a b s t r a c tThe effect of tool geometry on the plastic flow and material mixing during friction stir spot welding (FSSW) is investigated using the particle method approach. For spot welds made with a cylindrical pin tool with flat shoulder, the model predicts the material flow at the pin periphery to be in the upward direction and the material is pushed downward beneath the shoulder giving rise to the resultant hook geometry. Other pin geometries evaluated include tapered pin, inverse tapered pin, triangular pin, convex shoulder, and concave shoulder. With good correlation with experimental trials, this model is then used to predict the material flow for spot welds. The material flow, and thereby the resultant hook formation, is quantified using numerical methods and is expressed as standard deviation of the particle movement. A triangular pin with a concave shoulder is the preferred tool geometry from the current study that results in high strength spot welds.
In semiconductor manufacturing processes, it is important that the SiO 2 isolation films around aluminum connection lines have flat surfaces in order to produce the multilayered connection lines used in high-density devices. In this paper, we analyzed transient changes, in the thickness distributions of a liquid-SOG (Spin-on-Glass) film on a two-dimensionally (2-D) grooved substrate during the evaporative shrinking process. The flow due to surface tension of the shrinking liquid film was calculated. Since the film is thin, a boundary layer approximation could be applied, and fourth-order differential equations of film thickness were solved using an iteration method. The viscosity and the shrinkage rate were assumed to be functions of the concentration of the solvent in the film. When the parameter of ratio [(surface tension)=f(viscosity)2(shrinking speed)g] is large and the width of the grooves is small, final surface undulations of the film are shallow. The effect of the centrifugal force was also analyzed.
The electrocaloric effect in thin films of an electrocaloric material has the potential to be used for efficient cooling systems for high power electronic devices. We numerically calculated the effect of parameters in electrocaloric refrigeration with a thermal switch of fluid motion on the thermal performance. The system of changing air and water flow with the pulse generation of cold energy increased the heat transfer efficiency to 67% at a frequency of 5 Hz. The optimum time delay of water flow to increase the heat transfer efficiency was zero at low frequency and became half of the time period to change heat for a high frequency of 100 Hz. When the heat transfer efficiency was high, the final temperature change in water flow was not the maximum temperature change.
The purpose of this paper is to find an optimum surface geometry of vertical condenser tubes where condensation takes place on the outer surfaces. The guiding principle on optimum condensation performance is to make the thickness of condensate liquid on the surfaces as thin as possible. A vertical tube with longitudinally parallel tiny fins is preferable because condensate is made thinner over the widest possible region. According to an analysis, there are four controlling factors for the optimum fin; sharp leading edge, gradually changing curvature of fin surface from tip to the root, wide groove between fins to collect condensate and horizontal discs attached to the tube to remove condensate. The analytical result is checked by experiments using R-113. The optimum fin shape, fin pitch and spacing of discs are found by numerical calculations for R-113 and water.
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