This paper investigated the influences of surface properties of carbon support and nickel precursors(nickel nitrate, nickel chloride and nickel acetate) on Ni nanoparticle sizes and catalytic performances for steam re...This paper investigated the influences of surface properties of carbon support and nickel precursors(nickel nitrate, nickel chloride and nickel acetate) on Ni nanoparticle sizes and catalytic performances for steam reforming of toluene. Treatment with nitric acid helped to increase the amount of functional groups on the surface and hydrophilic nature of carbon support, leading to a homogeneous distribution of Ni nanoparticles. The thermal decomposition products of nickel precursor also played an important role, Ni nanoparticles supported on carbon treated with acid using nickel nitrate as the precursor exhibited the smallest mean diameter of 4.5 nm. With the loading amount increased from 6 wt% to 18 wt%, the mean particle size of Ni nanoparticles varied from4.5 nm to 9.1 nm. The as-prepared catalyst showed a high catalytic activity and a good stability for toluene steam reforming: 98.1% conversion of toluene was obtained with the Ni content of 12 wt% and the S/C ratio of3, and the conversion only decreased to 92.0% after 700 min. Because of the high activity, good stability, and low cost, the as-prepared catalyst opens up new opportunities for tar removing.展开更多
The geological and physico-mechanical properties characterization of deep soft rocks is one of the critical scientific issues for deep soft rock engineering. In the present study, X-ray diffraction(XRD) analysis,scann...The geological and physico-mechanical properties characterization of deep soft rocks is one of the critical scientific issues for deep soft rock engineering. In the present study, X-ray diffraction(XRD) analysis,scanning electron microscope(SEM), and mercury intrusion porosimetry experiments were carried out to investigate the mineral compositions, microstructure and porosity characteristics of the 13 claybearing soft rock samples collected from a deep coal mine in China. Water vapor absorption and uniaxial compressive experiments were also performed to examine water absorption characteristics and waterinduced strength degradation effect of the investigated deep soft rock samples. The results show that the dominant mineral components in mudstone, coarse sandstone and fine sandstone samples were calcite, quartz and clay respectively. The contents of clay minerals in all samples were relatively high and ranged from 12.3%(N-4) to 56.5%(XS-1). Water vapor absorption processes of all the soft rock samples follow an exponential law which is very similar to the water vapor absorption behavior of conglomerate samples reported in our earlier study. Correlation analyses also suggested that there were good positive correlation relationships between water absorptivity and clay minerals for both mudstone and sandstone samples. Furthermore, it was found that vapor absorption was not correlated with the porosity for mudstone, however, positive correlation relationship was found between them for sandstone. Correlation analysis between UCS, modulus of elasticity and water content demonstrated that both of them tend to decrease with the increase of their water content due to water absorption.展开更多
N2O represents a popular oxidizer for hybrid rocket motors for a variety of reasons, including safety, ease of access and self-pressurization. It is often used as a saturated two-phase fluid in these applications to t...N2O represents a popular oxidizer for hybrid rocket motors for a variety of reasons, including safety, ease of access and self-pressurization. It is often used as a saturated two-phase fluid in these applications to take advantage of self-pressurization. Recent interest in using this oxidizer in regeneratively cooled engines requires a detailed heat transfer process analysis to the coolant, in order to quantify performance. Since the injection of N2O typically takes place in the two-phase region, our study focuses on heat transfer rates in this region, and extends the region to include superheated vapor. This analysis is critical for these cooling applications, because the exothermic decomposition nature of N2O also means that unchecked heating in the superheated region may result in a runaway reaction in the cooling passages. Furthermore, provided that sufficient heat transfer rates are available, N2O is expected to accelerate in the cooling passages due to Rayleigh flow effects much like those of a calorically perfect gas. The proximity of superheated N2O to its saturated vapor curve, at the conditions studied here, makes the suitability of a perfect gas model questionable, but that benchmarks is still useful. This paper presents the development of an experimental apparatus （a ＂Rayleigh tube＂）, specifically designed to study this problem, and test the analytical methods developed to model it. Since we focus on the development of the apparatus, the data presented were uses primarily calorically perfect gas surrogates, but the goal is to apply the apparatus and method to N2O. The design and construction of the Rayleigh tube is presented, along with preliminary results with perfect gases. Finally, we present preliminary results on heated N2O flow. Using a simple model for predicted dry-out point, we investigate where superheating may be expected to occur. We present estimates of critical heating and compare them to the heat required to achieve self-decomposition.展开更多
A physical model is established in this paper to describe the heat transfer and two phase flow of a refrigerant in the evaporator and condenser of a vapor compression refrigeration system. The model is then used to de...A physical model is established in this paper to describe the heat transfer and two phase flow of a refrigerant in the evaporator and condenser of a vapor compression refrigeration system. The model is then used to determine the refrigerant charge in vapor compression units. The model is used for a sensitivity analysis to determine the effect that yaring design parameters on the refrigerant charge. The model is also used to evaluate the effect of refrigerant charge and the thermal physical properties on the refrigeration cycle. The predicted value of the refrigerant charge and experimental data agree well.The model and the method presented in this paper could be used to design vapour compression units such as domestic refrigerators and air conditioners.展开更多
基金Supported by the National Natural Science Foundation of China(21606008,21436002)the National Basic Research Foundation of China(2013CB733600)the Fundamental Research Funds for the Central Universities(ZY1630,JD1617,buctrc201616,and buctrc201617)
文摘This paper investigated the influences of surface properties of carbon support and nickel precursors(nickel nitrate, nickel chloride and nickel acetate) on Ni nanoparticle sizes and catalytic performances for steam reforming of toluene. Treatment with nitric acid helped to increase the amount of functional groups on the surface and hydrophilic nature of carbon support, leading to a homogeneous distribution of Ni nanoparticles. The thermal decomposition products of nickel precursor also played an important role, Ni nanoparticles supported on carbon treated with acid using nickel nitrate as the precursor exhibited the smallest mean diameter of 4.5 nm. With the loading amount increased from 6 wt% to 18 wt%, the mean particle size of Ni nanoparticles varied from4.5 nm to 9.1 nm. The as-prepared catalyst showed a high catalytic activity and a good stability for toluene steam reforming: 98.1% conversion of toluene was obtained with the Ni content of 12 wt% and the S/C ratio of3, and the conversion only decreased to 92.0% after 700 min. Because of the high activity, good stability, and low cost, the as-prepared catalyst opens up new opportunities for tar removing.
基金provided by the National Natural Science Foundation of China (No. 51134005)the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20130023120016)the Fundamental Research Funds for the Central Universities of China (No. 2010QL07)
文摘The geological and physico-mechanical properties characterization of deep soft rocks is one of the critical scientific issues for deep soft rock engineering. In the present study, X-ray diffraction(XRD) analysis,scanning electron microscope(SEM), and mercury intrusion porosimetry experiments were carried out to investigate the mineral compositions, microstructure and porosity characteristics of the 13 claybearing soft rock samples collected from a deep coal mine in China. Water vapor absorption and uniaxial compressive experiments were also performed to examine water absorption characteristics and waterinduced strength degradation effect of the investigated deep soft rock samples. The results show that the dominant mineral components in mudstone, coarse sandstone and fine sandstone samples were calcite, quartz and clay respectively. The contents of clay minerals in all samples were relatively high and ranged from 12.3%(N-4) to 56.5%(XS-1). Water vapor absorption processes of all the soft rock samples follow an exponential law which is very similar to the water vapor absorption behavior of conglomerate samples reported in our earlier study. Correlation analyses also suggested that there were good positive correlation relationships between water absorptivity and clay minerals for both mudstone and sandstone samples. Furthermore, it was found that vapor absorption was not correlated with the porosity for mudstone, however, positive correlation relationship was found between them for sandstone. Correlation analysis between UCS, modulus of elasticity and water content demonstrated that both of them tend to decrease with the increase of their water content due to water absorption.
文摘N2O represents a popular oxidizer for hybrid rocket motors for a variety of reasons, including safety, ease of access and self-pressurization. It is often used as a saturated two-phase fluid in these applications to take advantage of self-pressurization. Recent interest in using this oxidizer in regeneratively cooled engines requires a detailed heat transfer process analysis to the coolant, in order to quantify performance. Since the injection of N2O typically takes place in the two-phase region, our study focuses on heat transfer rates in this region, and extends the region to include superheated vapor. This analysis is critical for these cooling applications, because the exothermic decomposition nature of N2O also means that unchecked heating in the superheated region may result in a runaway reaction in the cooling passages. Furthermore, provided that sufficient heat transfer rates are available, N2O is expected to accelerate in the cooling passages due to Rayleigh flow effects much like those of a calorically perfect gas. The proximity of superheated N2O to its saturated vapor curve, at the conditions studied here, makes the suitability of a perfect gas model questionable, but that benchmarks is still useful. This paper presents the development of an experimental apparatus （a ＂Rayleigh tube＂）, specifically designed to study this problem, and test the analytical methods developed to model it. Since we focus on the development of the apparatus, the data presented were uses primarily calorically perfect gas surrogates, but the goal is to apply the apparatus and method to N2O. The design and construction of the Rayleigh tube is presented, along with preliminary results with perfect gases. Finally, we present preliminary results on heated N2O flow. Using a simple model for predicted dry-out point, we investigate where superheating may be expected to occur. We present estimates of critical heating and compare them to the heat required to achieve self-decomposition.
文摘A physical model is established in this paper to describe the heat transfer and two phase flow of a refrigerant in the evaporator and condenser of a vapor compression refrigeration system. The model is then used to determine the refrigerant charge in vapor compression units. The model is used for a sensitivity analysis to determine the effect that yaring design parameters on the refrigerant charge. The model is also used to evaluate the effect of refrigerant charge and the thermal physical properties on the refrigeration cycle. The predicted value of the refrigerant charge and experimental data agree well.The model and the method presented in this paper could be used to design vapour compression units such as domestic refrigerators and air conditioners.
