内锥流量计与孔板流量计的压力损失及能耗研究

通过CFD流体软件对内锥流量计压力损失进行了数值模拟,实验介质为汽油与柴油的混合物。内锥流量计和孔板流量计经常使用于流体计量,在保证两种流量计流通面积相等的条件下,对它们的压力损失进行了比较。结果表明,内锥流量计的压力损失仅为孔板流量计压力损失的30%左右,将内锥流量计应用于流体计量,可以起到节能降耗的作用。     

锥形孔板流出系数的研究及其在测量中的应用

通过对孔板流量计进行管内流动数值模拟,找到了孔板流出特性较差的原因。为了得到较好流出特性的孔板,笔者设计了3种不同入口锥角的锥形孔板,通过管内模拟结果得出锥形孔板流出系数随着入口锥角的减小而增大,但增大趋势递减。最终根据模拟得到的理想孔板设计了实物节流件,分析了实验结果和模拟结果的流出系数值产生偏差的原因。并将此种改进孔板应用到实际流量测量中。     

Design and optimization of a novel flowmeter for liquid hydrogen

The wide spreading hydrogen energy requires accurate flow measurement. Constriction type flowmeters could be a favorable candidate for liquid hydrogen. However, their permanent pressure losses and installation length could significantly increase the manufacturing, installation, metering, maintenance, and replacement cost. The high permanent pressure losses may also cause cavitation. The present research introduces a novel constriction type flowmeter with an optimized flow profile. Numerical simulation, as well as multidimensional and multi-objective optimization, was utilized in order to minimize the flowmeter's loss coefficient and the required installation length. The applied optimization technique results in significant improvements of the flowmeter design and performance. The proposed flowmeter is shorter than the standard Venturi nozzle by 67.2% and its loss coefficient is lower by up to 10.6%. It measures the flow rate of liquid hydrogen with up to 25.5% higher discharge coefficient and 83.7% lower loss coefficient compared to a corresponding perforated plate flowmeter. Cavitation was not detected inside the proposed flowmeter up to a Reynolds number of 2.2 × 10⁶. The present investigation shows that the proposed flowmeter is very promising for liquid hydrogen measurement.     

速度-高度-神经网络优化算法在水库用水计量中的应用

针对大口径非满圆型管超声波流量计量中存在精度差的问题,基于现有理论算法,提出了一种速度—高度—神经网络优化算法。首先通过多声路超声波流量计测量出圆形管道各层声路上的流速,然后通过液位计测得非满圆形管流态下的液位高度,再采用神经网络算法建立一个三层的BP神经网络,结合测得的流速、高度信息,计算出当前的流量,同时还通过高斯-雅可比数值算法确定了声路的数目及高度。仿真结果表明,该算法提高了大口径非满圆形管工况下用水测量精度。     

Investigation of convective heat transfer augmentation using acoustic streaming generated by ultrasonic vibrations

An investigation of acoustic streaming induced by ultrasonic flexural vibrations is experimentally and numerically presented. The investigation includes acoustic streaming pattern, velocity, and associated heat transfer characteristics. Acoustic streaming patterns visualized using Acetone agree well with the prediction by Nyborg’s theory. Tests of streaming velocity utilizing Styrofoam showed that the acoustic streaming velocity measured prove to be two orders greater than that by Nyborg’s theory. CFD simulations also showed the same order of the velocity as the one measured. By virtue of acoustic streaming, a notable temperature drop of 40 °C was obtained in 4 min and maintained. Tests identifying major heat flow paths indicated that gaps and the vibrating beam serve as major heat flow paths.CFD simulations were conducted to observe acoustic streaming patterns and velocities in the gap. Simulation results were validated by performing heat transfer analysis based on a lump-energy method. Simulation predicted that two symmetric vortices within half wavelength, rise of air at anti-nodes, and descent at nodes as Nyborg’s theory predicts. The presence of the upper plate has no effect on the acoustic streaming patterns. However, when an upper plate shorter than the vibrating plate is used, a drastic increase in streaming velocity occurs at the edges of the upper plate due to entrainment of air, which also alters streaming pattern in the vicinity of the open end. Estimated streaming velocities from CFD simulations are found to be two orders greater than those based on Nyborg’s theory.The results of CFD simulation indicated the vortical flows induced by a ultrasonic flexural standing wave (UFSW) can be reproduced. The CFD results are experimentally validated, qualitatively through flow pattern comparisons and quantitatively by the transient temperature drop comparison. The CFD results showed that the velocity near the plates is of the order of 10–100 cm/s, which is over 100 times higher than the results from theoretical studies based on sonically induced acoustic streaming assuming inviscid flow.     

CFD技术在汽轮机定子线圈冷却水流量测量中的应用

利用超声波流量计检测大型汽轮发电机定子线圈冷却水流量大小,可直接判断冷却水的堵、漏,从根本上解决定子绕组冷却水堵塞问题,但超声波流量计用于弯管段测量时存在误差。本文利用CFD技术计算了某火电厂定子线圈内冷却水的流速分布,分析了管内流动对超声波测流的影响,获得了不同测点处流量误差的变化趋势。采用CFD技术可确定超声波流量计的最佳安装位置,为获得准确的流量提供理论依据。     

Microscopic phenomena and macroscopic evaluation of heat transfer from plate fins/circular tube assembly using naphthalene sublimation technique

Flow and heat transfer in a plate fins/circular tube assembly is examined using naphthalene sublimation technique. The examined parameters are the gap (δ) to tube diameter (D) ratio δ/D, the Reynolds number Re_D and the tube location l/D for a single tube.A preliminary flow visualization shows large recirculating twin vortices and a weak downstream oscillatory streakline. The local heat/mass transfer coefficient is large at the leading edge of the plate and also in front of the tube. It is relatively small behind the tube and it approaches the fully developed asymptotic value far downstream. The high heat/mass transfer coefficient in front of the tube is considered to be due to the so-called horseshoe vortex. When the Reynolds number is as large as 2660, a smaller subsidiary horseshoe vortex is attached to the upstream of the main one. The positive effect of the horseshoe vortices is prominent when the tube is placed in the downstream region. In this case, the total heat/mass transfer rate increases up to 25%.     

循环流化床循环流率冲击法在线测量方法

开发了一种通过测量下落颗粒和靶板碰撞冲击力来确定颗粒流率的流量计,通过试验验证了该流量计的可行性,并研究了颗粒下落速度、颗粒粒度和颗粒密度对流量计的影响.建立了该冲击式流量计的理论模型,利用冷态流化床试验数据对理论模型进行了校验.结果表明：该流量计具有操作简便、测量准确、反应灵敏、易于校准、对提升管内的颗粒流动无干扰的特点;模型计算结果与试验数据较吻合,可利用模型简化流量计的校准程序,增加流量计的应用范围.     

转叶孔板螺旋流消能的影响因素试验分析

为解决供水工程中的过剩水头问题,常在有压输水管道中配置合适的消能装置,转叶孔板螺旋流消能是一种新型的内消能方式,通过转叶孔板螺旋流消能装置的水力特性试验,可知影响转叶孔板螺旋流消能效率的主要影响因素有雷诺数Re、转叶孔板开口角度和孔板之间的相互扭转角度,还有试验装置结构的设置。根据试验数据计算分析各个影响因素对消能效率的影响。结果表明,转叶孔板螺旋流消能效率与转叶孔板之间的扭转角成正比,与雷诺数成正比,与转叶板的开口角度成反比。试验装置在进口段和出口段设置管径突变均对消能有利,该装置比与其消能原理类似的孔板消能装置更实用,且消能效率更高,对下游建筑物设施起到良好的保护作用,可推广应用。     

Two-phase flow structure close to orifice contractions during horizontal intermittent flows

Two-phase horizontal intermittent flow through orifice contractions is experimentally investigated by means of a new impedance meter able to collect void fraction data simultaneously at different pipe locations. The investigation focuses on two-phase structure in the region downstream of orifice. Experiments were carried out on horizontal air–water flows in 40 mm inner diameter pipes. Six different orifice plates were considered, as combinations of two restriction ratios and three plate thicknesses. The results demonstrate that the orifices generally induce a marked increase in the downstream void fraction values, and that this is associated to a reduction in film thickness in the stratified regions.     

成品油管道顺序输送中V形锥流量计的模拟研究

针对顺序输送的成品油管道,阐述了V形锥流量计在管道混油流量计算中的应用,分析管道内部的速度分布,得到了V形锥流量计的流出系数与混油雷诺数的关系及管道壁面表面摩擦力系数的变化规律。结果表明,V形锥流量计能够克服传统流量计的不足,能更准确地测量混油段的流量。     

Local heat transfer characteristics of array impinging jets from elongated orifices

The aim of this research is to enhance the heat transfer on an impinged surface under an impinging jet array by minimizing a cross-flow effect. Conventional round orifices (aspect ratio, AR = 1) are substituted by the elongated orifices with aspect ratio AR = 4 and 8 with the same jet exit area. Two types of orifice arrangements; in-line and staggered arrays are compared. The experimental investigation was carried out at constant distance from orifice plate to impinged surface H = 2D_E (D_E is equivalent diameter of orifice). The heat transfer characteristic was visualized using thermochromic liquid crystal sheet (TLCs) and the Nusselt number distribution was evaluated by an image processing technique. The flow characteristic on the impinged surface was also visualized by oil film technique. The results show that the cross-flow in a case of the jets issued from the orifices with AR = 4 is considerably less significant than that in cases of the ones delivered from the orifices with AR = 1 and 8. At Reynolds number of 13,400, the Nusselt numbers for the jet arrays issued from the elongated orifices with AR = 4 with in-line and staggered arrangements are respectively 6.04% and 12.52% higher than those for the case of AR = 1.     

孔板混合流消能研究

在软基低堰掺气窄缝戽流消能研究基础上,提出一种新型消能工——孔板混合流消能工。试验结果表明:孔板混合流的下游冲刷深度平均减少50%,涌浪高度降低70%,从而减轻对下游及两岸的冲刷,减少了工程量。     

Effect of concentration,obstacles, and ignition location on the explosion overpressure of hydrogen-air in a closed-vessel

The report deals with the investigation of explosion safety parameters of hydrogen-air mixtures in a 17.17 L cylindrical closed-vessel with different concentrations, obstacles, and ignition locations. The experimental data including the maximum explosion pressure, laminar burning velocity, and corresponding flame radius were confirmed by using GASEQ code and theoretical calculation, respectively. The report shows the orifice plate reduced the maximum explosion pressure of the low-concentration hydrogen (φ＜20% v/v), while the maximum explosion pressure of high-concentration hydrogen (φ＞20% v/v) was increased, and the oscillation of the explosion pressure in the closed-vessel was obvious. The effect of the ignition location on the maximum explosion pressure was related to the interaction between the flame instability and the orifice plate for the φ = 30% v/v hydrogen-air mixture.     

Flow rate measurement via isothermal discharge method for hydrogen

The thesis of this study is to investigate that the measurement accuracy of the isothermal discharge method for hydrogen gas with an isothermal tank which is designed for measuring the flow rate characteristics of pneumatic components. Compressed hydrogen in an isothermal tank, which is combined three types of orifice, is discharged from 700 kPa (abs) to atmospheric pressure. The average temperature in the tank during discharge is measured experimentally. In consequence, when the maximum discharge rate is 37 kPa/s during discharge hydrogen, the measurement error is less than 3% in whole discharge time. The temperature response phenomenon in hydrogen is discussed qualitatively in the view point of the internal energy change. The internal energy change immediately after the discharge started was negative because the release enthalpy was larger than the quantity of heat obtained from the stuffing material. After a certain period of time elapsed, the enthalpy change became equal to the heat exchange between the internal hydrogen and the stuffing material.     

台架使用中的热膜式空气流量计修正方法研究

介绍了ABB热膜式空气流量计的工作原理,引入参比流量计对超差流量计进行误差提取。利用压气机特性曲线剔除因工况不一致引入的流量测量误差。分析了超差流量计信号处理单元对非线性误差修正的不足,建立了流量计偏差多项式拟合模型,基于极值理论提取出多项式系数,并应用于二次仪表。结果表明,经过修正后的空气流量计满足计量检定要求。     

Two-phase flow behaviour and pressure drop of R134a in a smooth hairpin

Adiabatic two-phase flow of refrigerant R-134a in a hairpin was studied. The hairpin consists of a smooth tube with an inner diameter of 8 mm and with a bend radius of 11 mm. Because of the forces exerted on the flow in the bend, the flow needs to redevelop downstream of the U-bend. The effects of this phenomenon on the pressure drop are studied and linked to visual observations of the flow. Pressure drop and videos of the flow behaviour are recorded in the straight sections upstream and downstream of the bend. These are then compared to the flow and pressure drop for developed flow. The pressure drop downstream of the bend was consistently higher than that for developed flow. It exceeded the pressure drop for developed flow by an average of 30% for all data points. Each video of the flow behaviour was reduced to a single image by calculating the standard deviation of the time signal of each pixel. The standard deviation profiles were compared in order to quantitatively evaluate the change of the flow behaviour. The flow recovery downstream of the bend stretches out over more than 30 tube diameters.     

Effect of orifice plates spaces on flame propagation in a square cross-section channel

This paper investigates the effect of orifice plate separation distance on flame behavior as well as pressure-time histories. Experiments were conducted in a 1 m long, 7 cm by 7 cm square cross-section channel, employing schlieren photography with high-speed camera for visualization to qualitatively identify the propagation mechanisms, and piezoelectric pressure transducers to measure pressure evolution. With two orifice plates in the path of the flame, the flame presents complicated propagating characteristics, i.e., compared to a planar flame, and a corresponding more intricate velocity time-history. It is found that acoustic waves generated in-between orifice plates, after reflection off the second plate, interact with the rear flame front to produce an approximately planar flame. This phenomenon vanishes with decrease in orifice plate separation distance, whereas, with increasing blocking effect the effect is enhanced. In addition, the pressure difference across the second orifice plate correlates with the jet flame length.     

Experimental study on induced accelerated combustion of premixed hydrogen-air in a confined environment

The study on induced accelerated combustion of premixed hydrogen-air in a confined environment is of great significance for the efficient utilization of hydrogen energy in internal combustion engines. The accelerated flame induced by the orifice plate is more stable and easy to control, which is beneficial to achieve controlled and rapid turbulent combustion. In this work, the accelerated combustion process induced by the orifice plate, and the influence of the orifice structure and initial conditions on the flame propagation and combustion characteristics were investigated by constant volume combustion bomb and schlieren method. The results show that the combustion process induced by the orifice plate consists of three stages: the initial stage of propagation, the accelerated stage of the orifice plate, and the end combustion stage. The reduction in aperture induces greater turbulence intensity and increases the perturbation of the orifice plate to the flame, resulting in a substantial increase in flame propagation speed through the orifice plate. As the initial pressure and the equivalence ratio increase, the velocity of turbulent flame induced by the orifice plate and the change rate of the velocity before and after the orifice plate increase. As the initial temperature increases, the turbulent flame propagation velocity does not change much, and the velocity change rate before and after the orifice plate decreases. The effect of the initial conditions on flame acceleration induced by the orifice plate is essentially the influence of flame propagation speed and instability. The greater the flame propagation speed and the stronger the flame instability, the stronger the induced turbulence and the greater the influence of the turbulent flow disturbance, and the greater the velocity of the turbulent flame induced by the orifice plate. There exists an optimum aperture for the shortest combustion duration at any initial conditions, but the optimal diameter is not sensitive to changes in initial conditions. The effect of orifice-induced combustion acceleration is remarkable, and the combustion durations induced by each orifice plate are shortened by more than 50%.     

Hydrogen production by Rhodopseudomonas palustris CQK 01 in a continuous photobioreactor with ultrasonic treatment

An ultrasonic treatment technique was applied to a continuous photobioreactor with Rhodopseudomonas palustris CQK 01 suspension to enhance photo-hydrogen production performance. After the start-up period, R. palustris CQK 01 suspension in the photobioreactor was intermittently agitated by ultrasonic wave with a frequency of 20 kHz and then the hydrogen production performance was evaluated. The ultrasonic agitation significantly dropped the hydrogen concentration in the suspension from 300 μmol/L to 50 μmol/L and thus increased the hydrogen production rate and hydrogen yield by nearly 2 times as compared with conventional photobioreactor. Furthermore, the effects of the ultrasonic power and time, influent substrate flow rate and concentration were investigated and discussed, respectively. The maximum hydrogen production performance of the continuous photobioreactor with ultrasonic treatment was obtained under the conditions of ultrasonic power 40 W, agitation/interval time 3/7 s, substrate concentration 75 mmol/L and substrate flow rate 40 ml/h, leading to the hydrogen production rate of 1.12 mmol/L/h and hydrogen yield of 0.23 mol-H₂/mol-glucose.