Tikrit Journal of Engineering Sciences

Despite the worldwide attended of pebble bed reactors (PBRs), there is a lack of fundamental understanding of the complex flow pattern. In this work, the non-ideal flow behavior of the gas phase, which is used, for cooling has been investigated experimentally in a 0.3 m diameter pebble bed. The extent of mixing and dispersion of the gas phase has been qualified. The effect of gas velocity on the axial dispersion has been investigated with range from 0.05 to 0.6 m/s covering both the laminar and turbulent flow regimes. Glass bead particles of 1.2 cm diameter and 2.5 gm/cm3, which is randomly and closely packed have been used to mimic the pebbles. An advanced gas tracer technique was applied to measure the residence time distribution (RTD) of gas phase using impulse tracer. The axial dispersion coefficients of gas phase in the studied pebble bed have been estimated using the axial dispersion model (ADM). It was found that the flow pattern of the gas phase deviates from plug flow depending on the superficial gas velocity. The results showed that the dispersion of the gas reduces as the gas velocity and Reynolds numbers increased.

The gas holdup and liquid phase axial dispersion coefficient are measured in two semi batch packed bubble columns, 10 and 15 cm diameter for an air–water system, at atmospheric conditions. The experiments were carried out using a transient method (the tracer response method). The dispersion coefficient was obtained by adjusting the experimental profiles of tracer concentration with the predictions of the model. Experiment results of packed bubble column, shows a considerable reduction of the back mixing. The investigations have been carried out using RTD measurements and the back mixing is usually characterized by the axial dispersion coefficient obtained from the one-dimensional axial dispersion model. Also, a decrease in superficial gas velocity reduces the liquid back mixing. It is observed that the liquid circulation comprises an upward flow in the column core and a downward flow along the wall. It also seen that the transition from the bubbly flow to the pulsation flow regime occurred at 5-6 cm/s superficial gas velocity.

Cement Kiln Dust (CKD) is produced as a solid waste with large quantities during manufacturing of Portland cement clinker. The possibility of utilizing CKD as partial replacement for Ordinary Portland Cement (OPC) and White Portland Cement (WPC) produced in factories of the Iraqi cement state company has been examined in this study to fulfil the environmental and economical aims. Different percentages of CKD were blended with OPC and WPC mixes. The results show that the amount of water for normal consistency were increased with about 39 % and 31 % for OPC and WPC blended with 25 % CKD. The setting time (initial and final) decreases with increasing percent of CKD added. Compressive strength decreases slightly with increasing CKD content up to 10 %. For 7- day curing time, it decreases 7 % and 9 % for OPC and WPC mixes, respectively. As percent of added CKD increases to more than 10 %, the compressive strength and other parameters where affected significantly. Overall results proved that OPC and WPC blended with up to 10 % CKD are admissible for passing relevant specification requirements.

Finite element method is used to investigate the ultimate bearing capacity of rectangular footing resting on cohesive soil near slope. The effect of footing aspect ratio (L/B), distance ratio (b/B), and slope angle (β) on the bearing capacity are calculated. A new reduction factor (Rs) is proposed to compute the ultimate bearing capacity for rectangular footing adjacent to slope of cohesive soil from ultimate bearing capacity for similar rectangular footing resting on ground level of cohesive soils. This study shows that the ultimate bearing capacity for rectangular footing adjacent to slope of cohesive soils decreases when slope angle (β) and aspect ratio (L/B) increases. Also the ultimate bearing capacity increases when the distance ratio (b/B) increases. Finally, the effect of slope diminishes as the distance ratio (b/B) equal, or exceeds 0.75

This study concerns with the effect of long-term soaking on the unconfined compressive strength, loss in weight and gypsum dissolution of gypseous soil stabilized with (4%) lime, take into account the following variables: initial water content, water temperature, soaking duration.
The results reveals that, the unconfined compressive strength was dropped, and the reduction in values was different according to the initial water content and water temperature, so that the reduction of the unconfined compressive strength of samples soaked in water at low temperatures (5° and 25° C) was greater than those soaked in water temperatures at (490 and 600 C). The results obtained shows that the increase in soaking period decreases the percentage amount of gypsum and loss in weight for all water temperatures and soaking durations.

This paper aims to find SEA (Specific Energy Absorber) for lateral crushing (statically) behavior for Aluminum (2024-T351) alloy with difference lengths (10, 20, and 30 mm). An experimental, finite element simulation, and theoretical models present to find force-deformation curves and then find SEA for difference lengths. Experimental results more agreements with finite elements simulation and theoretical when length of tubes is increase for load deformation curve, because when the length increases the plastic region increase with initial plastic collapse load (Pc). The experimental, ANSYS simulation and theoretical results have plotted and it has seen that the theory also underestimates the ANSYS results because in theoretical model, is customary to assume that the material is perfectly plastic; therefore, the finite element simulation might predict the experimental results better than the theoretical one. The results show that light density Aluminum alloy is suitable for SEA

This paper presents the design and analysis of Doherty power amplifier. The Doherty amplifier is used in a base station for mobile system because of its high efficiency. The class AB power amplifier used in the configuration of the main and auxiliary amplifier. The result obtained shows that the Doherty power amplifier can be used on a wide band spectrum, the amplifier works at 900MHz and has very good power added efficiency (PAE) and gain. The amplifier can also work at 1800MHz at input power greater than 20dBm.

This research deals with the viability of using polyester fiber (PF), crumb rubber tire (CRT) and cellulose fiber (CF) as stabilizing waste additives in producing Iraqi SMA mixtures that sustain drain down phenomenon and moisture damage sensitivity. Different ratios of these additives (0.1, 0.2, and 0.3% by weight of aggregate and filler) were mixed with 40/50 paving asphalt by means of dry process. Unmodified and modified SMA mixtures were subjected to drain down, Marshall, static indirect tensile strength, tensile stiffness modulus, static compressive strength, tensile strength ratio and index of retained strength tests. A set of regression equations between these tests were established. In addition, an optimization table based on these tests, which can be used to select the type or amount of additive for any field applications has been determined and reported. The results indicated that the inclusion of these additives in SMA mixtures could satisfy the performance requirement of high temperature and much rain zone.

In this study, the waste glass (WG) is considered as a fine aggregate in the concrete mixture. WG is used after grinding to size according to Iraqi sand specifications No.45. The waste glass has been used instead of sand in different proportions, which are 0%, 33%, 66% and 100%. The effects of WG on compressive strength of the concrete and unit weight are analyzed. As results of this study, WG is determined to have a significant effect upon the reduction of its compressive strength and there is a significant decreasing of its unit weight. As for cost analysis, it was determined to lower the cost of concrete production. This study was an environmental one in consideration of the fact that WG could be used in the concrete as fine aggregates without the need for a high cost or rigorous energy.

The computer graphics system performance is increasing faster than any other computing application. Algorithms for line clipping against convex polygons and lines have been studied for a long time and many research papers have been published so far. In spite of the latest graphical hardware development and significant increase of performance, the clipping is still a bottleneck of any graphical system. Therefore, its implementation in hardware is essential for real time applications. In this paper clipping operation is discussed and a hardware implementation of the line clipping algorithm is presented and finally formulated and tested using Field Programmable Gate Arrays (FPGA). The designed hardware unit consists of two parts: the first is positional code generator unit and the second is the clipping unit. Finally it is worth mentioning that the designed unit is capable of clipping (232524) line segments per second.

Durability is one of the most important subjects in the soil stabilization. Since there is no specifications concerned the durability of lime-stabilized soils, several factors were selected to show their effects on the durability, namely: wetting, drying, freezing, thawing and slaking.
The effect of each one of the above factors as well as the combined effect of two or more factors were studied on the volume change and soil strength and weight loss of soil samples stabilized with optimum lime content except the slaking test at which soil samples stabilized with different lime content.
Tests results showed that the higher the lime content the lower the slaking effect, also its found the soil strength decreased when the period of immersion or freezing increased. The strength of the lime stabilized soils decreased when subjected to the cycles of wetting and drying or to the cycles freezing and thawing. However, the combined effect of wetting, drying, freezing and thawing has a pronounced effect on reduction of the lime stabilized clayey soil. The worst condition recorded when lime stabilized soil undergo to freezing then drying then wetting which should be avoided in the field.

This research was studied the effect of H2SO4 (8%), HCl (8%) acidic and wastewater) pH= 5.1, SO4= = 850mg/L, Cl–=750 mg/L, TDS = 2500 mg/L (on the lightweight concrete by using limestone as lightweight aggregate and using the foam material (Light Crete). Super plasticizers (SP) also used to enhance the properties of the lightweight concrete. Studying the effect of acidic solution and wastewater was done by calculating the percentage of decrease in weight and compressive strength of concrete prisms (100 * 100 * 400) mm, where the small portion of the flexural modulus test was submerged completely in the above solutions, and the salt rising was observed by immersion (100) mm depth from the second portion of the prism in the above solutions. Results show that the H2SO4 have influence larger than HCl for the decrease of weight on the normal concrete while the effect of HCl was larger than H2SO4 on lightweight concrete with limestone and its effect was less than H2SO4 on the lightweight concrete with foam. The results also shown that the effect of H2SO4 on the normal concrete by decreasing of compressive strength was less than the effect of HCl, while the effect of H2SO4 on foam lightweight concrete was large and its effects was small on lightweight concrete containing SP and Limestone. The wastewater did not shown significant effect on the weight decrease percentage due to lack of concentration of sulfates and chlorides in the wastewater, but for the loss of compressive strength. The results showed that the wastewater does not significantly effect on the resistance of normal concrete and lightweight concrete containing Limestone, while the effect was larger on lightweight concrete with SP and Limestone used as fine and coarse aggregates and on lightweight concrete foam.