Effects Of Slot Dimensions Research Articles

The effect of slot dimensions and its vertical and horizontal position on the scour around bridge abutments with vertical walls

Scouring is one of the major threats to the stability of bridge abutments constructed over rivers. The present study investigated the usefulness of abutment slots in reducing the scour depth around bridge abutments with vertical walls, experimentally. Nine experiments with no slot and hundred experiments with slots were conducted in clear water conditions. Four subcritical flow conditions (Froude number less than 1) were investigated. For each flow condition, 25 different slot models having different sizes, and vertical and horizontal positions were considered. The results indicated that the slots having heights equivalent to half of the flow depth are more effective in reducing scouring if they are located closer to the bed. Increasing the slot height improves the performance. The best performance is achieved when the slot begins from the water surface and extends below the bed (equal to the scour depth in the model without the slot). Further, the results showed that the greater the distance of the slot is from the abutment nose and closer it is to the channel wall, the more effective the slot would be. Therefore, the most effective slot model is the model in which the slot height equals the distance from the water surface to below the bed, and when it is attached to the channel wall. For different slot models, in different flow conditions, the percentage of reduction of scour depth varies from 20 to 100%.

Experimental investigation on the flow regime and impingement heat transfer of dual synthetic jet

An experimental investigation is carried out to analyze the flow regime and impingement heat transfer of a dual synthetic jet (DSJ) actuator for the compact thermal management. The time-averaged flow field of DSJ is observed to consist of four regions, namely, the formation region, merging region, development region and decay region other than three regions of SJ without the merging region. The downstream vorticity-concentrated partitions of the SJ and the DSJ spread outwards at about 22.5° and 26.6°, respectively. The heat transfer characteristic of an impinging DSJ is analyzed by comparing with a synthetic jet (SJ). It is found that the local Nusselt number reaches a maximum at a same dimensionless impingement spacing of H/dh = 5.5 both for the SJ and the DSJ, and the maximum local Nusselt number of the impinging DSJ is 11.4% higher. The maximum area-averaged Nusselt number of the impinging DSJ is 8.6% higher at only half of H/dh than the impinging SJ, which is more preferable for the space-restricted electronic cooling. In addition, the effects of slot dimensions on the heat transfer of the impinging DSJ are studied. The peak Nusselt number is directly proportional to the slot neck length and inversely proportional to the slot aspect ratio at a same H/dh. The area-averaged Nusselt number reduces with the increase of the slot neck length at a smaller H/dh, and varies contrarily at a larger H/dh. The best heat transfer performance of the impinging DSJ is achieved at a midlevel aspect ratio. The results provide a design guideline for the cooling packages of space-restricted electronics.

Effect of ingredients on the rheological properties of extruded corn meal

A slit rheometer, mounted on a square cross section barrel extension, was attached to the exit of a single screw extruder to facilitate the simultaneous measurement of steady shear viscosity (ηsh), apparent planar extensional viscosity (ηpa), and the first normal stress differences (N1). The hole pressure method was used to determine N1 and the entrance pressure drop method with Cogswell’s analysis for abrupt planar contraction flow was used to determine ηpa. The effect of slot dimensions on N1 was investigated using low density polyethylene. Increasing the depth and width of the slot by 50% produced no significant change in the hole pressure. N1 predicted using the Higashitani–Pritchard–Baird (HPB) equation compared favorably with extrapolated N1 values obtained on a cone and plate rheometer. Addition of salt and sugar to corn grits affected the rheological properties of the melt, as observed by the changes in ηsh, N1, and ηpa. Of the three material functions, N1 and ηpa were more sensitive to the addition of ingredients. Corn grits exhibited thinning behavior in shear and planar extensional flows.