搅拌流化床干燥器传热特性的研究

以不同粒径的玻璃珠和分子筛为原料 ,对搅拌流化床干燥器进行了气固间传热特性的实验研究。比较了恒速干燥阶段带搅拌和不带搅拌时物料湿含量随时间的变化规律 ,研究了干燥器进口温度、进口气速、搅拌转速等因素对传热过程的影响 ,并得出了相应的传热膜系数关联式 ,计算值与实验值的误差小于 1 5     

烧结矿余热回收竖罐内气固传热特性

以自制气固传热实验装置为操作平台,实验研究了烧结矿颗粒填充床内的气固传热特性。结果表明:气体表观流速和烧结矿颗粒直径是影响颗粒床层内气固传热过程的主要因素。气体表观流速越大,颗粒直径越小,床层内气固传热系数就越大。当烧结矿颗粒直径和气体表观流速一定时,床层内烧结矿颗粒温度的升高导致床层气固传热系数的增加和传热Nusselt数的减小。由于计算误差较大,现有的经验关联式不适用于求解烧结矿颗粒床层内的气固传热过程。基于量纲分析法,并结合实验测量数据拟合得出了能够描述烧结矿颗粒床层内气固传热特性的实验关联式,平均计算误差为4.22%,显示了良好的预测性能。     

离心流化床中气固传热特性的实验研究

本文使用玻璃细珠、黄砂和氧化铝球在不同操作条件下进行了离心流化床气固两相间传热特性的实验研究．测定了气体入口、出口和床层温度随时间的变化．分析了床层厚度、粒径、物料性质、床体转速和气体流速等因素对气固传热特性的影响．首次获得了离心流化床气固两相传热的准则方程．     

气固流化床内宽筛分硅粉颗粒流化特性的数值模拟

为了探索气固流化床内宽筛分硅粉颗粒的流化特性,作者利用计算流体力学CFD软件,采用Eulerian气固多相流模型及SIMPLE算法,模拟了二维气固流化床内不同粒级硅粉颗粒在不同操作件下的气固流化特性;分析了气泡生成、长大和破裂的过程,研究了床内气固两相的流动特性.结果表明:模拟计算值与实验值吻合较好,最大相对误差为10...     

竖直管气固鼓泡流化床传热机理的CPFD模拟

针对细颗粒气固鼓泡流化床中床料与竖直传热管壁面间的传热行为,在前期实验的基础上,采用计算颗粒流体力学(CPFD)方法从颗粒在传热壁面更新的角度,深入分析了传热特性与壁面气固流动行为之间的关联性。结果表明,模拟得到的传热管壁面颗粒更新通量和基于颗粒团更新模型的颗粒团平均停留时间均能很好解释实验测得的传热系数变化规律,这证实颗粒团更新是影响传热过程的控制性因素。模拟还发现随加热管从床层中心向边壁的移动,加热管周向方向上颗粒更新通量和传热系数的不均匀性都呈增大趋势。随着表观气速的增大,气泡行为导致床层颗粒内循环流率增大,这是导致颗粒团在加热管壁面上的更新频率增大以及床层与壁面间传热系数增大的根源。     

气固搅拌流化床流化和干燥特性实验研究

通过测定不同搅拌速度、床层高度下床层压降与表观气速间的关系,研究了水平桨气固搅拌流化床的流化特性。实验表明,搅拌增强了气固接触,明显改善了流化床的流化质量。对不同气速、不同搅拌速度下气固流化床的干燥特性进行了实验研究,结果表明,搅拌能加快流化床的传热速率,提高干燥速度。     

竖直管气固鼓泡流化床传热机理的CPFD模拟

针对细颗粒气固鼓泡流化床中床料与竖直传热管壁面间的传热行为,在前期实验的基础上,采用计算颗粒流体力学(CPFD)方法从颗粒在传热壁面更新的角度,深入分析了传热特性与壁面气固流动行为之间的关联性。结果表明,模拟得到的传热管壁面颗粒更新通量和基于颗粒团更新模型的颗粒团平均停留时间均能很好解释实验测得的传热系数变化规律,这证实颗粒团更新是影响传热过程的控制性因素。模拟还发现随加热管从床层中心向边壁的移动,加热管周向方向上颗粒更新通量和传热系数的不均匀性都呈增大趋势。随着表观气速的增大,气泡行为导致床层颗粒内循环流率增大,这是导致颗粒团在加热管壁面上的更新频率增大以及床层与壁面间传热系数增大的根源。     

低温振动流化床气固传热的实验研究

在低温粉碎工程中,振动流化床常用于固体颗粒的预冷。为了深入认识振动流化床低温下气固传热的特性,本文介绍了不同的振幅,气流速度和料层厚度下低温实验的结果,通过分析实验结果首次得到了振动流化床中低温气固的传热关联式与普通流化床相比,由于引入了振动,振动流化床气固传热换热系数大幅度提高。     

浅层流化床水平埋管与床层间的传热

针对浅层气－固流化床床层与水平埋管间的传热特性进行了实验研究，同时利用光导纤维对床层与壁面间的接触动力学参数进行了检测，从而从流体力学的角度，分析了传热的实验结果。基于乳化团与气泡相与传热面的交替接触，通过理论分析，提出了浅层流化床中水平埋管传热的模型方程，模拟值能较好地与实验结果相符合。     

立式粉体干燥器中不同粒径湿颗粒流动特性研究

为了研究立式粉体干燥器内不同粒径聚甲醛颗粒流动特性，采用CFD-DEM模型耦合液桥力模块的方法，分析了含水率和颗粒粒径对聚甲醛颗粒流动特性的影响，并验证了该分析方法的正确性。研究结果表明：基于量纲分析法，结合已有实验数据拟合得出平均颗粒速度的经验关联式，计算值与实验值的最大误差为25.13%，可以较好地描述干燥单元内的平均颗粒速度变化。截面平均固含率随着颗粒直径的增大而降低，干燥单元内固含率在轴向和径向分布上分别呈现“上浓下稀”、“边壁高近流体低”的特点。当颗粒直径d_p<2 mm且含水率V_lb≥0.1%时，容易造成干燥单元入口堵塞，并且干燥单元内固含率剧减。截面平均颗粒速度随着轴向高度和颗粒直径的增大而增大，从边壁区到近流体区域的局部颗粒速度逐渐减小。当颗粒直径相同时，湿颗粒比干颗粒的颗粒速度小；当颗粒直径超过临界值2 mm时，随着含水率的增高，颗粒速度略微减小，颗粒平均停留时间和固含率总体上有所增加。     

固定床中丝状颗粒的传热传质特性

目前对于固定床中丝状填充颗粒传热传质特性的认识仍处于初始阶段。为了能够从颗粒尺度的微观层面揭示丝状颗粒与气体、颗粒与颗粒之间的热、质传递机理,建立了一种丝状颗粒传热传质数学模型,之后将离散单元法与计算流体力学相结合,对实验中较难获得的床层局部流动及传递信息进行了数值模拟,并着重分析比较了气流入口温度以及表观气速等关键因素对固定床中丝状颗粒温度和含水率变化的影响规律。通过模拟结果与实验数据的对比,验证了所建模型的可行性。研究结果表明:同一时刻,固定床中颗粒温度大体上是随着床层高度的增加而降低,含水率则是随着床层高度的增加而升高;气流入口温度对于固定床中丝状颗粒平均温度的提升起着主导作用,而颗粒的传质速度则受表观气速的影响更为明显。     

洗衣粉悬浮液在惰性粒子流化床中干燥的研究

针对气体分布板开直孔的惰性粒子流化床,开展了洗衣粉悬浮液在床内的干燥性能研究。测定了流化床的床层压降曲线,考察了进料量、进风温度、进风速度及惰性粒子直径对于流化床传热性能的影响,且与气体分布板开斜孔的传热性能进行了初步比较。结果表明,流化床的床层压降主要是由惰性粒子的流化阻力所致;适当增加进料量和进风速度,或减小惰性粒子直径,以及将气体分布板的孔道由直孔改为斜孔,均可提高流化床的传热性能,但过高的进风温度则可能导致传热性能的下降。     

Surface-to-bed heat transfer in fluidised beds of fine particles

This work reports experimental results on the heat transfer between a fluidised bed of fine particles and a submerged surface. Experiments have been carried out using different bed materials (polymers, ballotini, corundum, carborundum and quartz sand) with Archimedes number between 2 and 50. Dry air at ambient pressure and temperature has been used as fluidising gas. Three different exchange surfaces, namely a sphere and two cylinders with different base diameter and same height, have been used.Experimental results show that the heat transfer coefficient increases with particle Archimedes number and is almost independent from particle thermal conductivity for K_p/K_g > 30. Finally, the comparison of heat transfer coefficient for the different surfaces shows that the effect of the surface geometry may account for a 30% variation in the heat transfer coefficient, with higher differences occurring for coarser particles.     

Heat transfer in a swirling fluidized bed with geldart type-D particles

A relatively new variant in fluidized bed technology, designated as the swirling fluidized bed (SFB), was investigated for its heat transfer characteristics when operating with Geldart type D particles. Unlike conventional fluidized beds, the SFB imparts secondary swirling motion to the bed to enhance lateral mixing. Despite its excellent hydrodynamics, its heat transfer characteristics have not been reported in the published literature. Hence, two different sizes of spherical PVC particles (2.61 mm and 3.65 mm) with the presence of a center body in the bed have been studied at different velocities of the fluidizing gas. The wall-to-bed heat transfer coefficients were measured by affixing a thin constantan foil heater on the bed wall. Thermocouples located at different heights on the foil show a decrease in the wall heat transfer coefficient with bed height. It was seen that only a discrete particle model which accounts for the conduction between the particle and the heat transfer surface and the gas-convective augmentation can adequately represent the mechanism of heat transfer in the swirling fluidized bed.     

固定床内错流传热——II.床层对壁给热系数的经验关联式

采用3种导热性能不同的固体颗粒为填充物,以空气为介质,在床层被加热的情况下,研究了固定床中内置圆管的错流传热.采用最小二乘法对实验数据进行拟合,得到以床层对壁的平均给热系数、气体的导热系数和床层中被加热圆管的管径计算的Nusselt准数经验关联式:Nuf=31(lb0/ls)1.4(Db/Dp)0.2Rep0.33Pr0.62,Rep=10~180,Db/Dp=28~116,lb0/ls=0.5~0.2.Reynolds数以固体颗粒的等外表面积当量直径进行计算.结果表明,在错流传热过程中,表征气体流动特性的参数Rep仍是错流传热的重要影响因素,Nusselt准数除与床层的结构参数Db和颗粒的当量直径Dp有关外,还与颗粒的导热系数ls和床层的导热系数lbo密切相关.     

Total and gas convective heat transfer from a vertical tube to a mixed particle gas—solid fluidized bed

Experimental data were obtained for the average gas convective and total heat transfer coefficients for a vertical tube immersed in an air-fluidized bed of narrowly as well as widely distributed particle size mixtures. The gas convective heat transfer coefficient was determined by measuring the rate of mass loss from a vertical naphthalene tube 0.0262 m in diameter and 0.1012 m in length and using a heat and mass transfer analogy. These data were obtained at a bed temperature of about 330 K and superficial velocity of 0.1 to 1.1 m/s. The total heat transfer coefficients were measured under identical conditions using an electrically heated vertical tube. The total heat transfer coefficient decreased with an increase in particle diameter from 0.237 to 1.35 mm. The addition of fines was found to increase the total heat transfer coefficient. The gas convective heat transfer coefficient increased with increase in particle size and fluidizing velocity. The dependence of the gas convective heat transfer coefficient on gas velocity was more pronounced for large particles. The addition of fines resulted in decrease in gas convective coefficient. The relative contribution of the gas convective component of heat transfer coefficient was found to increase with increase in particle diameter. Its dependency on fluidizing velocity was found to be more complex. The experimental data were compared with the existing heat transfer models and correlations.     

Heat transfer between an isolated bubble and the dense phase in a fluidized bed

Heat transfer between the bubble and dense phases of a bubbling fluidized bed plays a very important role in the system performance, especially for applications involving solids drying and gas‐phase combustion. However, very few experimental data are available on this subject in the literature. An experimental and modelling investigation on the heat transfer behaviour of isolated bubbles injected into an incipiently fluidized bed is reported in this paper. A new single‐thermocouple technique was developed to measure the heat transfer coefficient. The effects of bed particle type and size, and bubble size on the heat transfer coefficient were examined. The heat transfer coefficient was found to exhibit a maximum as the bubble size increased in the bubble size range investigated. The bed particle size had a comparatively small effect on the heat transfer coefficient. A simple mathematical model was developed which provides good agreement with experimental data.     

离心流化床中强制对流换热的实验研究

对离心流化床干燥器中气体与被干燥颗粒物料之间的强制对流换热进行了实验研究,获得了各主要运行参数对气固换热系数的影响规律,并利用场协同原理分析了对流换热强化的机理. 实验证明,在一定转速范围内,在气流速度方向和热流方向（温度梯度方向）一致时,换热的准则关联式具有Nu＝CRePr的形式. 获得了满足Nu～RePr呈直线关系的Pe(Pe=RePr)数变化范围和临界Pe数,当Pe数大于临界值后,离心流化床中对流换热强度随Pe数增加而增大的趋势会明显减缓并偏离线性区.