钴基催化剂固定床有效导热系数

在165~265℃及常压条件下,采用稳态法测定了气体处于静态时活性组分呈蛋壳型分布的钴基催化剂固定床的有效导热系数,并根据稳态法理论,拟合实验数据获得了固定床有效导热系数与气体导热系数和催化剂导热系数之间的关联式. 实验数据与拟合结果的最大偏差和标准偏差的绝对值分别为1.74%和0.43%. 将实验数据与前人的相关预测模型计算值进行了比较,结果表明,二者吻合良好. 利用气体处于静态时固定床的有效导热系数、Re和Pr,获得了气体流动时固定床径向有效导热系数的计算式.     

异形多通孔催化剂工程研究(III)——12孔及24孔颗粒固定床传热参数测定

对两种薄片结构的异形多通孔催化剂颗粒的传热特性进行实验研究。在一可同时测定轴向和径向温度分布的壁冷式固定床中测定了12孔及24孔异形多通孔颗粒的温度分布，利用所测实验数据对拟均相二维模型进行了径向有效导热系数和壁给热系数的计算。将得到的传热参数与雷诺数相关联，并与相似条件下圆柱形及单孔环柱形催化剂颗粒的传热参数进行比较。结果表明，12孔及24孔异形多通孔颗粒能有效改善固定床传热性能。     

低流量下微细颗粒固定床的温度分布及有效传热参数研究

为探索微小型热生物传感器中反应器内部的传热特性,研究了恒壁温(60℃)条件下,低流量(5,3和1 mL·min-1)和微细颗粒直径(平均直径分别为1,0.75和0.45 mm)对固定床内部温度分布的影响,并结合二维均相传热理论模型,获得了有效径向导热系数和有效壁面传热系数等重要参数。研究结果表明,即使在流量非常小(如1 mL·min-1)的情况下,固定床入口段温度分布也很不均匀,存在明显的"入口段效应",但随着床层的增高,这种效应快速减弱;实验所采用树脂颗粒的导热系数很低,颗粒直径越小,接触热阻和流动阻力也越大,导致其有效传热参数越小,不利于热生物传感器中微量反应热信号的检测;在相同Rep时,本研究的有效径向导热系数明显小于文献值,而有效壁面传热参数与多数文献值比较接近。     

A301氨合成催化剂工程参数研究与测定Ⅱ床层传热参数的实验测定

实验测定了Ａ３０１氨合成催化剂填充床内的二维温度分布。采用正交配置法求解拟均相二维传热数学模型,获得了床层的径向有效导热系数和壁给热系数。并将其与雷诺数关联得到了可在实验条件范围内使用的经验关联式。     

活性焦传热系数的测定

为研究活性焦传热性能,把床层径向传热简化为径向有效导热,将轴向传热看成轴向有效导热和流体流动传热2项组成,自制传热系数测定装置,改变扰流气体流速,测定床层轴向和径向温度分布,利用Matlab软件,采用正交配置法进行数据处理,通过赋予初值,采用最优化方法求解模型偏微分方程,得出径向有效导热系数Ker及壁给热系数Hw。试验结果表明:活性焦有效导热系数约为1.39 W/(m·K),壁给热系数随着颗粒雷诺数的增加而增加。试验测定的壁给热系数与低传热系数材料的壁给热系数经验公式较吻合。     

环柱形颗粒填充床传热参数

在一可同时测定轴向与径向温度分布的壁冷式固定床实验装置上 ,通过实验测定了球形、圆柱形和环柱形填充颗粒的径向有效导热系数和壁给热系数 .采用计及内、外环外表面积的颗粒等比表面积当量直径 ,将这些传热参数与Reynolds数相关联 .     

固定床有效导热系数及壁给热系数的实验测定及其关联式

在固定床反应器设计时,需要计算床层温度分布及热点位置,因此测定传热参数数值具有重要意义。本文作者在直径为φ76×4mm长1040mm,内部充填φ4.5mm刚玉球的固定床实验装置上测定了床层不同高度,不同径向位置上的温度分布值,并分别用理论解法、有限差分法及最优化法求得床层径向有效导热系数K_e及壁给热系数H_w值。作者认为最优化法求出的K_e、H_w值准确可靠,计算温度和实测温度较为吻合。     

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.     

传热特性对褐煤热解过程的影响研究

利用氮气作为对流气体,在温度为450℃、气体流量为0~10 L/min的条件下,对褐煤的热解过程进行了实验研究;在一维拟均相模型上,利用热解数据对煤的导热系数进行了计算;结果表明,5~10 L/min的气体流量可在一定程度上促进热解炉内的传热,增加煤的导热系数;气体温度一定,且小于热解终温时,增大气体流量450~500℃时的热解时间会增加。     

热参数泵吸附床层中非稳态传热的研究

对热参数泵吸附分离床层中的非稳态传热问题进行了理论分析及实验测定,求出了实验范围内的有效导热系数,并给出了从传热角度计算热参数泵吸附分离过程的循环周期时间的关系式.用导出的模型及求出的参数计算出来的温度分布与实测值符合良好.     

Investigation into gas-solid heat transfer in a cryogenic vibrated fluidised bed

Experiments were carried out in a cryogenic vibrated fluidised bed to investigate the heat transfer between gas and rubber particles obtained from discarded tyres. The effects of parameters such as bed layer thickness and gas flow rate on the gas-solid heat transfer were investigated, and a heat transfer correlation obtained by regressing the experimental data. Theoretical analysis based on radial thermal conductivity indicated that higher heat transfer efficiency could be obtained by the use of a fluidised bed rather than a fixed bed or a moving bed, especially for rubber particles having low thermal conductivity under cryogenic conditions. A numerical modelling was developed, based on assumptions of the movement of the particles and the vibrating bed plate, using a unique method of regarding particles as the source term in the energy equation. Computational results from the modelling showed good agreement with the experimental data.     

Tubular reactor design—I Two dimensional model

Conservation equations for a packed tubular reactor are modelled using a radially varying axial velocity, radial diffusivity and radial thermal conductivity. Radial diffusivity and thermal conductivity profiles are obtained from relations presented in this work. Instead of using a wall heat transfer coefficient, the model accounts for the higher resistance to heat flow near the reactor wall by using a lower value of the thermal conductivity. Axial diffusion is not included in the bulk of the bed, but its effect on the inlet temperature and conversion profiles are accounted for by considering axial diffusion in the pre-reaction zone.The two partial differential equations are converted into ordinary differential equations by using orthogonal collocation in the radial direction. The conventional orthogonal collocation method is modified by adding balance equations at the center of the tube, so as to improve the prediction of hot spot temperature.The model was applied to the sulfur dioxide reactor of Schuler et al. The results agreed quite well with the experimental data without the need for adjustment of parameters or constants.     

ESTIMATION OF FIXED BED HEAT TRANSFER PARAMETERS WITH ORTHOGONAL COLLOCATION

Two heat transfer parameters in the fixed bed,radial effective conductiviw k_(er),and wall heat transfer coefficient h_ware estimated by using the method of orthogonal collocation and non-linear least square.The temperatures at forty collo-cation points distributed along the radial direction are measured simultaneously by means of multiehannel data logger.Theeffects of bed height,Re_p,d_t/d_p,gas inlet temperature and wall temperature on k_(er)and h_w are studied.The results indicatethat the effect of gas inlet temperature and wall temperature is negligible.Bed height will only influence the parameter es-timations in shallow bed and at low Re_p.Both k_(er)and h_w tend to reach a limit with increasing bed height.The asymptoticbed height which is independent of d_p is about 0.5 m,while the asymptotic values of k_(er)and h_w increase with d_p.The pa-rameters obtained with the wall being heated are about 10% lower than those with the wall being cooled.k_(er),h_w and stag-nant contribution terms k_(er)and h_w are all related to dp·k_(er)and h_w estimated at the asymptotic bed height are correlated bythe following equations:k_(er)=0.199+0.015 d_t/d_p+0.0020/(1+14.15(d_p/d_t)~2)Re_ph_w=33.4+4.23d_t/d_p+0.333/(1+8.54(d_p/d_t)~2)Re_p(5.5<d_t/d_p<13)(100<Re_p<500)     

填充床层热之传导——床层之温度分布

作者用低导热系数(包括玻璃、磁)的球体、圆柱体、环柱体与高导热系数(包括铜、铁的球体,圆柱体为填充物,以空气为传热介质,使其在管径为81毫米之填充床层内冷却,改变流体流量,床层高度及填充物大小,通过试验测出在不同的条件下床层的径向温度分布,并应用积分法、直流电模拟计算法及图解法求得床层的有效导热系数及管壁薄膜传热系数.在试验范围:低导热系数填充物D_P/D_t自0.074—0.254;高导热系数填充物D_p/D_t自0.12—0.2,L/D_t自5—15,Re汇数自130—1400,即直线速度自0.5—1.6公尺/分,若以床层进出口平均温度之数学平均值为定性温度,则床层之有效导热系数及管壁薄膜传热系数可分别归纳于下式:低导热系数填充物:K_e=0.182(D_t/D_p)~(0.45)Re~(0.75),h_w=65e~(-4)(D_p/D_t)(K/D_t)((D_t/L))~(0.2)Re~(0.4)高导热系数填充物:K_e=0.3k(D_t/D_p)~(0.6)Re~(0.72),h_w=5.1(K/D_t)(D_t/D_p)~(0.8)(D_t/L)~(0.1)Re~(0.46)填充物形状对K_e及h_w的影响,仅需将D_p用 D’_p代替,同时把K_e式中之常数0182及03各改为0.22及0.38即可.直流电模拟计算法系利用电压表示温度,电阻表示传热阻力,电流表示热的流动,是简单的模拟计算机的一种,它在近代工程上的应用日渐广泛,有了传热数据应用它来求床层的温度分布异常方便.     

Heat transfer of gas flow through a packed bed

This paper reports an experimental study of both the transient and steady-state heat transfer behaviour of a gas flowing through a packed bed under the constant wall temperature conditions. Effective thermal conductivities and convective heat transfer coefficient are derived based on the steady-state measurements and the two-dimensional axial dispersion plug flow (2DADPF) model. The results reveal a large temperature drop at the wall region and the temperature drop depends on the axial distance from the inlet. The 2DADPF model predicts the axial temperature distribution fairly well, but the prediction is poor for the radial temperature distribution. Length-dependent behaviour of the effective heat transfer parameters and non-uniform flow behaviour are proposed to be responsible. A comparison with previously published correlations and data in the literature shows that the relationships proposed by Bunnell et al. and Demirel et al. agree well with the measured effective radial thermal conductivity, whereas the wall-fluid heat transfer coefficient is better represented by the Li-Finlayson correlation.     

柱形流化床传热特性的数值模拟

对Shedid等搭建的圆柱体流化床采用欧拉?欧拉法进行三维数值模拟,考察了颗粒球形度、表观进气速度和床料初始堆积高度对流化床内垂直加热壁面与流动床料之间对流传热特性的影响,采用有效导热系数分别计算气相和固相的对流传热系数。结果表明,随表观进气速度增大,流化床内颗粒物料湍流运动加剧,加热壁面平均温度和流体平均温度下降,壁面流体间传热平均温度差减小,壁面流体间对流传热系数增大;随初始床料高度增加,流化床内颗粒与加热壁面的接触面积增大,导致固相平均对流传热系数增大。     

Wall-to-bed heat transfer in liquid—solid and gas—liquid—solid fluidized beds part II: Gas—liquid—solid fluidized beds

Wall-to-bed heat transfer in gas—liquid—solid fluidized beds with a cocurrent upflow was analyzed on the basis of a series thermal resistance model. The effective radial thermal conductivity and the apparent wall heat transfer coefficient were determined over a wide range of experimental conditions. The behavior of the effective thermal conductivity strongly depends on the flow mode for the three-phase fluidized bed, directly indicating the trend of the radial liquid mixing. The modified Peclet number for the radial thermal diffusivity takes on a minimum with respect to the liquid velocity in a manner similar to that in a liquid—solid fluidized bed, but the value of the modified Peclet number decreases significantly with gas velocity. The apparent wall heat transfer coefficient can be correlated well with a Colburn type equation which at zero gas velocity reduces to the same equation as that proposed for liquid—solid fluidization, as follows: j′_H = 0.137 Re′_l.g^?0.271