The refrigerant flow distribution in the parallel flow microchannel evaporators is experimentally investigated to study the effect of header configuration.Six different configurations are tested in the same evaporator...The refrigerant flow distribution in the parallel flow microchannel evaporators is experimentally investigated to study the effect of header configuration.Six different configurations are tested in the same evaporator by installing insertion device and partition plate in the header to ensure the consistency of the other structure parameters.The results show that the uniformity of refrigerant flow distribution and the heat transfer rate are greatly improved by reducing the sectional area of header.The heat transfer rate can increase by 67.93%by reducing the sectional area of both inlet and outlet headers.The uniformity of refrigerant flow distribution and the heat transfer rate become worse after installing the partition plate in the insertion devices and changing the inner structure of the header further.展开更多
The mechanical stress distribution and the stress concentrations of the superheater outlet header of a 600MW supercritical boiler were analyzed by the finite element method. The results showed that the stress concentr...The mechanical stress distribution and the stress concentrations of the superheater outlet header of a 600MW supercritical boiler were analyzed by the finite element method. The results showed that the stress concentrated at the inside conjunction area between the pipe and the header cylinder , and the value of the maximum mechanical stress concentration factor is 2.51.展开更多
The difficult problem of automatically welding nipples onto the header is first analyzed in this paper, and then the overall structure and operating principle of the robot working unit are introduced. The robot and th...The difficult problem of automatically welding nipples onto the header is first analyzed in this paper, and then the overall structure and operating principle of the robot working unit are introduced. The robot and the measuring device are located by employing the traveling lorry, and this unit enables the robot to adjust the tracks according to the errors received from the measuring device, and then the nipples are welded properly. This paper emphases on the development of the master-slave control system, in which the prograrmmable Logic Controller (PLC) is used as the master computer.展开更多
At present, the main attention of researchers is paid to the deterioration of heat transfer when heating the outer surface of the pipe with the liquid or steam, flowing inside it, in the presence of films or deposits ...At present, the main attention of researchers is paid to the deterioration of heat transfer when heating the outer surface of the pipe with the liquid or steam, flowing inside it, in the presence of films or deposits on its inner surface. However, when pipe is heating by heat carrier medium, flowing inside it, film on the inner pipe surface serve a dual protective function, protecting the pipe from corrosion and reducing its thermal stress. The article represents the results of the computational analysis of protective films influence on the thermal stressed state of headers and steam pipelines of combined-cycle power plants (CCPP) heat-recovery steam generators at different transient operating conditions particularly at startups from different initial temperature states and thermal shock. It is shown that protective films have a significant influence on the stresses magnitude and damage accumulation mainly for great temperature disturbances (for thermal shock). Calculations were carried out at various thicknesses of films and assuming that their thermal conductivity less than thermal conductivity of the steam pipelines metal.展开更多
Mobile sensor nodes such as hopping sensors are of critical importance in data collection.However,the occurrence of sensing holes is unavoidable due to the energy limitation of the nodes.Thus,it is evident that the re...Mobile sensor nodes such as hopping sensors are of critical importance in data collection.However,the occurrence of sensing holes is unavoidable due to the energy limitation of the nodes.Thus,it is evident that the relocation of mobile sensors is the most desirable method to recover the sensing holes.The previous research conducted by the authors so far demonstrated the most realistic hopping sensor relocation scheme,which is suitable for the distributed environment.In previous studies,the cluster header plays an essential role in detecting the sensing hole and requesting the neighboring cluster to recover the sensing hole that occurred in the sensor node.However,the limitations of the cluster header in the previously proposed relocation protocol are not fully considered.Because the cluster header jumps more frequently than non-header nodes,its energy con-sumption is relatively high compared to other nodes.Therefore,it is most likely to lead to header node failure and can lead to data loss on the network.In this paper,the jumping ability and energy consumption of the cluster header are seriously considered.Additional ability to replace cluster headers in case of failure is also implemented.Simulation results show that the data collection time can be further increased,which demonstrates the validity of the proposed algorithms.展开更多
One aspect of cybersecurity,incorporates the study of Portable Executables(PE)files maleficence.Artificial Intelligence(AI)can be employed in such studies,since AI has the ability to discriminate benign from malicious...One aspect of cybersecurity,incorporates the study of Portable Executables(PE)files maleficence.Artificial Intelligence(AI)can be employed in such studies,since AI has the ability to discriminate benign from malicious files.In this study,an exclusive set of 29 features was collected from trusted implementations,this set was used as a baseline to analyze the presented work in this research.A Decision Tree(DT)and Neural Network Multi-Layer Perceptron(NN-MLPC)algorithms were utilized during this work.Both algorithms were chosen after testing a few diverse procedures.This work implements a method of subgrouping features to answer questions such as,which feature has a positive impact on accuracy when added?Is it possible to determine a reliable feature set to distinguish a malicious PE file from a benign one?when combining features,would it have any effect on malware detection accuracy in a PE file?Results obtained using the proposed method were improved and carried few observations.Generally,the obtained results had practical and numerical parts,for the practical part,the number of features and which features included are the main factors impacting the calculated accuracy,also,the combination of features is as crucial in these calculations.Numerical results included,finding accuracies with enhanced values,for example,NN_MLPC attained 0.979 and 0.98;for DT an accuracy of 0.9825 and 0.986 was attained.展开更多
In discussing coal mine entry construction with rock bolt technology, examinedthe craft and machinery problems as well as the conditions in which to use each kind ofmachine and tool.It exposed the intrinsic flaws of t...In discussing coal mine entry construction with rock bolt technology, examinedthe craft and machinery problems as well as the conditions in which to use each kind ofmachine and tool.It exposed the intrinsic flaws of the widely used road header.The problemis that it was designed according to early timbering support state but is not suitable forrock bolt technology.The way to improve the function of existing road headers is notthrough parallel operations but using the SUDM (Shield Union Driving Machine), which isa new machine that improves construction.This article proposed a few solutions in designto solve this problem.展开更多
In this paper, taking AM-50 Road Heaer as an example, the metheds of structural dynamic modification optimization for road headers are studied using experimental modal analysis and physical parameters analysis. The ma...In this paper, taking AM-50 Road Heaer as an example, the metheds of structural dynamic modification optimization for road headers are studied using experimental modal analysis and physical parameters analysis. The machine’s modal model and lumped mass model are established and the vibration response simulation is calculated for the two models with the load spectral measured. On the above basis, the dynamic parameters of the models are optimised and some useful results have been obtained.The research methods in this paper can be used for the reference to the other lager type mining machines.展开更多
This paper investigates whether security headers are enforced to mitigate cyber-attacks in web-based systems in cyberspace. The security headers examined include X-Content-Type-Options, X-Frame-Options, Strict-Transpo...This paper investigates whether security headers are enforced to mitigate cyber-attacks in web-based systems in cyberspace. The security headers examined include X-Content-Type-Options, X-Frame-Options, Strict-Transport-Security, Referrer-Policy, Content-Security-Policy, and Permissions-Policy. The study employed a controlled experiment using a security header analysis tool. The web-based applications (websites) were analyzed to determine whether security headers have been correctly implemented. The experiment was iterated for 100 universities in Africa which are ranked high. The purposive sampling technique was employed to understand the status quo of the security headers implementations. The results revealed that 70% of the web-based applications in Africa have not enforced security headers in web-based applications. The study proposes a secure system architecture design for addressing web-based applications’ misconfiguration and insecure design. It presents security techniques for securing web-based applications through hardening security headers using automated threat modelling techniques. Furthermore, it recommends adopting the security headers in web-based applications using the proposed secure system architecture design.展开更多
A heat exchanger that arranges flat tubes horizontally has a vertical header that distributes the refrigerant to each tube. When the heat exchanger works as an evaporator, differences in flow conditions at each branch...A heat exchanger that arranges flat tubes horizontally has a vertical header that distributes the refrigerant to each tube. When the heat exchanger works as an evaporator, differences in flow conditions at each branch, such as the ratio and distribution of vapor and liquid, due to the differences in densities and momentums of vapor and liquid in the two-phase flow make equal distribution difficult. This paper describes the distribution characteristics of a four-branch header that has a rectangular cross-section without the internal protrusion of flat tubes in the case of the inflow of the refrigerant R32 from the bottom of the header by using an equipment that can estimate the distribution ratio of the liquid and vapor phase to each branch. This paper also discusses the distribution characteristics on the basis of the flow visualization in the header. The flow visualization shows that a liquid level that contains vapor phase exists in the header and affects the distribution greatly.展开更多
Supercritical carbon dioxide printed circuit board heat exchangers are expected to be applied in third-generation solar thermal power generation.However,the uniformity of supercritical carbon dioxide entering the heat...Supercritical carbon dioxide printed circuit board heat exchangers are expected to be applied in third-generation solar thermal power generation.However,the uniformity of supercritical carbon dioxide entering the heat exchanger has a significant impact on the overall performance of the heat exchanger.In order to improve the uniformity of flow distribution in the inlet header,this article studies and optimizes the inlet header of a printed circuit board heat exchanger through numerical simulation.The results indicate that when supercritical carbon dioxide flows through the header cavity,eddy currents will be generated,which will increase the uneven distribution of flow rate,while reducing the generation of eddy currents will improve the uniform distribution of flow rate.When the dimensionless factor of the inlet header is 6,the hyperbolic configuration is the optimal structure.We also reduced the eddy current region by adding transition segments,and the results showed that the structure was the best when the dilation angle was 10°,which reduced the non-uniformity by 21%compared to the hyperbolic configuration,providing guidance for engineering practice.展开更多
Flow distribution headers play a major role in heat exchangers.The selection of header diameter,branch pipe diameter,branch pipe spacing etc.is based on the designer＇s experience and general guide lines.The proper se...Flow distribution headers play a major role in heat exchangers.The selection of header diameter,branch pipe diameter,branch pipe spacing etc.is based on the designer＇s experience and general guide lines.The proper selection of the header dimensions will yield uniform flow distribution in heat exchangers,which in turn will enhance the heat exchanger efficiency.In this work,the flow distribution in branch pipes and the pressure variation across the branch pipes in laminar and low turbulence region is studied with two models of the inlet dividing headers.When the numerical analysis has been applied,its inability to predict the no flow condition through the branch pipes is revealed.The results are presented in the form of flow rate ratio through branch pipes and nondimensional coefficients across branch pipes which are useful to apply the existing mathematical models for the present experimental setup.展开更多
基金the Key Industry Common Key-Technology Innovation Project of Chongqing Municipal Science and Committee(No.cstc2015zdcy-ztzx60001)
文摘The refrigerant flow distribution in the parallel flow microchannel evaporators is experimentally investigated to study the effect of header configuration.Six different configurations are tested in the same evaporator by installing insertion device and partition plate in the header to ensure the consistency of the other structure parameters.The results show that the uniformity of refrigerant flow distribution and the heat transfer rate are greatly improved by reducing the sectional area of header.The heat transfer rate can increase by 67.93%by reducing the sectional area of both inlet and outlet headers.The uniformity of refrigerant flow distribution and the heat transfer rate become worse after installing the partition plate in the insertion devices and changing the inner structure of the header further.
文摘The mechanical stress distribution and the stress concentrations of the superheater outlet header of a 600MW supercritical boiler were analyzed by the finite element method. The results showed that the stress concentrated at the inside conjunction area between the pipe and the header cylinder , and the value of the maximum mechanical stress concentration factor is 2.51.
文摘The difficult problem of automatically welding nipples onto the header is first analyzed in this paper, and then the overall structure and operating principle of the robot working unit are introduced. The robot and the measuring device are located by employing the traveling lorry, and this unit enables the robot to adjust the tracks according to the errors received from the measuring device, and then the nipples are welded properly. This paper emphases on the development of the master-slave control system, in which the prograrmmable Logic Controller (PLC) is used as the master computer.
文摘At present, the main attention of researchers is paid to the deterioration of heat transfer when heating the outer surface of the pipe with the liquid or steam, flowing inside it, in the presence of films or deposits on its inner surface. However, when pipe is heating by heat carrier medium, flowing inside it, film on the inner pipe surface serve a dual protective function, protecting the pipe from corrosion and reducing its thermal stress. The article represents the results of the computational analysis of protective films influence on the thermal stressed state of headers and steam pipelines of combined-cycle power plants (CCPP) heat-recovery steam generators at different transient operating conditions particularly at startups from different initial temperature states and thermal shock. It is shown that protective films have a significant influence on the stresses magnitude and damage accumulation mainly for great temperature disturbances (for thermal shock). Calculations were carried out at various thicknesses of films and assuming that their thermal conductivity less than thermal conductivity of the steam pipelines metal.
基金supported by Incheon National University Research Grant in 2020(2020–0437)。
文摘Mobile sensor nodes such as hopping sensors are of critical importance in data collection.However,the occurrence of sensing holes is unavoidable due to the energy limitation of the nodes.Thus,it is evident that the relocation of mobile sensors is the most desirable method to recover the sensing holes.The previous research conducted by the authors so far demonstrated the most realistic hopping sensor relocation scheme,which is suitable for the distributed environment.In previous studies,the cluster header plays an essential role in detecting the sensing hole and requesting the neighboring cluster to recover the sensing hole that occurred in the sensor node.However,the limitations of the cluster header in the previously proposed relocation protocol are not fully considered.Because the cluster header jumps more frequently than non-header nodes,its energy con-sumption is relatively high compared to other nodes.Therefore,it is most likely to lead to header node failure and can lead to data loss on the network.In this paper,the jumping ability and energy consumption of the cluster header are seriously considered.Additional ability to replace cluster headers in case of failure is also implemented.Simulation results show that the data collection time can be further increased,which demonstrates the validity of the proposed algorithms.
文摘One aspect of cybersecurity,incorporates the study of Portable Executables(PE)files maleficence.Artificial Intelligence(AI)can be employed in such studies,since AI has the ability to discriminate benign from malicious files.In this study,an exclusive set of 29 features was collected from trusted implementations,this set was used as a baseline to analyze the presented work in this research.A Decision Tree(DT)and Neural Network Multi-Layer Perceptron(NN-MLPC)algorithms were utilized during this work.Both algorithms were chosen after testing a few diverse procedures.This work implements a method of subgrouping features to answer questions such as,which feature has a positive impact on accuracy when added?Is it possible to determine a reliable feature set to distinguish a malicious PE file from a benign one?when combining features,would it have any effect on malware detection accuracy in a PE file?Results obtained using the proposed method were improved and carried few observations.Generally,the obtained results had practical and numerical parts,for the practical part,the number of features and which features included are the main factors impacting the calculated accuracy,also,the combination of features is as crucial in these calculations.Numerical results included,finding accuracies with enhanced values,for example,NN_MLPC attained 0.979 and 0.98;for DT an accuracy of 0.9825 and 0.986 was attained.
文摘In discussing coal mine entry construction with rock bolt technology, examinedthe craft and machinery problems as well as the conditions in which to use each kind ofmachine and tool.It exposed the intrinsic flaws of the widely used road header.The problemis that it was designed according to early timbering support state but is not suitable forrock bolt technology.The way to improve the function of existing road headers is notthrough parallel operations but using the SUDM (Shield Union Driving Machine), which isa new machine that improves construction.This article proposed a few solutions in designto solve this problem.
文摘In this paper, taking AM-50 Road Heaer as an example, the metheds of structural dynamic modification optimization for road headers are studied using experimental modal analysis and physical parameters analysis. The machine’s modal model and lumped mass model are established and the vibration response simulation is calculated for the two models with the load spectral measured. On the above basis, the dynamic parameters of the models are optimised and some useful results have been obtained.The research methods in this paper can be used for the reference to the other lager type mining machines.
文摘This paper investigates whether security headers are enforced to mitigate cyber-attacks in web-based systems in cyberspace. The security headers examined include X-Content-Type-Options, X-Frame-Options, Strict-Transport-Security, Referrer-Policy, Content-Security-Policy, and Permissions-Policy. The study employed a controlled experiment using a security header analysis tool. The web-based applications (websites) were analyzed to determine whether security headers have been correctly implemented. The experiment was iterated for 100 universities in Africa which are ranked high. The purposive sampling technique was employed to understand the status quo of the security headers implementations. The results revealed that 70% of the web-based applications in Africa have not enforced security headers in web-based applications. The study proposes a secure system architecture design for addressing web-based applications’ misconfiguration and insecure design. It presents security techniques for securing web-based applications through hardening security headers using automated threat modelling techniques. Furthermore, it recommends adopting the security headers in web-based applications using the proposed secure system architecture design.
文摘A heat exchanger that arranges flat tubes horizontally has a vertical header that distributes the refrigerant to each tube. When the heat exchanger works as an evaporator, differences in flow conditions at each branch, such as the ratio and distribution of vapor and liquid, due to the differences in densities and momentums of vapor and liquid in the two-phase flow make equal distribution difficult. This paper describes the distribution characteristics of a four-branch header that has a rectangular cross-section without the internal protrusion of flat tubes in the case of the inflow of the refrigerant R32 from the bottom of the header by using an equipment that can estimate the distribution ratio of the liquid and vapor phase to each branch. This paper also discusses the distribution characteristics on the basis of the flow visualization in the header. The flow visualization shows that a liquid level that contains vapor phase exists in the header and affects the distribution greatly.
基金supported by the National Natural Science Foundation of China(No.52076006)National Key Research and Development Program of China(No.2022YFB4202402)。
文摘Supercritical carbon dioxide printed circuit board heat exchangers are expected to be applied in third-generation solar thermal power generation.However,the uniformity of supercritical carbon dioxide entering the heat exchanger has a significant impact on the overall performance of the heat exchanger.In order to improve the uniformity of flow distribution in the inlet header,this article studies and optimizes the inlet header of a printed circuit board heat exchanger through numerical simulation.The results indicate that when supercritical carbon dioxide flows through the header cavity,eddy currents will be generated,which will increase the uneven distribution of flow rate,while reducing the generation of eddy currents will improve the uniform distribution of flow rate.When the dimensionless factor of the inlet header is 6,the hyperbolic configuration is the optimal structure.We also reduced the eddy current region by adding transition segments,and the results showed that the structure was the best when the dilation angle was 10°,which reduced the non-uniformity by 21%compared to the hyperbolic configuration,providing guidance for engineering practice.
文摘Flow distribution headers play a major role in heat exchangers.The selection of header diameter,branch pipe diameter,branch pipe spacing etc.is based on the designer＇s experience and general guide lines.The proper selection of the header dimensions will yield uniform flow distribution in heat exchangers,which in turn will enhance the heat exchanger efficiency.In this work,the flow distribution in branch pipes and the pressure variation across the branch pipes in laminar and low turbulence region is studied with two models of the inlet dividing headers.When the numerical analysis has been applied,its inability to predict the no flow condition through the branch pipes is revealed.The results are presented in the form of flow rate ratio through branch pipes and nondimensional coefficients across branch pipes which are useful to apply the existing mathematical models for the present experimental setup.
