MED海水淡化蒸发器布水系统模拟与分析

低温多效海水淡化系统中,液体分布器结构直接影响水平降膜蒸发效率.本文以喷嘴式布液器为研究对象,建立数学模型,采用CFX软件模拟分析分布器内的流动状态,并着重分析了不同结构液体分布器内的流态.结果表明:喷嘴式布液器进水管口处流量不稳定,且非均匀开孔分布器流量分配偏差小于均匀开孔分布器.     

液体分布装置出口流型转换实验研究

针对一种液体分布装置,采用可视化方法,对三种工质流过不同开孔规格的液体分布装置时的出口流型转换过程进行了实验研究。研究发现液体分布装置出口流型转换与管间流型转换过程相似,也经历了片状流、柱状流、滴状流以及它们之间的过渡流型。发现液体分布装置的开孔孔径、孔中心距对布液器出口流型转换有较大影响:相同孔中心距下,孔径变大使得流型转换的边界流量变小;而相同孔径下,大孔中心距会使流型转换边界流量变大。开孔规格对柱状流、片状流之间的转换影响相对于其他流型的影响要大。同时给出了液体分布装置出口流型转换的准则关联式。     

水平螺旋槽管壁面液膜传热特性的研究--流体性质对液膜厚度的影响

考虑到薄膜表面张力和重力的影响,利用流体力学的基本方程建立了小流量液体在水平螺旋槽管外管壁形成壁面液膜的流动和强化传热的拟线性模型,得到了液膜厚度的解析表达式,进而分析了流体性质对壁面液膜厚度的影响。结果表明：对于同一种喷淋液体水,随着温度的升高,液膜厚度受表面张力和槽道表面曲率的影响逐渐减弱,液膜厚度趋向于均匀一致,具有更好的传热传质性能;用水作喷淋液体和煤油、原油相比较,有其特殊的优点,所以工业上常用水作为喷淋式换热器的喷淋液。     

锥形分布器下竖直圆管降膜的数值模拟

通过建立竖直圆管内降膜蒸发的物理模型,对锥形分布器管内的气液两相逆流的换热特性进行二维CFD数值模拟,采用VOF方法捕捉两相流的流动界面,分析了管壁上液膜的膜态、膜厚、速度和温度分布。结果表明:液膜的膜态和温度分布与喷淋量紧密相关,随着喷淋量的增大液膜的稳定性逐渐增加,在喷淋量为1.48 kg/(m·s)时液膜的稳定性最好,液膜表面温度逐渐降低;液膜的降膜膜态分布分为上端的稳定段和下端的震荡段;2 000Re10 000时,管壁的平均传热系数呈现逐渐增大的趋势;膜厚的模拟值与Nussult和Brauer的理论计算值吻合较好。     

盘式聚光系统吸热器热性能实验研究

该文研究设计制作了平顶锥形吸热器,安装在一部盘式聚光系统上,利用水作工质,进行了热性能实验研究.按照定流量、变流量及当地天气情况,测试了一段时间内吸热器进出口的温度变化,分析了吸热功率和热效率.实验显示,当太阳直射辐射的辐照度升高,不论是定流量还是变流量状态,吸热功率变化趋势相同(均增加);热效率变化趋势则不同,定流量状态下降低,变流量状态下升高.研究表明,利用盘式聚光系统通过吸热器对水进行加热,所涉及的太阳直射辐射辐照度和工质状态是影响盘式聚光系统吸热器的吸热功率和热效率的重要因素.以上研究,对太阳能中高温利用及实际研发一套盘式太阳能热发电系统有一定参考作用.     

具有二次聚光器的新型大开口槽式太阳集热器设计与光学性能分析

针对大开口和更高运行温度的槽式太阳能热发电系统,提出一种可实现高聚光比、低辐射热损及能流密度均匀的新型槽式太阳集热器,即在集热管内放置外壁具有太阳选择吸收膜层和内壁具有反射膜层二次聚光器的大开口槽式太阳集热器。建立圆弧为微元段的自适应设计新方法,提出3种典型的二次聚光器面型,利用蒙特卡洛光线追迹方法仿真新型集热器的能流密度分布特性,验证该光学仿真方法,分析影响集热器光学性能的各种因素。结果表明,该集热器可显著提升集热效率。     

槽式太阳能供热光伏系统集热器集热性能的实验研究

文章基于沧州地区的气候特点,通过实验分析了传热工质进口温度、直射辐射量对槽式太阳能供热光伏系统中集热器集热性能的影响情况。实验结果表明:沧州地区3月份晴朗天气条件下,槽式太阳能供热光伏系统的集热效率为0.35～0.65;当运行温度为20～100℃时,随着传热工质入口温度逐渐升高,槽式太阳能供热光伏系统中集热器的集热效率和火用效率均得到明显提高;直射辐射量的增大,会导致槽式太阳能供热光伏系统中集热器的集热效率和火用效率随之升高。     

空间太阳能热动力发电系统10kW聚能器焦平面热流分布计算

考虑了表面形状误差、指向误差、不同的半张角、太阳表面亮度不均匀对聚能器焦平面热流分布的影响，该算法是一种较为全面、可靠的计算焦平面热流分布算法。以10kW太阳能动力系统为例，介绍了采取该算法计算的聚能器焦平面的热流分布。     

平行流蒸发器内气液两相流分配均匀性实验研究

平行流蒸发器内气液两相(特别是液相)在各扁管间的分配对其传热性能影响较大,如果各扁管间的气液分配不均匀其传热性能将显著地下降.在不同气-液流量下实验研究了6种不同形式的平行流蒸发器的分支管液体流量分配情况,实验中观察到流型以环状流为主.研究发现,对于竖直向下流动和竖直向上流动,用通过增加管径的方法不能改善液体流量在各分支管的分配,而主管中气液入口的位置对于流量分配均匀性影响较大.     

横管降膜蒸发太阳能海水淡化装置的性能分析

在分析横管降膜蒸发机理的基础上，设计了一台降膜蒸发太阳能海水淡化装置，并对影响该装置性能的因素进行了实验研究。结果表明，该装置比传统的叠盘式太阳能海水淡化装置瞬态时间短，蒸发效果好，运行温度低。保持合理的海水喷淋密度，使海水在管外降膜蒸发，可使装置在较宽的温度范围内(70～9012)运行，且具有较高的淡水产量和能源利用率(7096以上)。     

Prediction of acoustic absorption performance of a perforated plate with air jets

The present study focuses on the prediction of acoustic absorption performance of a perforated plate with air jets by theoretical calculations.In addition,we experimentally measured the flow rate,internal pressure,acoustic pressure,and transfer function using an acoustic impedance tube.The normal incidence absorption coefficient was calculated from the measured transfer function using transfer function methods.We investigated the influences of background air space,flow velocity,thickness,aperture rate,and aperture diameter of a perforated plate on the acoustic absorption characteristics.The frequency characteristics of the acoustic absorption coefficient showed a maximum value at a local frequency.As the background air space increased,the peak frequency of acoustic absorption characteristics decreased.As the flow velocity passing through the apertures increased,the peak level of the acoustic absorption coefficient also increased.The theoretical results agreed well with the experimental ones qualitatively.     

EVALUATION OF PERFORATED PLATE SOLAR AIR HEATER

Perforated plates had been successfully used in recent years to achieve high heat transfer coefficient from the absorber plate to the flowing air stream in solar air heaters. Since pumping pressure to maintain a particular flow in the solar air heater utilizing this type of absorber has significant influence on collected energy, so the design of perforated plate configuration must be based on the net energy gained from that collector which is the difference between energy collected and energy paid to overcome pumping pressure. A mathematical model had been constructed and validated experimentally for perforated plate solar air heater to study the effect of plate configurations and airflow rate on both energy gained and pressure loss. The results show that, the flow rate of air and plate configurations have a great effect on net energy gained from the air heater. The results also show that a plate of certain configurations operates most efficiently at certain flow rate and more than one configurations can give optimum value of net energy gained for a particular flow rate.     

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.     

Mathematical model for gas–liquid two-phase flow and biodegradation of a low concentration volatile organic compound (VOC) in a trickling biofilter

A theoretical model is established for predicting the biodegradation of a low concentration volatile organic compound (VOC) in a trickling biofilter. To facilitate the analysis, the packed bed is simplified to a series of straight capillary tubes covered by the biofilm in which the liquid film flow on the surface of biofilm and the gas core flow in the center of tube. The theoretical formulas to calculate liquid film thickness in the capillary tube are obtained by simultaneously solving a set of hydrodynamic equations representing the momentum transport behaviors of the gas–liquid two-phase flow under co-current flow and counter-current flow. Subsequently, the mass transport equations are respectively established for the gas core, liquid film, and biofilm with considering the mass transport resistance in the liquid film and biofilm, the biochemical reaction in the biofilm, and the limitation of oxygen to biochemical reaction. Meanwhile, the surface area of mass transport in the capillary tube is modified by introducing the active biofilm surface area, namely the specific wetted surface area available for biofilm formation. The predicted purification efficiencies of VOC waste gas are found to be in good agreement with the experimental data for the trickling biofilters packed with ?8 mm, ?18 mm, and ?25 mm ceramic spheres under the gas–liquid co-current flow mode and counter-current flow mode. It has been revealed that for a fixed inlet concentration of toluene, the purification efficiency of VOC waste gas decreases with the increase in the gas and liquid flow rate, and increases with the increase in the specific area of packed materials and the height of packed bed. Additionally, it is found that there is an optimal porosity of packed bed corresponding to the maximal purification efficiency.     

Thermal analysis of plate condensers in presence of flow maldistribution

Flow maldistribution in plate heat exchangers causes deterioration of both thermal and hydraulic performance. The situation becomes more complicated for two-phase flows during condensation where uneven distribution of the liquid to the channels reduces heat transfer due to high liquid flooding. The present study evaluates the thermal performance of falling film plate condensers with flow maldistribution from port to channel considering the heat transfer coefficient inside the channels as a function of channel flow rate. A generalized mathematical model has been developed to investigate the effect of maldistribution on the thermal performance as well as the exit quality of vapor. A wide range of parametric study is presented, which shows the effects of the mass flow rate ratio of cold fluid and two-phase fluid, flow configuration, number of channels and correlation for the heat transfer coefficient. The analysis presented here also suggests an improved method for heat transfer data analysis for plate condensers.     

Two/three-dimensional reduced graphene oxide coating for porous flow distributor in polymer electrolyte membrane fuel cell

There are drawbacks to use stainless-steel plates as a flow distributor plate in fuel cell, due to some of their properties being inferior to graphite flow distributor plates in terms of electrical conductivity and corrosion resistance. To overcome these problems, many researches have been conducted to improve the properties of stainless-steel flow distributor plates through coating of carbon materials. Herein, two-dimensional Web-like graphene (WG) and self-assembled three-dimensional graphene (STG) are coated through superheat vaporization of micro-droplet method. WG is coated in porous Ni–Cr foam and STG is constructed on the flat flow distributor plate, and they exhibit the feasibility to be applied in flow distributors. Compared to uncoated Ni–Cr foam, the performance of the PEMFC system with the graphene coated foam is enhanced remarkably. Furthermore, the flow distributor plate with the STG exhibits potential to be used directly to flow distributor.     

Experimental research on the effects of distributor configuration on flow distribution in plate‐fin heat exchangers

The effects of different distributor configurations on the flow distribution in plate‐fin heat exchangers were studied. It was found that an irrational distributor configuration would lead to the flow maldistribution and a different degree of non‐uniformity of the flow distribution in the transverse and longitudinal directions. The distributor configuration and Reynolds number are the main factors affecting the flow distribution. An improved distributor configuration with a fluid complementary cavity has been brought forward. The experimental results showed that the improved distributor configuration can effectively improve the performance of flow distribution in heat exchangers. The best performance of flow distribution was obtained at h/H = 0.2. The correlations between the flow maldistribution characteristic and the flow Reynolds number for different distributor configurations were deduced according to the experimental data. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(6): 402–410, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20023     

人工神经网络模拟生物膜滴滤塔废气处理过程

在生物滴滤塔处理有机废气过程中，参数非线性度大，其处理过程适合用人工神经网络(ANN)模拟。通过建立神经网络模拟生物滴滤塔处理有机废气的过程，对遗传算法的改进能够提高其收敛速度，并采用改进遗传算法(MGA)与LMBP算法相结合(MGA—LMBP)，利用已有的实验数据样本训练神经网络，取得了较好的效果。     

新型加压填料饱和器及其关键结构研究

为了进一步揭示HAT循环的集成和运行的规律,促进HAT循环的商业化,搭建了100kW级的HAT循环示范系统。本文主要工作是研制HAT循环的关键部件加压饱和器及其内部气体分布器、液体分布器、气液两相测量装置等。在前人工作基础上,设计了分布性能好、压力损失小的双向环流式气体分布器。利用FLU-ENT软件对其进行了数值分析,结果显示该气体分布器可以满足饱和器内气流分布均匀性的要求。     

The effect of flow distributors on the liquid water distribution and performance of a PEM fuel cell

Water management is one of the important factors which determine the performance of a Proton Exchange Membrane (PEM) fuel cell using hydrogen as fuel. For developing efficient water management systems, it is important to know the potential locations of formation and the nature of distribution of liquid water in the fuel cell. In the present study a PEM fuel cell with three different types of flow distributors are modeled and numerically simulated to find out the water formation and distribution characteristics. The model is validated by comparing the simulated polarization curve to experimental data. It is found that the type of flow distributor used plays a major role in determining the distribution of liquid water in the cell. A parallel flow distributor exhibits poor water removal capabilities whereas a serpentine flow distributor exhibits better water removal. A mixed flow distributor is found to give better water distribution characteristics compared to the parallel and serpentine distributors. Further the effect of liquid water formation and distribution on the species transport, temperature distribution and current generation are also investigated.