Product distribution modelling in the thermal pyrolysis of high density polyethylene

The thermal fast pyrolysis of high density polyethylene (HDPE) has been carried out in a conical spouted bed reactor in the 450-715 degrees C range, and individual products have been monitored with the aim of obtaining kinetic data for the design and simulation of this process at large scale. Kinetic schemes have been proposed in order to explain both the results obtained in the laboratory plant and those obtained in the literature by other authors operating at laboratory and larger scale. Discrimination has been carried out based on the contribution of the variance of model parameters (stepwise regression) to the total variance explained by the model. The models based on that of Westerhout et al. [R.W.J. Westerhout, J. Waanders, W.P.M. Van Swaaij, Recycling of polyethene and polypropene in a novel bench-scale rotating cone reactor by high-temperature pyrolysis. Ind. Eng. Chem. Res. 37 (6) (1998) 2293-2300] do not adequately predict the experimental results, especially those corresponding to aromatics and char, which is probably due to the very short residence times attained in the conical spouted bed and, consequently, to the lower yields of aromatics and char. The model of best fit is the one where polyethylene degrades to give gas, liquid (oil) and wax fractions. Furthermore, the latter undergoes secondary reactions to give liquid and aromatics, which in turn produce more char.     

Dynamic characteristics of combined conical-cylindrical shells

The truncated conical shape having a superimposed top cylindrical cap is widely used as a containment vessel for elevated water tanks. The evaluation of the wind and seismic responses of these tanks requires the knowledge of the dynamic characteristics of the vessels. This study reports the results of the first experimental and numerical investigation conducted to assess the dynamic behaviour of combined conical vessels. Shake table testing is conducted on a small-scale combined conical shell model. The tested specimen is then simulated numerically in a three-dimensional finite element analysis. The numerical model is validated through comparison with experimental results. An extensive parametric study is then conducted using the validated numerical model in order to determine the dynamic characteristics of full-scale combined conical vessels. Equations and charts describing the natural frequencies, the mode shapes and the generalized and effective masses of the vessels are obtained from this parametric study.     

Wind pressures and buckling of cylindrical steel tanks with a conical roof

Tanks with a conical roof are studied in this paper under wind load, for a roof which is supported by rafters and columns. Buckling occurs in the form of deflections in the cylindrical shell and the buckling mode is localized in the windward region. Both bifurcation analysis and geometrically nonlinear analysis have been performed using finite element discretizations of the structure. The wind pressures have been obtained from wind tunnel experiments performed as part of the research, and have been obtained for tank geometries for which information was not previously available. The results show high imperfection sensitivity of tanks with a conical roof, and buckling loads for wind velocities in the same order as those expected to occur in the Caribbean region.     

Experimental and analytical evaluation of the dynamic characteristics of conical shells

Truncated conical shaped shell structures are used in various engineering applications such as components of missiles and spacecrafts and liquid containers for elevated water tanks. The purpose of this study is to evaluate the dynamic characteristics of such type of shell structures when subjected to a transverse dynamic excitation. This paper focuses on conical steel vessels as superstructure of elevated tanks. However, results of the study can be applied to other conical shell applications. The study is conducted experimentally using a shake table device and numerically using an in-house developed shell element model. In the experimental phase, the fundamental frequency and the corresponding mode shape of a small-scale aluminum conical shell model were evaluated. Results of this experiment were used to validate the numerical model by comparing the measured values to those predicted by the model. The analytical study was then extended to evaluate the dynamic characteristics of conical steel tanks covering a wide range of practical dimensions. The study included the case of open and fixed-roof tanks. The performed analyses led to the development of a number of charts that can be used to identify the natural frequency, the mode shapes and the generalized mass and stiffness of conical tanks for both the fundamental and the cos(θ)-modes of vibration. These results would be very useful in assessing the dynamic response of conical tanks when subjected to wind and earthquake loads.     

Cold flow characteristics of a novel bluff body hydrogen burner

The cold flow characteristics of a novel partial premixed bluff body (PPBB) low NO_x burner, capable of operating with hydrogen as well as methane-hydrogen blends, were investigated numerically. The PPBB burner features a frustum shaped conical bluff body generating a flame stabilizing recirculation zone. Fuel is partially premixed via jets in an accelerating cross-flow. Steady-state and transient non-reacting simulations using five different turbulence models, i.e. standard k-ε, realizable k-ε, shear stress transport (SST) k-ω, stress-blended eddy simulation (SBES) and large eddy simulation (LES), were conducted. The simulations were validated against particle image velocimetry (PIV) measurements of an unconfined non-reacting flow. All turbulent models were able to predict the recirculation zone length in good agreement with the experimental data. However, only scale resolving simulations could reproduce velocity magnitudes with sufficient accuracy. Time averaged and instantaneous results from the scale resolving simulation were analysed in order to investigate flow characteristics that are special about the PPBB burner design and of relevance for the combustion process. Two different burner configurations were studied and their effects on the flow field were examined. The recirculation zone volume as well as the entrainment into the wall jet around the bluff body were found to correlate with the elevation of the bluff body relative to the burner throat. Both of these parameters are expected to have a strong impact on the overall NO_x emission, since the near burner region is typically one of the main contributors to the NO_x formation.     

锥形凹模缩口应力场分析与缩口力计算

通过对锥形变形区和自由弯曲区的变形特点分析与应力场数学分析,建立了一种锥形凹模缩口应力场的数学模型和缩口力计算公式。探讨了各因素的影响和制约关系。进行了实验验证。所建模型和公式可用于设计和生产。     

国外塑料异型材挤出设备及技术进展

叙述了近年来国外在异型材挤出整套设备方面的最新进展,介绍了新研制的高速挤出机的特点及异型材挤出技术进展     

Time-series analysis of the characteristic pressure fluctuations in a conical fluidized bed with negative pressure

The negative pressure conical fluidized bed is widely used in the pharmaceutical industry. In this study, experiments based on the negative pressure conical fluidized bed are carried out by changing the material mass and particle size. The pressure fluctuation signals are analyzed by the time and the frequency domain methods. A method for absolutely characterizing the degree of the energy concentration at the main fre-quency is proposed, where the calculation is to divide the original power spectrum by the average signal power. A phenomenon where the gas velocity curve temporarily stops growing is observed when the mate-rial mass is light, and the particle size is small. The standard deviation and kurtosis both rapidly change at the minimum fluidization velocity and thus can be used to determine the flow regime, and the variation rule of the kurtosis is independent of both the material mass and particle size. In the initial fluidization stage, the dominant pressure signal comes from the material movement;with the increase in the gas veloc-ity, the power of a 2.5 Hz signal continues to increase. A method of dividing the main frequency by the aver-age cycle frequency can conveniently determine the fluidized state, and a novel concept called stable fluidized zone proposed in this paper can be obtained. Controlling the gas velocity within the stable flu-idized zone ensures that the fluidized bed consistently remains in a stable fluidized state.     

Differential quadrature solution for the free vibration analysis of laminated conical shells with variable stiffness

The free vibration analysis of laminated conical shells with variable stiffness is presented using the method of differential quadrature (DQ). The stiffness coefficients are assumed to be functions of the circumferential coordinate that may be more close to the realistic applications. The first-order shear deformation shell theory is used to account for the effects of transverse shear deformations. In the DQ method, the governing equations and the corresponding boundary conditions are replaced by a system of simultaneously algebraic equations in terms of the function values of all the sampling points in the whole domain. These equations constitute a well-posed eigenvalue problem where the total number of equations is identical to that of unknowns and they can be solved readily. By vanishing the semivertex angle (α) of the conical shell, we can reduce the formulation of laminated conical shells to that of laminated cylindrical shells of which stiffness coefficients are the constants. Besides, the present formulation is also applicable to the analysis of annular plates by letting α=π/2. Illustrative examples are given to demonstrate the performance of the present DQ method for the analysis of various structures (annular plates, cylindrical shells and conical shells). The discrepancies between the analyses of laminated conical shells considering the constant stiffness and the variable stiffness are mainly concerned.     

基于Solidworks的锥形橡胶弹簧的参数化设计系统开发

介绍了基于Solidworks平台的锥形橡胶弹簧计算机辅助设计,给出在Solidworks平台下实现该橡胶弹簧计算机辅助设计及三维造型的程序和相应实例.