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通过无因次分析的方法,在相界面两侧均是对流条件下,得到了平面冰层厚度和速度的时变规律、生长条件、极限厚度、温度场分布特点等重要结论,提出了凝固换热全传热系数和衰减特征时间的概念,并给出了理论公式用于换热量计算.结果表明,凝固换热是一个非稳态过程,初始阶段凝固潜热释放强化了换热,衰减特征时间之后,冰层热阻开始恶化换热效果,并最终无限趋近于一稳定状态. 相似文献
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提出一种具有盘腔扰流柱群的双辐板涡轮盘,利用靠近盘腔出口处叉排扰流柱群的强化对流换热,进一步提高了双辐板涡轮盘的换热效果。对壁面层网格进行细化,采用SST k-ω湍流模型,分别建立具有光滑盘腔、盘腔扰流柱群的双辐板涡轮盘对流换热模型,分析了扰流柱群对盘腔对流换热的影响。对比分析表明:扰流柱群明显增加了盘腔的局部对流换热,辐板上的低温区域明显增加,涡轮盘的最高温度相应降低,最高温度降低4 K;随着雷诺数的增加,扰流柱群局部对流换热系数相应增加,盘腔内壁的面积平均换热系数提高了20%,增强了双辐板涡轮盘的降温效果。 相似文献
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对循环流化床上部稀相区气固混合物横掠圆管的对流换热研究,多数是针对鼓泡床的研究,而对循环流化床上部稀相区的对流换热研究目前还很少。本文对稀相含尘气流横向冲刷圆管的对流换热进行了研究,并在理论分析的基础上,在热态循环流化床实验台的上部稀相区进行了实验。采用平均粒径分别为137μm,146μm和326μm的石英砂为床料。实验结果表明,稀相含尘气流与纯空气横掠圆管时的对流换热系数之比hd/hg主要受稀相含尘气流密度和颗粒粒径的影响,通过理论分析和实验数据的拟合,得到稀相含尘气流横掠圆管的准则方程。研究基于热态实验,结果更接近于实际工况,可为循环流化床的设计提供理论依据。 相似文献
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1 故障查找思路 GK1D型液力传动内燃机车的空压机主电路示意图和空压机起动时的控制关系示意图如图 1和图 2所示。当出现空压机不打风的故障时 ,我们一般按这两幅控制关系示意图所示的线路 ,分析查找问题所在。其基本思路如下 :一是沿空压机起动控制线路查。查PC机、功放块、空压机起动接触器、保险。若都没问题 ,则查主电路。二是沿主电路查找 ,空压机的电机、电机接线盒内 (接线柱、接线片 )、电机绕组。2 故障的分析处理 在实际检修过程中 ,具体可按如下步骤做 :( 1)看主电路中的空压机起动线路上的保险3RD、4RD是否烧… 相似文献
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The construction of conventinal solar air collectors and the fact that they will operate with a significant pressure difference between the heated air stream and ambient, suggests that significant quantities of air may leak into or out of them. A search of the literature reveals no consideration of the effects these air leaks may have on the validity of collector efficiency measurements, on the efficiency itself, or indeed what the meaning of efficiency is under such operating conditions. This paper discusses the meaning of collector efficiency when leaks into the collector occur, analyses the effects on efficiency measurements, and solves the collector efficiency for the simple case of a constant leakage rate along the collector. Assuming that air leaking in from ambient can replace deliberate fresh air supply to the load as in building heating, then significant measurement errors are made if air leaks in to the collector are not accounted for. Further, the collector efficiency is increased over the no leak case, so that complex construction methods to make the collector air tight are probably not warranted. 相似文献
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本文阐述了空压机增风改造的方法,并介绍了脱湿增风改造原理及其实践效果,在新余钢铁公司气体厂1TY-575/5.5-Ⅲ型空压机增风改造中应用,使空压机夏季平均风量可提高8%左右,而且空气压缩的单位电耗降低. 相似文献
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In this paper, the effect of an air leak on the air heater performance is investigated. “Air leaking in” and “air leaking out” systems are examined. The effect of various parameters like leakage rate, mass flow rate, solar insolation, plate length and ambient temperature has been studied. The possibility that air leakage can take place from any where along the length of the collector has been incorporated in the model. It is found that, for “air leaking in” systems, efficiency goes up, while for “air leaking out” systems, efficiency decreases from the no-leak situation, and it depends on the position of the leak. 相似文献
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Zhu ChenJa-Yeon Choi Haijiang WangHui Li Zhongwei Chen 《Journal of power sources》2011,196(7):3673-3677
The electrochemical stability of non-precious FeCo-EDA and commercial Pt/C cathode catalysts for zinc air battery have been compared using accelerated degradation test (ADT) in alkaline condition. Outstanding oxygen reduction reaction (ORR) stability of the FeCo-EDA catalyst was observed compared with the commercial Pt/C catalyst. The FeCo-EDA catalyst retained 80% of the initial mass activity for ORR whereas the commercial Pt/C catalyst retained only 32% of the initial mass activity after ADT. Additionally, the FeCo-EDA catalyst exhibited a nearly three times higher mass activity compared to that of the commercial Pt/C catalyst after ADT. Furthermore, single cell test of the FeCo-EDA and Pt/C catalysts was performed where both catalysts exhibited pseudolinear behaviour in the 12-500 mA cm−2 range. In addition, 67% higher peak power density was observed from the FeCo-EDA catalyst compared with commercial Pt/C. Based on the half cell and single cell tests the non-precious FeCo-EDA catalyst is a very promising ORR electrocatalyst for zinc air battery. 相似文献
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Violeta Misevičiūtė Kęstutis Valančius Violeta Motuzienė Genrika Rynkun 《Energy Efficiency》2017,10(4):989-998
In modern buildings, an increasing amount of the consumed energy falls on ventilation systems. The amount of energy needed for ventilation depends on weather fluctuations, wind, interaction between natural gravity and air tightness of the building, heat exchangers used in ventilation systems, efficiency of other ventilation equipment, and operating mode of ventilation systems in the building. Ventilation systems are comprised of a variety of elements that facilitate processes using energy of different types. The main elements that use energy in ventilation systems are fans, heat exchangers, and heaters. They have a significant effect on both energy needs of a public building and the exergy efficiency of a system. In order to achieve a more efficient use of exergy in heat exchangers, it is recommended to execute processes under as little temperature difference as possible; however, this increases the area of heat exchangers. Results of the analysis show that it is recommended to design ventilation systems based on the temperature that corresponds with the maximum demand of exergy in order to use the heat recovery unit as much as possible in the system. 相似文献
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讨论了二次回风系统在夏季工况下与一次回风系统相比的节能效果,以及在冬季工况如何更好降低能耗的问题,着重分析了冬季工况下机器露点对能耗的影响,并提出降低能耗的途径。 相似文献