浅谈变频器散热技术的发展现状

随着变频器的越来越广泛的应用,变频器的散热技术的研究变得越来越重要。目前电力电子设备常用的散热技术有自然空气散热、强制风冷、水冷和热管等,本文阐述了这几种散热技术的工作原理及其特点。     

结构及运行参数对闭式冷却塔冷却性能的影响分析

闭式冷却塔广泛应用于大型水冷空调系统中,其效率会对空调机组的COP产生很大影响.为了分析结构及运行参数对蒸发式闭式冷却塔冷却性能的影响,对冷却塔内部的换热机理进行分析,并建立了盘管传热传质的数学模型,选取了研究变量,确定了研究条件.结合Matlab改变单一参数对数学模型进行计算,得到结构及运行参数的改变对冷却水出口温度...     

区域供冷供热系统的应用研究

随着近年来市场经济的快速发展,我国的建筑能耗中的空调能耗日益增大,介绍了区域供冷供热系统(DHC系统)的国内外应用现状,并着重对武汉地区的光谷金融港的能源站建设进行了分析,最后提出了该系统在应用中的优劣势。     

Public interest in continued use of Chinese government portals: A mixed methods study

Public adoption of policies detailed on government websites is an important topic in the field of e-government research, and researchers have mainly focused on the key factors that influence initial adoption. However, there has been much less discussion on factors influencing the continued use of government websites. This study identifies and tests a theoretical model that predicts consumers’ intentions to continue using government portals, using a mixed methods approach based on Grounded Theory. To construct a theoretical framework of public interest in continued use of government information portals, we interviewed 56 respondents and coded the interview data. Next, we tested the resulting model using data collected from a questionnaire-based survey of 354 users. The Structural Equation Modeling (SEM) results indicate that continued use is influenced by psychological perception, user characteristics, service parameters of the government portals and the government’s idea. Of these, psychological perception was found to have the strongest effect. These findings enrich the theoretical system of e-government public adoption of intention and have important practical significance for the development of Chinese government portals.     

限量供氧对粟酒裂殖酵母絮凝颗粒酒精发酵的影响及连续发酵工艺的研究

本文以双酶法制备的淀粉糖化糖为底物,首先通过摇瓶分批式发酵实验,研究了限量供氧对粟酒裂殖酵母絮凝颗粒酒精发酵性能的影响,发现限量供氧可以使酒精发酵过程的增酸降低,同时能够有效地阻止絮凝颗粒酵母长期连续使用时发酵活性的衰减。维持颗粒的良好絮凝状态,但发酵终点的残糖有所增高。在此基础上,进行了三级悬浮床反应器串连操作的连续发酵实验,反应器以0.02vvm的通风量使絮凝颗粒酵母均匀悬浮,同时实现限量供氧,当底物糖浓度控制在190～195g几时,反应器以0.165h-1的总稀释率操作,平均设备生产强度达到13.2EtOH/L.h,发酵液中酒精浓度为80.0g/L,总糖转化率为90％。     

关于某大楼空调系统存在的问题和对策

某单位北大楼竣工后空调系统一直运行不正常 ,尤其是夏季供冷不能令人满意。经全面考查确认 ,主要问题出在冷水机组的冷却水循环系统上。本文阐述了空调制冷机冷却水循环系统中冷却塔、过滤器、管路等因素对冷却效率的影响及相应的改进方法。     

连续小波变换在使用中应满足的条件

本文讨论了连续小波变换使用中应注意的问题,提出了从连续小波能量误差的角度及Ｎｙｑｕｉｓｔ条件出发选择连续小波变换的时频域窗,小波采样率及伸缩因子等参数,并给出了具体的例子加以说明,为正确应用连续小波变换提供了一种依据。     

印制电路板的热设计

印制电路板(PWB)热设计时,布局上最好沿空气流动方向安装,封闭空间情况下最好竖直安装.板与板间的距离一般不应小于20mm,发热量小时距离可减小.PWB的等效导热系数与PWB的总厚度、铜箔剩余率及铜箔厚度有关,设计时需考虑相关因素.热设计的辅助散热包括用导热、对流及增加散热面积改善散热.     

Numerical modeling of a zeolite/water adsorption cooling system with non-constant condensing pressure

A new transient two-dimensional model with non-constant condensing pressure for a zeolite/water adsorption cooling cycle is proposed in this paper. This numerical model focuses on the heat and mass transfer behaviors in the adsorber and is solved by the control volume method. Due to the heat transfer limitation in the condenser, the simulated pressure during the isobaric generation phase of the cycle is not constant and will decrease with time. Compared with the model for constant condensing pressure, the cycle duration and cycled adsorbate for the base case are increased. Furthermore, the effect of mass flow rate of condenser cooling water on system performance is also investigated. It is found that both COP and SCP increase with an increase in the mass flow rate of cooling water in the condenser.     

MIM零件连续烧结炉及其控制

金属粉末注射成型技术(Metal Injection Molding,简称MIM)是近年来在粉末冶金学科和工业中发展最迅猛的领域。主要论述应将传统脱脂、烧结乃至后处理等单一工序融合为综合工序的必要性,及连续烧结设备的结构与工件输送的控制系统设计的发展目标。