Engineering Mechanics Commons^™

Solar Heater For Curing Tobacco Part I: Overview And Theory, J John

Tanzania Journal of Engineering and Technology (TJET)

This is two parl paper. In part one of the papet; an overview on the use Of packed beds on heat collectors To be used in natural convection systems is presented. A brief theoretical background and literature review has also been presented. Theoretical analysis and performance equations are pre- sented in detail. Two zypes of absorbers are proposed for investigation. The firs,' one will be with flow below the absorber and the other with flow "'through " {he absorber. These shall be compared with the conventional flat plate collector. For comparing the performance, packings of different materials, shapes, and sizes …

A Fracture Kinetics Analysis Of Hydrogen Embrwi'lement, J Mshana

Tanzania Journal of Engineering and Technology (TJET)

In studies on stress corrosion cracking caused by hydrogen embrittlement of metals, it has been observed that within the high remperature range rhe Armenius activation energy is negative. This is quite unusual Since ther- mall)' activated crack g.'vwth processes are controlled by positive appar- ent activation energy. The unders/auding of this effect is of inleavst to design and maintenance engineers. The study demonstrates, with a syn- thesis method, a physically rigorous and rational kinetics Of thermally activated processes of some aspects ofenvironment assisted crack growth. It is show that the observed crack growth behavior may be described by single barrier …

Model For Complete Drawdown Of Floating Solids In Stirred Tank Reactors, J Mmbaga

Tanzania Journal of Engineering and Technology (TJET)

A Semi-empirical model has been developed on the basis of Kolmogoroff's theory of isotropic turbulence to determine the minimum drawdown speed for floating solids in a mechanically agitated vessel. An adjustable pa- rameter in the model is found to be afunction of impeller type and position in a vessel. A simplified representation of macroscopicflow pattern, rep- resenting the circulation flow in a vessel depending on impeller pumping characteristic is developed to account for recirculation pattern.

Measurement Of Dust Resistivity And The Effect Of Filter Operating Parameters On Its Value, S Issangya

Tanzania Journal of Engineering and Technology (TJET)

Methods of measuring electrical sensitivity of a dust layer have been outlined and the porous electrodes cell was used to measure the electrical resistivity of a dust layer and to determine the influence of various parameters. Dust layer thickness and applied voltage had no influence. Resistivity depended on particle size, packing density, temperature, and air relative humidity. Glass beads and limestone powders of different mean particle sizes were used. Temperature was varied from 20–100 °C and air moisture ranged from dry to near saturation. The results may help in understanding the performance of electrically enhanced fabric filters, which are influenced …

Design Approach For Small Scale Continuous, Steady State Plants, O Kaunde

Tanzania Journal of Engineering and Technology (TJET)

One of the major steps in the design of a process plant is development of an appiopriate flowsheet. At this step, the technical solutions may be con- sidered in relation to the social and economic factors. In this paper, guide- lines for developing a flowsheet for continuous, steady State process in a developing country environment have been proposed. To illustrate the pro- posed guidelines, a case study involving design of an ethanol distillation plant has been used.

Improved Heat Transfer By Means Of Steam Injection In A Shell & Tube Heat Exchanger, O Kaunde

Tanzania Journal of Engineering and Technology (TJET)

When designing a heat exchanger; one aims at attaining high heat transfer rates SO as to minimise heat transfer area and therefore the overall cost. This paper presents a method of improving the overall heat travsfer coef- ficient of a conventional shell and tube heal exchanger. The method in- volves injecting steam into the process fluid as it enters the heat exchanger thus effecting mixing of fluid as it travels along the exchanger Tests car- • ried out using this technique showed a significant increase in the overall heat transfer coefficient values.

Application Of Improved Pressure Transducers For Pressure Measurements, P Mtui

Tanzania Journal of Engineering and Technology (TJET)

Substantial improvement of low sensitivity pressure transducers aiming at obtaining a more realistic output signal is discussed. The output signal direct from these transducers has deficiencies of amplitude attenuation and phase lag, thus the measured values are not necessarily the true in- stantaneous values. In order to correct for such shortcomings the unit step response of these transducers is also studied experimentally. A math- ematical model is established based on the experimental results to build up a compensation circuit which is then included in the instrumentation setup to eliminate these deficiencies. The effectiveness of the compensated transducer is demonstrated by …

Influence Of Arc Discharge Duration On Turbulent Mass Burning Rate, E Mushi

Tanzania Journal of Engineering and Technology (TJET)

The influence of arc discharge duration on turbulent mass burning rate was investigated for turbulent r.m.s vglocities of u '=1.73 m/s and u'=4.5 nfs. Methane air mixtures were used at equivalence ratios ranging from 0.83 to / .25. Flame size was obtained through schiieren photography while the intensity Of CH chemiluminescence emissions was used to measure mass burning rate. A variable spark duration unit was used for ignition sparks and all the experiments were done in a fan stirred bomb. Discharge duration has no effect when the equivalence ratio is I. For higher values longer duration inoeases the burning rate …

Development Of Vibration And Sensitivity Analysis Capability Using The Theory Of Structural Variations, Ting-Yu Rong

Mechanical & Aerospace Engineering Theses & Dissertations

In the author's previous work entitled "General Theorems of Topological Variations of Elastic Structures and the Method of Topological Variation," 1985, some interesting properties of skeletal structures have been discovered. These properties have been described as five theorems and synthesized as a theory, called the theory of structural variations (TSV). Based upon this theory, an innovative analysis tool, called the structural variation method (SVM), has been derived for static analysis of skeletal structures (one-dimensional finite element systems).

The objective of this dissertation research is to extend TSV and SVM from one-dimensional finite element systems to multi-dimensional ones and from statics …

Stress Fields In Composites With A Variable Interphase Under Thermo-Mechanical Loadings, Nianfeng Chen

Mechanical & Aerospace Engineering Theses & Dissertations

An interphase in a composite material has a important role for the composite performance. It influences directly or indirectly the strength, fatigue performance and effective properties of the composite. Recently, interphase has drawn increasing attention in composite mechanics. To the best of our knowledge, however, no one seems to have considered the effect of the variable material prope1ty in the interphase on the stress field in the composite material. In this research, the stress fields are determined in the continuous fiber composite and the particulate composite by using the four concentric circular cylinders model and the four phase spheres model, …

Investigation Of Computational And Spectral Analysis Methods For Aeroacoustic Wave Propagation, Florence Odile Vanel

Mechanical & Aerospace Engineering Theses & Dissertations

Most computational fluid dynamics (CFD) schemes are not adequately accurate for solving aeroacoustics problems, which have wave amplitudes several orders of magnitude smaller yet with frequencies larger than the flow field variations generating the sound. Hence, a computational aeroacoustics (CAA) algorithm should have minimal dispersion and dissipation features. A dispersion relation preserving (DRP) scheme is, therefore, applied to solve the linearized Euler equations in order to simulate the propagation of three types of waves, namely: acoustic, vorticity, and entropy waves. The scheme is derived using an optimization procedure to ensure that the numerical derivatives preserve the wave number and angular …

An Experimental And Analytical Investigation Of The Iosipescu Shear Test For Composite Materials, Barry Stuart Spigel

Mechanical & Aerospace Engineering Theses & Dissertations

Mechanical properties of composite materials under shear loading are difficult to determine. The Iosipescu Shear test, originally proposed for metals, has in recent years been applied to composites. It has the advantages of small specimen size, simple loading and a reasonably uniform shear stress in the test section.

The purpose of this work is to study the validity of the Iosipescu test method for measuring the shear modulus and shear strength of composites. Finite element analyses indicate that optimum specimen geometry and load locations depend upon the degree of orthotropy of the composite. Test results for a quasi-isotropic graphite/epoxy laminate …

Quality Problems Facing Tanzanian Industrial Firms, M Msafiri

Tanzania Journal of Engineering and Technology (TJET)

This paper reports on the results of a study of quality problems facing Tanzanian industrial firms. The results show that Tanzanian firms do not set goals with respect to quality and quality management, thus their qual- ity performance is generally poor. A Ithough there are a number of opera- tional problems constraining the companies, the main problems lie with the internal management of the quality function. Extensive ideas and sug- gestions for improving the performance of the quality function are given.

Influence Of Turbulence On Methane-Air Flame Speed, E Mushi

Tanzania Journal of Engineering and Technology (TJET)

Experimental study Of the influence qfturbulence on flame speed for meth- ane-air mixtures has been conducted in afan stirred bomb using schlieren photography. It has been observed that turbulence increases flame speed but above KLe=O. 18 (KLe is the product Of the dimensionless Karlovitz flame stretch factor and the Lewis number) turbulence quenches the flame. Inminarflame kernel is observed to prevail in the early stages of flame development in a turbulent mixture. Further, the laminar burning velocity plays a significant role in turbulent combustion. It is proposed that the increase in flame speed is a result of flame wrinkling.

An Alternative Method Of Interfacing A Dc Motor To A Microprocessor For Mo- Tion Control, M Selekwa

Tanzania Journal of Engineering and Technology (TJET)

A Simple and cheap alternative method Of interfacing a permanent mag- net dc motor to a motion control using switch- ing transistor motor drivers is presented. This method involves the use Of very few transistor-transistor logic (TTL) devices and a 555 timer to pro- duce a pulse width modulated (P WM) signal which is required by the mo- ror driver. The motor driver in this case should be of an H-bridge type. Like other methods currently in use, it relieves the MPU of all timing func- tions which are necessary in the generation of P WM signals. The present method, …

A Direct Numerical Simulation Of Vortex Breakdown Induced Tail Buffet, Steven James Massey

Mechanical & Aerospace Engineering Theses & Dissertations

A simulation of tail buffet is presented for a delta wing-vertical tail configuration. Flow conditions are chosen such that the wing primary-vortex cores experience vortex breakdown and the resulting turbulent wake flow impinges on the vertical tail. The dimensions and material properties of the vertical tail are chosen such that the deflections are large enough to insure interaction with the flow, and the natural frequencies are high enough to facilitate a practical computational solution. This multidisciplinary problem is solved sequentially for the fiuid flow, the elastic deformations and the grid displacements. The fluid flow is simulated by time accurately solving …

Transverse Stress Effects For Laminated Composite Beams In Bending, Christine Chatterton Schleicher

Mechanical & Aerospace Engineering Theses & Dissertations

A higher-order theory and an associated finite element formulation are developed for analysis of laminated planar beams in bending. The higher-order theory incorporates both transverse normal stress and transverse shear stress, and is developed using two approaches. The first approach is based on assuming the transverse normal strain distribution to be a cubic function through the beam thickness, while the second approach is based on assuming the transverse normal stress distribution to be a cubic function through the beam thickness. In both approaches, the transverse shear strain distribution is assumed to be a quadratic function through the beam thickness. Theoretical …