一种新型低下限差压流速传感器的设计及应用

差压式流速传感器因工作稳定可靠、成本低而广泛应用于各类矿山、巷道的气体流速监测,该文通过分析传统S型皮托管测量气体流速的原理及使用局限性,详细介绍了一种基于自导流S型皮托管的新型差压流速传感器的结构特点及传感器软、硬件设计,将差压式流速传感器测量下限提高到0.15 m/s,满足了《煤矿安全规程》对煤矿巷道最低风速监测的规定。在实验室完成了性能测试,试验结果表明传感器在-20~50℃范围内和煤泥附着的情况下基本误差均满足行业标准要求。

On the combined heat transfer of natural convection, radiation and conduction in the non-gray semitransparent thermal fibrous insulation

A detailed numerical modeling is performed to investigate heat transfer in high-porous, high-temperature non-gray semitransparent silica insulation materials. Radiation between fibers, conduction within fibers and convection from the fibers to the surrounding fluid are considered. Macroscopic (porous media) modeling is used to determine the velocity, pressure and temperatures fields for fibrous insulation with a random packing geometry under natural convection. Based on a non-gray application of the solution to the radiative transfer equation, the value of the refractive index(n,m)is used to generate macroscopic average radiative properties such as extinction coefficient, scattering albedo and phase function. Key features of the macroscopic model include two-dimensional effects,non-gray radiative exchange, and the relaxation of the local thermodynamic non-equilibrium. The effectiveness of this numerical model is validated by the previous experimental data.

酸压石灰岩储层中增强充填效果的一种稠化除垢剂的研制

新型除垢剂的特征在于其自身的变黏特性,这就意味着它可以在泵速小于10bbl/min的低流速下得到应用。它省去了使用机械式翻转器的麻烦,克服了层间窜流的问题,并使整个压裂过程中的化学剂顶替变得更为有效。对大量增黏剂和化学破胶剂以及不同类型的聚合物除垢剂之间的兼容性做了实验研究,并给出了实验的相关数据。本文通过计算机模拟研究,验证了实验数据的有效性,优化了其在油田的应用。除此之外,这种稠化除垢剂的优点还在于通过防垢控制延长了传统泵入设备的寿命,增加了日处理量,从而达到了经济性目标。

Non－Darcian and Anisotropic Anisotropic Effects on Natural Convection in Horizontal Porous Media Enclosure

Natural convection heat transfer in a horizontal enclosure filled with anisotropic porous media,being isothermally heated at bettom and cooled at top while the vertical walls being adiabatic, is numerically studied by applying the Brinkman model-a modified form of Darcy model giving consideration to the viscous effect. The results show that:(1)a larger permeability ratio (K*) causes a lower flow intensity in the enclosure and a smaller Nusselt number, all Nusselt numbers approach unity in the limit of K* → ∞;a larger thermal conductivity ratio (λ*) causes a stranger distortion of isotherms in the enclosure and a higher flow velocity near the walls, all the Nusselt numbers approach unity in the limit of λ*→0; the permeability and thermal conductivity ratios generally have opposing effects on the Nusselt number. (2) an increasing Darcy number decreases the flow intensity and heat transfer rates,which is more significant at a lower permeability ratio. In particular, with K*0.25, the Nusselt number for Da=10-3 would differ from that of Darcy flow up to an amount of 30%, an analysis neglecting the non-Darican effect will inevitably be of considerable error.

Numerical Investigation on the Self-Induced Unsteadiness in Tip Leakage Flow of a Micro-Axial Fan Rotor

The self-induced unsteadiness in tip leakage flow(TLF)of a micro-axial fan rotor is numerically studied by solving Reynolds-averaged Navier-Stokes equations.The micro-axial fan,which is widely used in cooling systems of electronic devices,has a tip clearance of 6%of the axial chord length of the blade.At the design rotation speed,four cases near the peak efficiency point(PEP)with self-induced unsteadiness and four steady cases which have much weaker pressure fluctuations are investigated.Using the"interface"separating the incoming main flow and the TLF defined by Duet al.[1],an explanation based on the propagation of the low energy spot and its multi-passing through the high gradient zone of the relative total pressure,is proposed to clarify the originating mechanism of the unsteadiness.At the operating points near the PEP,the main flow is weaker than the TLF and the interface moves upstream.The low energy spot which propagates along in the close behind of the interface has opportunity to circulate in the circumferential direction and passes through the sensitive interfaces several times,a slight perturbation therefore may be magnified significantly and develops into the self-induced unsteadiness.The explanation is demonstrated by numerical results.

Effect of Plate Position and Size for Self-Induced Flow Oscillation of Underexpanded Supersonic Jet Impinging on Perpendicular Plate

When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of oscillation have to be more clear to control the oscillation. This paper aims to clarify the effect of the plate position and the width for the self-induced flow oscillation of an underexpanded supersonic jet impinging on the perpendicular plate by the experiment and the numerical analysis. From the results, it is clear that the occurring domain of the self-induced flow oscillation and its dimension strongly depend on the plate position and the width.

Investigation of the Influence of Free Convection on the Heat Transfer of Cylinders with Different Aspect Ratios

The heat transfer from an electrically heated cylinder (wire) of finite length to the surrounding fluid can be divided into heat radiation, conduction and convection. A technical application of these cylinders with typical dimensions of 1-2 mm length and a few micrometers diameter is the Hot-Wire-Anemometry.This systematic study should clarify the influence of the convection to three dimensional heat transfer of cylinders. For this aim it is planned to investigate Reynolds numbers below Re = 1 (creeping flow). For this reason measurements should be done under 1g in the earth laboratory and also under microgravity (μg) conditions. Comparisons of these measurements under otherwise same conditions allows to distinguish between the pure convection heat transfer and the contributions due to conduction and other effects. For measarements under μg the Drop Tower Bremen can be used as research facility. Due to the fast response of convection to changes in the gravity conditions the Drop Tower is an ideal and cost efficient experimental tool. The experimental setup is build to operate at velocity range of 0-l m/s which includes the whole range of convection from pure free convection at 0 m/s over mixed convection up to pure forced convection at velocities above about 0.15 m/s. This velocity region corresponds to a range of the Reynolds number of Re = 0 - 0.18 for a cylinder of 5 μ m diameter at Tf= 140℃ in air at an ambient temperature of about 21℃.

An Experimental and Numerical Study of Natural Convection Heat Transfer in Horizontal Annuli between Eccentric Cylinders

Natural convection heat transfer in eccentric annuli made of two isothermal horizontal circular cylinders is numerically investigated. Bipolar coordinates are used for the eccentric annuli. The governingequations are transformed into finite difference equations (FDE) by the central difference approach.Heat transfer and flow convection pattern results are simulated for 5.0≤RaL≤1.0×105, withPr = 0.3 - 100, Do/Di = 1.25 - 5.0, andε= 0.01-0.95. The axis of the inner cylinder lies onan inclined plane with θp= 0°- 180°.A Mach-Zehnder interferometer is used for the experimentalstudy. The range is for RaL = 5.3×102-2.41×104, with Do/Di = 2.0, 2.5 and 3.125,ε= 0.0-0.85,and θp= 0°-180°.Air is used as the medium. Comparison of the numerical results with the experimental data shows good agreement.

Laminar Natural Convective Heat Transfer in theEnclosed Evacuated Collector Tube with East-West Symmetric Heat Input

Heat transfer in the evacuated collector tube is a three-dimensional laminar natural convection prob-lem driven by buoyancy. Because of its complexity, no effective theoretical model is available despiteof limited experimental work which is confined to one aspect- The present work aims to depict theconvective heat transfer inside a tweended inclined tube with East-West symmetric heat input us-ing numerical methods. Based on reasonable assumptions, governing equations of the inside fluid areestabllshed. The corresponding discretizated equations are solved by employing numerical methods.The calculated results are displayed for velocity and temperature profiles on different cross-sectionalplanes, which present the flow pattern characterized by upflow and dowallow along the axial direc-tion and adherent flow along the peripheral direction, and the heat transfer process from the wall tothe center. Furthermore, the transient Nusselt number and average temperature level are shown anddiscussed. Finally, the parametric effects of the tube radius and the heat input on the flow and heattransfer are also given.

Natural Convective Heat and Mass Transfer on a Vertical Heated Plate for Water Flow Containing Metal Corrosion Particles

Corrosion products of structural materials when contained in water usually are in two states:soluble state and colloidal particles with diameter about 10^(-3)—10^(-1)μm.Deposits of such corrosion products on tube surfaces under high pressure will jeopardize the operating economy of power plant equipment and even result in accidents. A numerical study is reported in this paper of the natural convective heat and mass transfer on a vertical heated plate subject to the first or mixed kind of boundary conditions for high-pressure water(P=17MPa)containing metal corrosion products with consideration of variable thermophysical properties.

Observation of robust edge superconductivity in Fe(Se,Te) under strong magnetic perturbation

The iron-chalcogenide high temperature superconductor Fe(Se,Te)(FST) has been reported to exhibit complex magnetic ordering and nontrivial band topology which may lead to novel superconducting phenomena. However, the recent studies have so far been largely concentrated on its band and spin structures while its mesoscopic electronic and magnetic response, crucial for future device applications, has not been explored experimentally. Here, we used scanning superconducting quantum interference device microscopy for its sensitivity to both local diamagnetic susceptibility and current distribution in order to image the superfluid density and supercurrent in FST. We found that in FST with 10% interstitial Fe,whose magnetic structure was heavily disrupted, bulk superconductivity was significantly suppressed whereas edge still preserved strong superconducting diamagnetism. The edge dominantly carried supercurrent despite of a very long magnetic penetration depth. The temperature dependences of the superfluid density and supercurrent distribution were distinctively different between the edge and the bulk.Our Heisenberg modeling showed that magnetic dopants stabilize anti-ferromagnetic spin correlation along the edge, which may contribute towards its robust superconductivity. Our observations hold implication for FST as potential platforms for topological quantum computation and superconducting spintronics.

The Self-induced Unsteadiness of Tip Leakage Flow in an Axial Low-Speed Compressor with Single Circumferential Casing Groove

Numerical investigation on the self-induced unsteadiness of tip leakage flow(TLF) for an axial low-speed compressor with smooth wall and six single grooved casings are presented. A ten-passage numerical scheme is used to solve the unsteady Reynolds averaged Navier-Stokes(URANS) equations. It is found that the single grooves at various axial locations could have a large impact on the self-induced unsteadiness and the stall margin improvement(SMI) of compressor. The trend of SMI with groove center location demonstrates that the groove located near the mid of blade tip chord generates the best SMI. The worst groove is located about 20% Cax after the blade leading edge. The root-mean-squre of static pressure(RMSP) contours at 99.5% span and fast Fourier transform for the static pressure traces recorded in the tip clearance region for each casing are analyzed. The results demonstrate that the single groove location not only affects the oscillating strength but also the frequency of the unsteady tip leakage flow. At the near-stall point of smooth casing, the self-induced unsteadiness of TLF is enhanced most by the best grooved casing for SMI. While, the self-induced unsteadiness disappears when the worst groove for SMI is added. The characteristic frequency of TLF is about 0.55 blade passing frequency(BPF) with smooth casing. The frequency components become complicated as the single groove moves from the leading edge to the trailing edge of the blade.

Performance analysis of the silicon waveguide-based wavelength converter

The conversion efficiency and noise figure (NF) of the silicon-on-insulator (SOI) waveguide-based wavelength converter are investigated with the coupled equations. The effects of the pump power, the nonlinear absorption and the waveguide length on the conversion efficiency and noise figure are discussed. The conversion efficiency decreases with the increasing pump power and the noise figure is degraded due to the two-photon absorption (TPA) and the TPA-induced free-carrier absorption (FCA) at the higher pump power. With the increasing of the free carrier lifetime, the conversion efficiency will decrease and the noise figure will increase accordingly. The optimal waveguide length depends on the pump power and the free carrier lifetime. In practical applications, the high conversion efficiency and low noise figure can be achieved by choosing suitable parameters of the silicon waveguide.

Natural Convective Heat and Mass Transfer of Water with Corrosion Products at Super-Critical Pressures under Cooling Conditions

A numerical study is reported of laminar natural convective heat and mass transfer on a vertical cooled plate for water containing metal corrosion products at super-critical pressures. The influence of variable properties at super-critical pressures on natural convection has been analyzed. The difference between heat and mass transfer under cooling or heating conditions is also discussed and some correlations for heat and mass transfer under cooling conditions are recommended.