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1.
Liquid or gaseous fuel scramjet technology has made great progress, and there has been some research attention to solid-fuel scramjet. A new scramjet configuration using solid fuel as propellant, namely solid-fuel rocket scramjet, is tested experimentally. It consists of two combustors. One is a rocket combustor used as gas generator, and the other is a supersonic combustor used for secondary combustion. The experiment simulates a flight Mach number of 4 at high altitude (stagnation temperature and pressure are 1170 K and 1.16 MPa, respectively), and metalized solid fuel is used as propellant. The results reveal that fuel-rich gas from the gas generator can burn with air in the supersonic combustor. Preliminary evaluation results show that the combustion efficiency of the propellant is about 90%, and the total pressure recovery coefficient in the supersonic combustor is about 0.6. These results indicate that the configuration of solid-fuel rocket scramjet is feasible.  相似文献   

2.
This paper presents an experimental study on the emission characteristics and combustion instabilities of oxy-fuel combustions in a swirl-stabilized combustor. Different oxygen concentrations （Xoxy=25%-45%, where Xoxy is oxygen concentration by volume）, equivalence ratios （φ=0.75-1.15） and combustion powers （CP= 1.08-2.02 kW） were investigated in the oxy-fuel （CH4/CO2/O2） combustions, and reference cases （Xoxy=25%-35%, CH4/N2/O2 flames） were covered. The results show that the oxygen concentration in the oxidant stream significantly affects the combustion delay in the oxy-fuel flames, and the equivalence ratio has a slight effect, whereas the combustion power shows no impact. The temperature levels of the oxy-fuel flames inside the combustion chamber are much higher （up to 38.7%） than those of the reference cases. Carbon monoxide was vastly produced when Xoxy〉35% or （φ〉0.95 in the oxy-fuel flames, while no nitric oxide was found in the exhaust gases because no N2 participates in the combustion process. The combustion instability of the oxy-fuel combustion is very different from those of the reference cases with similar oxygen content. Oxy-fuel combustions excite strong oscillations in all cases studied Xoxy=25%-45%. However, no pressure fluctuations were detected in the reference cases when Xoxy〉28.6% accomplished by heavily sooting flames which were not found in the oxy-fuel combustions. Spectrum analysis shows that the frequency of dynamic pressure oscillations exhibits randomness in the range of 50-250 Hz, therefore resulting in a very small resultant amplitude. Temporal oscillations are very strong with amplitudes larger than 200 Pa, even short time fast Fourier transform （FFT） analysis （0.08 s） shows that the pressure amplitude can be larger than 40 Pa.  相似文献   

3.
In this study, a porous inserted regenerative thermal oxidizer （PRTO） system was developed for a 125 kW industrial copper-melting furnace, due to its advantages of low NOr emissions and high radiant efficiency. Zirconium dioxide （ZrOz） ce- ramic foams were placed into the combustion zone of a regenerative thermal oxidizer （RTO）. Different performance characteris- tics of the RTO and PRTO systems, including pressure drop, temperature distribution, emissions, and energy efficiency, were evaluated to study the effects of the porous inserts on non-premixed CH4 combustion. It was found that the PRTO system achieved a significant reduction in the NOx emission level and a fuel saving of approximately 30% compared to the RTO system. It is most suitable for a lean combustion process at an equivalence ratio 〈0.4 with NOx and CO emission levels within 0.002%~）.003% and 0.001%q3.002%, respectively.  相似文献   

4.
In this paper,a new pressure reducing valve(PRV) with an orifice plate is proposed.The main objective is to explain the mechanisms of pressure reduction and energy conversion in the new PRV.A numerical simulation method was used to investigate the PRV internal flow field and to analyze the throttling effects of the orifice plate and the transform of thermal parameters as outlet pressure,outlet temperature,velocity,and superheat.A structure improvement method for the valve body and orifice plate is put forward to reduce energy loss.The governing equations for internal flow numerical simulation are composed of the continuity,momentum,energy and k-ε transport equations,based on isotropic eddy viscosity theory.Different valve plug displacement models were built to describe the double throttling process.Our analysis shows that the steam pressure drops twice and the degree of superheat increases.There are also lots of eddies which clog the flow channel and disturb the steam flow in the valve cavity after the valve plug and the outlet cavity.After modifying the structure,the numerical results show a better performance of steam flow.  相似文献   

5.
设计制造了工业燃烧技术和加热炉技术的教学实验与科研装置,主要包括水套加热炉、燃油及燃气全自动燃烧机、烟气分析仪等。由全自动燃烧机为水套炉提供热源,通过燃烧室外侧水套及管式换热器,将热量传递给循环水,出口烟气温度为70~150℃;利用穿过水套的测量孔,测量燃烧室的温度场、速度场、浓度场,在烟道出口测定烟气成分。利用该装置能够进行科学全面的燃烧技术的研究和评价,并已在教学实验中取得了很好的教学效果。  相似文献   

6.
This study presents experimental results focused on a performance comparison of a transcritical CO2 ejector system without an internal heat exchanger (IHX) (EJE-S) to a transcritical CO2 ejector system with an IHX (EJE-IHX-S). The comparison includes the effects of changes in operating conditions such as cooling water flow rate and inlet temperature. Experiments are conducted to assess the influence of the IHX on the heating coefficient of performance (COPr), heating capacity, entrainment ratio, pressure lift, and other parameters. The primary flow rate of the EJE-IHX-S is higher than that of the EJE-S. The pressure lift and actual ejector work recovery are reduced when the IHX is added to the transcritical CO2 ejector system. Using a more practical performance calculation, the compression ratio in the EJE-S is reduced by 10.0%–12.1%, while that of EJE-IHX-S is reduced only by 5.6%–6.7% compared to that of a conventional transcritical CO2 system. Experimental results are used to validate the findings that the IHX weakens the contribution of the ejector to the system performance.  相似文献   

7.
Does an online, multimedia case study influence students’ performance, motivation, and perceptions of science in collegiate level biology classes, and if so, how? One hundred and eight students in 5 classes from 4 campuses in the United States and Puerto Rico participated in data collection (performance tests, surveys and focus group interviews). Pre- and post-test results increased after students participated in the learning environment (F(1, 80) = 17.256, p ≤ 0.01, η2 = 0.177). Student confidence in their knowledge also increased. During focus group interviews students reported that the project was a good learning experience (95 %), would help with future classes or careers (87 %), and stimulated student curiosity by demonstrating the application of theoretical knowledge in real-world situations (64 %). The learning environment motivated students by making material relevant, which resulted in better performance. This pedagogical tool is not instructor dependent, and is adaptable.  相似文献   

8.
对微型燃气轮机旋流燃烧室内湍流流动PIV测量中产生的非轴对称性误差的原因进行了分析,提出了基于CFD技术的旋流燃烧室内湍流流动PIV测量误差的修正方法,将修正后的实验数据与数值计算结果进行了比较,结果表明,该修正方法可以有效地减小旋流燃烧室内湍流流动PIV测量中产生的非轴对称性的误差。  相似文献   

9.
The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.  相似文献   

10.
In iron ore sintering, the granulation process is the first and an important step. As the fine particles adhere to the coarse coke particles, the NO x emission generated from coke combustion may be expected to be influenced by that adhering layer. In this study, the granule size distributions and adhering ratios were evaluated by a granulation model. Granulation experiments were also carried out to obtain the granule size distribution and adhering ratio. The influence of the adhering layer on NO x emissions from the combustion of S type granules was studied by tube furnace experiments. Conclusions include: (1) The adhering ratio predicted from the granulation model can be used as a qualitative index for the evaluation of NO x emission from coke combustion. (2) The influence of the adhering layer on NO x emissions was enhanced with increasing adhering layer thickness of S type granules, and the NO x reduction was enhanced at higher temperatures (around 1373 K), but weakened at lower temperatures (around 1173 K).  相似文献   

11.
A lithium-ion polymer battery cell is an ideal energy source for underwater vehicles due to its high energy density and small volume. However, the performance of lithium-ion batteries in a 10 000 m deep sea is still unknown and is of particular concern in the design of 10 000 m autonomous remote vehicles (ARVs). In this paper, we explore how the external characterizing parameters of a LiFePO4 polymer battery during discharge are affected by a high pressure of 100 MPa and low temperature of 3 °C for simulating the conditions experienced in a 10 000 m deep sea environment. An unscented Kalman filter (UKF) algorithm is applied to estimate the state of charge (SoC) of a battery to investigate the influence of high hydrostatic pressure on SoC estimation due to changes in parameters. The results indicate that the LiFePO4 polymer battery works under 100 MPa hydrostatic pressure, but its parameters change obviously and influence SoC estimation. SoC estimation accuracy was improved through compensating the functions of open circuit voltage (OCV) versus the state of charge (OCV-SoC) of the battery in a 100 MPa hydrostatic pressure and a low temperature environment.  相似文献   

12.
Departing from a realistic classroom context, this study focuses on the relationship between students’ perception of task demands and their learning performance. History teachers (N=20) and their 11th-grade students (N=375) rated the relative importance of sections of an instructional text on which teachers would be giving a test. In addition, test grades were collected. It was hypothesized that the degree of correspondence between ratings of individual students and those of their teacher would reflect the accurateness of students’ perception of task demands and therefore would be positively related with test grade. Multilevel analysis revealed partly support for this hypothesis. Students with higher grades more consistently showed a relative close correspondence with their teacher than students with lower grades. Nonetheless, a substantial number of students who showed a relatively close correspondence with their teacher, obtained a low test grade. This suggests that a more accurate perception of task demands did not guarantee a higher test performance.  相似文献   

13.
Abstract

The intention of the study was to identify predictable opportunities for teachers to scaffold middle year students’ philosophical learning. Such opportunities were identified in terms of students’ readiness to learn certain behaviours in the context of a ‘community of inquiry’. Thus it was hoped that the project would provide a useful resource for the teaching of philosophy to middle year students by ascertaining how amenable philosophical learning was to this approach. The study investigated the following questions: (i) what are the indicators of the development under the influence of the COI?; (ii) do these indicators cluster in any particular way? and (iii) is it possible to identify any clustering of indicators that suggests developmental bands?  相似文献   

14.
The main purpose of the current study is to validate the framework of knowledge management (KM) capabilities created by Gold (Towards a theory of organizational knowledge management capabilities. Doctoral dissertation, University of North Carolina, Chapel Hill) 2001) in a study of South Korean companies. However, the original framework did not provide a thorough explanation of the effect of incentives, which motivate and encourage the knowledge management process. In this study, the modified framework that includes incentives in the knowledge infrastructure capability was tested. Moreover, since there is a weak linkage between KM and organizational performance, this study used empirical evidence to identify the relationship between KM capabilities (KMC) and four perspectives of organizational performance. Since structural equation modeling (SEM) is mostly used to describe causal relationships among unobserved (latent) and observed variables, this study used SEM procedures to determine whether there were any structural relationships between knowledge management capabilities and four perspectives of organizational performance. Moreover, the SEM procedure is “a statistical test to find whether a model fits a set of data, whether it matches a theoretical expectation” (Vogt, Dictionary of statistics & methodology. Sage Publications Inc., Thousand Oaks, CA, p 135, 2005). Therefore, this study also used SEM procedures to test a hypothesized model that had a good fit indicates that the model adequately describes the sample data. This study assumed that knowledge management capabilities could be divided into two types: knowledge infrastructure and process capabilities. The original hypothesized model showed that there was a positive relationship between knowledge management capabilities and organizational performance, but the overall model fit was insufficient to be accepted, because knowledge infrastructure and process capabilities were highly correlated. This study proposed two alternative models to find the best fit and found that knowledge infrastructure and process capabilities should be combined under the higher-order latent variable as subordinate latent variables. Lastly, there was a positive relationship between KMC and organizational performance. This study might not be free from common method bias to some degrees. It would be better to divide participants into two groups to respond to either the knowledge management capabilities survey or the organizational performance survey and to investigate the correlation between them. There are two main contributions for the field of knowledge management. First, this study attempted to integrate the fragmented literature of knowledge management into a holistic view and develop a framework for knowledge management. Moreover, this study found that there is a strong and positive relationship between KM infrastructure and process, which could refer that, to improve organizational performance, an organization should support KM processes, as well as build decent KM infrastructure. The results of this study would help KM practitioners to advocate the importance of KM to top managements.  相似文献   

15.
This study tested the constructivist hypothesis that the acquisition of domain-specific conceptual knowledge (declarative knowledge) requires use of general procedural knowledge. More specifically, it was hypothesized that use of a general pattern of hypothetico-deductive reasoning is necessary for the acquisition of novel domain-specific concepts. To test this hypothesis 314 high school biology and chemistry students were first tested to determine whether or not they were skilled in the use of hypothetico-deductive reasoning. Based on this test, students were classified as reflective, transitional, or intuitive thinkers. All students were then presented with a series of four concept-acquisition tasks. It was predicted that reflective (hypothetico-deductive) thinkers would acquire the concepts while intuitive (empirico-inductive) thinkers would not. Transitional thinkers were expected to be partially successful. These predictions were confirmed as skill in hypothetico-deductive reasoning (developmental level), but not age, was highly correlated with performance on the concept acquisition tasks (X2 = 71.14, p < 0.00001). This result was interpreted to be supportive of the constructivist hypothesis.  相似文献   

16.
This study attempted to replicate a prior intervention study focused on reducing students' perceptions of cost to enhance their course performance. Undergraduate biology students (N = 147) were randomly assigned to complete a cost-focused intervention or a control condition. The intervention was designed to help students re-attribute their course challenges more adaptively, with a goal that this would help students perceive less cost associated with the challenges. Contrary to hypotheses, the intervention increased students’ perceptions of cost at two time points. However, it also predicted higher scores on one of two course exams. Results demonstrate that cost-focused interventions may increase cost in some contexts, pointing to the context-specificity of intervention materials and the importance of replicating successful motivational interventions. However, results also suggest that increased cost does not necessarily correspond to lower academic performance in the context of an intervention aiming to help students re-appraise course challenges.  相似文献   

17.
液体燃料小尺度扩散火焰影响因素分析   总被引：2，自引：0，他引：2  
针对乙醇液体燃料小尺度层流扩散燃烧的影响因素进行了分析。影响因素包括燃料流量、喷管口径、外加电场的电压大小、电极距等等,并且定性分析散热损失对燃烧火焰的影响,为微小尺度燃烧器的设计提供了一定的参考。  相似文献   

18.
《Africa Education Review》2013,10(2):267-285
Abstract

This article reports on the implementation of a teaching approach based on Gardner's theory of multiple intelligences (MI) at a school in the Hammanskraal area in Gauteng, South Africa. The aim was to determine the impact that such an approach would have on teachers, learners and learner performance. This article discusses the implementation process and the impact thereof on learner results and conduct, as well as learners' opinion on the implementation of the MI approach in the classroom. The study showed that the implementation of a new approach should be monitored regularly and that teachers should receive ample support. An MI approach to teaching had a positive influence on learners' conduct and academic achievement. It also made learners more aware of their own strengths and weaknesses and how to overcome weaknesses. Learners indicated that they prefer an MI approach in teaching.  相似文献   

19.
在内燃机中,很多参数对性能的影响是相互制约,互有影响的,但以往的试验方法都采用单项试验,不仅试验次数多,周期长,费用大,且要求试验者必须具有较丰富的理论知识和实践经验。通过试验分析,认为正交试验法是一种研究多因素影响结果的软科学的试验方法,它在内燃机燃烧室改进试验中取得了良好的效果。  相似文献   

20.
INTRODUCTION The propagation of stress-waves in an elasticmedium containing a cavity that are due to arbitrarydynamic loading applied on the cavity is of greatimportance in the fields of seismology, geophysicalprospecting, underground tunnels and deeply buriedpipelines, particularly as a model of an earthquakesource. Ben-Menahem and Cisternas (1963) devel-oped the theory for the dynamic response of an elastichalf-space medium to an explosion spherical cavity.Norwood and Miklowitz (…  相似文献   

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