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61.
部分种子成分的特征X射线在等效生物材料中衰减的测定 总被引:6,自引:5,他引:1
用Si(Li)探测器实现了Na、Mg、S、Cl的特征X射线在有机膜中的相对衰减以及与O、K元素的特征X射线能量相当的X射线或轫致辐射在有机膜中的相对衰减,分别得出了它们减的数学描述,并把实验得到不同能量的X射线在有机膜中的质量吸收系数与Berkeley的OCG软件计算出的结果相比,相关都小于30%。 相似文献
62.
63.
本文主要论述了面流消能五种典型流态近底紊动流速特性,总结出了近底时均流速和紊动强度沿程变化规律,提出了近底紊动流速可能出现的最大瞬时值及相应位置的计算公式。面流消能工程的下游防冲设计中考虑的主要水力参数之一是,消能段近底流速紊动可能出现的最大瞬时值及其相应的部位,但目前国内外研究成果较少。笔者通过水工模型试验重点研究了面流消能各典型流态近底流速及其紊动纵向分量沿程的变化规律,并提出了计算公式,为优化面流设计提供科学依据。 相似文献
64.
在BSO晶体中同时掺入Ce和Eu离子,生长了Ce:Eu:BSO晶体,对晶体的二波耦合和四波混频性能了测试。结果表明,Ce和Eu离子对晶体的光折变效应起到了增强的作用。 相似文献
65.
66.
A study on the prediction of heat transfer coefficient (HTC) and pressure drop of refrigerant mixtures is reported. HTCs and pressure drops of prospective mixtures to replace R12 and R22 are predicted on the same cooling capacity basis. Results indicate that nucleate boiling is suppressed at qualities greater than 20.0% for all mixtures and evaporation becomes the main heat transfer mechanism. For the same capacity, some mixtures containing R32 and R152a show 8.0–10.0% increase in HTCs. Some mixtures with large volatility difference exhibit as much as 55.0% reduction compared with R12 and R22, caused by mass transfer resistance and property degradation due to mixing (32.0%) and reduced mass flow rates (23.0%). Other mixtures with moderate volatility difference exhibit 20.0–30.0% degradation due mainly to reduced mass flow rates. The overall impact of heat transfer degradation, however, is insignificant if major heat transfer resistance exists in the heat transfer fluid side (air system). If the resistance in the heat transfer fluid side is of the same order of magnitude as that on the refrigerant side (water system), considerable reduction in overall HTC of up to 20% is expected. A study of the effect of uncertainties in transport properties on heat transfer shows that transport properties of liquid affect heat transfer more than other properties. Uncertainty of 10.0% in transport properties causes a change of less than 6% in heat transfer prediction. 相似文献
67.
The influence of irreversibility of finite-rate heat transfer on the performance of an absorption refrigerator is investigated using an endoreversible cycle model with continuous flow. The cooling rate is adopted as an objective function for refrigerator optimization. The maximum cooling rate and the corresponding coefficient of performance are derived. The optimal performance with respect to heat transfer areas of the refrigerator is analysed. In addition, certain significant conclusions are reached. 相似文献
68.
William N. Gill Rajiv M. Ginde John Verhoeven 《Chemical Engineering Communications》1993,124(1):49-56
The linear theory of Pearson (1958) and Nield (1964) is modified here to study liquid tin and include the finite thermal resistances of the bounding layers of boron nitride, copper and air (∼10-2 torr) in the experiments of Ginde et al. (1989). The magnitude of the ΔTc across the layer of liquid tin required for the onset of convection depends on the ratios of the thermal conductivities and thicknesses of the supporting layers of boron nitride and copper to those of the tin.
According to our theory surface tension contributes more than buoyancy to the instability observed experimentally. The critical ΔTc observed required for the onset of convection in the layer of tin, is up to 25% lower than that predicted, which shows the layer is less stable than the theory indicates. Thus the surface of the tin was uncontaminated, or a significantly larger observed critical ΔTc would be expected.
The boundary condition on the thermal fluctuations at the base of the supporting layer of copper does not appear to be important in these experiments. However, the thermal resistance of the boron nitride would have to be assumed to be unrealistically large to obtain agreement within experimental error with the theory. 相似文献
According to our theory surface tension contributes more than buoyancy to the instability observed experimentally. The critical ΔTc observed required for the onset of convection in the layer of tin, is up to 25% lower than that predicted, which shows the layer is less stable than the theory indicates. Thus the surface of the tin was uncontaminated, or a significantly larger observed critical ΔTc would be expected.
The boundary condition on the thermal fluctuations at the base of the supporting layer of copper does not appear to be important in these experiments. However, the thermal resistance of the boron nitride would have to be assumed to be unrealistically large to obtain agreement within experimental error with the theory. 相似文献
69.
It is demonstrated that glassy carbon powder can be thermochemically activated. During activation, a film with open pores is created on the glassy carbon particles. This film has a large internal surface area, which is accessible to liquids and gases. A simple model for the evolution of the internal surface area in glassy carbon powder during thermochemical gas-phase oxidation is also presented and compared with experimental data. Experimental results are in qualitative agreement with the model. We found that a sharp particle size distribution is desirable with regard to potential technical applications. 相似文献
70.