Advanced numerical method for a thermally induced slug flow: application to a capillary closed loop pulsating heat pipe

An advanced hybrid lumped parameter code for the simulation of Pulsating Heat Pipes is developed. Being able to simulate transient operative conditions and removing common physical simplified assumptions, it represents a step forward with respect to the present models of passive two‐phase systems. Mass, momentum and energy balances account for the thermal and fluid‐dynamics phenomena. Heterogeneous and homogeneous phase changes are directly integrated. In addition, a fitting correlation for the wall/vapour heat transfer coefficient is implemented and tuned against experimental data in order to evaluate the influence of the liquid film on conjugate heat transfer. The resulting numerical tool have been validated against experimental data achieved testing a copper pulsating heat pipe during the 58th ESA Parabolic Flight Campaign in several operative conditions and transient gravity levels. The predicted results show very good matching with the actual thermo‐physical behaviour of the system. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamics of a pipe conveying fluid flexibly restrained at the ends

The subject of this paper is the study of dynamics and stability of a pipe flexibly supported at its ends and conveying fluid. First, the equation of motion of the system is derived via the extended form of Hamilton׳s principle for open systems. In the derivation, the effect of flexible supports, modelled as linear translational and rotational springs, is appropriately considered in the equation of motion rather than in the boundary conditions. The resulting equation of motion is then discretized via the Galerkin method in which the eigenfunctions of a free-free Euler–Bernoulli beam are utilized. Thus, a general set of second-order ordinary differential equations emerges, in which, by setting the stiffness of the end-springs suitably, one can readily investigate the dynamics of various systems with either classical or non-classical boundary conditions. Several numerical analyses are initially performed, in which the eigenvalues of a simplified system (a beam) with flexible end-supports are obtained and then compared with numerical results, so as to verify the equation of motion, in its simplified form. Then, the dynamics of a pinned-free pipe conveying fluid is systematically investigated, in which it is found that a pinned-free pipe conveying fluid is generally neutrally stable until it becomes unstable via a Hopf bifurcation leading to flutter. The next part of the paper is devoted to studying the dynamics of a pinned-free pipe additionally constrained at the pinned end by a rotational spring. A wide range of dynamical behaviour is seen as the mass ratio of the system (mass of the fluid to the fluid+pipe mass) varies. It is surprising to see that for a range of rotational spring stiffness, an increase in the stiffness makes the pipe less stable. Finally, a pipe conveying fluid supported only by a translational and a rotational spring at the upstream end is considered. For this system, the critical flow velocity is determined for various values of spring constants, and several Argand diagrams along with modal shapes of the unstable modes are presented. The dynamics of this system is found to be very complex and often unpredictable (unexpected).     

A perturbation solution for forced convection in a porous-saturated duct

Fully developed forced convection through a porous medium bounded by two isoflux parallel plates is investigated analytically on the basis of a Brinkman–Forchheimer model. The matched asymptotic expansion method is applied for small values of the Darcy number. For the case of large Darcy number the solution for the Brinkman–Forchheimer momentum equation is found in terms of an asymptotic expansion. With the velocity distribution determined, the energy equation is solved using the same asymptotic technique. The results for limiting cases are found to be in good agreement with those available in the literature and the numerical results obtained here.     

基于管道模型的榆树水分年轮输导模式研究

根据管道模型理论并通过生物染色剂染色实验,对榆树的水分年轮输导模式进行了研究.研究发现,榆树不同年轮的水分输导能力不同;不同年轮间水分横向输导不明显,纵向输导在同一年轮内也不是均衡向上输导,呈明显的管道状输导,这一结果完全符合管道模型理论.     

应用概率方法计算室内给水管道设计秒流量

本文在深入研究现有室内给水管道设计秒流量计算方法的基础上，应用概率论，以满足使用保证率的室内给水管道设计秒流量为出发点，提出了一种新的计算方法。通过实例计算，分析了使用保证率和卫生器具放水使用概率对设计秒流量的影响，与平方根法和已有概率法作了比较，说明了该方法的合理性和通用性。     

对给水管网解算程序的一点改进

本文针对现行给水管网电算程序的一些缺陷，作了若干改进，使其输入原始数据简单方便，并能自动圈划回路，适用于不同结构或多水源管网设计与运行管理，能输出管段流量、结点水压、水塔高度或水泵工况及其轴功率等结果，比现行程序更方便、通用、有效。简例介绍了新程序的功能     

Detecting and describing a notch in a pipe using singularities

A hybrid Semi-Analytical Finite Element (SAFE) and standard finite element procedure is adopted to simulate ultrasonically generated waves traveling in an infinitely long steel pipe having an open, rectangular notch. Numerical illustrations indicate that dispersive guided waves can be used to locally detect and characterize such a notch. A frequency oriented approach is preferred because a problematic separation in time is circumvented when incident waves overlap their reflections from the nearby notch. The notch is discerned straightforwardly because distinctive singularities are introduced that differ from those observed at the modal cutoff frequencies in a Frequency Response Function (FRF) of a comparable but undamaged pipe. Its characterization is (suggested) demonstrated for a (non)axisymmetric notch by using several of the smallest differences in the frequencies at which the two set of singularities occur. Consequently an external stimulus that simultaneously excites more than one mode is beneficial.     

Prediction of the remaining lifetime of polyethylene pipes after up to 30 years in use

Plastics pipes made of polyethylene (PE) play an outstanding role in gas and water supply. While for modern pipe grades typical lifetimes of 50 years are taken for granted and service times of 100 years are discussed, pipes made of PE with a lower performance have been used for decades. As the repair and rehabilitation of existing pipe systems involve immense costs, the question of their qualitative condition has to be considered. In this paper, four different pipes used in the gas and water distribution in Austria with an age up to 30 years have been investigated. After a morphological and mechanical study, particular attention was paid to material stabilization, which is essential for long-term applications. Fracture mechanics tools have been used to gain information on the resistance to crack initiation and slow crack growth. Furthermore, a fracture mechanics extrapolation procedure has been applied to predict the remaining lifetime of the pipes. The results have indicated that all the pipes investigated are still in a very good condition and are likely to be sufficiently safe to remain in use.     

切管自动送料装置的设计

在以各种管材为原料的产品生产过程中,管件切割的送料方式直接影响到切割的精度和生产效率,继而影响产品的质量和成本。目前管材切割的送料方式大都是人工操作,切割精度和效率低,劳动强度大。根据管材自动切割的精度、效率、安全性和稳定性等方面的需求,对自动送料装置的驱动、传动和控制方式等进行了设计。通过步进电机和滚珠丝杠传动机构进行自动送料,气动驱动组合夹具进行不同数量和截面形状管材的可调装夹,参照企业生产需求设计了机架,装置实现了管材切割送料的自动化。