Thermodynamic design of methane liquefaction system based on reversed-Brayton cycle

A thermodynamic design is performed for reversed-Brayton refrigeration cycle to liquefy methane separated from landfill gas (LFG) in distributed scale. Objective of the design is to find the most efficient operating conditions for a skid-mount type of liquefaction system that is capable of LNG production at 160 l/h. Special attention is paid on liquefying counterflow heat exchanger, because the temperature difference between cold refrigerant and methane is smallest at the middle of heat exchanger, which seriously limits the overall thermodynamic performance of the liquefaction system. Nitrogen is selected as refrigerant, as it is superior to helium in thermodynamic efficiency. In order to consider specifically the size effect of heat exchangers, the performance of plate-fin heat exchangers is estimated with rigorous numerical calculations by incorporating a commercial code for properties of methane and the refrigerant. Optimal conditions in operating pressure and heat exchanger size are presented and discussed for prototype construction under a governmental project in Korea.     

An efficient multi-stage Brayton–JT cycle for liquefaction of natural gas

Combined multi-stage Brayton–JT refrigeration cycles are investigated as a governmental effort in Korea to develop an original liquefaction process of natural gas in accordance with recent demand of higher efficiency and larger capacity. Based upon thermodynamic optimization theory, a combined refrigeration system is proposed with nitrogen (N2) Brayton cycle, ethylene (C2) JT cycle, and propane (C3) JT cycles, which are used for cooling the feed gas in a series of heat exchangers. Since no mixed refrigerants are used, this system is simple in operation and robust in reliability. A complete cycle design is presented to confirm its feasibility and estimate the liquefaction performance. It is expected that the proposed N2–C2–C3 cycle could have a reasonably high efficiency and the potential of great liquefaction capacity. Next steps are underway for patent application and practical process development.     

基于夹点技术的修正布雷顿循环优化分析

为提高修正布雷顿循环氦液化系统的液化率及效率,基于夹点技术的优化方法对该系统进行优化分析。通过建立夹点技术的T-H组合曲线图分析系统的夹点所在、利用Fortran模拟计算来定性、定量地分析系统的主要性能指标,如系统压缩机出口压力、膨胀机中间压力等与系统的液化率及效率之间的关系。发现当膨胀机中间压力为600—800 MPa时,系统的液化率和效率最高。     

高温气冷堆氦气透平循环流动阻力特性分析

采用更加真实的阻力模型分析了流动阻力对10MW高温气冷堆(HTR-10)氦气透平循环特性的影响规律。分析结果表明,高温气冷堆氦气透平循环的压力损失主要由局部阻力和摩擦阻力组成。10MW高温气冷堆闭式氦气透平循环(HTR-10GT)发电系统在实际充装量调节及额定工况下,氦气在部件连接管道的局部压降占82.4%,沿程阻力压降占17.6%。氦气充装量减小时,局部压损系数不变而沿程阻力系数增大,导致循环效率降低;当充装量由100%降低到30%,连接管道的局部压降份额下降约20%,系统效率下降15%左右。随着充装量的减小,做功部件的进出口压力随充装量的变化线性变化,压气机的压比略有增大,透平的膨胀比有较大幅度的非线性增大。     

液氦温区大型低温制冷系统的可靠性评估

针对改进Claude循环的大型氦低温制冷系统,以制冷量不足为顶事件建立了故障树模型。利用结构法对故障树模型进行定性分析,分析得到系统的最小割集为18个。利用来自不同数据库的部件失效率对故障树模型进行定量计算,得到了不同的结果,并分析其原因。对各部件的关键重要度进行了计算,以衡量各个部件对系统发生故障的贡献程度。并通过增加系统冗余部件和提高关键部件可靠度等措施,为提高系统可靠性找到了有效的解决途径。     

Improved correlations for computations of liquid helium two phase flow in cryogenic transfer lines

The available experimental data, Vishnev et al. [6], implies that the widely used homogenous equilibrium model and the Martinelli–Nelson equation do not map correctly the pressure drop data for horizontal liquid helium two phase flow particularly in cases for high vapour fraction. Hence, considering the empirical nature of Martinelli–Nelson equation, suitable parameters and terms have been suggested so that, the pressure drop can be better predicted. The proposed equation being a third order in ‘x’ (vapour fraction) is more accurate to predict the characteristic behavior of liquid helium two phase flow as observed in experiments [6], Mamedov et al. [7], and Deev et al. [8], which the available equations are unable to predict.     

The generation of particles to observe quantized vortex dynamics in superfluid helium

We describe a method to prepare a sample of superfluid helium-4 with hydrogen particles suspended within it. The method is to dilute hydrogen gas with helium at room temperature, and bubble the mixture through liquid helium at a temperature above the superfluid phase transition temperature, T_λ ≈ 2.17 K. The procedure yields a suspension of micron-sized particles whose total volume is about 10⁵ times smaller than the fluid volume. The fluid and suspension are then cooled to a temperature below T_λ. We show that the particles, so prepared in superfluid helium, are useful for studying superfluid flows and, in particular, the dynamics of quantized vortices. In addition, the particle-superfluid helium system is rich in not yet fully explained interactions. We review preliminary investigations that include observing the vortex lattice in rotating helium, vortex reconnection in quantized vortex turbulence, and vortex ring decay. These data illustrate the basic mechanisms of dissipation in superfluid turbulence.     

A vibration free cryostat using pulse tube cryocooler

This paper introduces a new vibration free cryostat cooled by liquid helium and a 4 K pulse tube cryocooler. The cryogenic device mounts on the sample cooling station which is cooled by liquid helium. The boil off helium is recondensed by the pulse tube cryocooler, thus the cryostat maintains zero boil off. There is no mechanical contact between the cryogenic part of the cryocooler and the sample cooling station. A bellows is used to isolate the vibration which could transfer from the cryocooler flange to the cryostat flange at the room temperature. Any vibrations generated by the operation of the cryocooler are almost entirely isolated from the cryogenic device. The cryostat provides a cooling capacity of 0.65 W at 4.21 K on the sample cooling station while maintaining a vapor pressure of 102 kPa. The sample cooling station has a very stable temperature with oscillations of less than ±3 mK during all the operations. A cryogenic microwave oscillator has been successfully cooled and operated with the cryostat.     

Dynamic modeling of a liquid helium cryostat at the Canadian Light Source

This work includes the creation and validation of a computer model of a liquid helium cryostat located at the Canadian Light Source (CLS) in Saskatoon, Canada. This cryostat contains a superconducting radio frequency (RF) cavity, and requires careful pressure and level modulation to ensure proper RF control. A detailed mathematical model of the cryostat is generated based on gas and liquid mass balances for a boiling vessel, along with pressure-volume-temperature relations. The model is discretized and solved, and model results are compared with experimental data taken from the actual cryostat at the CLS to determine the accuracy of the simulation. The model is found to reasonably represent the cryostat at the CLS from a process perspective.     

Liquid helium centrifugal pump characteristics from 80 g/s to 1200 g/s

The large amount of data collected from three different centrifugal liquid helium pumps tested, namely with 80, 600 and 1200 g/s nominal mass flow are reviewed. The data include the analysis of the characteristic curves, their total efficiencies, their Net Positive Suction Head (NPSH) and the slip factor. The 1200 g/s pumps tested are of the full emission type, with curved blades, whilst the other pumps have straight blades. The pumps were also tested at different rotary speeds. The pumps were manufactured by Barber & Nichols (Denver, USA).     

小型氮膨胀天然气液化流程的设计及优化分析

根据气源条件,设计了3套氮膨胀天然气液化流程,选择PR(Peng-Robinson)方程进行混合物的相平衡计算,采用大型数值模拟软件Aspen Plus进行了数值模拟计算;分析比较了不同液化流程的关键热力学参数,并进行了关键设备的可行性分析.结果表明:丙烷预冷氮膨胀液化天然气流程的比功耗比无预冷的单级氮膨胀天然气液化流程的低,比无预冷的两级氮膨胀天然气液化流程的稍高,两级氮膨胀天然气液化流程较难实现.综合分析结果,选用了丙烷预冷氮膨胀液化天然气流程.     

Uncertainty considerations in AC loss measurement of multifilamentary superconducting wires performed via a pickup coil method

The uncertainty of AC loss measurements for multifilamentary superconducting wires by a pickup coil method is evaluated on the basis of the law of propagation of uncertainty. In this evaluation, the effects of measurement conditions, signal processing, and the division of the AC loss into its components (hysteresis loss and coupling loss) are taken into account as elements of uncertainty. The effect of the measurement conditions is evaluated using theoretical expressions of the two main components. Additionally, the effect of signal processing is considered in accordance with the actual processes of the AC loss measurement using experimental outputs. The main factors that contribute to the uncertainty in the propagation process are discussed. The estimated resultant uncertainties are compared to experimental ones for round robin tests of AC loss measurement of Nb-Ti multifilamentary wires exposed to an alternating transverse magnetic field.     

基于液氮冷源超导磁体氦气循环预冷系统设计

为了提高超导磁体300-80 K预冷过程中的降温效率和安全性,开发了一种新的预冷方法.设计了一台以液氮为冷源、氦气为循环介质的可控温预冷装置,对其内部结构进行了优化设计,包括低温风机、板式换热器、气动调节阀、翅片换热器等主要组成部分,整个装置与磁体构成一个闭合循环系统.在预冷装置的作用下,该超导磁体从300 K到80 ...     

基于全寿命周期费用分析法的风管系统的选择

针对目前国内还没有一种有效的方法用于选择和评价风管系统的现状,提出采用全寿命周期费用分析法来选择和评价风管系统,并在实际工程中,采用该方法比较和分析国内4种常见风管系统的一次性投资、能耗费和维护费,重点对各风管的全寿命周期费用进行评估,认为酚醛铝箔复合风管的费用最低,是一种值得推广的风管系统。     

Method of quantitative analysis of filler dispersion in composite systems with spherical inclusions

In this work, a quantitative analysis method for the estimation of filler dispersion degree of filler particles in composite systems is presented and described. According to the procedure offered dispersion of filler particles of any form is associated with their area and the dispersion parameter D is defined as the probability to fall in a certain range of the particle area distribution. The method has been applied to both model and real systems characterized by different dispersion levels and various filler content. Final results highlight that for the case of better filler dispersion, the characteristic parameter, D, increases, since the quantity of filler particles having identical area and, accordingly, the homogeneity of the systems increase.     

Flow of non-Newtonian liquid polymers through deformed composites reinforcements

The flow of non-Newtonian liquid polymers through fibrous reinforcements is a phenomenon which is often encountered during polymer composites manufacturing. In a previous work, we have proposed from a multiscale theoretical approach a method to model this phenomenon when the polymer can be regarded as a generalised Newtonian fluid [Orgéas et al. J. Non-Newtonian Fluid Mech. 2007; 145]. In this paper, the capability of the method is tested with power-law fluids flowing through deformed plain weave fabrics. For that purpose, the flow problem is firstly analysed at the mesoscale from numerical simulations performed on representative elementary volumes of the fabrics. The influences of both the current deformation of the fabrics and the fluid rheology on the macroscopic flow law are emphasised. Secondly, it is shown that the proposed method allows a nice fit of numerical results.     

氦冷却法制备氮浆中液滴凝固过程的模拟与分析

采用氦冷却法制备氮浆的工艺所制氮浆颗粒尺寸均匀,制备过程中杜瓦内可维持正压,从而防止周围空气的漏入。通过对氦冷却法制备氮浆过程中液滴凝固时固氮颗粒的形成过程进行分析,建立起相应的物理模型以及微分方程,并对微分方程进行数值求解。着重考察了液滴的凝固过程,并对液滴群完全凝固时的氦气温度、压力、流速以及扩散腔长度进行了研究,进而探讨了采用该方法制备氮浆时氦气工作参数、喷管尺寸以及扩散腔长度等的选择问题。     

Thermo-mechanical vibration analysis of nonlocal temperature-dependent FG nanobeams with various boundary conditions

In this paper, the thermal effect on free vibration characteristics of functionally graded (FG) size-dependent nanobeams subjected to an in-plane thermal loading are investigated by presenting a Navier type solution and employing a semi analytical differential transform method (DTM) for the first time. Material properties of FG nanobeam are supposed to vary continuously along the thickness according to the power-law form. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The nonlocal equations of motion are derived through Hamilton's principle and they are solved applying DTM. According to the numerical results, it is revealed that the proposed modeling and semi analytical approach can provide accurate frequency results of the FG nanobeams as compared to analytical results and also some cases in the literature. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as thermal effect, material distribution profile, small scale effects, mode number and boundary conditions on the normalized natural frequencies of the temperature-dependent FG nanobeams in detail. It is explicitly shown that the vibration behavior of an FG nanobeams is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of FG nanobeams.     

A comprehensive filling and tooling force analysis for rigid mould LCM processes

A comprehensive tooling force analysis is presented for rigid tool Liquid Composite Moulding (LCM) processes such as Resin Transfer Moulding (RTM) and Injection/Compression Moulding (I/CM). This has been implemented within SimLCM, a generic LCM filling simulation under development at the University of Auckland. The simulation has been verified against existing analytic and semi-analytic solutions, considering fill times and clamping force due to reinforcement compaction. Industrial application is demonstrated through consideration of a fireman’s helmet, which has demonstrated the complex evolution of both local and global tooling forces during RTM and I/CM cycles. Resultant forces are computed in the closing and lateral directions, having practical benefits for design of moulds and supporting equipment. The evolution of tooling forces has been shown to be sensitive to the accuracy of the applied fibre reinforcement compaction model, which is used to predict normal and tangential stresses exerted on mould surfaces.