Abstract:

The basic physical and mechanical properties of Libyan soil are analyzed through some experiments, including direct shear test, grading analysis test and compression test. According to the test results, the soil is named as low liquid limit silt featured by weak strength, high compressibility and permeability, which directly influences sub-grade stability, durability and pavement’s usability. In order to solve these problems, measures are discussed from two aspects, namely, soil improvement and construction method. The strength of the soil is apparently increased by the cement and lime adding, and the compressibility is decreased at the same time. And the rising height of capillary water reducing and protection forms for silt soil slope are also proved to be effective in the subgrade construction

The higher strength 7xxx aluminum alloys exhibited low resistance to stress corrosion cracking (SCC) when aged to the peak hardness (T6 temper). The overaged alloys (T7 temper) developed to enhance the SCC with loss in the strength of the alloy. Recently, retrogression and re-aging (RRA) heat treatments are used for improving the SCC behavior for alloys in T6 tempers such as 7075, 7475 and 8090. In this study, an application of retrogression and re-aging heat treatment processes are carried out to enhance toughness properties of the 7079-T651 aluminum alloy, while maintaining the higher strength of T651-temper. The results of charpy impact energy and electrical conductivity tests show a significantly increases in absorbed energy and electrical conductivity values, when the alloys are exposed to various retrogression temperatures (190, 200, 210°C) and times (20, 40, 60 minutes), and then re-aged at 160°C for 18 hours.

A new physical, compact and continuous Model for extremely Scaled MOSFET Device is formulated, based on the Maxwellian approximation where the electron temperature is controlled by acoustic phonon scattering which simultaneously includes the hot electrons and the thermoelectric effects. The demonstration involving predicted current voltage characteristics and ring oscillator propagation delays reveals a significant benefit of velocity overshoot is also presented for circuit simulation. The extracted model describes current characteristics from linear to saturation operating regions with a single IV expression, and guarantees the continuities of Ids, conductance and their derivative throughout all Vgs, Vbs and Vds bias conditions. The model has been implemented in the circuit simulation such as HSPICE, Smart Spice and BSIM4v6. The new model has extensive built-in dependencies of important dimensional and processing parameters. Furthermore, the model accounts for all the major physical effects of the MOSFET characteristics.

Experimental and numerical investigations have been performed to study the natural convection heat transfer from a longitudinal fin arrays at different orientation angles. For such purpose, an experimental test rig was manufactured to be used for these investigations. It basically consists of base plate, an array of parallel longitudinal fins, heating unit and layers of thermal insulation. During the experiments, the fin spacing (S) was varied from 3.375 to 33 mm, while the fin height (H) from 15 to 60 mm. The orientation angle (Ф) was changed from 0° to 180°, and temperature difference between fin and surrounding (∆T) from 35 to 95 °C. To understand the general flow patterns dominating flows from the heat sink, the three-dimensionless elliptic governing equations were solved using finite volume computational fluid dynamics (CFD) code. A comparative study between the experimental and numerical results was performed to verify the numerical code. It was found for the configuration tested that the heat transfer rate per unit base area increases with the increase in the fin spacing and reaches a maximum value then decreases with farther increase in the fin spacing. The maximum heat dissipation occurs at optimal spacing 5. 6 S opt = mm. Moreover, the average heat transfer coefficient was found to have a maximum value at Ф = 0° and decreased with the increase of (Ф) to reach a minimum value at Ф = 90°. Empirical correlations between Nussult number, Rayleigh number, fin spacing, fin height, orientation angle, temperature difference between the fin and surroundings were derived.

Parallel plate combustor wall cooling was investigated. The combustor air flowed down the gap between two flat surfaces in a low pressure loss configuration. The work was aimed at combustor liner external air cooling for regenerative combustor cooling prior to entering a lean low NOx combustor. The test rig was 152 mm square and the test section was a duct of 152mm width and height of 10 and 5mm with a 152mm length. The experimental investigation involved the measurement of the heat transfer coefficient using the lumped capacity method. together with overall wall cooling effectiveness measurements in a hot duct test rig. The compromise between increased pressure loss and enhanced heat transfer for obstacles in the duct was investigated. It was shown that at coolant flow rates comparable with combustor requirements, adequate wall cooling effectiveness could be achieved using this technique. The cooling effectiveness performance was compared with the alternative technique of impingement cooling using low impingement jet pressure loss

This paper presents computational predictions of adiabatic film cooling effectiveness for effusion cooling systems with 90o and 30o holes. Predictions are performed for a range of coolant injection mass flow rates per unit surface area, G, of 0.1kg/sm2 - 1.6 kg/sm2 for 90o holes with constant pitch-todiameter ratio of X/D = 11 and 10 rows of holes and for 30o inclined holes with X/D = 11 and 15 rows of holes over a 152mm surface length. The computational works performed are steady-state and the turbulent governing equations are solved by a control-volume-based finite difference method with second-order upwind scheme and the k-epsilon turbulence model. The velocity and pressure terms of momentum equations are solved by the SIMPLE method. The CFD prediction were validated by comparing the predictions with literature data for single rows of inclined holes and then applied to effusion cooling. The predictions included the use of a tracer gas in the coolant, which was used to predict the mixing of the coolant with the hot mainstream gases. Also the surface distribution of the tracer gas was a direct prediction of the cooling effectiveness. The mixing of coolant with the mainstream was studied and boundary layer temperature and coolant mixing profiles were predicted. These were compared with temperature measurement in a hot effusion cooling test rig.