大型多支线供水工程的爆管水力过渡过程分析

鉴于爆管是危及大型供水工程安全运行的严重事故工况,基于瞬变流基本理论,结合超压泄压阀的工作原理,建立了地下埋管爆管工况的水力过渡过程计算分析数学模型,并提出了供水系统中最危险的爆管位置的确定方法。实例应用结果表明,该模型能反映爆管过程中管道内压力和流量的瞬变过程,确定的爆管位置具有合理性。     

百万级核电汽轮机高压外缸汽封接管焊接工艺的研究

介绍了百万级核电汽轮机高压外缸汽封接管焊接工艺的试验研究过程,从焊前装配、焊接工艺方法和焊接操作等方面阐述了实际的生产过程,为核电汽轮机汽缸的生产总结了宝贵的经验.     

Numerical simulation on the spontaneous ignition of high-pressure hydrogen release through a tube at different burst pressures

Spontaneous ignition induced by high-pressure hydrogen release is one of the huge potential risks in the promotion of hydrogen energy. However, the understanding of the microscopic dynamic characteristics of spontaneous ignition, such as ignition initiation and flame development, remains unresolved. In this paper, the spontaneous ignition caused by high-pressure hydrogen release through a tube is investigated by two-dimensional numerical simulation at burst pressure ranging from 2.67 to 15 MPa. Especially, the thermal and species characteristics in hydrogen shock-induced ignition under different strengths of shock wave are discussed carefully. The results show that the stronger shock wave caused by higher burst pressure leads to larger heating area and higher heating temperature inside the tube, increasing the possibility of spontaneous ignition. The shortening effect of initial ignition time and initial ignition distance will decrease with the increase of the burst pressure. Ignition will be initiated when the temperature is raised to about 1350–1400 K under the heating effect of shock waves. It is also found that the ignition occurs under the lean-fuel condition firstly on the upper and lower walls of the tube. The flame branch after spontaneous ignition is observed in the mixing layer. Two ignition kernels show different characteristics during the process of combustion and flow. The evolution of HRR and mass fraction of key species (OH, H, HO₂) are also compared to identify the flame front. The mass fraction of H has the better trend with HRR. It is suggested that H radical is a more reasonable choice as the indicator of the flame front.     

Optical evaluation and analysis of an internal low-concentrated evacuated tube heat pipe solar collector for powering solar air-conditioning systems

An optical evaluation and analysis of an internal low-concentrating evacuated tube heat pipe solar collector designed to enhance the collection of solar radiation for medium temperature applications is presented in this paper. The internal low-concentrating evacuated tube heat pipe solar collector was designed with an acceptance angle of 20° given a geometrical concentration ratio of 2.92. The truncation of the upper part of the reflector giving a geometrical concentration ratio of 1.95 was carried and enabled the internal low-concentrating evacuated tube heat pipe collector to be enclosed by a borosilicate glass tube with 100 mm and 93 mm outer and inner diameters, respectively. Ray trace analysis at different transverse angles determines optical efficiencies, related optical losses and flux distribution on the absorber of the internal low-concentrating evacuated tube heat pipe solar collector. A detailed two dimensional ray trace techniques considering only the direct insolation component predicated overall ray’s acceptance of 93.72% and optical efficiency of 79.13% from transverse angles of 0° to 20°.     

Effect of bundle geometries on the detonation velocity behaviors in stoichiometric hydrogen-air mixture

In this study, the effects of pipe bundle geometries on the detonation velocity behaviors are examined systematically in a circular tube with 6 m long and an inner diameter of 90 mm. The tube bundle structures are created by inserting several small pipes (20 mm outer diameter, 2 mm wall thickness) into the tube. Three different bundle structures can be obtained by varying the number of small pipes n of 3, 4 and 5. The ionization probes and pressure transducers (PCB102B06) are used to determine the average velocity while the smoked foil technique is employed to register the detonation cellular structures. The experimental results indicate that detonation can propagate at about the theoretical CJ velocity with a small deficit when the initial pressure (P₀) is greater than the critical value (P_c). The average velocity gradually decreases and deviates from the CJ value as the approaches of critical condition by gradually decreasing the initial pressure. The failure of detonation can be observed below the critical pressure. In the smooth tube, three different propagation mechanisms can be observed, i.e., super-critical condition, critical condition and sub-critical condition. After the bundle structures are introduced into the tube, a sudden velocity drop is seen at the critical pressure. Moreover, the detonation re-initiation phenomenon occurs with the velocity from the flame back to over-driven state quickly. Of note is that nearly no difference is seen between n = 3 and 4. However, in the case of n = 5, the detonation velocity experiences a more violent fluctuation with a high frequency, and the critical pressure is also increased to 28 kPa sharply. Finally, the critical condition analysis of detonation successful transmission is performed. The critical condition can be quantified as D_H/λ > 1. However, the critical values of D_H/λ are not uniform among various bundle geometries, but in a small range, i.e., from 1.52 to 1.97.     

回填钢管管周土压力分布特性研究

目前市政行业广泛采用Spangler理论进行回填钢管的设计,但水利水电行业中钢管规模和运行条件与市政行业存在较大差距,Spangler理论的适用性有待研究。基于有限单元法,考虑管土之间的接触作用,建立回填钢管三维有限元计算模型,计算不同埋设深度、开槽宽度、管道刚度下回填钢管的管周土压力,通过绘制管周土压力分布图研究管周土压力的分布特性及Spangler理论的适用性。结果表明,竖直土压力在回填钢管管顶和管底处有"波谷"产生,在高埋深、小槽宽时尤为明显;此外,回填钢管刚度越大,管顶土压力越接近抛物线分布,管腰处出现的"波谷"越明显。总体而言,Spangler理论一般更适用于埋深小于2m、管道刚度t/D值小于1/120的回填管道,在实际工程回填钢管的设计中要加以判断。     

油水分离技术优化研究

现阶段,我国大部分陆上油田已进入开发后期,不仅带来了严重的经济问题,更增加了油水分离的困难程度.目前对于油水分离技术的研究集中于螺旋管和波形板凝结分离器方面,其中波纹板和螺旋管油水分离技术应用广泛.利用CFD软件采用VOF模型对直管、波形管、螺旋管油水分离进行数值模拟,得到了油水分离规律:(1)在输油直管中,离管心越远...     

Numerical study of assisting and opposing mixed convective nanofluid flows in an inclined circular pipe

A numerical investigation of mixed convection is carried out to study the heat transfer and fluid flow characteristics in an inclined circular pipe using the finite volume method. The pipe has L/D of 500 and it was subjected to a uniform heat flux boundary condition. Four types of nanofluids (Al₂O₃, CuO, SiO₂, and TiO₂ with H₂O) with nanoparticles concentration in the range of 0 ≤ φ ≤ 5% and nanoparticles diameter in the range of 20 ≤ dp ≤ 60 nm were used. The pipe inclination angle was in the range of 30^∘ ≤ θ ≤ 75^∘ using assisting and opposing flow. The influences of Reynolds number in the range of 100 ≤ Re ≤ 2000, and Grashof numbers in the range of 6.3 × 10² ≤ Gr ≤ 8.37 × 10³ were examined. It is found that the velocity and wall shear stress are increased as Re number increases, while the surface temperature decreases. There is no significant effect of increasing Gr number on thermal and flow fields. The velocity and wall shear stress are increased and the surface temperature is decreased as φ and dp are decreased. It is concluded that the surface temperature is increased as the pipe inclination angle increases from the horizontal position (θ = 0^°) to the inclined position (θ = 75^°). In addition, it is inferred that the heat transfer is enhanced using SiO₂ nanofluid compared with other nanofluids types. Furtheremore, it is enhanced using assisting flow compared to opposing flow.     

Experimental investigation of shock wave propagation,spontaneous ignition,and flame development of high-pressure hydrogen release through tubes with different obstacles arrangements

Experiments on shock waves propagation, spontaneous ignition, and flame development during high-pressure hydrogen release through tubes with symmetrical obstacles (O_1-1) and asymmetrical obstacles (O_1-2) are conducted. The obstacle's side is triangular with a length of 4 mm, a height of 3.6 mm, and its width is 15 mm. In the experiments, a reflected shock wave generates and propagates both upstream and downstream when the leading shock wave encounters the obstacle. At the same burst pressure, the reflected shock wave intensity in tube O_1-1 is significantly greater than that in tube O_1-2. Moreover, the presence of obstacles in the tube can induce spontaneous ignition. The minimum burst pressures for spontaneous ignition for tubes O_1-1 and O_1-2 are 2.84 MPa and 3.28 MPa respectively, lower than that for the smooth tube. Furthermore, both the initial ignition position and ignition time are greatly advanced in obstruction tubes, mainly affected by obstacle positions and burst pressures. Finally, the flame separation process near the obstacle is observed. After passing the obstacle, the flames grow rapidly in radial and axial directions on the tube sidewalls. And at the same burst pressure, the flame convergence time in tube O_1-2 is usually longer than that in tube O_1-1.     

河北丰宁抽水蓄能电站高强钢岔管设计优化与技术研究

河北丰宁抽水蓄能电站是当前世界上在建装机容量最大的抽水蓄能电站,本文根据设计方案按初拟缝隙值和围岩弹性抗力系数,在联合受力条件下对岔管体形参数进行三维有限元设计优化,经优化后最终方案岔管的结构既满足明岔管准则的应力控制标准又符合埋管工况下的抗力限值要求,体形参数选择也满足规范要求,其成果对工程应用及国内外同类型电站钢岔...     

大口径预应力钢筒混凝土管当量粗糙度取值探究

为了探究大口径预应力钢筒混凝土管（PCCP管）当量粗糙度取值问题,以新疆三个泉倒虹吸管（DN2 800 mm）及天津新地河泵站PCCP试验管（DN1 600 mm）为例,通过库尔干诺夫式判别大口径PCCP管水流流态,选用齐恩公式、哈兰德公式计算PCCP管9个典型当量粗糙度对应的多组流量工况下的管道水头损失值,并将计算结果与实测资料做了对比分析。结果表明,新疆三个泉倒虹吸PCCP管当量粗糙度取值范围为0.03~0.07 mm;天津新地河泵站PCCP试验管当量粗糙度取值范围为0.05~0.07 mm;建议大口径PCCP管当量粗糙度取0.10 mm。研究成果为下一步研究奠定了基础。     

Study on hazards from high-pressure on-board type III hydrogen tank in fire scenario: Consequences and response behaviours

Exploration of thermal performances of composite high-pressure hydrogen storage tank under fire exposure were critical issues to reduce the risk of tank rupture. Three bonfire tests of type III tanks of 210 L-35 MPa with full compressed hydrogen were exposed to a pool fire to study the response behaviours in fire scenarios. Detailed data on the tank wall temperature and inner pressure were presented in this work. Prototype bonfire tests for the type III tank indicated the failure pressure limits amounted to 41.1–41.8 MPa (average 41.4 MPa). Two consequences (rupture and hydrogen blowdown) will be caused when the inner pressure beyond this limits in fire scenario. The loading-bearing capacity of the tank reduced nearly 3 times under the prescribed fire condition when compared to its average burst pressure of 123.5 MPa conducted from the hydraulic burst test. Results also shown that fire resistance rating (FRR, time to rupture) of the three tanks were 784, 666, and 596, respectively. The FRR got shorter when the tank was exposed in the engulfing fire in advance at hydrogen blowdown case.     

External overpressure of vented hydrogen-air explosion in the tube

Vented explosion experiments involving hydrogen-air mixtures are performed in a 2 m-long cylindrical tube under the influences of the hydrogen concentration and vent burst pressure. Photos of the external flame shot by a high-speed camera show that the jet flame was expelled outside the vessel, and the relation between the flame propagation and external overpressure is summarized. The internal peak overpressure increases and then decreases with increasing hydrogen concentration. In contrast, the external peak overpressure exhibits the opposite correlation in comparison with the internal peak overpressure. The variations in the pressure peaks of the internal pressure curves are also discussed. When the hydrogen concentration is lower than 40 vol %, the second pressure peak plays a more dominant role than the other pressure peaks. However, when the hydrogen concentration is higher than 40 vol %, the third pressure peak becomes more dominant.     

Failure pressure of straight pipe with wall thinning under internal pressure

The failure pressure of pipe with wall thinning was investigated by using three-dimensional elastic–plastic finite element analyses (FEA). With careful modeling of the pipe and flaw geometry in addition to a proper stress–strain relation of the material, FEA could estimate the precise burst pressure obtained by the tests. FEA was conducted by assuming three kinds of materials: line pipe steel, carbon steel, and stainless steel. The failure pressure obtained using line pipe steel was the lowest under the same flaw size condition, when the failure pressure was normalized by the value of unflawed pipe defined using the flow stress. On the other hand, when the failure pressure was normalized by the results of FEA obtained for unflawed pipe under various flaw and pipe configurations, the failure pressures of carbon steel and line pipe steel were almost the same and lower than that of stainless steel. This suggests that the existing assessment criteria developed for line pipe steel can be applied to make a conservative assessment of carbon steel and stainless steel.     

Experimental studies on heat transfer and friction factor characteristics of turbulent flow through a circular tube with small pipe inserts

Heat transfer performance and pressure drop tests were performed on a circular tube with small pipe inserts. These inserts with different spacer lengths (S = 100, 142.9 and 200 mm) and arc radii (R = 5, 10 and 15 mm) were tested at Reynolds numbers between 4000 and 18,000. Tap water was used as working fluid. The use of pipe inserts allowed for a high heat transfer coefficient with relatively low flow resistance. The Nusselt number and friction factor increase with the decrease in spacer length. Optimal results were obtained for S = 100 mm (R = 10 mm). Heat transfer rates and friction factors were enhanced by 2.09–2.67 and 1.59–1.85 times, respectively, to those in the plain tube. Performance evaluation criterion (PEC) values were approximately 1.79–2.17. The Nusselt number and friction factor increase with the decrease in arc radius. Small pipe inserts with R = 5 mm and S = 100 mm show maximal heat transfer rates of 2.61–3.33 and friction factors of 1.6–1.8 times those of the empty tube. The PEC values were 2.23–2.7. Compared with other inserts, pipe inserts can transfer more heat for the same pumping power for their unique structure.     

Experimental study on spontaneous ignition and flame propagation of high-pressure hydrogen release through tubes

An experimental study was conducted to research the mechanism of spontaneous ignition induced by high-pressure hydrogen release through tubes with a diameter of 10 mm and varying lengths from 0.3 to 3 m. The pressure and light signals inside the tube were collected. The propagation of shock wave inside and outside the tube was also systematically investigated. The development process of the jet flame in the atmosphere was completely recorded, and the multiple Mach disks at the tube exit were observed by using a high-speed camera. The results show that the minimum release pressure, at which the jet flame is formed, is found to be 3.87 MPa with the tube length of 1.7 m. When the tube length was longer than 1.7 m, the critical pressure for forming jet flame increased rapidly. The velocity attenuation of the shock wave is mainly affected by the burst pressure but not sensitive to the tube length, and the flame propagates in the tube at a slower velocity than the shock wave. The compression of the hydrogen-air mixture by the Mach disk causes it to burn more violently after passing through the Mach disk. It is confirmed that the flame at the tube exit is lifted in the atmosphere, then a jet flame initiates behind the second Mach disk.     

Numerical study and sensitivity analysis on convective heat transfer enhancement in a heat pipe partially filled with porous material using LTE and LTNE methods

An improved design for convective heat transfer in a heat pipe partially filled with porous medium is presented. In the present study, porous media is used to increase heat transfer in laminar flow inside the tube with a constant heat flux boundary condition. The porous segments are set in different positions in the tube, while the ratio of porous volume to total volume of tube is considered to be constant. A performance evaluation criteria (PEC), which takes account of both heat transfer and pumping power, is defined to find the enhanced mode of porous media arrangement. According to the current results, PEC increases with the number of porous segments. Moreover, the sequence of unequal segments arrangement within the tube is from the largest to the smallest part for a higher PEC. Effects of parameters including porosity, Darcy number, and ratio of effective coefficient of thermal conductivity to coefficient of thermal conductivity of fluid (TKR) are investigated for sensitivity analysis. Simulations are conducted using the local thermal equilibrium method. In addition, the local thermal nonequilibrium is also used for comparison. For TKR numbers less than 10, these models show the same results with negligible differences except for TKR more than 10.     

Effects of severe blockage on heat transfer from a sphere in power-law fluids

The momentum and thermal energy equations describing the forced convection heat transfer from a heated sphere settling at the axis of a long cylindrical tube filled with a power-law fluid have been solved numerically. The extensive new results reported herein encompass wide ranges of conditions as: Reynolds number, 1 ≤ Re ≤ 100; Prandtl number, 5 ≤ Pr ≤ 100, power-law index, 0.2 ≤ n ≤ 2 and blockage ratio, 0.5 ≤ λ ≤ 0.95. The range of values of the power-law index (n) used here include both the shear-thinning (n < 1) and shear-thickening (n > 1) fluid behaviours. The overall heat transfer is strongly modulated by Re, n and λ depending upon whether the recirculation region is formed in the rear of the sphere and/or on the proximity of the tube wall. Furthermore, the results reported herein elucidate the effect of the type of thermal boundary condition (isothermal or isoflux) on the surface of the sphere as well as that of the velocity profile (uniform or fully developed Poiseuille profile) in the tube. Overall, the average Nusselt number bears a positive dependence on the Reynolds and Prandtl numbers and blockage ratio. The shear-thinning behaviour (n < 1) augments heat transfer over and above the corresponding Newtonian value whereas shear-thickening behaviour (n > 1) adversely influences it. The present numerical results (~ 4000 data) have been consolidated by incorporating the blockage factor into an existing expression valid for λ = 0 for Newtonian fluids.     

A study on the thermal contact conductance in fin–tube heat exchangers with 7 mm tube

The thermal contact resistance has been frequently neglected in the process of design of heat exchangers because of the difficulty of measurement and the lack of accurate data. However, the thermal contact resistance is one of principal parameters in heat transfer mechanism of fin–tube heat exchangers. The objective of the present study is to investigate new factors such as fin types and manufacturing types of the tube affecting the thermal contact conductance and to find a correlation between the thermal contact conductance and the effective factors in fin–tube heat exchangers with 7 mm tube. The thermal contact conductances in the 22 heat exchangers with 7 mm tube have been investigated through the experimental–numerical method. A numerical scheme has been employed to calculate the thermal contact conductance and the portion of thermal resistances using the experimental data. As a result, the thermal contact conductance has been evaluated quantitatively, and a new correlation including the influence of new factors such as fin types and manufacturing types of the tube has been developed in the fin–tube heat exchanger with 7 mm tube. Also, the portion of each thermal resistance has been evaluated in each case.     

管袋堤坝波浪作用下波浪压力的数值模拟研究

波浪作用是影响管袋筑坝的最主要外部荷载,关系到管袋结构的安全与稳定。为了解管袋堤坝在波浪作用下的波浪压力,基于流体力学计算软件FLUENT建立数值水槽模型,通过设定不同的边界条件,采用源造波法模拟不同波高、周期、水深、坡率下波浪与管袋坝面的相互作用,计算管袋受力和波陡、坡率之间的关系,并拟合相应关系曲线得到管袋坝的受力和波陡、坡率之间的函数关系式。结果表明,该方法的结果与物理试验过程中获得的规律相符,具有一定的实用性。