and industrial engineer. Although
fluidization phenomena have been the subject of many hundreds of papers we still cannot dispense with experimentation in order to predict bed behaviour even for relatively simple operations, let alone complex chemical reactions.
This thesis provides a broad but brief scrutiny of the fluidization behaviour of a wide variety of powders and then focuses on one specific but important question: how can we predict the sizes of bubbles under given conditions in a large fluidized bed?
Experimental work on a wide variety of sands and other materials has been carried out in cylindrical columns 5 cm and 50.8 cm diameter, and in addition films from two two-dimensional beds have been analysed.
Fluidized solids have been classified into four groups characterised by density differences Pg-Pf, mean particle size, and gas viscosity.
A critical examination of the results of previous workers together with the new experimental work has shown that within one of the largest groups, bubble size is independent both of mean particle size and - more significantly - of particle size distribution.
An equation has been developed which relates bubble size to the gas distributor design, distance above the distributor and the excess gas velocity U-U0 , and good agreement is obtained with published data relating to larger beds fitted with commercial distributors.
Measurements of bed expansion combined with the analysis of films from two- and three-dimensional equipment have proved useful in evaluating the distribution of gas between dense and bubble phases.
For a given value of U-U0, the visible bubble flow rate decreases as particle size increases. This is because the through-flow of gas from bubble to bubble is proportional to the minimum fluidization velocity U0. As a result both bubble concentration and bed expansion decline with increasing particle size but bubble size is not affected.
An equation has been developed which enables the visible bubble flow rate to be calculated from measurements of bed expansion and U-U0 alone.
bubble concentration, frequency and size have been compared at the surfaces of two- and three-dimensional beds under corresponding conditions of distributor design, bed height and gas velocity. Bubble sizes are significantly larger in the three-dimensional equipment and this is believed to be due to the predominance of out-of-line coalescence. A transformation procedure has been developed for the prediction of dimensional bubble sizes from two-dimensional data, and has been successfully applied to the only sand so far tested
Measurement of steady and pulsating flow, by transit time analysis of temperature fluctuations
Full text linkThe applicability of the temperature cross correlation method to measurement of flow under steady and pulsating flow conditions is investigated. The factors to be considered in applying this technique to different flow systems are discussed and its advantages over the conventional techniques are highlighted. The method involves monitoring random temperature variations in the flow at two points along the pipe and determining the transit time between the two points using the cross correlation technique. The velocity of flow is thus determined by the time and distance between the two points.
The method is proved in the laboratory to be an absolute, reliable and accurate method of volumetric flow measurement in laminar flow of highly viscous liquids (e.g. oils) and for the turbulent flow of liquids under steady and pulsating flow conditions. For low viscosity liquids (e.g. water) under laminar flow conditions the measurement is dependent on the flow characteristics and fluid properties and hence sensitive to upstream effects and pulsations. The flow characteristics of laminar and turbulent flow under steady and pulsating flow conditions and their influence on the heat transport mechanism are examined. Theoretical models are presented for developed and developing flow conditions and the experimental results show fair agreement with theory. Errors in the measurement technique are discussed and design conditions are recommended so as to minimise these errors.
It is shown theoretically and experimentally that an important parameter called the ‘frequency parameter’ (KR) governs the applicability of the technique to measurement of pulsating laminar flow. Only if KR<1 can the flowmeter, calibrated for steady flow measurement, meter pulsating flow accurately. This condition is satisfied easily by highly viscous liquids and hence this method is an accurate method for metering highly viscous liquids under pulsating flow conditions. The measurement of developing laminar flow with moderate amplitude pulses (<50% of mean) and turbulent flow with small and large amplitude pulses, is independent of the frequency parameter.
This technique of flow measurement offers minimum pressure drop, no mechanical wear, no blockage of pipe lines and can be used under adverse environmental conditions using a simple and robust sensing element. The flowmeter gives a linear output and accuracy better than +/- 2% can be achieved. The temperature signals used have rather narrow bandwidths and therefore averaging times of between 2 and 4 mins are required. However a better heat injection technique is described which will provide wider band width signals which should give a quicker response flowmeter
A detailed study of the induced polarization and earth resistivity techniques of geophysical prospection including instrumentation, the detectability of a buried sphere and data interpretation of archaeological sites
No full textThis thesis is an account of the research carried out by the author as a member of the Postgraduate
School of Applied Physics at the University, during the years 1967 to 1970.
The induced polarization and earth resistivity techniques of geophysical prospection are considered in detail, with respect to their application in the detection of discrete, near-surface features. The research includes the design and development of instruments to facilitate these measurements, in both laboratory and field environments. Field surveys over a variety of small scale features, are carried out to define the operation and usefulness of the instruments under such conditions.
In the laboratory, the phenomena contributing to the induced polarization effect are investigated and a particular
solution of the buried sphere problem is used to define the properties of several electrode configurations. The proposed solution is investigated by model experiments and is extended, with partial success, to include the responses from features of an arbitary shape. The interpretation of field data, by the use of a digital computer is studied and is applied to some of the survey examples.N .E .R .C. and University of Bradford ScholarshipThe files have been scanned from print. They are large files and can take a long time to download. Please be patient when downloading
Experimental Study of Coupling Compensation of Low Profile Spiral Antenna Arrays Response for Direction-finding Applications
No full textNoAn experimental study of coupling compensation for AOA estimation using compact low profile antenna arrays with element separations of a quarter wavelength has been conducted. Two circular arrays of low profile miniaturised logarithmic spiral antennas deployed on a circular metal plate were used for data acquisition. Using the MUSIC direction-finding algorithm, the AOA estimation errors in receiving mode were observed before and after compensation: the errors were significantly decreased by coupling compensation
Revisiting the European social model(s) debate: challenges and prospects
No full textNoOne of the distinctive features of the post-war process of European economic and political integration is the debate about the emergence of a European Social Model (ESM). Advocates and critics have clashed over the precise meaning of the ESM concept, whether it exists in a meaningful and singular form, and whether it challenges or bolsters – by providing some sort of discursive justification – the current neoliberal trajectory of the European Union (EU). While some of the claimed elements of the ESM do exist/have been adopted, this article argues that they do not constitute a coherent alternative to the dominant market liberal model and bias towards negative integration that has underpinned the EU since the 1980s. Furthermore, contemporary developments have served to further entrench these tendencies at the expense of progressive social forces that seek to construct a genuine ESM