柴油机喷嘴入口圆角对线空化影响的试验研究

柴油机喷嘴内的线空化是一种呈现线状形态的特殊空化现象,具有高瞬态性。本文利用自搭建的稳态试验台,设计了双孔min-SAC比例放大喷嘴。并在稳定喷射压力和固定针阀升程条件下开展了试验研究。研究表明,随着喷射压差的升高,喷嘴内部线空化程度随之增加;喷孔入口圆角会影响喷嘴内部涡旋运动,进而影响线空化的分布特征;在高针阀升程下,几何诱导空化对线空化有促进作用;当喷孔入口存在倒圆角时,喷嘴内几何诱导空化被明显抑制,线空化分布特征明显不同。     

η string formation in QCD chiral phase transition

In the paper we discuss the role of the axial U（1）A symmetry in the chiral phase transition using the U（Nf）R × U（Nf）L linear sigma model with two massless quark flavors. It is expected that above a certain temperature the axial U（1）A symmetry will be restored. A string-like static solution, the η string can be formed and detected in the ultrarelativistic heavy-ion collision process.     

QCD手征相变中的π介子增强(英文)

讨论了在LHC的Pb-Pb碰撞过程中,如果QGP SU(2)手征相变出现二级相变,那么系统将会有π弦产生,并且π弦最终将衰变为π介子。于是以上效应将导致在低动量区域（p~150—400 MeV）内的π介子增强。对应于不同的冷却温度T_f=130,120,110 MeV,产生于π弦衰变的π介子的数量分别是Nt≈270,150, 60. It is pointed out that if the QGP SU(2) chiral phase transition in the LHC Pb Pb collision process is taken place and the phase transition is in the second order, then pion strings will be formed, and decay. These phenomena lead to the pion enhancement in the low momentum region(p150—400 MeV) and the number of pions produced from pion string decay can be estimated about Nt≈270, 150, 60 for different freeze temperature Tf=130, 120, 110 MeV respectively.     

平板热管相变传热特性的实验研究

平板热管具有很好的均热性,能够避免电子器件散热时热点的产生,使热沉具有更好的散热效果.为了研究平板热管的相变传热特性,制作了可视化平板热管,通过实验研究了加热功率、冷却风速、不同工质对平板热管性能的影响.同时,还研究了槽道结构对平板热管内部沸腾换热的强化作用.     

照明用大功率LED回路热管散热器的研究

分析了照明用大功率LED封装的散热特性,提出了一种用于大功率LED系统散热的回路热管;研究了热负荷、倾角、加热方式等对热管的起动性、均温性、热阻等的影响。试验结果表明,所设计的热管散热器的热阻在0.19K/W~3.1K/W之间,蒸发器的均温性被控制在1.5℃以内,满足大功率LED封装的均温性要求,在热负荷为100W时,蒸发器的温度被控制在100℃以下,满足大功率LED结点温度的控制要求。     

A direct numerical simulation of axisymmetric liquid–gas two‐phase laminar flows in a pipe

An accurate finite‐volume‐based numerical method for the simulation of an isothermal two‐phase flow, consisting of a liquid slug translating in a non‐reacting gas in a circular pipe is presented. This method is built on a sharp interface concept and developed on an Eulerian Cartesian fixed‐grid with a cut‐cell scheme and marker points to track the moving interface. The unsteady, axisymmetric Navier–Stokes equations in both liquid and gas phases are solved separately. The mass continuity and momentum flux conditions are explicitly matched at the true surface phase boundary to determine the interface shape and movement. A quadratic curve fitting algorithm with marker points is used to yield smooth and accurate information of the interface curvatures. It is uniquely demonstrated for the first time with the current method that conservation of mass is strictly enforced for continuous infusion of flow into the domain of computation. The method has been used to compute the velocity and pressure fields and the deformation of the liquid core. It is also shown that the current method is capable of producing accurate results for a wide range of Reynolds number, Re, Weber number, We, and large property jumps at the interface. Copyright © 2010 John Wiley & Sons, Ltd.     

Mathematical modelling and parameter optimization of pulsating heat pipes

Proper heat transfer management is important to key electronic components in microelectronic applications. Pulsating heat pipes (PHP) can be an efficient solution to such heat transfer problems. However, mathematical modelling of a PHP system is still very challenging, due to the complexity and multiphysics nature of the system. In this work, we present a simplified, two-phase heat transfer model, and our analysis shows that it can make good predictions about startup characteristics. Furthermore, by considering parameter estimation as a nonlinear constrained optimization problem, we have used the firefly algorithm to find parameter estimates efficiently. We have also demonstrated that it is possible to obtain good estimates of key parameters using very limited experimental data.     

The double copy: gravity from gluons

Three of the four fundamental forces in nature are described by so-called gauge theories, which include the effects of both relativity and quantum mechanics. Gravity, on the other hand, is described by General Relativity, and the lack of a well-behaved quantum theory – believed to be relevant at the centre of black holes, and at the Big Bang itself – remains a notorious unsolved problem. Recently a new correspondence, the double copy, has been discovered between scattering amplitudes (quantities related to the probability for particles to interact) in gravity, and their gauge theory counterparts. This has subsequently been extended to other quantities, providing gauge theory analogues of e.g. black holes. We here review current research on the double copy, and describe some possible applications.     

长输管线整体下沟技术研究

 长输管线整体下沟技术是施工难点之一. 通过模拟大变形时的挠度曲线,建立力学计算模型,对管线下沟各阶段不同状态下的应力和变形进行分析,找出最不利的受力状态,得出吊点间距、起吊高度等指导施工的关键控制参数,并成功用于实践. 分析的结果可供矿浆管道、油气管道等长输管线整体下沟参考.     

Quantitative assessment of deformation-induced damage in polyethylene pressure pipe

This paper presents results from a study that quantifies the influence of excessive deformation on the damage development in polyethylene (PE) pressure pipe. The experimental investigation is through the application of a novel two-stage approach to the D-split test of notched pipe ring (NPR) specimens. The first test is to introduce damage by subjecting the specimens to different levels of tensile strain at crosshead speeds of 0.01, 1, 10 or 100 mm/min. The second test is to apply monotonic tensile loading at a crosshead speed of 0.01 mm/min to characterize the mechanical properties for specimens that have had damage generated in the first test. Experimental results suggest that elastic modulus and yield stress decrease and yield strain increases with increase of the strain introduced in the first test. Variation of experimentally measured elastic modulus is used to establish influence of crosshead speed on the damage evolution in the PE pressure pipe.