Blast Effects of High Explosive Charges Detonating in Cylindrical Steel Tubes

Described are tests of cylindrical high explosive charges with an L/D ratio of 2, centrally detonating in steel tubes of different radii and wall thicknesses to measure the bulge respectively the damaging effects of these steel tubes. The results can be described with analytical equations. For a protecting container with minimum weight the radius should be as large as possible, because the necessary tube wall thickness is quadratically decreasing and therefore the weight of the tube is linearly decreasing with increasing tube radius.     

水平微肋管内流动蒸发换热特性的实验研究

为了研究微肋管结构尺寸及工况等对管内流动蒸发性能的影响,对4种微肋管和1根9.52 mm光管进行了实验,4根微肋管中管外径为9.52 mm和7 mm的各2根,所用工质为R22.实验中质量流速变化范围为90～400kg•m^-2•s^-1,所选工况为：蒸发温度7℃,入口干度15%～20%,出口过热度5～6℃.获得了蒸发换热性能随质量流速的变化,讨论了微肋结构尺寸和管径等对蒸发换热性能的影响.两根9.52mm微肋管的传热系数比光管分别分别提高了130%和180%,而其内表面积只比光管分别增加了40%和70%.     

Effect of Scale and Confinement on Gap Tests for Liquid Explosives

The factors influencing initiation of detonation in gap tests for liquid explosives are investigated experimentally. A calibrated donor charge (nitromethane) and PMMA attenuator disk arrangement are used to transmit shocks of known strength (2–10 GPa) into a test explosive of nitromethane sensitized with 5% diethylenetriamine. The test explosive is contained in capsules of different wall materials (PVC, Teflon, aluminum), and the dimensions of the charges vary from 25 mm to 100 mm in diameter. For the small‐scale charges, the presence of the confining wall of the test capsule is seen to have a pronounced effect on the detonation initiation. Certain wall materials (PVC, Teflon) exhibit a multi‐valued critical gap thickness, meaning that a weaker shock may result in initiation while a stronger shock does not. The effect of the wall materials could not be correlated with their acoustic or shock impedance, and the only way to eliminate these effects was to make the diameter of the test charge larger than the donor charge. When the size of the donor charge was increased, the critical pressure required for initiation decreased. These results could be correlated to “ideal” shock initiation experiments that use flyer plates as shock sources assuming that lateral rarefactions quench detonation initiation if they reach the central axis of the charge before the onset of detonation is complete.     

太阳能真空管吸附集热器集热与制冷性能研究及其经济分析

以分子筛 -水为吸附工质对对真空管型太阳能吸附集热器的集热性能进行了详细的分析计算 ,其中包括真空管内、外玻璃间非均匀温度表面的辐射换热 ,两相邻管之间的辐射换热 ,真空管与背板间的辐射换热以及背板的反光等 .同时以制冷量、成本和集热器面积三要素构成新的评判指标 ,对吸附器的结构参数 (管径、管距和吸附剂厚度 )进行了分析 .计算结果表明 ,以大直径的真空管作吸附集热器时 ,可获得较好的综合性能 ;从评判指标来看 ,应用大管径吸附器且两相邻管的中心距离等于 2 .5倍的管径 ,吸附剂的最佳厚度大约为 10mm时经济效果最佳     

溢流管结构对天然气水合物用旋流器分离性能的影响

建立了主直径100 mm的旋流器模型,采用计算流体力学(CFD)方法研究了溢流管内径、插入深度及壁厚对旋流器分离天然气水合物性能的影响规律。结果表明,入口流速为9 m/s时,随溢流管内径增大,水合物分离效率增大,砂的分离效率降低,旋流器的压力降逐渐减小;随溢流管壁厚增大,水合物和砂的分离效率稍有增大,旋流器的压力降先增大后减小;随溢流管插入深度增大,水合物分离效率先减小后增大,砂的分离效率先增大后减小,旋流器的压力降波动较小。溢流管内径对旋流器分离天然气水合物性能的影响最大,插入深度次之,壁厚的影响最小。     

Modeling of the Wall Effect in Packed Bed Adsorption

A model developed for catalytic packed bed reactors and consistently accounting for the influence of the tube wall on porosity, flow and transport phenomena is used in order to simulate the operation of packed bed adsorbers. By comparison of simulation results with reduced versions of the model the influence of the wall on the adsorber performance is worked out and found to be major at low ratios between tube and particle diameter. The interaction between maldistribution, thermal effects and intraparticle resistances in such adsorber tubes is discussed.     

Local Heat Transfer in Tubes after Sudden Change of Diameter

The influence of the sudden change of diameter on the local heat transfer in the entry region of tubes was experimentally investigated. An electric direct current was passed through the wall of a tube made of stainless steel and the temperature of the external surface of the tube was measured by infrared thermography. The ratios of diameter were changed between 3/29 mm and 94/29 mm and the Reynolds number between 1000 and 100 000. For cross sectional contraction no significant influence of the diameter ratio on the heat transfer could be seen. But for cross sectional extension the heat transfer increased by a factor of eight in comparison to the classical formula for heat transfer in tubes. The maximum heat transfer is a distance of 2 to 3 diameters from the entrance. After this maximum a correlation is given for the Nusselt function with the diameter ratio as a parameter.     

Detonation velocities of the Non-Ideal Explosive Ammonium Nitrate

In order to gain a better understanding of the detonation behaviour of the non-ideal explosive ammonium nitrate, the detonation velocities of low density prilled ammonium nitrate were measured in steel tubes with different diameters and wall thicknesses. It was found that the tube diameter has a much greater effect on the detonation velocity than the confinement. The highest value observed (3.95 km/s) coincides with the ideal detonation velocity as predicted by the TIGER code in combination with the JCZ3 equation of state.     

复合多孔表面管竖直管束在液氮中的沸腾传热

复合Gewa-T多孔表面管是在机械加工Gewa-T表面上再覆盖一层烧结多孔层而形成的强化传热管,针对复合Gewa-T多孔表面管竖直单管和管束在液氮池中的核态沸腾进行了实验研究,通过改变管束管间距、热负荷等得到了不同情况下的管束沸腾传热特性.沸腾的最佳管间距与管外径比为1.2,此时管束沸腾特性优于单管.     

Pool boiling of water-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and water-Cu nanofluids on horizontal smooth tubes

Experimental investigation of heat transfer during pool boiling of two nanofluids, i.e., water-Al₂O₃ and water-Cu has been carried out. Nanoparticles were tested at the concentration of 0.01%, 0.1%, and 1% by weight. The horizontal smooth copper and stainless steel tubes having 10 mm OD and 0.6 mm wall thickness formed test heater. The experiments have been performed to establish the influence of nanofluids concentration as well as tube surface material on heat transfer characteristics at atmospheric pressure. The results indicate that independent of concentration nanoparticle material (Al₂O₃ and Cu) has almost no influence on heat transfer coefficient while boiling of water-Al₂O₃ or water-Cu nanofluids on smooth copper tube. It seems that heater material did not affect the boiling heat transfer in 0.1 wt.% water-Cu nanofluid, nevertheless independent of concentration, distinctly higher heat transfer coefficient was recorded for stainless steel tube than for copper tube for the same heat flux density.     

Study on a System with a Neutral Barrier for High Explosives and a Zirconium‐Based Solid Incendiary

In the aim of defeating targets protected by fortification, it is necessary to develop systems that are able to create a leak in the fortification and destroy targets inside the fortification. A boat‐tailed hemispherical high explosive charge was designed to create the leak and an incendiary charge was prepared to burn the targets inside the fortification. A metallic neutral barrier was used to attenuate the back pressure generated by the front end hemispherical high explosive charge. In order to reduce the back blast, a boat‐tailed hemispherical charge with the composition cyclotrimethylene trinitramine and trinitrotoluene (RDX/TNT 60/40) was prepared. The blast pressure obtained from unconfined boat‐tailed high explosive charges using a linear pressure gauge brought to light that the pressure at the front end had a value of 2.3 MPa at 100 cm; and a value of 0.4 MPa at 75 cm distance at the rear end. A hemispherical boat tailed shaped charge with a mild steel liner of 1 mm thickness and 40 mm curvature radius was prepared. The incendiary composition comprised of finely divided metal powder dispersed in a polymer matrix consisting of 77 % zirconium and 20 % ester gum resin with 3 % polymeric binder (SBR, PIB). The incendiary composition was prepared and pelletized. Experiments for the design of the neutral barrier were conducted with the boat‐tailed hemispherical charge. A mild steel plate of 7.5 mm thickness was selected as neutral barrier. Static evaluation of the system against a hard target was carried out. It created a hole of 190 mm diameter in a reinforced concrete cement (RCC) target of 100 mm thickness. A neutral barrier of 7.5 mm thickness attenuates the back blast of the hemispherical boat‐tailed charge. Burning incendiary cinders were passed through this hole and dispersed at approx. 5 m distance. These cinders burnt for > 3 min with a temperature output of 1873 K.     

Counter-current gas-liquid flow and incipient flooding in inclined small diameter tubes

Free flowing liquid layer characteristics, counter-current gas-liquid two-phase flow and incipient flooding were studied in small diameter inclined tubes (7 and 9 mm). Experiments were carried out at various inclination angles from the horizontal (30°, 45°, 60° and 75°), while several liquids covering a wide range of physical properties were employed. Fast video recordings and conductivity probes were used for liquid layer thickness measurements, from which mean layer thickness and its statistical quantities were calculated. The wall shear stress at the tube bottom was also measured using an electrodiffusion technique.The new experimental data confirm previous interpretation that in almost all cases the dominant flooding mechanism is wave growth and upward dragging by the gas phase. Consequently, incipient flooding is strongly affected by the liquid layer characteristics, which in turn are influenced by the liquid properties. New correlations based on dimensionless groups for the prediction of flooding in inclined small diameter tubes are proposed.     

MC尼龙管浇铸量计算公式及生产验证

介绍旋转浇铸法制作ＭＣ尼龙管浇铸量计算公式。公式引入己内酰胺熔体平均相对密度、“壁厚效应”的校正值和漏斗残留校正值,使计算结果比较符合生产要求。设计要求值与制得的ＭＣ尼龙管内径偏差,中、小管为＋１～＋５ｍｍ,大管不大于１０ｍｍ,该公式特别适合于套铁芯管浇铸量的计算。笔者还讨论了“壁厚效应”产生的原因。     

Extrusion of ceramic tubes with complex structures of non-uniform curvatures made from nano-powders

A computer-controlled extrusion technique was introduced for making ceramic tubes (with a wall thickness of 2 mm and external diameter of 8.0 mm) with tightly controlled bends from ceramic pastes prepared from nano-size boehmite powders. Firstly, the rheological flow behaviour of the paste and related flow parameters were calculated in order to show their effect on the curvature of the tubes. Secondly, an extrusion die with three adjustable pins set 120° apart, an extrusion device and a computer program were developed. The bending of the tube is adjusted automatically through stepper motor-driven pins and 2-D or near 3-D shapes are produced by altering the geometrical flow conditions during the paste extrusion. The computer program developed allows the extrusion time to be controlled for any desired die configuration, i.e. the time between the movement of the pins in any direction, therefore, this adjustment alters the geometrical configuration for flow, inducing bending in the tube. Finally, the effects of the extrusion speed and geometrical flow conditions on the curvature and shape of the tubes were reported. It is also shown that complicated shapes, such as near helical tubes or spiral ceramic tubes can be produced by moving the pins in an appropriate manner.     

排气结构对导叶式旋风管内颗粒运动的影响

采用fluent软件对导叶式旋风管在不同排气芯管结构参数下的颗粒逃逸规律以及分离性能进行了数值模拟.结果表明,小颗粒在旋风管内逃逸位置主要集中在芯管侧缝、分离区和灰斗区;当芯管开缝面积比为1.936,下口直径、开缝高度分别为130、200mm时该旋风管的粒级效率最高.     

The effect of vapour shear and condensate drainage in condensers using roped tubes

It is well known that the heat transfer performance of a condensing heat exchanger can be improved by using roped or spirally indented tubes. Most of the published work refers to experiments carried out on single tubes in closely controlled laboratory experiments. If such tubes are to be used in practical situations the designer must know how they will perform in tube bundles. One of the main problems in condensers is the effect of condensate drainage (inundation) and vapour shear on the performance of that condenser. A series of experimentals have been carried out in three different tube bundles of 21 tubes in order to investigate the above phenomenon. One of the bundles was of plain tubes the other two were of roped tubes of the same diameter, groove pitch and groove depth but of differing helix angle. These values were 11mm., 0.2mm. and 6.4mm. respectively. The tubes were all 0.69.m long. The main experimental variables were cooling water velocity and logarithmic mean temperature difference.The results show that, as would be expected, condensate inundation reduces heat transfer in condensers. In addition, the flow pattern of the vapour in the condenser has a significant effect on the heat transfer performance of tubes in the bundle. Experiments with the roped tubes show that their performance is not as adversely affected by condensate drainage as is the plain tube bundle.     

基于流型的小直径圆管内流动凝结换热机理

通过流型的可视化观察和传热实验 ,探讨不同管径下小直径圆管内流动凝结过程中流型的演化规律以及不同流型的凝结换热特性 .分析表明 ,随着管径的减小 ,以凝结液沿管壁周向均匀分布为主的环状流型在流型图上的面积增加 ,相应地换热温差对凝结换热数Nu的影响降低 .本研究深化了对小尺度下凝结换热机理的认识 ,为推动相关技术的进一步发展提供了理论依据     

Energy release of mixed explosives during propagation of a nonideal detonation under conditions similar to the operation conditions of a blasthole charge

Detonation experiments were performed in a specially developed explosive device simulating a blasthole using charges of fine-grained and coarse-grained (granular) 30/70 TNT/ammonium nitrate mixtures of identical density 0.89 g/cm³ in steel shells with an inner diameter of 28 mm and a wall thickness of 3 mm at detonation velocities of 4.13 and 2.13 km/sec, respectively. Despite significant differences in detonation velocity (pressure), identical expansion of the charge shells was observed. On the other hand, numerical simulations of detonation propagation in the explosive device with the corresponding velocities ignoring the possibility of energy release behind the shock front show that the expansion of the charge shell is always greater in the case of a high-velocity regime. It is concluded that under the conditions simulating detonation propagation and the work of explosion products in a blasthole, effective additional energy release occurs behind the low-velocity (nonideal) detonation front. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 111–120, July–August, 2007.     

自然循环蒸发器往复螺旋流体动力清洗实验研究

针对蒸发器结垢严重及强制循环泵能耗高的问题,提出了一种用于自然循环蒸发器加热管内往复螺旋在线清洗技术,依靠气液两相流速度场的脉动实现工作螺旋轴向往复振动实现均匀防、除垢. 以水为实验介质,设计了6根加热管的常压蒸发实验台,用不同往复弹簧和工作螺旋组成的清洗装置进行了实验,并在优化参数下得到了工作螺旋轴向往复行程、循环流速与传热温差的关系. 结果表明,加热管规格为外径38 mm、壁厚2 mm、管长2 m的常压蒸发条件下,往复弹簧弹性系数K=7.0~8.0 N/m、工作螺旋螺距与管内径比为0.676~0.764且传热温差大于18℃时,系统循环流速不低于0.57 m/s,工作螺旋往复行程稳定大于一个螺距,满足均匀除垢需求.     

降膜蒸发管内插往复螺旋强化传热实验研究

为有效解决降膜蒸发器加热管中传热效率与结垢问题,提出了一种降膜蒸发管内插往复螺旋强化传热技术,强化管内插螺旋运动与管壁碰撞过程。实验研究内插螺旋的结构参数、螺旋往复行程,以及热通量、蒸发压力以及溶液喷淋密度等工艺参数对降膜蒸发过程传热性能影响。实验结果表明,此技术的除垢防垢性能及传热性能优于空管及单纯的内插螺旋性能,在螺旋外径d=30 mm、螺距f=45 mm、丝径e=1.8 mm、往复行程H=100 mm时,其传热系数分别是空管和单纯的内插螺旋的2.08和1.26倍。通过对管内蒸发侧传热系数进行分析,总结得到与热通量、蒸发压力以及溶液喷淋密度相关的降膜蒸发传热系数关联式。