Waste heat water pumping model with direct contact cooling

The performance of a patented water pumping model with steam-air power was presented, which operates automatically by direct contact cooling method. The main objective was to study feasibility of a pumping model for underground water. In this model, a heater installed within the heat tank represented sources of waste heat as energy input for finding appropriate conditions of the 10 L pump model. The system operation had five stages： heating, pumping, vapor flow, cooling, and water suction. The overall water heads of 3, 4.5, 6 and 7.5 m were tested. At the same time, it was found that the pump with 50% air volume is sufficient for pumping water to a desired level. In the experiment, the temperatures in the heating and pumping stages were 100-103 ℃and 80-90 ℃, respectively. The pressure in the pumping stage was 12-18 kPa, and the pressure in the suction stage was about-80 kPa, sufficient for the best performance. It could pump 170 L of water at a 2 m suction head, 120 L at a 3.5 m suction head, 100 L at a 5 m suction head, and 65 L at a 6.5 m suction head in 2 h. A mathematical model for larger pumps was also presented, which operates nearly the same as the present system. Economic analysis of the 10 L pump was also included.

Parameters optimization for direct contact membrane distillation based on orthogonal experiment

Parameter optimization integrating operation parameters and structure parameters for the purpose of high permeate flux,high productivity and low exergy consumption of direct contact membrane distillation (DCMD) process was conducted based on Taguchi experimental design. L16(45) orthogonal experiments were carried out with feed inlet temperature,permeate stream inlet temperature,flow rate,module packing density and length-diameter ratio as optimization parameters and with permeate flux,water productivity per unit volume of module and water production per unit exergy loss separately as optimization objectives. By using range analysis method,the dominance degree of the various influencing factors for the three objectives was analyzed and the optimum condition was obtained for the three objectives separately. Furthermore,the multi-objectives optimization was performed based on a weight grade method. The combined optimum conditions are feed inlet temperature 75℃,packing density 30% ,length-diameter ratio 10,permeate stream inlet temperature 30 ℃ and flow rate 25 L/h,which is in order of their dominance degree,and the validity of the optimization scheme was confirmed.

Transient Heat Transfer Study of Direct Contact Condensation of Steam in Spray Cooling Water

We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of noncondensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 1045 mm. We applied a new analysis method for the steam state equation to analyze the molar quantity change in steam over the course of the experiment and determined the transient steam variation. We also investigated the influence of flow rates and temperatures ofcooling water on the efficiency ofsteam condensation. Our experimental results show that appropriate increasing of the cooling water flow rate can significantly accelerate the steam condensation. We achieved a rapid increase in the total volumetric heat transfer coefficient by increasing the flow rate of cooling water, which indicated a higher thermal convection between the steam and the cooling water with higher flow rates. We found that the temperature ofcooling water did not play an important role on steam condensation. This method was confirmed to be effective for rapid recovering ofsteam.

Performance and fouling mechanism of direct contact membrane distillation(DCMD) treating fermentation wastewater with high organic concentrations

In this study,direct contact membrane distillation（DCMD）was used for treating fermentation wastewater with high organic concentrations.DCMD performance characteristics including permeate flux,permeate water quality as well as membrane fouling were investigated systematically.Experimental results showed that,after 12 hr DCMD,the feed wastewater was concentrated by about a factor of 3.7 on a volumetric basis,with the permeate flux decreasing from the initial 8.7 L/m^2/hr to the final 4.3 L/m^2/hr due to membrane fouling;the protein concentration in the feed wastewater was increased by about 3.5 times and achieved a value of 6178 mg/L,which is suitable for reutilization.Although COD and TOC in permeate water increased continuously due to the transfer of volatile components from wastewater,organic rejection of over 95%was achieved in wastewater.GC–MS results suggested that the fermentation wastewater contained 128kinds of organics,in which 14 organics dominated.After 12 hr DCMD,not only volatile organics including trimethyl pyrazine,2-acetyl pyrrole,phenethyl alcohol and phenylacetic acid,but also non-volatile dibutyl phthalate was detected in permeate water due to membrane wetting.FT-IR and SEM–EDS results indicated that the deposits formed on the membrane inner surface mainly consisted of Ca,Mg,and amine,carboxylic acid and aromatic groups.The fouled membrane could be recovered,as most of the deposits could be removed using a HCl/Na OH chemical cleaning method.

Analysis of ice slurry production by direct contact heat transfer of air and water solution

In this paper, a novel system using direct contact heat transfer between air and water solution was proposed to generate ice slurry. The heat transfer process and the system performance were studied; energy efficiency coefficients of 0.038, 0.053, and 0.064 were obtained using different solutions. An empirical relationship between the volumetric heat transfer coefficient U v and the main parameters was obtained by fitting the experimental data. The U v calculated from the empirical formula agreed with the experimental U v quite well with a relative error of less than 15%. Based on the empirical formula, a laboratory-scale direct contact ice slurry generator was then constructed, with practical application in mind. If the air flow rate is fixed at 200 m 3 /h, the ice production rate will be 0.091 kg/min. The experimental results also showed that the cold energy consumption of the air compressor accounted for more than half of the total amount. To improve the system energy efficiency coefficient, it is necessary to increase the air pipes insulation and the solution's thermal capacity, and also it is appropriate to utilize the free cold energy of liquefied natural gas (LNG).

Poly(vinylidene fluoride-co-hexafluoro propylene) membranes prepared via thermally induced phase separation and application in direct contact membrane distillation

A non-toxic and environmentally safe diluent,acetyl tributyl citrate,was employed to prepare poly(vinylidene fluoride)-co-hexafluoropropylene membranes via thermally induced phase separation.Effects of the polymer concentration on the phase diagram,membrane morphology,hydrophobicity,pore size,porosity and mechanical properties(tensile stress and elongation at break)were investigated.The results showed that the pore size and porosity tended to decrease with increasing polymer concentration,whereas the contact angle,liquid entry pressure and mechanical properties showed the opposite trend.In direct contact membrane distillation operation with 3.5 wt-%sodium chloride solution as the feed solution,the prepared membranes performed high salt rejection(>99.9%).Furthermore,the prepared membranes retained excellent performance in long-term stability tests regarding the permeate flux and salt rejection. ne distillation.

Experimental Study on Latent Heat Storage Characteristics of W/O Emulsion-Supercooling Rate of Dispersed Water Drops by Direct Contact Heat Exchange

Recently, much attention has been paid to investigate the latent heat storage system. Using of ice heat storage system brings an equalization of electric power demand, because it will solved the electric -power-demand-concentration on day-time of summer by the air conditioning. The flowable latent heat storage material, Oil/Water type emulsion, microencapsulated latent heat material-water mixture or ice slurry, etc., is enable to transport the latent heat in a pipe. The flowable latent heat storage material can realize the pipe size reduction and system efficiency improvement. Supercooling phenomenon of the dispersed latent heat storage material in continuous phase brings the obstruction of latent heat storage. The latent heat storage rates of dispersed water drops in W/O (Water/Oil) emulsion are investigated experimentally in this study. The water drops in emulsion has the diameter within 3 ~ 25μm, the averaged water drop diameter is 7.3μm and the standard deviation is 2.9μm. The direct contact heat exchange method is chosen as the phase change rate evaluation of water drops in W/O emulsion. The supercooled temperature and the cooling rate are set as parameters of this study. The evaluation is performed by comparison between the results of this study and the past research. The obtained experimental result is shown that the 35K or more degree from melting point brings 100% latent heat storage rate of W/O emulsion. It was clarified that the supercooling rate of dispersed water particles in emulsion shows the larger value than that of the bulk water.

The efficiency of direct integration methods in elastic contact-impact problems

A comparison of direct integration methods is madeand their efficiency is investigated for impact problems.New-mark,Wilson-θ,Central Difference and Houbolt Methodsare used as direct integration methods.Impact analysisincludes that of elastic and large deformation based uponupdated Lagrangian including buckling check.The resultsshow that the direct integration methods give differentresults in different contact-impact cases.

蒸汽射流直接接触凝结的界面及声压特性

蒸汽射流在液体中的直接接触凝结引发的剧烈界面振荡及声压振荡,可能导致工业管道系统振动甚至失效,采用高速摄像机与高频水听器,捕捉了射流的界面演化行为及其诱导的声压。研究了3种典型凝结流型下射流界面的径向、轴向振荡与声压振荡特性,并阐明声压振荡产生机理。研究发现:声压波动的概率密度函数在间歇流型下呈左偏单峰分布,在界面振荡流型下呈双峰分布,而在稳定流型下呈对称单峰分布;随蒸汽质量流速升高,无量纲径向、轴向界面振荡强度及声压振荡强度整体呈下降趋势,表现出极强的相关性。建立了基于声压参数的射流喷射长度预测模型,预测值与实验值的误差在±1%内。概率密度及相关性分析结果表明,蒸汽射流凝结的声压振荡是由其界面振荡引起的。

Multi-Pollutant Formation and Control in Pressurized Oxy-Combustion:SO_(x),NO_(x),Particulate Matter,and Mercury

Oxy-combustion is a promising carbon-capture technology,but atmospheric-pressure oxy-combustion has a relatively low net efficiency,limiting its application in power plants.In pressurized oxycombustion(POC),the boiler,air separation unit,flue gas recirculation unit,and CO_(2)purification and compression unit are all operated at elevated pressure;this makes the process more efficient,with many advantages over atmospheric pressure,such as low NO_(x)emissions,a smaller boiler size,and more.POC is also more promising for industrial application and has attracted widespread research interest in recent years.It can produce high-pressure CO_(2)with a purity of approximately 95%,which can be used directly for enhanced oil recovery or geo-sequestration.However,the pollutant emissions must meet the standards for carbon capture,storage,and utilization.Because of the high oxygen and moisture concentrations in POC,the formation of acids via the oxidation and solution of SO_(x)and NO_(x)can be increased,causing the corrosion of pipelines and equipment.Furthermore,particulate matter(PM)and mercury emissions can harm the environment and human health.The main distinction between pressurized and atmospheric-pressure oxy-combustion is the former’s elevated pressure;thus,the effect of this pressure on the pollutants emitted from POC—including SO_(x),NO_(x),PM,and mercury—must be understood,and effective control methodologies must be incorporated to control the formation of these pollutants.This paper reviews recent advances in research on SO_(x),NO_(x),PM,and mercury formation and control in POC systems that can aid in pollutant control in such systems.

摇摆运动下低流率蒸汽冷凝换热特性和气泡受力数值模拟

蒸汽直接接触冷凝具有高效的传热传质性能,广泛应用于核能安全等领域。低质量流率蒸汽直接接触冷凝具有低频压力振荡,易引发设备共振。相比陆地稳定工况,海洋条件下摇摆运动可能加剧气液界面振荡,进一步影响设备的安全运行。为此,通过数值模拟对摇摆条件下低流率蒸汽凝结过程进行研究,分析了摇摆条件下压力、换热特性和气泡受力的变化规律,结果表明压力和传热系数剧烈波动主要集中于气泡颈缩和脱离阶段,此时气泡受力也达到最大值,气泡主要受惯性力和凝结力作用。此外,对比静止工况和摇摆工况,发现摇摆条件下由气泡速度变化导致的惯性力部分增大,摇摆运动带来的附加摇摆速度强化了气液界面的换热性能,平均传热系数远高于静止工况。

蒸汽射流直接接触凝结诱导振动特性研究

蒸汽射流在管内过冷水流中的直接接触凝结会诱导严重的管道振动。采用高速摄像机与加速度传感器,捕捉了蒸汽射流气羽演化及其诱导的管道振动。通过实验定量描述了考虑气羽形貌的气羽灰度质心振荡与管道振动特性。发现界面振荡流型下气羽灰度质心的振荡幅度最大,间歇振荡流型下次之,稳定凝结流型下最小。随着蒸汽质量流速升高,质心振荡及管道振动强度都向着趋于稳定的方向发展,表现出极强相关性。在此基础上绘制了管道振动强度随蒸汽质量流速及过冷水温度的分布图,振动强度随着过冷水温度的升高而升高。相关性分析表明气羽灰度质心的轴向振荡是沿蒸汽喷射方向的管道振动强度的主导因素。

PVDF/SiC疏/亲水Janus复合膜的制备及其膜蒸馏处理酸性废水性能

着眼于采用直接接触式膜蒸馏(DCMD)技术对酸性废水进行处理和资源再利用,针对传统蒸馏膜机械稳定性不高、通量低等问题,使用刮涂法和非溶剂致相分离(NIPS)法在亲水碳化硅(SiC)微滤膜表面构建疏水聚偏氟乙烯(PVDF)多孔薄层,制备得到具有不对称润湿性的PVDF/SiC疏/亲水双层Janus复合膜,用于DCMD性能研究.使用N,N-二甲基乙酰胺(DMAc)为溶剂,水-乙醇体系为非溶剂凝固浴,探究了制膜过程中PVDF铸膜液浓度、凝固浴成分、凝固浴温度等因素对PVDF层表面形貌和浸润性的影响,研究了复合膜在DCMD浓缩稀硫酸和处理模拟酸性矿山废水中的性能.结果表明,铸膜液中质量分数10%PVDF和纯乙醇凝固浴为最佳制膜条件,所得复合膜水接触角达140°,分离层孔隙率为45%,平均孔径为0.6μm,并且PVDF层与SiC基体结合力强.复合膜在DCMD浓缩质量分数10%(107 g/L)稀硫酸溶液和处理模拟酸性矿山废水实验中水的膜通量均达10 L/(m^(2)·h)以上,对非水组分截留率近100%,并具有长期运行稳定性,表现出DCMD处理酸性废水的应用潜力.

微细通道内蒸汽直接接触间歇凝结压力振荡特性

为探究微尺度条件下蒸汽直接接触间歇凝结瞬时压力振荡特性,开展了T型微细通道内间歇凝结压力测量实验及频谱分析等。研究发现,在蒸汽温度100℃、蒸汽质量流量0.45g/min、过冷水温度40℃以及过冷水质量流量12.65g/min工况下,间歇凝结压力时域信号在−29.5~8.8kPa之间波动,压力值在2.5kPa附近的概率密度最大。此外,通过频谱分析发现压力频域信号的第一主频为10Hz,与1s内间歇凝结经历的周期数量相近。

聚偏氟乙烯双疏膜的制备及其膜蒸馏性能

膜蒸馏处理含表面活性剂等复杂料液时,常规疏水膜存在易被润湿和污染的问题.目前,多层嵌入型表面结构的双疏膜受到广泛关注.本研究提出了一种新的无多层嵌入表面的聚偏氟乙烯(PVDF)双疏膜.首先,采用复合相转化法制备了PVDF和聚苯乙烯-马来酸酐(SMA)共混基膜,再经低表面能的全氟癸基三乙氧基硅烷(17-FAS)改性制备出双疏膜.该膜上、下表面对水和乙二醇接触角分别为135.9°、147.3°和112.2°、123.5°.在含表面活性剂和有机污染物的盐水料液中表现出高于0.4 MPa的优异液体穿透压力(LEP)。采用直接接触式膜蒸馏处理含盐含表面活性剂十二烷基硫酸钠(SDS)及有机污染物黄腐酸(FA)或腐殖酸(HA)的复杂料液,结果表明,PVDF双疏膜的水通量达36kg/(m^(2)·h),盐截留率达99.9%,表现出优异的抗润湿和耐污染性能.

载有螺旋扰流装置的直触式换热器结构设计

本文探讨直触式技术在高温烟气-低温液体间换热的应用研究。所开发直触式换热器主要由立式布局的上、下锅体组成,采用喷淋为主要换热方式,重点针对气-液间直触换热过程设计螺旋扰流装置。主要结构特点:通过螺旋式扰流盘所形成的过流通道,优化烟气流动路径,增大烟气行程的同时也能起到导流换热作用;通过给水供给机构,利用产出蒸汽预热水管,提高烟气利用效率。通过理论计算完成直触式换热器结构关键尺寸和性能指标的设计,设计出载有螺旋扰流装置的换热器,此装置结构紧凑、换热效率更高、避免了雾化和液滴漂移等不足,且具有提前预热、增大烟气行程等优势,可以更好地适用于小型工业生产和满足居民日常生活所需。

土壤-水稻前茬离散元仿真参数标定及其旋耕轨迹分析

在进行稻油轮作区域水稻收获后旋耕作业中的前茬运动、受力仿真分析时,由于缺乏可靠的离散元仿真参数难以准确计算土壤-水稻前茬运动规律和相互间受力。该研究采用EDEM软件对土壤-水稻前茬混合物内部各物质的物理与接触参数进行离散元仿真标定。首先测定了土壤-水稻前茬混合物内各物质物理与相互间接触参数,以堆积角作为评价指标,利用仿真试验进行了显著因素筛选、最优水平取值范围确定及二阶回归模型下最佳参数寻优,对参数进行了标定,得到土壤-水稻前茬混合物模型极显著参数的最优组合为土壤-土壤恢复系数0.407、土壤-土壤动摩擦系数0.123、土壤-水稻前茬静摩擦系数0.596、土壤表面能1.860 J,此时与试验堆积角误差为0.58%。并进行了土壤-水稻前茬间的直剪试验与仿真,得到了稳定后不同垂直应力下试验与仿真的直剪切应力误差分别为:5.4%(50 kPa),4.1%(100 kPa),3.1%(150 kPa)。最后在最优参数组合下,开展了基于MBD-DEM的旋耕土壤-水稻前茬轨迹分析试验,前茬跟随旋耕刀及直接被掩埋两种埋覆场景下仿真与土槽试验轨迹的Spearman秩相关系数分别为0.91、0.84,验证了仿真模型标定参数的准确性。研究结果可为水稻前茬旋耕轨迹调控过程的离散元仿真分析提供可靠的接触参数。

SV型直接接触换热器换热过程的数值模拟

为研究SV静态混合器对液-液直接接触沸腾换热过程混合及传热的影响规律,分析了相同高度下SV静态混合器长径比对直接接触沸腾换热过程的影响。搭建了直接接触换热实验平台,验证了数值模拟结果的可行性与准确性。结果表明,实验结果与模拟结果误差在3%以内;与长径比为0.5和2.0的2种混合器相比,长径比为1.0的SV静态混合器压力降最高降低了18 Pa,湍流动能大于0.002 m2/s2,容积换热系数最高提高了9.7%;压力降和容积换热系数随着长径比的减小而增大,存在最佳长径比1.0使湍流动能达到最大值。综上所述,适当减小SV混合元件长径比有利于增强换热,对直接接触换热器结构参数设计具有指导意义。

T型微细通道内含不凝气蒸汽直接接触凝结数值模拟研究

利用VOF多相流模型和大涡模拟LES湍流模型,结合“双阻力”模型和Fick定律,对微细通道内含不凝气蒸汽的直接接触凝结过程进行了数值模拟。开展了不凝气对蒸汽直接接触凝结过程中气羽形态、压力分布以及凝结速率的影响机制研究。结果表明:在少量不凝气存在的工况,汽液相界面仍呈现周期性变化,随不凝气含量增加,其在汽液界面处聚集形成的不凝气层厚度增加,气羽无周期性变化。此外,随着不凝气含量的升高,压力振荡强度减弱,凝结形成的负压值变小,凝结速率降低。

具有仿生结构的并联微细多通道蒸汽直接接触凝结数值模拟

为进一步丰富微细尺度条件下蒸汽直接接触凝结(DCC)流动换热现象的研究,基于哺乳动物动脉或静脉的分支血管树系统,设计了一种具有仿生结构的并联微细多通道模型。在商业软件Fluent上采用VOF多相流模型、大涡模拟(LES)湍流模型和凝结双阻力模型,进行并联微细多通道的蒸汽直接接触凝结数值模拟,获得了并联多通道中的汽羽形态、温度和压力分布以及凝结速率随时间的变化情况。结果表明:汽羽在水平主管凝结过程中会发生聚并,过冷水会周期性进入各竖直支管且各进入高度接近;压力分布在各竖直支管中存在一定差异;微细尺度下凝结仍发生在汽液界面附近,且每个凝结周期中平均凝结速率在汽羽完全聚并之前达到最大值,约为220 kg/(m3·s),在过冷水进入各竖直支管的过程达到最小值,约为17 kg/(m3·s)。