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In this paper the construction and operation characteristics of a high power Nd r YAG laser system are described. The laser system consists of an active-passive mode-looked oscillator in colliding pulse regime, a single pulse selector and a fourpass amplifier. The oscillator generates mode-locked pulse trains with widely variable pulsewidths (20ps~2.5ns) and a fluctuation of the pulse-train envelope <±4%. For a 0.1mJ, 200-ps laser pulse, the four- pass amplification of 7×102 has been achieved. 本文描述一台由两级Nd:YAG激光器组成的紧凑高功率激光系统的结构及其工作性能。激光系统分成三个部分:对撞脉冲式的主-被动锁模振荡器,单脉冲选择器和四程放大器。振荡器输出锁模脉冲列的包络幅度起伏小于±4%,其脉冲宽度可以在宽范围内(20ps~2.5ns)方便地切换。对于单个0.1mJ、200ps的激光脉冲,四程放大器能提供7×10~2的放大倍数。 In order to obtain supreme economic results for heat exchanger to recover waste heat, this paper deduces the calculation formulae of optimal component efficiency, optimal heat transfer area and optimal heat-exchanging temperature of n-pass A unmixing and B mixing cross flow heat exchanger. For convenient calculation,the paper also makes a chart of optimal component efficiency of common-used two and four-pass cross flow heat exchanger,illustrates with examples how to use these formulae and chart in desigh... In order to obtain supreme economic results for heat exchanger to recover waste heat, this paper deduces the calculation formulae of optimal component efficiency, optimal heat transfer area and optimal heat-exchanging temperature of n-pass A unmixing and B mixing cross flow heat exchanger. For convenient calculation,the paper also makes a chart of optimal component efficiency of common-used two and four-pass cross flow heat exchanger,illustrates with examples how to use these formulae and chart in desigh calculation. 基于热交换器回收余热取得最大经济效益出发,导出了n行程A不混合B混合叉流热交换器的最佳分效率、最佳换热面积和最佳换热温度计算公式.为了方便计算,绘制了常用的2、4行程叉流热交换器的最佳分效率线图,并举例说明在设计计算中怎样使用这些公式和线图。 In this paper, an extensive experimental investigation was made on the pressure drop of two-phase flow of air-water mixtures across the tube bundle in a shell and tube heat exchanger. A verticalshell and tube heat exchanger model was constructed and the tube bundle in the cylindrieal shell wascomposed of 49 tubes with three baffies giving four passes. The friction pressure drop and minor pres-sure drop were measured as the air-water mixtures horlzontally entered the model from its bottom andflowed up across... In this paper, an extensive experimental investigation was made on the pressure drop of two-phase flow of air-water mixtures across the tube bundle in a shell and tube heat exchanger. A verticalshell and tube heat exchanger model was constructed and the tube bundle in the cylindrieal shell wascomposed of 49 tubes with three baffies giving four passes. The friction pressure drop and minor pres-sure drop were measured as the air-water mixtures horlzontally entered the model from its bottom andflowed up across the tube bundle. Based on separated flow model and the experimental results, corre-lations for pressure drop (friction pressure drop & minor pressure drop) were developed. 本文对垂直布置的管壳式换热器中,气液两相流冲刷管束时的流动阻力进行了实验研究。实验段采用管壳式换热器模型,其圆形外壳内的管束由49根管子组成,并沿长度方向用三块折流板将管束分成四个冲刷流程。当气液两相流自下而上冲刷管束时,分别测量摩擦阻力和局部阻力,并用分相流动模型进行分析,得到良好的计算关联式。
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