Experimental and numerical analysis of cylindrical turbulators in a double pipe heat exchanger under turbulent flow conditions

In the present work, the use of cylindrical turbulators in a double pipe heat exchanger has been investigated. Cylindrical fin type of turbulators has been placed circumferentially separated by 90° on the outer side of an inner pipe at a regular pitch. Experimental studies were undertaken for different air flow rates in a turbulent regime whose Reynolds number range between 2500 and 10000. Heat transfer characteristics like Nu and friction factor have been experimentally determined. Parametric studies were conducted by changing the pitch and also the orientation of the turbulators. Nu and friction factor were found to increase as the pitch is reduced. A model with alternatively changed orientation outperformed others by exhibiting highest Nu and reduced friction factor.     

激光投影显示中光棒匀光的照明光路设计

在方棒照明系统的基础上,根据激光光源的发光特性和准直性,设计了一款用于激光投影显示的,基于光棒匀光的照明光路系统。此系统具有结构简单、开发周期短、加工成本低的优点。仿真结果表明:设计的激光投影机光能量利用率达到78%,均匀度达到85%,满足激光投影显示中对集光和照明的设计要求。     

Vibration of strings with nonlinear supports

The dynamic string motion, which displacement is unilaterally constrained by the rigid termination condition of an arbitrary geometry has been simulated and analyzed. The treble strings of a grand piano usually terminate at a capo bar, which is situated above the strings. The apex of a V-shaped section of the capo bar defines the end of the speaking length of the strings. A numerical calculation based on the traveling wave solution is proposed for modeling the nonlinearity inducing interactions between the vibrating string and the contact condition at the point of string termination. It was shown that the lossless string vibrates in two distinct vibration regimes. In the beginning the string starts to interact in a nonlinear fashion with the rigid terminator, and the resulting string motion is aperiodic. Consequently, the spectrum of the string motion depends on the amplitude of string vibrations, and its spectral structure changes continuously with the passage of time. The duration of that vibration regime depends on the geometry of the terminator. After some time of aperiodic vibration, the string vibrations settle in a periodic regime where the resulting spectrum remains constant.     

测量透明管壁厚的理论研究

透明管（如玻璃管）壁厚几何尺寸的公差大小是玻管生产中产品质量优劣的重要指标之一;因此透明管的壁厚测量的精度尤为重要。根据光矢量场的电磁场理论仔细分析了透明管在平面光波中的透射和反射的光学特性;并研究其能量分布。用ＣＣＤ作接收器件,进行非接触测量实验系统实验,将理论值与实验值相比较,提出了精确测量透明管壁厚的可行性方法     

由正负磁单极对相互作用诱导的孤立狄拉克弦

基于三维旋量Gross-Pitaevskii(GP)方程研究在含时周期性外磁场作用下玻色-爱因斯坦凝聚体的动力学行为.结果显示,在含时周期外磁场的作用下,铁磁态自旋为1的玻色-爱因斯坦凝聚体将发生拓扑形变.当磁场的两个零点进入凝聚体后,自旋向上态的密度布居图在z轴上分别形成向上和向下的凸起.随着磁场的两个零点在凝聚体内...     

基于流量测点的热网变动阻力系数优化辨识

随着供热计量系统的普及,系统可以根据负荷的变化进行调整,管网的阻力系数随即发生变化.对变动阻力系数进行优化辨识是了解供热管网实时运行状况的有效手段.提出一种基于流量监测数据的供热管网变动阻力系数优化辨识方法,并利用遗传算法进行求解.对洛阳市某小区供暖季管网实际运行数据进行验证,辨识结果的相对误差在5％以内.结果表明:该...     

Non-Static Local String in Higher-Dimensional Gravity

We analyze the space-time structure of local gauge string with a phenomenological energy–momentum tensor, as prescribed by Vilenkin, in an arbitrary number of space-time dimensions with a non-zero cosmological constant Λ. A set of solutions of the full non-linear Einstein's equations for the interior region of such a string is presented.     

A stabilization law for two semi-infinite interacting strings of characters

We consider a Markov chain that describes the evolution of two interacting strings of symbols. The transitions probalitities of this Markov chain depend only on the rightmost symbols of both strings. The main goal of the present paper is to prove a limit theorem (stabilization law): the distribution of the rightmost symbols converges to some limit correlation function.1 Partially supported by FAPESP (2002/01501-9) and RFBR (02-01-00415)2 Partially supported by RFBR (02-01-00415)     

Hydrogen-bonded assemblies of trinuclear metal string complexes

Three kinds of trinuclear metal string complexes, [Ni₃(dpa)₄(L¹)₂]?·?H₂O?·?C₂H₅OH (L¹?=?(E)-3-(2-hydroxyl-phenyl)-acrylic acid) (1), [Ni₃(dpa)₄(L²)₂]?·?2C₂H₅OC₂H₅ (L²?=?(E)-3-(3-hydroxyl-phenyl)-acrylic acid) (2) and [Ni₃(dpa)₄(L³)₂]?·?3CH₂Cl₂?·?1.5CH₃OH (L³?=?(E)-3-(4-hydroxyl-phenyl)-acrylic acid) (3). (dpa^??=?bis(2-pyridyl)amido), have been synthesized. The structures of 1 and 2 have been analyzed by the X-ray single-crystal diffraction showing hydrogen-bonded networks.