旋转型气-液雾化喷嘴的雾化特性研究

使用激光相位多普勒分析仪PDA对旋转型气-液雾化喷嘴的雾化特性进行了实验研究。使用水代替油作为被雾化的液体,采用压缩空气作为雾化介质,测量了不同工况下的喷雾特性参数,如：喷雾液滴粒子的索太尔平均直径SMD和粒子速度等。实验测量结果表明,喷嘴在较小的气液比条件下可以达到较好的雾化状态,中心的液滴平均SMD可以达到40μm。随着压力和气液比的增加,雾化水平也随之提高,但是受喷嘴结构的影响很小。本文的研究为喷嘴的实际设计提供了基础依据。     

沿垂直壁面气-液降膜流动传质过程的数值研究

在考虑气-液两相间质量源项和能量源项的条件下,基于VOF算法,建立了水和空气沿竖直平板壁面两相降膜流动传热传质的CFD模型。利用该模型研究了水和空气两相间的传质特性,分析了液膜波动、进气进液速度以及温度对传质的影响,计算结果表明:一定程度的液膜波动、进气速度和进液速度的提高、气-液之间的温差的增加,都能强化气-液之间的传质过程。     

旋流式发生器内部气-液两相流场的数值模拟研究

在一定的冷负荷下,文章对以耦合热源驱动吸收式热泵的发生器内部气-液分离率进行了研究。采用RNG k-ε湍流和多相流Mixture模型,通过Fluent软件对旋流式发生器的传热传质过程进行数值模拟,得到内部的速度、压力和气-液相态的分布情况。模拟结果表明,旋流器内部分离段径向压力分布呈现阶梯状。随着溶液入口速度的增加,分离段流体扰动更加剧烈,所受离心力不断增大,发生器内部的压降也随之增大,充分降低了溶液的饱和温度,有利于溶液中水的蒸发。与传统发生器比较,在同样制冷量的情况下,旋流式发生器可以降低驱动热源温度,提高对低温废热的利用率。     

旋流烟气下喷雾干燥脱硫塔中气液分布及混合特性的数值研究

针对喷雾干燥脱硫塔中的混合问题,采用离散颗粒相模型(DPM)对塔内液滴群径向位移、液滴群散布及气液混合进行数值分析,重点考察烟气入口旋流强度S和液滴群平均粒径■的影响。结果表明：烟气入口旋流强度从0增加到0.5时,液滴群径向位移先缓慢减小后迅速增大;液滴群平均粒径从65 μm增加至150 μm时,液滴群径向位移近似线性增大;随着烟气入口旋流强度和液滴群平均粒径增加,液滴群散布程度呈先增加后减小的趋势;合适的烟气入口旋流强度和液滴群平均粒径能有效减小气液混合度,显著改善气液混合效果;烟气入口旋流强度为0.3时,液滴群径向位移和气液混合度最小,与无旋流相比,分别平均减小了约20%和34.45%;液滴群平均粒径为150 μm时,液滴群散布程度最大,气液混合度最小,与液滴群平均粒径65 μm相比,气液混合度平均减小了约51.85%。     

振荡条件下金属颗粒对气液两相流动与混合特性影响的试验研究

为进一步提升柴油机活塞腔的换热性能,通过加入金属颗粒来提升振荡状态下的两相混合程度。采用振荡流动试验方法,结合数字图像处理技术,研究金属颗粒在振荡状态下的运动学特性和两相振荡流动特性,进一步讨论转速、充液率对金属颗粒运动和最大气泡直径和混合率的影响。结果表明：转速是影响气液两相流振荡流动效果的主要因素。随着转速的增加,金属颗粒到达方腔上壁面时间缩短,瞬时速度增大,相对于270 r/min,330 r/min冲击上壁面的平均速度变化率增加133%,冲击壁面的强度增加。相对于25%充液率,75%充液率的金属颗粒冲击上壁面的最大瞬时速度降低68%,充液率过高,降低颗粒冲击上壁面强度。50%充液率左右和高转速条件下,颗粒冲击壁面强度降低,但气液两相流混合程度最好。     

天然气液化工艺的相平衡计算

天然气液化流程广泛采用的是丙烷预冷混合制冷剂液化流程.为了进一步优化流程,减少能源的消耗,需要对整个流程进行模拟,而模拟过程中热力学参数的计算便是整个流程计算的基础.使用两种状态方程（SRK和PR方程）对热力学参数进行相平衡计算,为后续计算焓、熵等参数提供相应的解决办法,并判断选择的状态方程是否符合要求.     

Study on real-gas equations of high pressure hydrogen

High pressure hydrogen storage has become an important transportation channel in areas of new energy development and utilization. Actual hydrogen demonstrations require the exploration of the physical and chemical properties in detail before the practical employment, which is completely different from the ideal gas under high pressure conditions. However, the existing real-gas state equations are not easy to use in calculation of high pressure hydrogen due to its complex behavior, and may lead to an unacceptable error. In this paper, a real-gas state equation of hydrogen in a simplified form is proposed. Compared with the NIST datum, the results obtained from this equation have a maximum error 1.1% and 3.8% respectively within the temperature ranges of 253 K < T< 393 K and 173 K < T< 393 K. Also, the proposed equation exhibits higher precision for the state parameters of hydrogen than existing models. Based on the real-gas state equation of hydrogen, formulas of thermodynamic properties which are necessary for solving the hydraulic and thermal aspects of gas transfer are also proposed.     

Numerical analysis of gaseous hydrogen/liquid oxygen flamelet at supercritical pressures

Supercritical conditions are typically encountered in high-pressure combustion devices such as liquid propellant rockets and gas turbine engines. Significant real fluid behaviors including steep property variations occur when the fluid mixtures pass through the thermodynamic transcritical regime. The laminar flamelet concept is a robust and reliable approach that correctly accounts for real fluid effects, the large variation in thermophysical properties, and the detailed chemical kinetics for turbulent flames at transcritical and supercritical conditions. In the present study, the flamelet equations in the mixture fraction space are extended to treat the flame field of general fluids over transcritical and supercritical states. Flamelet computations are carried out for gaseous hydrogen and cryogenic liquid oxygen flames under a wide range of thermodynamic conditions. Based on numerical results, the detailed discussions are made for the effects of real fluid, pressure, and differential diffusion on the local flame structure and the characteristics encountered in liquid propellant rocket engines.     

Characteristics of heat transfer and temperature rise of hydrogen during rapid hydrogen filling at high pressure

An experiment has been done to measure the rise in temperature of a gas during filling a tank at high pressure. The experimental condition is that filling gases are nitrogen and hydrogen at a pressure of 5 to 35 MPa and at a filling mass of G=45 to 324 g/min for hydrogen. The temperatures are measured either horizontally or vertically at five positions in the tank. It is found that heat loss transferred from compressed gas to the tank wall has a significant effect on the rise in the filled gas temperature. The heat transfer coefficient is estimated after the end of filling and is about α_h=270 W/(m²K) for the hydrogen at 35 MPa. A theoretical procedure is proposed to calculate the temperature increase of the gas on a basis of assumption that the gas temperature in the tank is uniform at any time, and the heat transfer coefficient is given. The calculation shows that the temperature is in reasonable agreement with the measured temperatures by assuming α_h=500 W/(m²K) during the filling of hydrogen at 35 MPa, although the estimated heat loss after the end of filling becomes larger than the actual one. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(1): 13–27, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20140     

Effects of fillers on the hydrogen uptake and volume expansion of acrylonitrile butadiene rubber composites exposed to high pressure hydrogen: -Property of polymeric materials for high pressure hydrogen devices (3)-

To develop sealing materials for high-pressure hydrogen devices, the effects of filler type and amount on the hydrogen uptake and volume expansion of rubber composites were evaluated up to 90 MPa. The amount of hydrogen in the rubber matrix and carbon black was elucidated using nuclear magnetic resonance, and the hydrogen elimination behavior of the composites was analyzed by thermal desorption analyses. As hydrogen physically adsorbed on carbon black, the hydrogen uptake of carbon black-filled composites increased. The hydrogen uptake of the composites filled with nonabsorbent silica was smaller, depending on the weight fraction of silica. The ratio of volume expansion to the amount of hydrogen in the matrix of carbon black-filled composites was suppressed by the reinforcement effect of carbon black, which did not expand with hydrogen uptake. The suppression of silica-filled composites was limited by the volume fraction of silica.     

An experimental study on static solid-liquid phase equilibrium in the pores of a porous medium

The so-called Clausius-Clapeyron equation, that is, the static equation of state for “solid-liquid-porous media” systems without liquid flow through the pores, has been experimentally examined by measuring the pore liqiud pressure at the solid-liquid interface in order to verify the accuracy of our method of measuring unfrozen pore liquid pressure. Several series of experiments have been carried out using water-saturated Ohya-Tuff as a porous medium specimen cooled from the top down. In these experiments, the solid-liquid interface was always fixed at the top surface of the specimen. The experimental results imply that the measurement method should be useful in determining the relative value of the unfrozen pore water pressure. © 1998 Scripta Technica, Inc. Heat Trans Jpn Res, 26(2): 69–83, 1997     

Effect of ignition,initial pressure and temperature on the lower flammability limit of hydrogen/air mixture

In this research, the effect of ignition, initial pressure (50–250 kPa) and temperature (20–100 °C) on the lower flammability limit (LFL) of hydrogen/air mixture are investigated experimentally and numerically. The results show that with the ignition energy increases, the LFL of hydrogen decreases. When high voltage direct current power supply (HVDC) is used, the time for the flame to propagate to the edge of the window is much shorter than that of 15 kV high voltage transformer (15 kV HVT) ignition. As the initial pressure increases, the LFL of hydrogen increases. When HVDC is used, the time to reach the peak deflagration overpressure increases with the increase of initial pressure. However, when 15 kV HVT is used, the time to reach the peak deflagration overpressure is almost the same. As the initial temperature increases, the LFL of hydrogen decreases. The change of the LFL of hydrogen with 15 kV HVT ignition is greater than that of HVDC. Through the analysis of chemical kinetic factors, the effect of OH radical generation when the LFL of hydrogen increases with the increase of initial pressure is revealed.     

Laminar flame speed correlations of ammonia/hydrogen mixtures at high pressure and temperature for combustion modeling applications

Ammonia/hydrogen mixtures are among the most promising solutions to decarbonize the transportation and energy sector. The implementation of these alternative energy carriers in practical systems requires developing suitable numerical tools, able to estimate their burning velocities as a function of both thermodynamic conditions and mixture quality. In this study, laminar flame speed correlations for ammonia/hydrogen/air mixtures are provided for high pressures (40 bar–130 bar) and elevated temperatures (720 K–1200 K), and equivalence ratios ranging from 0.4 to 1.5. Based on an extensive dataset of chemical kinetics simulations for ammonia/hydrogen blends (0-20-40-60-80-90-100 mol% of hydrogen), dedicated correlations are derived using a regression fitting. Besides these blend-specific correlations, a generalized (i.e., hydrogen-content adaptive) formulation, with hydrogen content used as additional parameter, is proposed and compared to the dedicated correlations.     

Modulating the textural properties and photocatalytic hydrogen production activity of TiO2 by high temperature supercritical drying

We report a facile method for the synthesis of TiO₂ aerogels by a single step high temperature supercritical drying (HTSCD) of sol–gel derived TiO₂. The morphological and structural features of the resultant materials were determined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, Diffuse Reflectance (DR) spectra, and Fourier Transform infra-Red spectroscopy (FT-IR) measurements. The materials exhibited enhanced solar hydrogen production from water using methanol as sacrificial reagent under Ultra-Violet (UV) light in the absence of Pt as a co-catalyst. Among the TiO₂ aerogel samples synthesized, TiO₂-M-6h evolved 390 μmol g⁻¹ of H₂ after 4 h of irradiation, whereas TiO₂-M-2h produced 217 μmol g⁻¹ of H₂ after 4 h of irradiation under identical conditions, indicating the importance of aging the gels prior to HTSCD step. The enhancement was credited to increase in surface area, and decrease in particle size in TiO₂-M-6h as evidenced from N₂-sorption and DRS studies respectively. Upon comparison with a room temperature synthesized TiO₂-xerogel, the aerogel materials exhibited enhanced hydrogen production. The results validate the superior performance of TiO₂ aerogel materials over TiO₂ xerogels and indicate the potential of HTSCD method for the preparation of titania aerogels for solar energy applications.