Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers, the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as wel as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20° (20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overal heat transfer coefficient K, shel-side heat transfer coefficient ho and shel-side average comprehensive index ho/Δpo. 相似文献
Bulletin of Engineering Geology and the Environment - Many uncertainties exist in pile-stabilized slopes which make their design substantially complicated. In this paper, a first-order reliability... 相似文献
This paper focuses on dealing with the tracking challenges such as target occlusion and deformation. It proposes a new tracking method via extracting and evaluating multi-features for both target region and its adjacent surroundings. The multi-features separately describe the key factors to detect target including the color feature, the shape and contour feature, and the distributions of structure and intensity described by the Pearson Correlation Coefficient. These multi-features are proposed as the basic representation of target template and candidates and used to define a matching algorithm between them. The best matched candidate is taken as the final tracking result. To improve the efficiency of target template and candidates, the region of importance (ROI) for target is proposed by evaluating the distribution of salient values on many extended regions. The ROIs produce more accurate regions to form target template and candidates. Finally, a new template update method is defined based on the precision of tracked result to adapt to target state and achieve the follow target tracking. Using 25 videos in visual tracking benchmark, we achieve the quantitative and qualitatively evaluations of 12 different trackers. Many experiments demonstrate that our tracker produces much better results than the present trackers in dealing with target occlusion, deformation, rotation, background clutters.
China's household registration system allows local governments to control migration by limiting migrants' eligibility to local public services. Many cities exclude migrant residents from important social benefits, which reduces labor mobility and contributes to the socioeconomic gap between migrants and urban natives. This study measures the extent of China's local migration restriction from the perspective of inclusive provision of public services and explains cross-city disparities. We define urban inclusiveness as the extent to which migrants can access social benefits provided locally and construct an urban inclusiveness index using factor analysis. We find significant cross-city differences in urban inclusiveness toward migrants. Statistical analyses suggest that local fiscal capacity and labor demand, instead of cultural tradition, are the major determinants of urban inclusiveness. We further use the gap between the inclusiveness toward high- and low-skilled migrants to measure local skill-based migration selectivity. We find that more developed cities, i.e., cities with larger populations, higher levels of gross regional product per capita, and greater shares of industrial sector, are more selective based on migrants' skills, while cultural openness does not help bring down skill-based selectivity. Our research suggests an instrumental view of migrants in China's urban policy that contributes to social inequality and the lack of labor mobility, which can restrict China's development in the long term. 相似文献
In this work, coupling effects of water content, temperature, oxygen density, and polytetrafluoroethylene (PTFE) loading on oxygen transport through an ionomer thin film on a platinum surface in a catalyst layer of a proton exchange membrane (PEM) fuel cell are investigated using molecular dynamics approach. Taguchi orthogonal algorithm is employed to comprehensively analyze the coupling effects in a limited number of cases. It is found that the effect of operation temperature is the weakest among the four factors, which has the smallest effect index 14.4. Coupling effects including the PTFE loadings on the oxygen transfer through the ionomer thin film is uncovered. Less PTFE loadings should be beneficial for the oxygen transfer. The chemical potential gradient is considered as the major driven force for the oxygen transport through the ionomer thin film, and oxygen density is the dominating factor, significantly affecting the chemical potential in the thin film. 相似文献
The present study reports foaming of polycaprolactone (PCL) and PCL nano- and micro-composites with dispersed hydroxyapatite (HA) particles by means of binary mixtures of supercritical CO2 (scCO2) and either ethyl lactate (EL) or ethyl acetate (EA) as plasticizer. The effect of the size and concentration of HA particles, as well as the effects of the plasticizer type and the incorporation route were investigated aiming to fabricate porous scaffolds with uniform morphology and controlled pore size distribution. For this purpose, foaming experiments were carried out by selecting two operating temperatures, 40 and 45 °C, and two soaking times, 1 and 17 h. Furthermore, a double step of depressurization was used to promote the development of a double-scale pore size structure in porous scaffolds useful for tissue engineering.The results of this study indicated that supercritical foaming of PCL and PCL–HA composites is enhanced when the selected operating temperature and time are 45 °C and 17 h, respectively. Furthermore, although both EL and EA plasticizers enhanced the low temperature foaming of the materials, we demonstrated that the route of incorporation of the plasticizer is a critical aspect for enhancing composite foaming and scaffold fabrication. From this point of view, the best results were achieved when EA was pre-mixed with the polymeric powder for preparing a dough for the foaming process. 相似文献
Many cities in China are undergoing large-scale demolition of urban villages. The difficulty of finding suitable housing for migrant workers has caused widespread concern because the lack of proper housing may lead to the outflow of migrant workers that would affect the normal operation of the city. Based on data collected by questionnaire survey in Hangzhou and a multivariate logistic model, this study analyzed the influence of housing demolition on the housing choices of migrant workers. We found that nearly a third (29.2%) of migrant workers spend >30% of their income on rent, and 14.1% of migrant workers plan to return to rural areas. This means that migrant workers face significant housing pressure and some migrant worker outflow from the city exists. Further empirical analysis corroborates that nine variables—including gender, age, education, marriage, occupation, RIR, RRS, HCW, and CMW—have a significant impact on migrant worker housing choices. Based on the results of multivariate logistic regression analysis, we recommend that the government expand the coverage of public rental housing, build temporary low-rent housing, stimulate businesses to provide housing subsidies to their workers, improve the educational conditions for migrant children, and intensively develop long-term, low-income rental apartments. 相似文献