Flow characteristics in the entrance of plate-fin heat exchanger have been investigated by means of particle image velocimetry (PIV). The flow field was measured using the two-frame cross-correlation technique. Stream...Flow characteristics in the entrance of plate-fin heat exchanger have been investigated by means of particle image velocimetry (PIV). The flow field was measured using the two-frame cross-correlation technique. Streamline and velocity contour graphs at different cross-sections were obtained in the experiment. The experimental results indicate that flow maldistribution in the conventional header is very serious, while the improved header configuration with punched baffle can effectively improve the uniformity. The flow maldistribution parameter in plate-fin heat exchanger has been reduced from 1.21 to 0.21, and the ratio of the maximum velocity to the minimum is reduced from 23.2 to 1.8 by install-ing the punched baffle. The results suggest room for the optimum design of plate-fin heat exchanger.展开更多
The indirect boundary element method(IBEM) was established to solve the problem of 3-D seismic responses of 2-D topographies,by calculating the free-field responses with the direct-stiffness method and simulating the ...The indirect boundary element method(IBEM) was established to solve the problem of 3-D seismic responses of 2-D topographies,by calculating the free-field responses with the direct-stiffness method and simulating the scattering wave fields with the dynamic Green's functions of moving distributed loads.The proposed method yields accurate results,because the 3-D dynamic stiffness matrixes used are exact and the fictitious moving distributed loads can be acted directly on the interface between the alluvial valley and the layered half-space without singularity.The comparison with the published methods verifies the validity of the proposed method.And the numerical analyses are performed to give some beneficial conclusions.The study shows that 3-D scattering by an alluvial valley is essentially different from the 2-D case,and that the presence of soil layer affects not only the amplitude value of surface displacements but also the distribution of surface displacements.展开更多
Natural monopoly,because of its spontaneous or natural characteristics, must have some mysterious causes of reasonableness.Thus,the regulations to its efficiency loss would have a different way compared to other monop...Natural monopoly,because of its spontaneous or natural characteristics, must have some mysterious causes of reasonableness.Thus,the regulations to its efficiency loss would have a different way compared to other monopolies. That the characteristics of natural monopoly,in the case of water industry, are that the infrastructure investments are very large,most of which are used to build the transportation system? The webs for transporting their products to their customers,and the products are identity goods or services.By examining the characteristics of natural monopoly,this paper proposed away to break upand remodel the industry of“natural monopoly”.The main clue of remodeling is that the governments,who represent the public and who have the power to control over public resources,should build and maintain a public web platform for the goods’ transportation uses, and break up the barrier ofthe entry so as to produce a market-oriented competitive structure.The running modeland the condition of remodeling are put forward and the cost-revenue analysis of the operation is briefly under consideration.展开更多
基金Supported by the Foundation for Excellent Doctoral Dissertation Author by Ministry of Education of China (No.199933).
文摘Flow characteristics in the entrance of plate-fin heat exchanger have been investigated by means of particle image velocimetry (PIV). The flow field was measured using the two-frame cross-correlation technique. Streamline and velocity contour graphs at different cross-sections were obtained in the experiment. The experimental results indicate that flow maldistribution in the conventional header is very serious, while the improved header configuration with punched baffle can effectively improve the uniformity. The flow maldistribution parameter in plate-fin heat exchanger has been reduced from 1.21 to 0.21, and the ratio of the maximum velocity to the minimum is reduced from 23.2 to 1.8 by install-ing the punched baffle. The results suggest room for the optimum design of plate-fin heat exchanger.
基金Supported by National Natural Science Foundation of China (No. 50978156 and 50908183)Tianjin Research Programof Application Foundation and Advanced Technology(12JCQNJC04700)
文摘The indirect boundary element method(IBEM) was established to solve the problem of 3-D seismic responses of 2-D topographies,by calculating the free-field responses with the direct-stiffness method and simulating the scattering wave fields with the dynamic Green's functions of moving distributed loads.The proposed method yields accurate results,because the 3-D dynamic stiffness matrixes used are exact and the fictitious moving distributed loads can be acted directly on the interface between the alluvial valley and the layered half-space without singularity.The comparison with the published methods verifies the validity of the proposed method.And the numerical analyses are performed to give some beneficial conclusions.The study shows that 3-D scattering by an alluvial valley is essentially different from the 2-D case,and that the presence of soil layer affects not only the amplitude value of surface displacements but also the distribution of surface displacements.
文摘Natural monopoly,because of its spontaneous or natural characteristics, must have some mysterious causes of reasonableness.Thus,the regulations to its efficiency loss would have a different way compared to other monopolies. That the characteristics of natural monopoly,in the case of water industry, are that the infrastructure investments are very large,most of which are used to build the transportation system? The webs for transporting their products to their customers,and the products are identity goods or services.By examining the characteristics of natural monopoly,this paper proposed away to break upand remodel the industry of“natural monopoly”.The main clue of remodeling is that the governments,who represent the public and who have the power to control over public resources,should build and maintain a public web platform for the goods’ transportation uses, and break up the barrier ofthe entry so as to produce a market-oriented competitive structure.The running modeland the condition of remodeling are put forward and the cost-revenue analysis of the operation is briefly under consideration.
