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1.
气体雾化法作为3D打印粉体的主要制备方法,在气雾化法应用过程中技术不断更新迭代,其工艺和技术有了长足的发展。参照3D打印粉体应用要求,从目前国内外相关气体雾化技术进行对比,并从气体雾化过程和气体雾化条件对粉体性能的影响进行分析,探索气体雾化粉体的关键工艺及技术发展的可能性。  相似文献   

2.
描述了超声波气体射流的形成机理及超声波气雾化的原理;讨论了超声波气雾化过程中雾化气体压力对雾化气体的超声波频率和速度的影响;简述了设计制造 Hartmann 冲击波管和超声波气雾化器的技术关键;综合评价了几种典型的超声波气雾化器的结构、特征及其适用范围。并对该技术的应用作出了展望。  相似文献   

3.
雾化气体和熔滴速度的研究   总被引:1,自引:1,他引:0  
从理论与实验两方面研究了雾化气体流速场和雾化熵滴与气体流场的交互作用,建阙雾化气体和熔滴流速的数学模型,探讨了雾化熵滴对雾化气体流速的影响。  相似文献   

4.
熊建新 《特殊钢》2008,(1):47-47
气体钻井技术是一种由气体设备在地面注入气体到井眼内,以气体代替泥浆等钻井液作为循环介质实施钻进的钻井技术。1953年美国犹他州首次使用空气钻井技术进行钻井。以后,该技术经过半个多世纪的发展,已经发展为纯气体钻井、雾化钻井、泡沫钻井。  相似文献   

5.
雾化参数对H70黄铜粉粒度分布的影响   总被引:1,自引:0,他引:1  
从气体动力学和流体力学分析了雾化气体压力、金属熔体温度和导液管内径对H70黄铜雾化粉末粒度分布的影响。结果表明:适当地提高气体压力和金属熔体温度或者减小导液管内径,均能使雾化粉末细粉量增加。当雾化气体压力为1.3MPa,金属熔体温度为1160℃,导液管内径为3.5mm时,所制得粉末的粒度分布最理想。  相似文献   

6.
在气体雾化液态金属时,加热的气流可使其更加有力。如果所有其他的雾化参数保持不变,加热气流可降低粉末平均粒度。它适于生产金属注射成形用廉价粉末。316不锈钢粉的雾化试验表明,热气雾化比冷气雾化可提高金属注射成形用粉的收得率约40%。其原理是,雾化用超声气体喷嘴的气体出口速度随雾化驻点温度的升高而显著增大。  相似文献   

7.
非限制式雾化器的气体动力学分析   总被引:4,自引:0,他引:4  
对非限制式雾化器的气体动力学过程进行了实验研究,着重考察了喷射顶角,雾化压力对气体雾化过程的动力学影响规律,对其机理进行好初步探讨,并经实验验证,得出了使雾化过程正常进行的关键动力学条件。  相似文献   

8.
气雾化制粉技术因粉末球形度高、气体杂质含量低等优点已经成为现在一种重要的粉末制备方法。雾化过程可粗略分为破碎和凝固两部分,涉及传热,物质交换以及多相流相互耦合等复杂现象。目前,人们对与雾化机理以及工艺参数的控制方法没有系统认识,制约了气雾化技术快速发展和工业化生产。本文简述了气雾化制粉中合金熔体的破碎行为机理,总结了最近几年关于气体流场结构、雾化工艺参数优化和计算流体力学在气雾化技术中的研究新进展,并且介绍了一些新技术在气雾化研究中的应用。  相似文献   

9.
铝合金低压气雾化技术研究   总被引:7,自引:0,他引:7  
根据气体动力学原理和雾化机制,在以自行设计的限制式雾化喷嘴为核心的雾化装置上,研究了当雾化介质压力较低时工艺参数对铝合金雾化效果的影响,结果表明,当雾化介质为氮气,压力为1.0MPa,合金液温度为780℃,液流率主0.8kg/min时,可获得符合喷射沉积技术要求的雾化效果。  相似文献   

10.
本文基于增材制造工艺对金属粉末的应用需求,概述了几种国际上高性能球形金属粉末制备技术,包括真空感应气体雾化(VIGA)、电极感应气体雾化(EIGA)、等离子雾化(PA)、等离子球化(PS)和等离子旋转电极(PREP),对比了气雾化粉末和旋转电极粉末用于增材制造零部件显微组织和力学性能差异。重点论述了粉末制备技术的发展趋势,为粉末制备技术的选择和增材制造选材、用材提供参考。  相似文献   

11.
金属粉末气体雾化制备技术的研究现状与进展   总被引:7,自引:0,他引:7  
依据气体雾化中喷嘴的结构特征,分析了国外几种具有工业实用价值的雾化技术的原理、性能与发展状况,评述了其优缺点和应用情况。  相似文献   

12.
This paper describes the psychological and psychosocial aspects of prenatal care, which are believed to be of particular importance for medical/psychological practice. The emotional changes that "normally" take place during pregnancy are surveyed and evidence is provided linking these changes with potential adverse effect on pregnancy and labour. The salience of anxiety and life stresses in pregnancy research is highlighted as well as their intricate inverse relationship with social support. Antenatal classes are offered as an example of social support provision. The different kinds of such classes and evaluation of their effectiveness are briefly presented, as well as a number of controlled trials of enhanced support during pregnancy. Finally, the effect provision of prenatal care has on women as well as their role in their own care are raised. The need is stressed for further sophisticated longitudinal and multivariate research exploring further the causative links between quality of prenatal care, pregnancy outcome, and subsequent child development.  相似文献   

13.
Numerous studies have shown fathers to be less engaged and less involved with their children and adolescents. This paper discusses the possible function that fathers' lower involvement may play in the development of their children. Data from two studies conducted on adolescents show that on the one hand fathers spend less time and are less engaged with their adolescents, but when they are together, the nature of their interaction is distinctive. For example, fathers are more engaged in play-like activities. This apparently distant and distinctive model is what adolescents need at this period of separation--a model of a "close enough" parent that allows and respects separation and support strivings for individuation. As results show, adolescents are satisfied with the role fathers play in their lives. Moreover, fathers are perceived as models for subsequent developmental goals such as marital life. It is suggested that fathers in their natural attitude are more capable of balancing closeness and separateness than mothers do and as such they are more flexible in response to varying developmental goals of their adolescent offspring.  相似文献   

14.
Niobium and tantalum are rare refractory metals of important industrial value. Their reserves are a “critical” raw material, which leads to the necessity of evaluating the risks associated with the presence of primary and industrial raw-material sources of niobium and tantalum, as well as the influence of these factors on the supply and demand for these metals and their compounds allowing for their traditional and new application regions. In this article we analyze the world reserves of niobium and tantalum, and the dynamics of varying the raw-material base and industrial solutions implemented and proposed for their processing is considered. A modern market of niobium-based and tantalum-based materials is described, the main players on this market are listed, and the tendencies in the variation in the structure of consuming functional materials based on these metals are considered.  相似文献   

15.
In construction, many large firms are diversified, and their diversification is recognized as a corporate strategy for growth and risk management. Diversification indicates extended competition into a different market sector. It is a departure from a firm’s experience base, and it can be riskier than improving performance in the currently operating market. Then, contractors’ diversification and their aggregate pattern in the market, if there is any, are realized outcomes through competition among contractors over different market sectors. The competing contractors may have different risk attitudes, which are the subconscious but critical basis of their risk-taking behaviors in competition. This study investigates the association of contractors’ organizational risk attitudes with their diversification on the basis of simulated competition among multiple contractors. The simulation replicates the actual diversification pattern of large U.S. construction contractors. The results provide new insight on the relationship between contractors’ risk attitude and their diversification as well as their competitive success.  相似文献   

16.
Molecular and biotechnological aspects of microbial proteases   总被引:1,自引:0,他引:1  
Proteases represent the class of enzymes which occupy a pivotal position with respect to their physiological roles as well as their commercial applications. They perform both degradative and synthetic functions. Since they are physiologically necessary for living organisms, proteases occur ubiquitously in a wide diversity of sources such as plants, animals, and microorganisms. Microbes are an attractive source of proteases owing to the limited space required for their cultivation and their ready susceptibility to genetic manipulation. Proteases are divided into exo- and endopeptidases based on their action at or away from the termini, respectively. They are also classified as serine proteases, aspartic proteases, cysteine proteases, and metalloproteases depending on the nature of the functional group at the active site. Proteases play a critical role in many physiological and pathophysiological processes. Based on their classification, four different types of catalytic mechanisms are operative. Proteases find extensive applications in the food and dairy industries. Alkaline proteases hold a great potential for application in the detergent and leather industries due to the increasing trend to develop environmentally friendly technologies. There is a renaissance of interest in using proteolytic enzymes as targets for developing therapeutic agents. Protease genes from several bacteria, fungi, and viruses have been cloned and sequenced with the prime aims of (i) overproduction of the enzyme by gene amplification, (ii) delineation of the role of the enzyme in pathogenecity, and (iii) alteration in enzyme properties to suit its commercial application. Protein engineering techniques have been exploited to obtain proteases which show unique specificity and/or enhanced stability at high temperature or pH or in the presence of detergents and to understand the structure-function relationships of the enzyme. Protein sequences of acidic, alkaline, and neutral proteases from diverse origins have been analyzed with the aim of studying their evolutionary relationships. Despite the extensive research on several aspects of proteases, there is a paucity of knowledge about the roles that govern the diverse specificity of these enzymes. Deciphering these secrets would enable us to exploit proteases for their applications in biotechnology.  相似文献   

17.
The importance of family relations for the therapy of psychiatric disorders in children and adolescents is discussed reporting results from an empirical study carried out in an inpatient sample of a child and adolescent psychiatric unit with regard to the quality of mother-child resp, father-child relation and its influence on coping processes. Whether adolescents suffering from a psychiatric disorder are able to cope with their problems during the course of a therapy, depends on their individual and social resources. Therapy outcome is to a great extent influenced by the emotional quality of their family relations. Hostility and rejection as well as unstructured and disorganized parental behavior contribute to a negative outcome. A differentiated analysis shows further that the relation between the adolescents and their fathers is particularly important for therapy prognosis. Nevertheless, one has to consider the respective relations with both parents for therapy prognosis, as problems with one parent may be partly compensated by a good relationship with the other parent. Finally, the cooperation between parents and clinical staff is discussed. Data and experiences show that interest and readiness of parents (mothers as well as fathers) for a close cooperation are higher than generally expected.  相似文献   

18.
The guidelines of the committee on health protection in medical exposure contain, as required by the international commission on radiation protection, the requirement for the determination of values for reference levels for medical exposure, their use, and their fulfillment. Here we discuss the basis for their determination and point out that their control only appears to be meaningful in combination with quality requirements for which parameters are given in the guidelines of the German Medical Chamber and the European Guidelines.  相似文献   

19.
The present study evaluates the impact of an early stimulation program for 24 mother-infant (0-6 months) vulnerable dyads from the Montérégie region. These dyads participate in a series of ten stimulation workshops. Twenty four other dyads form a witness group. The program's major objective aims at developing positive interactions for the mother and stimulative interactions for the infant. The hypotheses state that at the end of the program, the mother from the intervention group will feel less isolated, possess a higher level of knowledge on the development of their child, perceive more positively the temperament of their child and have behaviors that are more contingent to their infants as well as more functional to this development. The two first hypotheses are not confirmed. However, at the end of the program, the mothers of the intervention group perceive the temperament of their child as foreseeable. Also, they imitate more frequently the verbal and facial behaviors of their infant and emit more vocalizations when they are interacting with the child. The discussion of results bears on the importance of modifying conditions in which the parent-child interactions are held to prevent deficits in the development of the children.  相似文献   

20.
Total shoulder arthroplasty has become an effective treatment for advanced glenohumeral arthritis. The results depend, in part, on the underlying degenerative process. This article reviews the indications for glenohumeral arthroplasty, including important preoperative considerations. The different types of glenohumeral arthritides are discussed with respect to their clinical and radiographic manifestations, as well as their impact on preoperative planning.  相似文献   

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