Research on Cavitation Characteristics of Two-Throat Nozzle Submerged Jet

Ship fouling not only increases ship resistance and fuel consumption but is equally a type of biological invasion, which causes severe ecological damage. Submerged cavitation jet cleaning is an environmentally friendly, high-efficiency, and energy-saving cleaning method. The nozzle structure has an essential influence on the cleaning effect. Thus, a two-throat nozzle was designed for application in submerged cavitation jet cleaning. To investigate the cavitation characteristics of the two-throat nozzle, a high-speed photographic visualization experiment and an erosion experiment concerning the submerged cavitation jet were carried out in this study. The frame-difference method (FDM) was used to analyze the dynamic changes in the cavitation cloud in a single period. The dynamic changes in the cavitation cloud and the characteristics of the submerged cavitation jet were investigated under different inlet pressures. The sample mass loss and the macroscopic and microscopic changes in surface morphology were used to evaluate the cavitation intensity of the two-throat nozzle submerged jet. The experimental results demonstrate that the two-throat nozzle has a good cavitation effect, and the cavitation cloud of the submerged jet has obvious periodicity. With the increase in inlet pressure, the length, width, and area of the cavitation cloud continue to increase, and the shedding frequency of the cavitation cloud continues to decrease. The intensity of cavitation erosion is related to target distance and impact time. There is an appropriate target distance by which to achieve the optimal cavitation effect. The collapse of cavitation bubbles near the sample surface is related to the erosion distribution on the sample surface. Moreover, the magnitude of the absolute values of the root-mean-square surface roughness and surface skewness increase with cavitation intensity. The results in this paper are helpful for a better understanding of the cavitation characteristics of the two-throat nozzle submerged jet.

Susceptibility of domain experts to color manipulation indicate a need for design principles in data visualization

Color is key for the visual encoding of data, yet its use reportedly affects decision making in important ways. We examined the impact of various popular color schemes on experts’ and lay peoples’ map-based decisions in two, geography and neuroscience, scenarios, in an online visualization experiment. We found that changes in color mappings influence domain experts, especially neuroimaging experts, more in their decision-making than novices. Geographic visualization experts exhibited more trust in the unfavorable rainbow color scale than would have been predicted by their suitability ratings and their training, which renders them sensitive to scale appropriateness. Our empirical results make a strong call for increasing scientists’ awareness for and training in perceptually salient and cognitively informed design principles in data visualization.

Boiling-condensation heat transfer and flow characteristics in ultrathin limited enclosed space based on numerical simulation and visualization experiment

Boiling-condensation heat transfer in ultrathin flat heat pipes are complicated and difficult to observe. In this study, a visualization experiment and simulation analysis in an ultrathin limited enclosed space were carried out. Width of the ultrathin enclosed space was 1 mm, with anhydrous ethanol as the working medium. The enclosed space was oriented vertically with the heating section on the bottom and the cooling section on the top. Flow characteristics of the anhydrous ethanol were photographed using a high-speed camera through the quartz cover. The boiling-condensation heat transfer and fluid flow in the limited enclosed space were simulated. Effective heat transfer coefficient calculated based on the experimental data varied from 1.0 to 1.1 W/?C, while that of the inner wall obtained by the simulation varied within the range of 1.068-1.076 W/?C. The maximum error was 2.9%, which verified the reliability of the simulation results. By analyzing the pressure change in condensation section, it was found that the boiling-condensation heat released in the enclosed space changed periodically, because of the growth and bursting of bubbles and falling of the working medium due to gravity. Restricted by the thickness, the bubbles produced by boiling of the working medium grew in flat and irregular shapes, promoting the upward movement of the rest of the liquid working medium, and a liquid film was formed at the heated inner surface for evaporation heat transfer, which enhanced the heat transfer capacity of the heating section.

Joint Study of Impingement Combustion Simulation and Diesel Visualization Experiment of Variable Injection Pressure in Constant Volume Vessel

In this paper, the visualization experiments of spray, ignition, and combustion of diesel under variable injection pressure (from 90 to 130 MPa) were studied by using a constant volume vessel and impinging combustion plate system. With the development of the down-sizing of diesel engines, the wall impinging combustion without liquid spray collision will be the research focus in the diesel engine combustion process. The flame natural luminosity in the experiment represents the soot formation of diesel combustion. Besides, the detailed information of diesel spray mixing combustion was obtained by using the CFD (Computational Fluid Dynamics) simulation of alternative fuels in CONVERGE™. The specific conclusions are as follows. The high velocity of the spray under the higher injection pressure could reduce the low-mixing area near the impinging wall by entraining more air. Under higher injection pressure in simulation, the gas diffused more extensively, and more heat was released after combustion. Therefore, a large amount of soot formed in the early stage of combustion and then oxidized in high-temperature regions, which agreed with the conclusions in the experiments. Under the influence of the superposition of image pixels of the flame, the change of soot generation with injection pressure is smaller than the actual value, so the visualization experiment can be used as the basis of combustion prediction.