For a successful enhancement of mechanical properties of metal matrix nanocomposites, a homogeneous nanoparticle dispersion and distribution in the solidified metal is required. Mechanical mixing can be used for initial break-up of agglomerates, and its study can be simplified with dimensional analysis. Using this technique, mixing time and vortex height were assessed while varying fluid properties, impeller angle, and angular speed. Three relevant dimensionless numbers were recognized: the Reynolds (Re), Froude and Galilei (Ga) numbers. Based on blade and impeller shaft angles, a modified Froude number (Fr*) was defined. These parameters were calculated experimentally, varying angular speed from 200 to 1000 rpm for three different impeller angles: 0°, 15° and 30°. This procedure was performed with three fluids: water, and two aqueous glycerin solutions (25% and 50% by volume). Digital images were taken and processed to measure vortex height. Mixing time was measured for water at 0° impeller angle, angular speed ranging from 200 to 1200 rpm. Results showed an optimal dimensionless mixing time with respect to Re. A linear relationship was found between dimensionless vortex height and Fr*. The first had a second order polynomial relationship with the product ReFr*, regardless of impeller angle. This relationship, together with the Ga, specific for each fluid, allows scaling the results to other fluids such as molten pure aluminum. This study allows experimenting in simpler systems that involve transparent fluids, room temperature and low cost, to then elaborate a prediction of vortex height in fluids where measurements are difficult and costly, such as molten metals. 相似文献
Objective: The present study investigated the relationships between safety climate and driving behavior and crash involvement.
Methods: A total of 339 company-employed truck drivers completed a questionnaire that measured their perceptions of safety climate, crash record, speed choice, and aberrant driving behaviors (errors, lapses, and violations).
Results: Although there was no direct relationship between the drivers' perceptions of safety climate and crash involvement, safety climate was a significant predictor of engagement in risky driving behaviors, which were in turn predictive of crash involvement.
Conclusions: This research shows that safety climate may offer an important starting point for interventions aimed at reducing risky driving behavior and thus fewer vehicle collisions. 相似文献
The focus of the present study is on the implementation and some of the results of an evaluation of a safety culture campaign that partly was aimed at increasing workmate interventions (care). I focus on three groups either working on or with a Norwegian offshore platform: onshore managers, crane operators and process operators. The research questions are: “Has the safety culture campaign contributed to new safety cultures related to care in the three groups, why/why not and what can we learn from this?”. The study indicates that two of the groups have developed new safety cultures that sensitize them to new hazards, motivate and legitimize new preventive practices. In accordance with the interpretive approach to culture in organizations, these changes are discussed in light of members’ of each group’s negotiation over the meaning and relevance of campaign efforts on workmate interventions. Lessons that can be learned from the study are discussed. 相似文献