新型环形喷动床的喷动机制与喷动特性

在传统喷动床的基础上,设计出一种多喷口环形喷动形式的新型喷动床.实验研究了喷口型式、喷口速度、颗粒类型对这种喷动床床内密相喷动流化区高度、可喷动静止床层高度及床层压降等参数的影响情况.结果表明:颗粒在床内的喷动形式沿床高方向呈现独特分区现象;随着喷口速度的增加,密相喷动高度和可喷动静止床层高度也相应增加;在同样的静止床层高度的情况下,直向型式的喷口更易形成喷动,床层的最小喷动速度几乎与静止床层高度呈线性关系;当床内形成较稳定的喷动后,床层压降随喷口速度的变化不明显,可视为常数.     

加压喷动流化床最小喷动速度的试验研究

在内径100 mm的有机玻璃冷模装置上进行了加压喷动流化床试验.床料直径为1.6 mm、2.3 mm的小米.研究了压力、静止床高及流化风对最小喷动速度的影响.试验结果表明:喷动流化床的最小喷动速度随压力的增大而减小,但减小幅度逐渐变小;静止床高增大,最小喷动速度增大,但床高的增加对最小喷动速度的影响随着压力的增大而减弱.流化风风量增加导致最小喷动速度降低.根据试验数据进行了线性回归,分别得出了uf=0和uf＞0(uf为流化风床内表观气速)时最小喷动速度的关联式,相关系数分别为0.964和0.920,关联式和试验值吻合较好.     

增压导向式喷动流化床流动特性的试验研究

在内径２００ｍｍ，高３．５ｍ，６０°“Ｖ”形布风板的钢制试验装置上，采用密度为２４５０ｋｇ／ｍ３，粒径分别为（１．５～２．５）ｍｍ和（０．１～１．０）ｍｍ窄筛分玻璃珠，以及密度为２２００ｋｇ／ｍ３，粒径为（０．４５～６．０）ｍｍ的宽筛分溢流渣为物料，对各种压力下的导向式喷动流化床最小喷动流化速度、导向与环形区压降、中心喷泉高度以及颗粒循环量和气体旁路特性进行了试验研究。试验结果表明：最小喷动流化速度、导向与环形区压降以及中心喷泉高度与系统几何参数和操作参数密切相关，卷吸段气体射流的性质直接决定了颗粒循环量及其趋势，气体旁路的程度取决于卷吸段两股气流的相互作用。文章中用修正的弗劳德数归纳了中心喷泉高度试验关联式。     

导流管喷动床内液固两相流动特性研究

为了探究不同参数对液固导流管喷动床内颗粒流动行为的影响,本文基于欧拉-欧拉双流体模型结合颗粒动理学对喷动床内液固两相的流动特性进行数值模拟。本文在导流管喷动床的底部引入辅助入口,通过改变颗粒粒径和液体粘度,得到了颗粒轴向速度、颗粒浓度、颗粒拟温度、静压力、动压力等参数的变化规律。模拟结果显示,在一定范围内增大颗粒粒径和液体粘度,颗粒的轴向速度减小,颗粒拟温度显著升高,喷动床内的静压力增加,液体动压力减小,床层膨胀高度明显增大。但当液体粘度增加到一定值后,喷泉区不再明显,并且出现了颗粒回流的现象。因此,综合考虑颗粒粒径和液体粘度,可以显著减小颗粒的堆积,提高喷动效率,使颗粒流化更加充分。     

加压喷动流化床流动和扩散规律冷态实验研究

在一个加压喷动流化床装置上进行了冷态实验,研究加压条件下床中的气固流动状态和气体在各部分的扩散特性。结果表明：加压喷动流化床与常压喷动流化床中气固流动状态差异较大,其喷动流化速度与Ｐ＾－０．５成正比。实验还发现,气体由中心喷动区向周边环形区扩散速度与Ｐ＾－０．５３９成正比。在试验的基础上提出了适合常压和加压喷动流化床最小喷动流化速度的实验关联式、气体扩散速度关联式和喷动区发展段直径的实验关联式。     

加压导向管喷动流化床部分气化炉颗粒循环倍率的研究

以宽筛分的灰渣和2种不同粒径的窄筛分玻璃珠为实验原料，对加压导向管喷动流化床部分气化炉内颗粒循环倍率进行了试验研究。提出了导向管喷动流化床颗粒循环倍率和床内压降理论关系，分析了环形区的充气量在不同系统压力、导向管位置和喷动管直径对颗粒循环倍率增加因子的影响，在此基础上提出了预测颗粒循环倍率增加因子的试验关联式。结果表明：环形区充气后不仅改善了环形区的气固接触，而且显著增加了环形区和喷动区的颗粒交换，有利于床内气固非均相反应的进行。图10表1参10     

加压喷动流化床流型的试验研究

在一个内径100 mm的柱锥型喷动流化床上进行了喷动流化床流型的试验研究.试验中发现了5种不同的流型:固定床(FB)、鼓泡射流流化床(JFB)、节涌射流流化床(JFS)、充气喷动床(SA)和喷动流化床(SF).研究了静止床高、操作压力对喷动流化床流型的影响.结果表明:随着静止床高的增加,稳定的喷动流化床区域减少;随着操作压力的增加,稳定的喷动流化床区域增加.     

二维喷动流化床内气体混合的实验研究

在300 mm×30 mm×2 000 mm的喷动流化床冷态试验台上,在喷动区和环形区分别采用CO和SO2作为示踪气体的方法,获得了不同喷动气流速和流化气流率这两个重要的操作参数下,不同床层高度上示踪气体的径向分布,考察了床内喷动区与环形区之间气体的混合特性。结果表明,示踪气体在不同床层高度的径向分布呈现较大的差异,并沿床层高度依次降低。在稳定的流动状态下,喷动气速度的增大,使喷动气向环形区的传质加强,也促进了流化气在环形区的混合;流化气流率的增大,气体由环形区向喷动区的传质大于由喷动区向环形区的传质,且流化气在环形区混合加强。在不稳定的流动状态下,气体的径向浓度分布曲线两边出现不对称。     

底饲进料循环喷动床内压力脉动信号的SHANNON信息熵分析

为了研究底饲进料循环喷动床内气固两相流的流动特性,通过冷态实验测量反应塔内轴向不同高度上的压力脉动信号.应用SHANNON信息熵分析压力信号,并比较不同操作条件对塔内气固流动的影响.结果表明:压力脉动及其功率谱在不同床层高度上表现出不同的特性;SHANNON信息熵能够很好地反映特征信号的复杂程度和稳定程度;提高流化速度和循环倍率能够导致塔内轴向上的颗粒浓度上升,从而使压力脉动的幅度增加;提高喷射速度和喷嘴位置,能使反应塔底部气固湍动更加强烈,SHANNON信息熵随之上升.     

加压导向管喷动流化床气化炉气体扩散规律研究

采用CO2作为示踪气体在内径200mm，高5m的全尺寸加压导向管喷动流化床中对床内气体扩散特性进行了研究，主要考察了操作参数（喷动气流率，流化气流率，操作压力，颗粒粒径和物性参数）对床内气体扩散的影响，归纳了喷动气旁路份额和流化气旁路份额随操作参数影响的试验关联式，可作为工程设计计算和实际操作的参考。     

Spouted BED combustion of paddy husk

This communication reports the results of an experimental study of spouted bed combustion of paddy husk. The results indicate that husk combustion intensity of the order of 350 kg/h — m² of reactor area is possible with a combustion efficiency of over 85 per cent. Selection of sand size and bed-depth for the spouted bed have emerged to be important parameters in view of pressure drop across bed and entrainment from combustor. The changes in efficiency of combustion were insignificant for different particle size and different bed depths. However there seems to be an optimum combustion intensity i.e. 350 kg/h — m² below and above which combustion efficiency decreases.     

增压导向式喷动流化床流动特性的数值模拟

采用双流体模型对增压导向式喷动流化床内喷动区和环形区气固运动速度和空隙率进行数值模拟。计算结果表明,喷动区颗粒速率在初始阶段急剧上升而气体速度则急剧下降,进入导向管后趋于平缓,而且颗粒加速程度不写系统压力有关,还形区气体速度在卷吸段增大,进入隔离流区后保持不变,而颗粒下降速度一直保持不变,喷动区的空隙率在卷吸段下降,进入导向管后又开始上升。     

内置过滤元件流化床的阻力特性及结构优化

对三维流化床颗粒层过滤器的阻力特性进行了研究。并对过滤元件的结构进行了优化。研究表明．流化床颗粒层过滤器的系统阻力主要决定于过滤元件的阻力,优化过滤元件应该是系统优化的主要方向;优化后的颗粒层过滤器能够有效地减少系统的阻力达到23％以上;在权衡过滤效率和床层压降时,有一个恰当的操作气速和静止床层高度。     

Bed-to-wall heat transfer behavior in a pressurized circulating fluidized bed

An experimental investigation has been made to study the effect of pressure and other relevant operating parameters on bed hydrodynamics and bed-to-wall heat transfer in a pressurized circulating fluidized bed (PCFB) riser column of 37.5 mm internal diameter and 1940 mm height. The experiments have been conducted with and without bed material for the consideration of frictional pressure drop due to gas density at elevated pressures. The pressure drop measured without sand particles is assumed as the pressure drop due to gas density for the calculation of bed voidage and suspension density profiles. The specially designed heat transfer probe is used to measure the bed-to-wall heat transfer coefficient. The experimental results have been compared with the published literature and good agreement has been observed. The axial bed voidage is less in the bottom zone of the riser column and is increasing along the height of the bed. With the increase in system pressure, the bed voidage is found to be increasing in the bottom zone and decreasing in the top zone. The heat transfer coefficient increases with the increase in system pressure as well as with the gas superficial velocity. The heat transfer coefficient is also observed to be increasing with the increase in average suspension density.     

Combustion in crater beds

A preliminary study of a new type of heat-recirculating particulate bed combustor has been carried out with a view to overcoming some limitations arising in the scaling up of spouted bed combustors. A fountain of particles, somewhat similar to that produced in spouted beds, is raised by a jet of gaseous reactants flowing downward into a crater formed below the bed surface. Reactants are preheated prior to combustion both by heat transfer from the products across the walls of the inlet tube and by the interaction of reactants with the inert particles heated by the flame. Combustion characteristics are studied for single and multiple inlet tubes in small laboratory burners and in a much larger 50 KW system. Crater beds are compared with other two-phase combustors, especially spouted beds. They readily lend themselves to scaling up by the use of multiple jets, from one or from several inlets, and recirculate heat between products and reactants both within the craters and by heat transfer to the inlet tubes. Tests show that they can be used either with gaseous reactants entering through the jet or with only oxidant introduced in that way, fuel being included within the bed. Stability limits established for the laboratory burners show a leaner burning capability than is achievable in spouted or fluidized beds and the device offers several advantages over other circulating two-phase systems.     

Performance evaluation of flattened tube in boiling heat transfer enhancement and its effect on pressure drop

An experimental investigation has been carried out to study heat transfer and pressure drop characteristics of R-134a flow boiling inside a horizontal plain tube and different flattened tubes. Round copper tubes with an inner diameter of 8.7 mm were flattened into an oblong shape with an internal height of 6.6 mm, 5.5 mm, 3.8 mm, and 2.8 mm. The test apparatus was basically a vapor compression refrigeration system equipped with all necessary measuring instruments. Analysis of the collected data showed that, by flattening the round tube, the heat transfer coefficient and pressure drop increased simultaneously. The performance of these tubes from the point of view of heat transfer enhancement and pressure drop increasing were evaluated. It was concluded that, the tube with an internal height of 5.5 mm has the best performance compared with the other flattened tubes. Finally, based on the present experimental pressure drop data, a correlation was developed to estimate the pressure drop in flattened tubes. This correlation predicts the experimental data of the present study within an error band of ± 20%.     

引水式水电站变顶高尾水洞水力特性和体型优化

考虑引水式水电站常用的有压尾水洞和变顶高尾水洞两类布置型式,采用基于特征线法的有压管道瞬变流分析模型和适用于明满流过渡过程分析的改进狭缝法模型,分别分析系统的过渡过程特性和尾水洞体型参数的敏感性,研究不同的尾水洞型式下尾水系统的水力特性,进一步揭示了变顶高尾水洞的底宽、洞高和顶坡对尾水管进口最小内水压力的影响规律。结果表明,与增大面积的有压尾水洞比较,变顶高尾水洞是一种可行的布置型式,可有效提高尾水管进口的最小内水压力且水锤过程衰减较快;合理增大变顶高尾水洞底宽、洞高或顶坡均可不同程度地改善尾水管进口最小内水压力,其中顶坡的影响相对明显,为体型优化设计提供了参考依据。     

Heat transfer and pressure drop performance of twisted oval tube heat exchanger

Twisted oval tube heat exchanger is a type of heat exchanger that aims at improving the heat transfer coefficient of the tube side and also decreasing the pressure drop of the shell side. In the present work, tube side and shell side heat transfer and pressure drop performances of a twisted oval tube heat exchanger has been experimentally studied. The tube side study shows that the tube side heat transfer coefficient and pressure drop in a twisted oval tube are both higher than in a smooth round tube. The shell side study shows that the lower the modified Froude number Fr_M, the higher the shell side heat transfer coefficient and pressure drop. In order to comparatively analyze its shell side performance of the heat exchanger, a rod baffle heat exchanger with similar size of the twisted oval tube heat exchanger is designed and its performance is calculated with Gentry's method. The comparative study shows that the heat transfer coefficient of the twisted oval tube heat exchanger is higher and the pressure drop is lower than the rod baffle heat exchanger. In order to evaluate the overall performance of the twisted oval tube heat exchanger, a performance evaluation criterion considering both the tube side and shell side performance of a heat exchanger is proposed and applied. The analyze of the overall performance of the twisted oval tube shows that the twisted oval tube heat exchangers works more effective at low tube side flow rate and high shell side flow rate.     

Experimental investigation of heat transfer and pressure drop in serrated-fin tube bundles with staggered tube layouts

An experimental investigation of the heat transfer and pressure drop performance of ten finned tube bundles using serrated fins is presented. All tube bundles had staggered layouts, and the influence on varying tube bundle layout, tube and fin parameters are presented. The heat transfer coefficient experienced a maximum when the flow areas in the transversal and diagonal planes were equal. An increase in the fin pitch increased the heat transfer coefficient; the same was observed with an increase in fin height. The pressure drop coefficient showed no influence of the tube bundle layout for small pitch ratios, but dropped significantly for higher ratios. Increasing fin pitch reduced the pressure drop, whereas varying fin height had insignificant effect. None of the literature correlations were able to reproduce the experiments for the entire range of tested conditions. A set of correlations were developed, reproducing the experimental data to within ±5% at a confidence interval of 95%.