Flow Structures of a Liquid Film Falling on Horizontal Tubes

Patterns of a liquid film falling across a vertical array of horizontal tubes change from droplet mode at low flow rates to liquid sheet at high flow rates. Between these limits, liquid columns form as a further stable flow pattern. The transition from one flow mode to another occurs via unstable structures consisting simultaneously of droplets and columns or of merging columns. The boundaries of the flow modes can be obtained from relationships expressing the flow rate as a function of physical properties, that is, the Reynolds number as a function of the Kapitza number. Correlations for the pattern boundaries recommended in the literature are compared with each other and found to be in acceptable agreement for practical purposes.     

锅炉省煤器管穿孔原因分析

某型号为KCTK35／40-100锅炉省煤器，在运行两年多时间内发生多次爆管事故。采用化学分析、金相检验及扫描电镜等分析方法对锅炉省煤器穿孔漏水原因进行了分析。结果表明，省煤器管内外壁共同腐蚀是引起其快速穿孔的原因，内壁产生了溶解氧腐蚀，外壁产生了氧化腐蚀及硫腐蚀。     

Optimization of the Heat Transfer Rate and Pressure Drop of Inside Profiled Tubes – Part 1

Nine inside profiled tubes were developed and investigated for optimization of the heat transfer rate and pressure drop behavior. The results of this work are presented in two parts. This part describes the comparative investigation of five tubes with different inside profiles to simulate the heat transfer and friction loss of fired tubular heaters in petrochemical processes. In part 2, a further four tubes with different inside profiles will be compared. To test the efficiency of the new profiles a test rig was modified. Using the similarity laws by Reynolds, the Reynolds number calculated for the gas flow in the heater tubes was converted into the flow rate, as well as the pressure and temperature of a distilled water system. Axial and peripheral velocities were measured using a Laser‐Doppler‐Velocimeter (LDV). Friction pressure drop and heat transfer were measured to determine the efficiency of each tested tube under the constant conditions of the distilled water system. The results of the investigations on these five inside profiles showed that profiles with eight flat and symmetrically distributed straight fins (tube III) or with a twist angle of 30° to the tube axis (tube IV), produced heat transfer rates higher that that of the bare tube by 120 % and 156 %, respectively, with increases in pressure drop only 46 % and 76 %, respectively.     

Experimental Investigation on the Holdup Distribution of Oil‐Water Two‐Phase Flow in Horizontal Parallel Tubes

An experimental investigation was conducted to study the holdup distribution of oil and water two‐phase flow in two parallel tubes with unequal tube diameter. Tests were performed using white oil (of viscosity 52 mPa s and density 860 kg/m³) and tap water as liquid phases at room temperature and atmospheric outlet pressure. Measurements were taken of water flow rates from 0.5 to 12.5 m³/h and input oil volume fractions from 3 to 94 %. Results showed that there were different flow pattern maps between the run and bypass tubes when oil‐water two‐phase flow is found in the parallel tubes. At low input fluid flow rates, a large deviation could be found on the average oil holdup between the bypass and the run tubes. However, with increased input oil fraction at constant water flow rate, the holdup at the bypass tube became close to that at the run tube. Furthermore, experimental data showed that there was no significant variation in flow pattern and holdup between the run and main tubes. In order to calculate the holdup in the form of segregated flow, the drift flux model has been used here.     

Numerical Analysis of Isothermal Gaseous Flows in Microchannel

Two‐dimensional compressible momentum equations were solved by a perturbation analysis and the PISO algorithm to investigate the effects of compressibility and rarefaction on the local flow resistance of isothermal gas flow in circular microchannels. The computations were performed for a wide range of Reynolds numbers and inlet Mach numbers. The explicit expression of the normalized local Fanning friction factor along the microchannel was derived in the present paper. The results reveal that the local Fanning friction factor is a function of the inlet Mach number, the Reynolds number and the length‐diameter ratio of the channel. For larger Reynolds and inlet Mach numbers, the friction coefficient in the microchannel is higher than the value in a macrotube, and the gas flow in the microchannel is dominated only by compressibility. For smaller Reynolds and inlet Mach numbers, the Fanning friction factor of gas flow in the microchannel is lower than that in a circular tube of conventional size due to slip flow at the wall and thus, rarefaction has a significant effect on the fluid flow characteristics in a microchannel.     

Comprehensive Composite Inelastic Fiber Element for Cyclic Analysis of Concrete-Filled Steel Tube Columns

This paper presents the development of a comprehensive composite beam-column fiber element for large displacement nonlinear inelastic analysis of concrete-filled steel tube (CFT) columns. The bond/slip formulation represents the interaction between concrete and steel over the entire contact surface between the two materials. Thus, the modeling accounts for the two factors that cause the slippage between steel shell and concrete core. The first factor is the difference between axial elongation of the steel shell and the concrete core, and the second is the difference between curvatures in the cross section for the concrete core and the steel shell. These effects are integrated over the perimeter and are added to the virtual work expression of the basic element. Furthermore, the constitutive models employed for concrete and steel are based on the results of a recent study and include the confinement and biaxial effects. A 13 degree of freedom (DOF) element with three nodes, which has five DOF per end node and three DOF on the middle node, has been chosen. The quadratic Lagrangian shape functions for axial deformation and the quartic Hermitian shape functions for the transverse directions are used. The model is implemented to analyze several CFT columns under constant concentric axial load and cyclic lateral load. The effect of semi- and perfect bond is investigated and compared with experiments. Good correlation has been found between experimental results and theoretical analyses. The results show that the use of a studded or ribbed steel shell causes greater ultimate strength and higher dissipation of energy than the columns with nonstudded steel shells.     

Low-velocity impact on carbon/epoxy tubes subjected to torque – Experimental results,analytical models and FEM analysis

This paper investigates the effect of torsional loads on the damage introduced by lateral impacts on cylindrical T300-carbon/epoxy specimens. A total of 16 specimens were subjected to a 7 J transverse impact under various torsional preloads. Four different lamination sequences were studied. A two-degree-of-freedom spring-mass model was developed to investigate the impact dynamics. To account for the damage propagation, a non-linear model of the tube flexural stiffness is proposed. Moreover, impact damage initiation was studied in detail by various FEM analyses. For each laminate, results show an invariant delamination threshold contact force, suggesting that the delamination initiation is not affected by the torsional preload. On the other hand, as evidenced by the variation in the contact duration and the tube maximum deflection, delamination propagation is highly affected by the torsional load.     

Energy-absorbing effectiveness factor

A study is reported on the energy-absorbing effectiveness factor which was introduced recently. The factor is defined as the quotient of the total energy, which can be absorbed in a system, to the maximum energy up to failure in a normal tensile specimen, which is made from the same volume of material. This dimensionless parameter allows comparisons to be made of the effectiveness of various geometrical shapes and of energy absorbers made from different materials. The influence of material properties and various geometrical parameters on the value of the dimensionless parameter has been examined for the static and dynamic axial crushing behaviours of thin-walled sections. The influence of foam fillings and the stiffening of circular and square tubes is examined.     

制氢原料变化对转化炉炉管温度的影响及对策

介绍了扬子石化有限公司制氢装置因原料改变进行的流程改造及运行情况,探讨原料由轻石脑油改为天然气后对转化炉炉管温度的影响。通过热力学分析及模拟数据的比较,认为影响炉温分布的主要原因是炉管内化学反应的变化,即甲烷转化所需热量少于烃类转化反应吸热;提出更换催化剂、优化工艺参数等解决炉管超温问题的对策;通过更换催化剂,大幅降低了转化炉管上部管壁温度,消除了制氢装置高负荷生产的瓶颈。