Numerical simulation of double-pipe condensers and evaporators

A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behaviour of double-pipe heat exchangers (evaporators and condensers) has been carried out. The governing equations (continuity, momentum and energy) inside the internal tube and the annulus, together with the energy equation in the internal tube wall, external tube wall and insulation, are solved iteratively in a segregated manner. The discretized governing equations in the zones with fluid flow are efficiently coupled using an implicit step by step method. This formulation requires the use of empirical correlations for the evaluation of convective heat transfer, shear stress and void fraction. An implicit central difference numerical scheme and a line-by-line solver was used in the internal and external tube walls and insulation. A special treatment has been implemented in order to consider transitions (single-phase/two-phase, dry-out,…). All the flow variables (enthalpies, temperatures, pressures, mass fractions, velocities, heat fluxes,…) together with the thermophysical properties are evaluated at each point of the grid in which the domain is discretized. Different numerical aspects and comparisons with analytical and experimental results are presented in order to verify and validate the model.     

Simulation of gas–solid two-phase flow in the annulus of drilling well

This paper investigates the hydrodynamic behavior of gas–solid two-phase flow in the annular space of an air drilling well under different arrangements by using three-dimensional approach. Two-fluid model is used to solve the governing equations in the Eulerian–Eulerian framework. Effect of eccentricity and drill pipe rotation on the pressure drop, volume fraction and velocity profile are examined. The results are compared with available data in the literature and good agreement is found. The results show that the presence of solid particles in the annulus change the air velocity profile significantly and create two off-center peaks velocity close to the walls instead of one peak velocity in the middle. Eccentricity of drill pipe makes more accumulation of the cuttings in the smaller space of the annulus. Increasing the eccentricity increases pressure drop due to impact of particles with annulus wall and also particles collision with each other. Rotation of the drill pipe shifts maximum air velocity location toward smaller space of the annulus which results more uniform cutting distributions in the annulus and improvement in their transportations. Pressure drop in the annulus increases as eccentricity and rotation of drill pipe increase.     

流道倾斜对环形通道内汽-水两相流压降的影响

以去离子水为工质,在P=1-3 MPa、(G=190～1050 kg/m/(m2·s)、ΔTsub,in=20～70℃、q=304～1873 KW/m2的参数范围内,研究了垂直上升、倾斜向上30°、倾斜向上600°3个不同方向下环形通道内汽-水两相流压降.环形通道当量直径为7mm,加热方式为内管单面加热.通过分析流道倾斜角度和空泡份额对两相流压降的影响,提出了倾斜上升流中两相流压降受流道倾斜影响程度的判据式.在判据式的基础上,进一步提出了倾斜上升流道内两相流压降计算修正关系式.结果表明,用修正后的压降关系式验证本实验倾斜两相流压降,预测结果令人满意.     

小井眼钻井液技术及其流变性控制初探

小井眼钻井液技术的关键是流变性设计和控制要符合小井眼环空水力学的特征;认为流变模式应选用较全面和较复杂的修正幂律模式,小井眼钻井液的流变性能要满足减小环空压耗、提高携屑效果、稳定井壁的要求;并对两种实用于现场的小井眼钻井液体系的流变性作了分析。     

汽轮机外环高效切削稳定性研究

针对汽轮机外环加工中的切削振动和刀具破损问题，进行马氏体不锈钢铸件数控加工切削层参数与切削力变化规律研究，建立切削力预报模型，提出控制汽轮机外环铸件数控加工切削力载荷变化幅度，实现高效稳定切削的方法。结果表明：受马氏体不锈钢铸件状态影响，外环数控加工切削层参数与切削力处于非稳定状态；依据切削力变化幅度约束条件，按刀具切削运动方向规划背吃刀量，汽轮机外环加工中切削力变化引起的振动和刀具破损得到有效抑制，切削稳定性和加工效率得到明显改善。     

Dispersion in steady and time-oscillatory flows through an eccentric annulus

A multiple-scale perturbation is conducted to derive an averaged equation for predicting the longtime solute transport in an eccentric annulus in which the uniaxial flow may oscillate periodically in time. A proof for the positiveness of the dispersivity is presented, implying that over a cycle of oscillation a solute cloud always broadens. For a steady flow driven by a fixed pressure gradient, increasing the eccentricity and annulus size gives rise to stronger dispersion. This relationship holds when the flow becomes unsteady. In the limit of slow oscillation, dispersion due to an oscillatory flow asymptotes to one-half of that by a steady flow. Increasing the oscillation frequency leads to a two-step decay of the dispersivity. The maximum dispersion in an oscillatory flow can be achieved in the limit of slow oscillation and large eccentricity, where dispersion can be O(10³) times larger than that in an otherwise concentric annulus.     

评价双层安全壳直接旁路泄漏的设计思路研究

本文探讨了评价压水堆全压双层安全壳直接旁路泄漏的设计思路,特别是如何识别潜在旁路泄漏途径和如何确定旁路泄漏率,提出环廊初始维持较大负压使事故后不出现"正压"阶段从而不需评价"正压"期间旁路泄漏,和环廊初始维持较小负压且需评价事故后"正压"阶段持续时间两种主要设计思路,可指导研发先进压水堆核电厂时选择系统设计方案。     

Lattice Boltzmann simulation of mixed convection heat transfer in eccentric annulus

Mixed convection heat transfer in eccentric annulus was simulated numerically by lattice Boltzmann model (LBM) based on multi-distribution function double-population approach. The effect of eccentricity on heat transfer at various locations was examined at Ra = 10⁴ and σ = 2. Velocity and temperature distributions as well as Nusselt number are obtained. The results are validated with published results and shown that multi-distribution function approach can evaluate the velocity and temperature fields in curved moving boundaries with a good accuracy in comparison with the previous studies. The results show that the average Nusselt number increases when the inner cylinder moves downward regardless of the radial position.     

Conjugate natural convection in air filled tube inserted a square cavity

Numerical analyses of fluid flow and heat transfer due to buoyancy forces in a tube inserted square cavity filled with fluid were carried out by using control volume method in this study. The cavity was heated from the left wall and cooled from the right isothermally and horizontal walls were adiabatic. A circular tube filled with air was inserted into the square cavity. The case that the inside and outside of the tube were filled with the same fluid (air) was examined. Varied solid materials were chosen as the tube wall. Results were obtained for different Rayleigh numbers (Ra = 10⁴, 10⁵ and 10⁶), thermal conductivity ratio of the fluid to the tube wall (k = 0.1, 1 and 10) and different location centers of the tube (c (0.25 ≤ x ≤ 0.75, 0.25 ≤ y ≤ 0.75)). Comparison with benchmark solutions of the natural convection in a cavity was performed and numerical results gave an acceptable agreement. It was found that varied location of the tube center can lead to different flow fields and heat transfer intensities which are also affected by the value of Rayleigh number.     

地下储气库注采井不同井段水泥环密封性能实验

针对我国西南地区首座地下储气库——相国寺储气库投产后注采井出现较大比例的B环空异常带压问题,采用室内实验的方法,根据注采井100 m、900 m、2 000 m垂深处温度和压力差异,设计了不同的水泥石养护温度和加载围压,并采用小尺寸的水泥环完整性测试装置基于应力等效原理测试了从井底到井口水泥环在试压和注采时的密封能力。实验结果表明:①井筒不同深度段水泥候凝温度和围压差异较大,同一种水泥浆体系在实际固井后沿井筒深度具有不同的机械性能,导致不同井段水泥环密封性能存在着巨大的差异;②交变载荷会导致水泥环的压实和累积损伤,加剧水泥环的密封失效;③注采井2 000 m处水泥环在试压和注采工况条件下,密封性完好,没有发生泄漏,1 000 m处水泥环在试压工况下能保持完好,在循环交变载荷下存在着水泥环密封失效的现象,井口附近100 m处水泥环在试压工况和注采工况时均出现了泄漏;④实验结果揭示,在试压和注采工况下,井筒中上部水泥环密封失效是造成B环空异常带压的根本原因。结论认为,该研究成果可以为提高地下储气库注采井固井水泥环密封的可靠性提供实验数据支撑。