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- ItemOpen AccessAdaptation of a Global Orthometric Height Model to Local Height Datum using 'Satlevel' Collocation.(2014) Aleem, K.F
Show more Three-dimensional (3D) maps are of immense value in the planning and execution of engineering and other projects aimed at harmonious environmental development. In many real-life situations, the knowledge of heights is crucial for understanding the relative vertical positions of neighboring entities in a common reference system called datum - an important reference surface for elevations of terrain points. In many countries, the reference surface for heights is the geoid which is approximated by the Mean Sea Level (MSL). Conceptually, two approaches are used to determine the geoid - deterministic and empirical; and can also be determined in absolute or in relative terms. The recent success in the determination of reliable global geoid gave opportunities and preferences to the relative geoid determination using the global Geopotential Earth Model (GEM-XX), as platform. The latest edition named GEM2008 defines the global geoid to submeter accuracy. The global model generalizes the geoid in any locality; and therefore, it is not the best fit for any country or place. The fitness of the global geoid is always tested in the locality for its adequacy by comparing the GNSS derived Orthometric Heights with those obtained by direct geodetic levelling. In practice, the discrepancies are usually attributed to the imperfection of the global geoid model. The direct methods of determining Orthometric Heights by geodetic leveling is physically demanding and even almost impossible in some areas such as the rain forested areas and Niger Delta region of Nigeria due to the presence of swamp and the nature of the terrain. Thus, it is preferable to develop a mathematical model for the global model imperfections with the hope of obtaining Orthometric Heights by applying the geoidal error model to GNSS heights (which are easier to acquire) in other to obtain the Orthometric Heights. The challenge in this approach is to get the appropriate geoidal error model and this is the focus of this research. In this study, an empirical error models code named ‘Satlevel’ Collocation model is developed, and compared with other existing predictive models developed and used by researchers in other countries. The ‘Satlevel’ uses an optimal numerical model which transforms the global model to local datum using geoid modelling techniques aided by GNSS measurements. GNSS is used to obtain ellipsoidal heights at some selected control points, while the Orthometric Heights of those points were determined by geodetic levelling. Orthometric and ellipsoidal Heights were related by Geoidal Undulation (N) for which empirical error model was sought. Spherical and Rectangular ‘Satlevel’ models were explored. GEM2008 Orthometric Heights were computed in the two selected study areas (Port Harcourt, Rivers State and Lagos State of Nigeria). The results show that the geoidal undulation determination with Spherical ‘Satlevel’ models gave average values of 18.946m and 22.854m for Port Harcourt and Lagos State respectively, while Rectangular ‘Satlevel’ models gave average values of 18.948m and 22.857m for the two areas. The Mean Square Error (MSE) for Spherical ‘Satlevel’ were 6.151mm and 0.0033mm; while Rectangular ‘Satlevel’ gave 1.728mm and 0.00032mm for Port Harcourt and Lagos State respectively. The statistics show that there are no significant differences between the observed Geoidal Undulations and the computed Geoidal Undulations from ‘Satlevel’ collocation models. Also, the goodness of fit of the model was checked and satisfied 95% significant level. The geoidal map and 3D surface models of the areas were produced. ‘Orthometric height on the fly’, a user-friendly interactive program was developed to compute the local Geoidal Undulation and Orthometric Height from “Satlevel’ collocation model. Although, all the models considered give comparable accuracy of the orders of millimeters, Spherical ‘Satlevel’ model is more preferable than the Rectangular ‘Satlevel’ because of its advantage of accepting data format that is most common on maps and GNSS devices over other models. GEM2008 fits perfectly in the Port Harcourt Coastal area of Nigeria and therefore adapted for Orthometric Height with the use of ‘Satlevel’ Collocation Models developed in this research. The study recommends re-observation of the Nigerian Vertical control network and its integration with GNSS observations so that a general model applicable to the entire country can be determined.Show more - ItemOpen AccessAnalysis of Dynamic Stress Propagation of a Vibrating Subsea Structure in a Pressurized Environment(2011-08) Ogunmola, O.Y
Show more Offshore pipeline and flow line systems define a variety of subsea architectures associated with Floating Production Storage and Offloading units (FPSOs) or Floating Storage and Offloading units (FSOs) that are usually employed for oil and gas production in deep and ultra deep waters. The design of such transmission facilities, must satisfactorily account for various phenomena such as hydrodynamic wave loading, fluid transport velocity, operating pressure and temperature of the internal fluid as well as limitations imposed by the seabed subsoil layer geotechnical properties. In fact the transverse and longitudinal dynamic responses of these pipeline and flow line systems are strongly modulated by these effects. Subsea pipelines are on the high demand to function at high temperatures and pressures. The natural behavior of a pipeline is to relieve the attendant high axial stress in the pipe-wall by buckling. Such uncontrolled buckling can have serious implication on the integrity of a pipeline. Hence, the usual practice to date, in the industry is to restrain pipelines by trenching and burying, or relieving the stress with inline expansion spools. In this work, the effect of transverse and longitudinal vibrations on the dynamic stresses induced by the fluid flow was studied with special reference to onset of buckling or bursting of such pipes. For this purpose, an offshore pipeline was idealized as a fluid conveying elastic beam on an elastic foundation and the corresponding set of equations governing the transverse and longitudinal motion of the pipe were formulated. Particularly, by employing integral transforms, an analytic solution for the induced stresses was computed and simulated for design applications while comparison with corresponding formulae currently in use in the field was also carried out. Furthermore, the earlier work was extended to capture the effect of deliberate or natural sediment covering of pipe that occurs over a long period of time, by examining the dynamic stress propagation through a partially or fully buried offshore pipeline. For this problem a boundary valued partial differential equation for the fluid- structure- soil interaction mechanics was formulated. In particular, by employing operational methods, the burst and buckling pressure profiles as modulated by the seabed sediment layer history were reported for design analysis and applications. Lastly this research reported an analytic solution for the induced stresses in polar coordinates coupled with von Mises yield criterion in conjunction with the corresponding set of equations governing the transverse and longitudinal motions of an offshore pipeline on an elastic foundation. Interesting results were simulated for practical analysis and applications.Show more - ItemOpen AccessAnalysis of Dynamic Stress propagation of a Vibrating Subsea Structure in a Pressurized Environment.(2012) Ogunmola, O.Y
Show more Offshore pipeline and flow line systems define a variety of subsea architectures associated with Floating Production Storage and Offloading units (FPSOs) or Floating Storage and Offloading units (FSOs) that are usually employed for oil and gas production in deep and ultra deep waters. The design of such transmission facilities, must satisfactorily account for various phenomena such as hydrodynamic wave loading, fluid transport velocity, operating pressure and temperature of the internal fluid as well as limitations imposed by the seabed subsoil layer geotechnical properties. In fact the transverse and longitudinal dynamic responses of these pipeline and flow line systems are strongly modulated by these effects. Subsea pipelines are on the high demand to function at high temperatures and pressures. The natural behavior of a pipeline is to relieve the attendant high axial stress in the pipe-wall by buckling. Such uncontrolled buckling can have serious implication on the integrity of a pipeline. Hence, the usual practice to date, in the industry is to restrain pipelines by trenching and burying, or relieving the stress with inline expansion spools. In this work, the effect of transverse and longitudinal vibrations on the dynamic stresses induced by the fluid flow was studied with special reference to onset of buckling or bursting of such pipes. For this purpose, an offshore pipeline was idealized as a fluid conveying elastic beam on an elastic foundation and the corresponding set of equations governing the transverse and longitudinal motion of the pipe were formulated. Particularly, by employing integral transforms, an analytic solution for the induced stresses was computed and simulated for design applications while comparison with corresponding formulae currently in use in the field was also carried out. Furthermore, the earlier work was extended to capture the effect of deliberate or natural sediment covering of pipe that occurs over a long period of time, by examining the dynamic stress propagation through a partially or fully buried offshore pipeline. For this problem a boundary valued partial differential equation for the fluid- structure- soil interaction mechanics was formulated. In particular, by employing operational methods, the burst and buckling pressure profiles as modulated by the seabed sediment layer history were reported for design analysis and applications. Lastly this research reported an analytic solution for the induced stresses in polar coordinates coupled with von Mises yield criterion in conjunction with the corresponding set of equations governing the transverse and longitudinal motions of an offshore pipeline on an elastic foundation. Interesting results were simulated for practical analysis and applications.Show more - ItemOpen AccessAnalysis of the Dynamics and Stability of Visco- Elastic Pipes Conveying a Non-Newtonian fluid.(2012) Kuye, S.I
Show more Flow induced vibration of pipeline and riser systems are strongly dependent on internal fluid flow parameters as well as the mechanical properties of the conveyance vessel. The steady growing demand on the transport of primary energy sources such as oil and gas necessitated larger diameters and higher operating pressures. In order to reduce the amount of steel in the pipes there was a search for higher strength materials that could be used to reduce the wall thickness, as permitted by advances in manufacturing processes. Some studies on the mechanics of sandwich elastic systems as effective vibration and noise reduction mechanisms have stimulated the possibility of replacing stainless steel pipes with sandwich pipes especially in deepwater environment. Recent analysis has indicated that crude oil is a Newtonian fluid at high temperature, but exhibits non-Newtonian behaviour due to its complex mixture of hydrocarbons. This thesis presents our attempt to find an alternative material to steel as offshore fluid conveyance medium, by analytically investigating the dynamics of viscoelastic pipes in offshore environment using Euler-Bernoullis beam theory. By idealising the viscoelastic pipeline resting on the sea bed as a viscoelastic beam that is resting on an elastic continuum, a non-linear, boundary value partial differential equation governing the fluid- structure- soil interaction mechanics is formulated. The material property of the beam-model pipe is described by the Kelvin-Voigt type viscoelastic constitutive relation. By linearizing the governing partial differential equation matching the problem physics, under slight perturbation of the internal fluid velocity and other flow variables closed form analytical results for the system dual natural frequencies and consequently stability under external excitation are computed for field designs. We were able to find out that stability for both single and sandwich viscoelastic pipes is low in offshore environment compared with that of steel pipe. However, when sandwich pipes are arranged in such a way that thicker viscoelastic material is on the inside and thinner steel material on the outside, natural frequency is tremendously improved which demonstrates good stability. Results also show that the more the flow behaviour index of the conveyed fluid the more the stability, which makes dilatant fluid to be more stable than Newtonian fluid which in turn is more stable than pseudoplastic fluid. In the case of sandwiched pipes, the results obtained in this work emphasized the importance of arrangement of the pipes for offshore applications.Show more - ItemOpen AccessAn Analytical and Autographic Method for Highway Geometric Design(School of Postgraduate Studies, University of Lagos., 2007) Akiije, I
Show more Full text attachedShow more - ItemOpen AccessAnalytical and Autographic Method for Highway Geometric Design.(School of Postgraduate Studies University of Lagos., 2007) Akiije, I
Show more Full text attachedShow more - ItemOpen AccessArithemetic Operations on Elliptic Curve Defined over Radix-7 Synmetrical Quaternary Signed- Digit Finite Fields and their application in Secure Communication Systems(2010) Daikpor, M.N
Show more This thesis proposes a Restricted Radix-7 Symmetrical Quaternary Signed Digit Number system (RR7SQSDNS) both as an alternative processing logic threshold system and as a signed digit algebraic structure. The thesis also presents the arithmetic operations on elliptic curves defined over this special type of finite field and develops Restricted Radix-7 Symmetrical Quaternary Signed Digit (RR7SQSD) modular exponentiation scheme that uses a multiply-by-7 addition/subtraction chain to compute the product of very large word length integer operands in data word length constrained compute environments. The multiply-by-7 addition/subtraction chain is also used to develop a one-stop multiply-by-7 point multiplication computation strategy for elliptic curves defined over RR7SQSD finite fields. A Complementary Pass (CP) gate derived 7-valued symmetrical quaternary signed-digit T-gate realized as a basic building block for implementing the SMVL arithmetic unit VLSI circuit operates on RR7SQSD profile voltage signals. The VLSI functional logic circuits were thus synthesized on this basic building blocks level. Multisim Electronic Work Bench was used to analogue simulate the T-gate’s MOSFET circuit. The T-gate’s multiplexing ability, the RR7SQSD full adder and quasi-multiplier circuits’ accuracy were simulated using qbasic language hardware-descriptive-styled source code program with results that confirmed the efficiency of RR7SQSD arithmethicShow more - ItemOpen AccessAn Artificial Neutral Network Model for the Optimal Operation of Shiroro Reservoir(School of Postgraduate Studies University of Lagos., 2008) Akanmu, J.O
Show more - ItemOpen AccessBiomechanical Analysis of Lower Limb Segments During Variable Speed Cycling.(2014) Ajayi, A.B
Show more This work undertakes the biomechanical analysis of the lower limb segments during variable speed cycling using inverse dynamics approach. Cycling interventions have been suggested for cardio-respiratory fitness as well as for patients with spinal cord injuries, stroke, mobility impairments and osteoarthritis. In the course of variable speed cycling, fatigue does set in at the lower limb after a period of usage or when there are abuses. Attempts by cycling athletes to outdo one another can impact negatively on their lower limbs during sports. Similar things do occur in recreation and rehabilitation. Therefore, it is important to understand the dynamics of the biomechanics of the lower limb segments (comprising the ankle, the knee joint and the hip) during variable speed cycling so as to mitigate the effects. The lower limb segments are model as a dynamic five bar linkages with kinematics, kinetics, and joints moments equations developed using inverse dynamics. Parametric studies are carried out using known values in order to evaluate the effects of saddle height; horizontal acceleration and crank speed on the lower limb segments are evaluated. Results show that at crank speeds above 64 rpm, the knee joint moment was the highest, followed by hip and then the ankle. A horizontal acceleration of 2 m/s2 was discovered to be appropriate and is therefore recommended. It was also discovered that as the saddle height was reduced below 50% of the total length of the lower limb segments, the joints moments become very high; this can eventually lead to fatigue. A saddle height of 75% of the total length of the lower limb segments minimizes all the three joint moments. It is therefore concluded that in other to minimize knee joint related fatigue which can lead to injuries during recreation and fitness, the saddle height should be 75% of the total length of the lower limb segments and crank speed not exceeding 64 rpm. For competition, the saddle height should be 90 – 100 % of the total length of the lower limb segments and horizontal acceleration of 2 m/s2 to be maintained.Show more - ItemOpen AccessBioremediation Potential of Microorganisms in selected Hydrocarbon-contaminated soils of the Niger-Delta, Nigeria(2017-10) Olanipekun, O.O
Show more Niger Delta, being the centre of petroleum production and process activities in Nigeria, is directly exposed to large and repeated oil spills or leaks that result in hydrocarbon pollution. As a consequence, there is a strong need to give attention toremediationtechniques such assoil replacement, encapsulation, thermal desorption, and bioremediation. This study focuseson bioremediation, especially in-situ bioremediation. This requires the establishment of indigenous microbial potential and evaluation of the limiting factors such as physicochemical properties of the soil and the nature of substrate. This study, therefore seeks to evaluate the bioremediation potentials of the microbial population in selected petroleum hydrocarbon contaminated soils in the Niger Delta area of Nigeria. Soil samples were collected from two towns, Effurun and Jesse in Delta State, as well as three towns, Eleme, Bori and Pete in Rivers State. Conventional methods of isolation of microorganisms using serial dilution and plating on nutrient agar and potato dextrose agar were adopted to evaluate the population densities of the total heterotrophic bacteria and fungi as well as total hydrocarbon utilizing bacteria and fungi in the soil samples. The abilities of undefined consortium in the various sites were studied and the isolates were screened for selection using specific test on different hydrocarbon sources. The abilities of the selected isolates were tested on mineral salts medium (MSM) spiked with 1-2 % (V/V) hexadecane and 2- methylnaphthalene. In addition, the ability of a consortium of selected isolates to biodegrade mixture of polyaromantic compounds such as 1-methylnaphthalene (1MN), 2-methylnapthalene (2- MN) and 1, 3-dimethylnaphthalene (1, 3-DMN), and aliphatic compounds such as hexadecane (HX) and heneicosane (HN) was studied. The heterotrophic bacterial counts were found to range from 1.8 x 105- 2.85 x 106cfu g-1 while the total hydrocarbon utilizing bacterial counts ranged from 3.0 x 103 - 5.75 x 104 cfu g-1. The heterotrophic fungal counts ranged from 5.5 x 107 - 5.57 x 108cfu g-1 while the total hydrocarbon utilizing fungi ranged from 1.8 x 105- 2.18 x 106cfu g-1. The physicochemical properties such as the pH, organic matter, moisture content, water holding capacity and nutrient level were evaluated experimentally, and the result indicates that the total organic matter ranged from 1.80 - 21.30 %. The pH in CaCl2 (pH(C)) solutionof the soil samples was in the range of 4.28 - 6.28, while that of the pHin water (pH (W)) was within the range of 5.4 - 7.3. The concentration of nitrate ions (NO3 -1) in all the soil samples varied from 27.2– 218.0 mg kg-1 and that of sulphate ions (SO4 -2) varied from 9.71- 327.0 mg kg-1. The moisture content of contaminated soils ranged from 11.30- 39.30 %(w⁄w) while that of uncontaminated soils was in the range of 9.30- 26.30 % (w⁄w). The study showed that the obtained microbiological and physicochemical parameters of the soils are consistent with the conditions in an environment that encouraged microbial activity. The consortia of the microbial in the different soil samples studied showed different degrees of capabilities on the crude oil, as these removed high number of components of the crude oil and thus make the areas potentially suitable for in-situ bioremediation. The selected isolates degraded hexadecane and 2-methylnaphthalene respectively ranging from 89.98- 97.94 % and 84.27- 93.48 % at the end of 21 days. At the end of the 120 hours the extent of degradation of the various components of mixture, 2-MN, 1MN, 1, 3-DMN, HX and HN were 86.54, 81.85, 81.71, 59.65 and 73.61 % respectively by the formulated consortium. The kinetic parameters such as the associated saturation constant (43.8- 602.0) and maximum specific substrate consumption rate (0.564-3.674) indicated that the consortium grew on the constituent of the substrate. A suitable mathematical model was developed to predict the fate of multicomponent substrate in a porous media, especially soil that incorporated appropriate biodegradation kinetics that is adjudged to describe the consumption rate of the substrates. The Equation was solved using Finite Volume Method and simulated in a Matlab environment. The model was validated using a column experiment, and it was observed that the model appropriately described the degradation process and predicted extent of degradation in multicomponent substrate systems. Therefore, the formulated consortium has the ability to substantially degrade most of the components of the hydrocarbon mixture though at different rates.Show more - ItemOpen AccessCarbide Precipitate Deactivation and Module Characteristics in Thin Wall Ductile Iron (TWDI) Castings(2016-01) Ochulor, E.F
Show more Ductile iron (DI) thin section profiles (≤ 3mm) known as Thin Wall Ductile Iron (TWDI) offer significant potentials in automotive applications because of their high strength with good ductility, wear resistance, castability, machinability and good fatigue properties. “Globally” as-cast TWDIs in many foundries suffer macrostructural and microsructural defects such as solidification shrinkages, coldshuts, misrun, incomplete filling, carbide precipitation, poor graphite morphological characteristics, which jeopardize the enhancement of mechanical properties required for automotive applications. Production of “defect-free” TWDI castings is hindered by difficulty in channeling molten metal appropriately into the mould cavity. This study considers the effect of casting design and sprue/metal head height on mould filling, microstructure and mechanical properties of TWDI casting. The suppression of carbide formation and non-nodular graphite is dependent on the nodularisation and inoculation treatments (liquid treatments), hence the effect of nodularisation treatment temperatures of 14500C-15500C is investigated. This study also investigates effect of incorporation of 2-12 wt. % aluminum dross (AlDr) and 1-6 wt.% rice husk ash (RHA) on thermal properties of moulding sand, the microstructure and mechanical properties of TWDI castings, as literature on these is found to be scanty. The results show that side feeding casting design enabled completely filled mould cavities. At metal/sprue height of 50 mm the melt could not push through the gating channel, but as it is increased from 100-350 mm, complete mould-fill is achieved. However, between 200 mm and 350 mm, carbide precipitates and flow related defects namely; misrun, coldshut, incomplete filling and air entrapment are evident. These defects significantly lower the strength and ductility of TWDI. Desirable nodularity ratings above 90%, good nodule count of 450-610 nodules/mm2, reduction of deleterious carbides with improved elongations are achieved at 14500C-14700C melt treatment temperatures. Below 14500C and above 14900C, poor nodularity and nodule count with reduction in ductility are obtained. RHA significantly reduced the thermal conductivity of the moulding sand from 1.631 to 1.141 W/m. K, for 0 to 6 wt. % RHA in sand mix respectively, (a 30% reduction). TWDI castings with nodularity ratings above 90%, high nodule count above 1000 nodules/mm2, high strengths of 564, 575 and 596 MPa for 2, 3 and 4 mm respectively, occurred at 4 wt. % RHA addition. High ductility of 4.7, 5.8 and 6.1 for 2, 3 and 4 mm thick samples respectively occurred at 6 wt. % RHA additions. This study has shown that sound TWDI castings are achievable with proper gating design and dimensions. Sprue/metal height is an important gating system parameter to be considered during casting of TWDIs. Lower treatment temperatures of 1450 0C and 1470 0C are adequate for good nodularity and nodule count. Incorporation of RHA to silica moulding sand significantly reduced thermal conductivity leading to reduction in cooling rate with controlled carbide precipitation and enhancement of nodular graphite of desired morphological characteristics.Show more - ItemOpen AccessCharacterisation of Locally Produced Diaphragm Cells For the Production of Caustic Soda.(School of Postgraduate Studies University of Lagos., 2008) Olufemi, B.A
Show more - ItemOpen AccessCombined Free and Forced Laminar Convection in Inclined Wide Rectangular Channels Heated from Below and Cooler from Above.(University of Lagos, 1980-12) Ochende-Bello, F. L.
Show more The steady-state two-dimensional problem of combined free and forced laminar convection with upward flow in inclined rectangular channels heated from below and cooled from above, has been investigated by numerical, parameter perturbation and experimental methods.Show more - ItemOpen AccessComparative Kinetic Investigation of the Prolysis of Pure Hydrocarbons and their Mixtures(University of Lagos, 1985-11) Aribike, D. S.
Show more The kinetic and product distributions of the thermal decompositions of the n-butane, n-heptane, cyclohexane and methyl-cyclohexane as well as liquified petroleum gas (LPG), cyclohexane methylcyclohexane (CYH-MCH) and cyclohexane - heptane - benzene (CYH-HEP-BEN) synthetic mixtures were investigated in a stainless steel annular reactor at one atmosphere pressure and with excessive nitrogen dilution. Experimental data were obtained over a wide range of conversions at temperatures from 6400 to 8600C and residence times of 0.26 - 1.87 seconds. Ethylene, propylene, methane and hydrogen were formed as major products of n-butane pyrolysis. Besides, mole percent of propylene and methane did not change with temperature below 7600C, while ethylene increased. Mole percent of propylene was considerably higher than that of methane in contrast to the results of Blakemore et al (74) who observed equal molar amounts of these two products. The ratio ([C3H6] + [CH4]}/{[C2H4] + [C2H6]) decreased with increasing temperature (conversion). Methane, propylene and ethylene were the main products of LPG pyrolysis. Also methane selectivity generally increased with residence time, while those of ethylene and propylene passed through maxima. There is evidence of the accelerating effect of the H2S additive on the cracking reactions of LPG. Relatively substantial amount of methane and less ethylene and propylene were produced in the pyrolysis of LPG than pure n-butane. In n-heptane pyrolysis selectivities of ethylene and methane increased steadily with conversion, while propylene selectivity went through a broad maximum and those of the higher &-olefins (1-butene, 1-pentene and 1-hexene) decreased. R-k theory is inadequate in predicting the secondary reactions of &-olefins, though it predicts their formation. N-heptane pyrolysis was well represented by first order kinetic law; the estimated Arrhenius parameters are E = 206.1' kJ mo1-1 and A = 5.88 x 1010 sec-1. Selectivities of ethylene, propylene and methane increased with conversion in cyclohexane, pyrolysis while 1, 3-butadiene decreased. In addition, ethylene and propylene yields increased with residence time at 7000C - 8600C, while yield of 1, 3-butadiene increased at 7000C - 8600C, passed through a maximum at 6200C and decreased at 8400C. Similar observations were made by Levush et al (30) in cyclohexane pyrolysis at 9000 - 13000C. Relatively lower selectivities of ethylene and propylene and higher 1,3-butadiene selectivity were observed in cyclohexane pyrolysis than n-heptane. Ethylene, propylene, methane and 1,3-butadiene were the major products of CYH-MCH pyrolysis. Appreciable yields of benzene and isoprene were also formed. Selectivities of ethylene, methane and 1,3-butadiene showed little or no change with increasing conversion, while propylene decreased tremendously. Less methane, ethylene, 1,3-butadiene and hydrogen and more of propylene were formed in MCH pyrolysis than cyclohexane. The Arrhenius plot of MCH pyrolysis showed appreciable curvature in the region of temperature below 8000C; an evidence of strong surface effect and hence of heterogeneous mechanism on the kinetics of MCH pyrolysis. Ethylene, propylene and 1,3-butadiene were the major products of CYH-MCH pyrolysis. The order of the quantities of ethylene formed from the pyrolyses of CYH-MCH, pure cyclohexane and MCH was: Cyclohexane > CYM-MCH > MCH Conversely more propylene was formed in MCH pyrolysis than the other two reactants. The comparison of the variations of the major product yields and selectivities with temperature and residence time for the three hydrocarbon reactants showed that the decomposition reactions of the components play central role in overall mixture cracking. Comparison of the Arrthenius parameters of pure components with those estimated for mixture cracking showed that cyclohexane strongly inhibited in former slightly. Ethylene, propylene, 1,3-butadiene, methane and hydrogen were the main products of CYH-HEP-BEN pyrolysis. The order of the amounts of ethylene formed in the pyrolyses of CYH-HEP-BEN, pure cyclohexane and heptane was N-Heptane > CYH-HEP-BEN > Cyclohexane. Conversely, the order in the case of 1,3-butadiene was Cyclohexane > CYH-HEP-BEN > N-Heptane. Selectivity to products of pure component decomposition was maintained in the mixture cracking, confirming the results of Murata et al (36). There was strong effect of component interaction on the overall decomposition reactions of CYH-HEP-BEN. Futhermore, higher yields of C2+C3 olefins and lower yields of liquid products (C6+) were produced in CYH-HEP-BEn pyrolysis than CYH-MCH. Mechanistic models that fit the pyrolyses of n-butane and n-heptane fairly well were developed. Simulated radical concentrations showed appreciable changes with reaction time thus the assumption of pseudo steady stage for radical concentrations is not valid in reality. Molecular model developed for cyclohexane pyrolysis predicted the product distributions fairly well.Show more - ItemOpen AccessA Comparative Study of Direct Labour and Design-Tender-Construct Procurement Systems in Nigeria.(School of Postgraduate Studies University of Lagos., 2007) Godwin, I.I
Show more - ItemOpen AccessA Comparative Study of Direct Labour and Design-Tender-Construct Procurement Systems in Nigeria.(School of Postgraduate Studies University of Lagos., 2007) Idoro, G.I
Show more Full text attachedShow more - ItemOpen AccessA Comparison of some Transformation Procedures for the Nigerian Geodetic Network.(School of Postgraduate Studies University of Lagos, 2008) Oyewusi, A.M
Show more - ItemOpen AccessConstruction Professionals Motivation and Job Performance: A Comparison of Indigenous and Expatriate Construction Contractors in Nigeria.(School of Postgraduate Studies University of Lagos., 2008) Onukwube, H.N
Show more - ItemOpen AccessControl Systems Design for Nonlinear Multivariable Systems(University of Lagos, 1990-12) Ajayi, O.T
Show more The Linearising Transformation technique developed for single-input, single output systems has been extended to multivariable systems. However this technique was found to be impractical for general nonlinear multivariable systems because of the complexity involved, and the fact that you cannot always guarantee a transformation. As a result, two alternative, more practical, controller design techniques have also been developed for nonlinear multivariable systems. The first technique termed External Systems Restructuring is designed primarily for state-space models, and uses the concept of a structural modifier to design a controller with desirable features for the linearized process model. The second technique, termed Direct Synthesis theory for linear systems. This technique is designed primarily for transfer function models, and allows the pre-specification of a desired closed-loop process response; the controller required to achieve this response is then synthesized. The resulting direct synthesis controller is seen to be structurally similar to a multivariable-Pl-type controller. Different compensation options have also been developed for use with this controller. These controllers achieve decoupling of the system variables, compensate for both measurable and unmeasurable disturbances, and, most importantly, take into account the unavoidable discrepancies between actual plant response and model prediction. The control laws are practical in that they are easy to understand, design and implement. The effectiveness of these techniques in controlling nonlinear multivariable processes is demonstrated by simulation.Show more - ItemOpen AccessCorrelation of Equilibrium Data for Multicomponent Distillation Design.(School of Postgraduate Studies University of Lagos., 2007) Afolabi, T.J
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