旋转条件下U形通道转弯段形状对流动和传热特性的影响

In this paper,the flow and heat transfer characteristics in U-shaped channel with three different turn shapes are studied.The rotation number ranges from 0~0.251,Reynolds number are 11500,23000,34500,respectively.The results show that the flow separation and reattachment in the turning section are the key factors affecting the local heat transfer and pressure loss of U-shaped channel.The square turn will generate corner vortices at the outside of the turning section,and the size of the inner separation vortex and reattachment vortex is larger than that of the other two turn shapes.The existence of vortex system will increase the mixing and enhance heat transfer,but increase the pressure loss,so its relative Nusselt number and pressure loss are the largest.There are corner vortices on the outside of the turning section of the channel with a inner circle turn and outer square turn,but the arc-shaped inner edge makes its separation delay and the separation vortex decrease,and the size of the reattachment vortex also decreases.The arc shaped outer edge of the channel with circle turn in both inner and outer further inhibits the generation of corner vortices,so its relative Nusselt number and pressure loss are the lowest.Rotation will cause the fluid to deflect under the influence of Coriolis force,strengthen the heat transfer on the trailing surface of radial outflow and the leading surface of radial internal flow,and generate secondary flow and separation vortex in the turning section,resulting in the change of vortex structure in the turning section.With the increase of rotation number,the Nusselt number of the three types of turning section structures increases.The thermal performance factor of the three channels increases with the increase of rotating speed,and the channel with a inner circle turn and outer square turn is the highest,which is 9.6%higher than the channel with circle turn in both inner and outer on average,and 17.8%higher than the channel with square turn in both inner and outer.

Polyoxometalate-encapsulated metal-organic frameworks with diverse cages for the C-H bond oxidation of alkylbenzenes

Exploring new heterogeneous catalysts to achieve efficient C-H bond oxidation is momentous in industrial chemical production.Herein,three Fe-incorporated polyoxometalate-encapsulated metal-organic frameworks(POM@MOFs),[Fe(H_(2)O)_(3)(dtb)][Fe(dtb)_(2)][HBW_(12)O_(40)]-12H_(2)O(1),[Fe(H_(2)O)2(dtb)]_(2)[Fe(dtb)_(2)(Hdtb)][SiW^(Ⅵ)_(9)W^(Ⅴ)_(3)O_(40)]·16H_(2)O(2),[Fe(H_(2)O)_(2)]_(4)(dtb)_(5)[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]_(2)·18H_(2)O(3),(dtb=1,4-di[4H-1,2,4-triazol-4-yl]-benzene),were hydrothermally synthesized for catalytic C-H bond oxidation.They exhibited three-dimensional(3-D)POM-based metal-organic host-guest frameworks with diverse cages.In compound 1,cationic metal-organic frameworks constructed by binuclear[Fe_(2)(dtb)_(6)(H_(2)O)_(2)]^(4+)clusters and dtb ligands present a pcu alpha-Po primitive cubic topological net and abundant twisted quadrangular prism-shaped cages,in which the monoprotonated[HBW_(12)O_(40)]^(4-)polyoxoanions are encapsulated.In compound 2,two-dimensional(2-D)cationic metal-organic layers constructed by trinuclear[Fe_(3)(dtb)_(6)(H_(2)O)_(4)]^(6+)clusters and dtb ligands display a sql/Shubnikov tetragonal plane net topology,in which the rhomboid-shaped metal-organic windows in adjacent parallel-arranged 2-D layers are enclosed to form an open parallelepiped cage.The[SiW^(Ⅵ)_(9)W^(Ⅴ)_(3)O_(40)]^(7-)poly-oxoanions locate in the parallelepiped cages between 2-D bilayers.In compound 3,the 3-D cationic metal-organic frameworks constructed by binuclear[Fe_(2)(dtb)_(3)(H_(2)O)_(4)]^(4+)clusters and dtb ligands possess a bnn hexagonal BN topology,in which the hexagonal prismatic metal-organic cages accommodate four[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]^(4-)poly-oxoanions.Employing diphenylmethane(DPM)oxidation as C-H bond oxidation model reaction,compounds 1-3 displayed distinct catalytic activities owing to the synergistic effect of polynuclear Fe nodes and poly-oxoanions.Among them,[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]^(4-)-contained compound 3 exhibited higher catalytic activity than polyoxotungstate-based compounds 1-2 with 99%DPM conversion and 99%benzophenone(BP)selectivity within 6 h as well as good recyclability and structural stability.

Liquefaction structures induced by the M5.7 earthquake on May 28, 2018 in Songyuan, Jilin Province, NE China and research implication

An earthquake of magnitude M5.7 occurred in Yamutu village,Songyuan City,Jilin Province,NE China(45°16′12″N/124°42′35″E)on May 28,2018,with a focal depth of 13 km.The epicenter is located at the intersection of the Fuyu/Songyuan-Zhaodong Fault,Second Songhua River Fault and Fuyu North Fault which lies northwest of TanchengLujiang Fault(Tan-Lu Fault).The earthquake-induced widespread liquefaction structures and ground surface fissures within 3 km from the epicenter,caused serious disasters to the local surroundings.The visible liquefied structures include sand volcanoes,liquefied sand mounds,sand dikes and sand sills.Sand volcanoes can be divided into sand volcano with a crater,sand volcano without a crater and water volcano(no sand).Other soft-sediment deformation structures(SSDS)induced by the earthquake include deformation lamination,load and flame structures,deformation folds,dish structures,convolute bedding and water-escape structures.The formation process of the sand volcanoes comprises three stages:(1)building up excess pore-fluid pressure in the liquefied layer,(2)cracking of the low-permeable overlying layer,and(3)mixture of sand-water venting out of the ground surface.During the upward movement,the liquefied sand is injected into the low-permeable layer to form sand veins,sand sills and various types of deformation structures.Vertical distribution of seismic liquefaction structure can be divided into four zones:the thoroughly liquefied zone,the lower liquefied zone with SSDS,the upper liquefied zone with SSDS,and the ground surface liquefied zone.The liquefaction occurred at a burial depth of 2–5 m,and the thickness of liquefied sand is 2 m.NE-SW(35°–215°)trending compressive stress is possibly the seismogenic trigger of the Songyuan M5.7 earthquake that caused the fault(Fuyu/Songyuan-Zhaodong Fault)to reactivate.The study of the Songyuan seismic liquefaction structures gives insight into the prediction of modern earthquakes and disasterprone areas.Meanwhile it provides abundant basic material for studying earthquake-induced SSDS in both ancient and modern sediments.The research is obviously of great significance to reveal that the northern Tan-Lu Fault has entered a stage of active seismic activity since the twenty-first century.