Blowing/suction effect on steady two-dimensional laminar combined convection owing to the stagnation flow against a vertical flat plate with linear wall temperature with distance in a saturated porous medium is numerically analyzed. The nonlinear coupled boundary-layer equations were transformed and the resulting ordinary differential equations were solved by Keller box method. Numerical results for the local friction coefficient and the local Nusselt number are presented for various parameters. In general, it is observed that in the buoyancy assisting (opposing) flow both the local friction coefficient and the local Nusselt number increase (decrease) because of the increase of buoyancy parameter, blowing/suction parameter and permeability parameter. The local Nusselt number becomes nearly constant when Ω is very small (pure fluid flow) and Ω is very large (pure Darcy flow).

The solidification of a phase change material (PCM), exemplified by a molten metal, in a thick-walled container is analyzed in this paper. The effects of natural convection and several important controlling parameters are investigated extensively. These parameters include the initial temperature of the PCM, external cooling conditions, thickness and thermal properties of the wall, and the thermal contact resistance at the PCM/wall interface. Two representative configurations are examined in this study. A modified version of the enthalpy formulation in which the sensible heat is separated from the latent heat, is employed to construct the energy equation for the PCM. Vorticity-stream-function approach is adopted for solving the flow field. The governing equations pertinent to the problem are discretized by the weighting function scheme and finally solved by the SIS (Strongly Implicit Solver) algorithm. It is demonstrated that for both configurations natural convection has prominent effect on the temperature distribution of the liquid phase of the PCM; however, the effect of natural convection on the shape of the solid/liquid interface and the overall solid fraction is case dependent. It is also shown that the above-mentioned controlling parameters have a direct impact on the solidification process. Specifically, an increase in the Biot number (from 1 to infinity) and the thermal diffusivity of the mold (from 0.8 to 5) enhances the solidification rate. Reverse effect was found for the other controlling parameters.

Based on the weight function theory and Hutchinson's technique, the analytic form of the toughness change near a crack-tip is derived. The inhomogeneity toughening is treated as an average quantity calculated from the mean-field approach. The solutions are suitable for the composite materials with moderate concentration as compared with Hutchinson's lowest order formula. The composite has the more toughened property if the matrix owns the higher value of the Poisson ratio. The composite with thin-disc inclusions obtains the highest toughening and that with spheres always provides the least effective one. For the microcrack toughening, the variations of the crack shape do not significantly affect the toughness change if the Budiansky and O'Connell crack density parameter is used. The explicit forms for three types of the void toughening and two types of the microcrack toughening are also shown.

To study the performance and estimate the oscillating bearing loads of a twin screw air compressor, a theoretical model is proposed in this paper. Based on the model, a computer simulation program is developed and effects of different design parameters such as rotor profile, geometric clearance, oil injected position, oil temperature, oil flow rate and other operational conditions are investigated. Output variables such as bearing loads, specific power, compression efficiency, volumetric efficiency, discharge temperature are obtained. Some of the results are then compared with experimentally measured data, and good agreements are found between the simulation results and the measured data.

Destabilizing effect of magnetic damping on the supersonic panel flutter is investigated. The linear piston theory is available to formulate the air force at high Mach numbers. A plate in supersonic flow can be stabilized by reducing the compression force perpendicular to the flow. However, once the dynamic pressure parameter exceeds some critical value, the time rate of motion becomes complex then the flutter occurs. In this paper, the strength of in-plane magnetic field to reduce the panel flutter under higher dynamic pressure parameter is determined. Due to the complexity in finding the exact solution of plate motion, Galerkin solution with different terms of truncation is adopted herein. Therefore, the exact solution can be obtained by using the four-term solution as an initial value. The most attractive feature is that the supersonic flutter can be avoided efficiently through the application of in-plane magnetic field.