In order to reduce the losses caused by tip-leakage flow, axisymmetric contouring is applied to the casing of a two-stage unshrouded high pressure turbine(HPT) of aero-engine in this paper. This investigation focuses ...In order to reduce the losses caused by tip-leakage flow, axisymmetric contouring is applied to the casing of a two-stage unshrouded high pressure turbine(HPT) of aero-engine in this paper. This investigation focuses on the effects of contoured axisymmetric-casing on the blade tipleakage flow. While the size of tip clearance remains the same as the original design, the rotor casing and the blade tip are obtained with the same contoured arc shape. Numerical calculation results show that a promotion of 0.14% to the overall efficiency is achieved. Detailed analysis indicates that it reduces the entropy generation rate caused by the complex vortex structure in the rotor tip region, especially in the tip-leakage vortex. The low velocity region in the leading edge(LE) part of the tip gap is enlarged and the pressure side/tip junction separation bubble extends much further away from the leading edge in the clearance. So the blocking effect of pressure side/tip junction separation bubble on clearance flow prevents more flow on the tip pressure side from leaking to the suction side, which results in weaker leakage vortex and less associated losses.展开更多
Using tetraethyl orthosilicate(TEOS)as the pre-cursor of silica,the silica aerogel and xerogel,which were used as supports of nickel-based catalysts for liquid hydroge-nation of m-dinitrobenzene to m-phenylenediamine,...Using tetraethyl orthosilicate(TEOS)as the pre-cursor of silica,the silica aerogel and xerogel,which were used as supports of nickel-based catalysts for liquid hydroge-nation of m-dinitrobenzene to m-phenylenediamine,were prepared by the sol-gel method combined with supercritical drying(SCD)and conventional drying,respectively.Then,a series of nickel-based catalyst samples supported on these supports were prepared by the incipient wetness impregna-tion method with an aqueous solution of nickel nitrate as well as lanthanum nitrate as impregnation liquids.Based on the characterization results of nitrogen adsorption-desorption(BET),X-ray diffraction(XRD),temperature programmed reduction(TPR),temperature-programmed desorption of hydrogen(H2-TPD),and catalytic activity evaluation,the physico-chemical properties and catalytic performances of the catalysts were investigated.The results show that the nickel crystallites on the binary nickel catalyst using silica aerogel as support are of smaller particle size.However,com-pared with the sample supported on silica xerogel,the nickel catalyst supported on the silica aerogel exhibits lower activity and selectivity for the hydrogenation of m-dinitrobenzene because it has a lesser amount of active sites and weaker absorption ability to reactants caused by sintering of the nickel crystallites.The addition of promoter La2O3 could increase the activity and selectivity of the catalysts.Among all the nickel-based catalyst samples prepared,the La2O3 promoted ternary nickel-based catalyst supported on silica xerogel exhibits the highest activity and selectivity for the hydrogenation of m-dinitrobenzene to m-phenylenediamine,which could be attributed to its highest active surface area and appropriate absorption strength to reactants.Over this prom-ising catalyst,the conversion of m-dinitrobenzene and the yield of m-phenylenediamine could reach 97.0%and 93.1%,respectively,under proper reaction conditions of hydrogen pressure 2.6 MPa,temperature 373 K,and reaction time 1 h.展开更多
文摘In order to reduce the losses caused by tip-leakage flow, axisymmetric contouring is applied to the casing of a two-stage unshrouded high pressure turbine(HPT) of aero-engine in this paper. This investigation focuses on the effects of contoured axisymmetric-casing on the blade tipleakage flow. While the size of tip clearance remains the same as the original design, the rotor casing and the blade tip are obtained with the same contoured arc shape. Numerical calculation results show that a promotion of 0.14% to the overall efficiency is achieved. Detailed analysis indicates that it reduces the entropy generation rate caused by the complex vortex structure in the rotor tip region, especially in the tip-leakage vortex. The low velocity region in the leading edge(LE) part of the tip gap is enlarged and the pressure side/tip junction separation bubble extends much further away from the leading edge in the clearance. So the blocking effect of pressure side/tip junction separation bubble on clearance flow prevents more flow on the tip pressure side from leaking to the suction side, which results in weaker leakage vortex and less associated losses.
文摘Using tetraethyl orthosilicate(TEOS)as the pre-cursor of silica,the silica aerogel and xerogel,which were used as supports of nickel-based catalysts for liquid hydroge-nation of m-dinitrobenzene to m-phenylenediamine,were prepared by the sol-gel method combined with supercritical drying(SCD)and conventional drying,respectively.Then,a series of nickel-based catalyst samples supported on these supports were prepared by the incipient wetness impregna-tion method with an aqueous solution of nickel nitrate as well as lanthanum nitrate as impregnation liquids.Based on the characterization results of nitrogen adsorption-desorption(BET),X-ray diffraction(XRD),temperature programmed reduction(TPR),temperature-programmed desorption of hydrogen(H2-TPD),and catalytic activity evaluation,the physico-chemical properties and catalytic performances of the catalysts were investigated.The results show that the nickel crystallites on the binary nickel catalyst using silica aerogel as support are of smaller particle size.However,com-pared with the sample supported on silica xerogel,the nickel catalyst supported on the silica aerogel exhibits lower activity and selectivity for the hydrogenation of m-dinitrobenzene because it has a lesser amount of active sites and weaker absorption ability to reactants caused by sintering of the nickel crystallites.The addition of promoter La2O3 could increase the activity and selectivity of the catalysts.Among all the nickel-based catalyst samples prepared,the La2O3 promoted ternary nickel-based catalyst supported on silica xerogel exhibits the highest activity and selectivity for the hydrogenation of m-dinitrobenzene to m-phenylenediamine,which could be attributed to its highest active surface area and appropriate absorption strength to reactants.Over this prom-ising catalyst,the conversion of m-dinitrobenzene and the yield of m-phenylenediamine could reach 97.0%and 93.1%,respectively,under proper reaction conditions of hydrogen pressure 2.6 MPa,temperature 373 K,and reaction time 1 h.
