The backward-facing step is a critical problem existing in many engineering and industrial applications.In this study,a semi-porous baffle(the root of the baffle is a porous medium and the tip is solid) is placed behi...The backward-facing step is a critical problem existing in many engineering and industrial applications.In this study,a semi-porous baffle(the root of the baffle is a porous medium and the tip is solid) is placed behind the step.The effects of the length of the porous part,and the baffle location on the energy transfer and pressure drop are studied in different Reynolds numbers(Re=100,200,300,400,500).The effect of the Darcy number of the porous medium on the aforementioned parameters is also investigated.Both the local maximum and average relative Nusselt numbers(divided by the Nusselt of the base case with no baffle at the same Reynolds) and relative pressure drop(calculated as the relative Nusselt number) are reported.The results show that by adoption of the proper length of the porous medium,the average relative and maximum local Nusselt numbers could be enhanced by 20% and 90%,respectively.Low permeable porous media give better energy transfer.For example,porous media with Da=10^(-5) give 30% better maximum local Nusselt number and about 7% higher average Nusselt number with respect to the same case with Da=10^(-2).展开更多
Forced convective heat transfer in a plate channel filled with metallic spherical particles was investigated experimentally and numerically. The test section, 58 mm×80mm×5mm in size, was heated by a 0.4 mm t...Forced convective heat transfer in a plate channel filled with metallic spherical particles was investigated experimentally and numerically. The test section, 58 mm×80mm×5mm in size, was heated by a 0.4 mm thick plate electrical heater. The coolant water now rate ranged from 0.015 to 0.833 kg/s.The local wall temperature distribution was measured along with the inlet and outlet fluid temperatures and pressures. The results illustrate the heat transfer augmentation and increased pressure drop caused by the porous medium. The heat transfer coefficient was increased 5-12 times by the porous media although the hydraulic resistance was increased even more. The Nusselt number and the heat transfer coefficient increased with decreasing particIe diameter, while the pressure drop decreased as the particle diameter increased. It was found that, for the conditions studied (metallic packed bed),the effect of thermal dispersion did not need to be considered in the physical model, as opposed to a non-metallic packed bed, where thermal dispersion is important.展开更多
A highly porous nickel-film electrode with satisfactory mechanical strength was prepared by a facile vertical template-assisted composite electrodeposition method using polystyrene(PS) microspheres templates, with the...A highly porous nickel-film electrode with satisfactory mechanical strength was prepared by a facile vertical template-assisted composite electrodeposition method using polystyrene(PS) microspheres templates, with the aim of improving the electrocatalytic activity for the hydrogen-evolution reaction(HER). During the composite electrodeposition process, the hydrophobic PS microspheres were highly dispersed in the electrolyte with the help of a surfactant, and then co-deposited with Ni to form the film electrode. After removing the PS templates by annealing, a porous Ni film containing large amount of uniformly dispersed pores with narrow size distribution was obtained, and then applied as the electrode for the HER in an alkaline medium. As evidenced by the electrochemical analysis, the porous Ni film electrode exhibits higher catalytic activity as compared to a dense Ni film electrode and is superior to a Ni/Ru O2/Ce O2 commercial electrode. The effect of temperature on the catalytic properties of the porous Ni film electrode was also investigated; the activation energy was calculated as 17.26 k J/mol. The enhanced activity toward the HER was attributed to the improved electrochemical surface area and mass transportation facilitated by the high porosity of the synthesized Ni film electrode.展开更多
文摘The backward-facing step is a critical problem existing in many engineering and industrial applications.In this study,a semi-porous baffle(the root of the baffle is a porous medium and the tip is solid) is placed behind the step.The effects of the length of the porous part,and the baffle location on the energy transfer and pressure drop are studied in different Reynolds numbers(Re=100,200,300,400,500).The effect of the Darcy number of the porous medium on the aforementioned parameters is also investigated.Both the local maximum and average relative Nusselt numbers(divided by the Nusselt of the base case with no baffle at the same Reynolds) and relative pressure drop(calculated as the relative Nusselt number) are reported.The results show that by adoption of the proper length of the porous medium,the average relative and maximum local Nusselt numbers could be enhanced by 20% and 90%,respectively.Low permeable porous media give better energy transfer.For example,porous media with Da=10^(-5) give 30% better maximum local Nusselt number and about 7% higher average Nusselt number with respect to the same case with Da=10^(-2).
文摘Forced convective heat transfer in a plate channel filled with metallic spherical particles was investigated experimentally and numerically. The test section, 58 mm×80mm×5mm in size, was heated by a 0.4 mm thick plate electrical heater. The coolant water now rate ranged from 0.015 to 0.833 kg/s.The local wall temperature distribution was measured along with the inlet and outlet fluid temperatures and pressures. The results illustrate the heat transfer augmentation and increased pressure drop caused by the porous medium. The heat transfer coefficient was increased 5-12 times by the porous media although the hydraulic resistance was increased even more. The Nusselt number and the heat transfer coefficient increased with decreasing particIe diameter, while the pressure drop decreased as the particle diameter increased. It was found that, for the conditions studied (metallic packed bed),the effect of thermal dispersion did not need to be considered in the physical model, as opposed to a non-metallic packed bed, where thermal dispersion is important.
基金supported by the National Natural Science Foundation of China(51125007)the National Key Technology R&D Program of China(2009BAE87B00)
文摘A highly porous nickel-film electrode with satisfactory mechanical strength was prepared by a facile vertical template-assisted composite electrodeposition method using polystyrene(PS) microspheres templates, with the aim of improving the electrocatalytic activity for the hydrogen-evolution reaction(HER). During the composite electrodeposition process, the hydrophobic PS microspheres were highly dispersed in the electrolyte with the help of a surfactant, and then co-deposited with Ni to form the film electrode. After removing the PS templates by annealing, a porous Ni film containing large amount of uniformly dispersed pores with narrow size distribution was obtained, and then applied as the electrode for the HER in an alkaline medium. As evidenced by the electrochemical analysis, the porous Ni film electrode exhibits higher catalytic activity as compared to a dense Ni film electrode and is superior to a Ni/Ru O2/Ce O2 commercial electrode. The effect of temperature on the catalytic properties of the porous Ni film electrode was also investigated; the activation energy was calculated as 17.26 k J/mol. The enhanced activity toward the HER was attributed to the improved electrochemical surface area and mass transportation facilitated by the high porosity of the synthesized Ni film electrode.
