非木材制浆技术的未来

目前,非木浆厂已能采用现代木浆厂的最先进技术。泵送、筛选、洗涤、漂白等可在更高浆浓下运行,减少了新鲜水用量和废水量。最新安装的世界上最大的麦草浆和蔗渣浆生产线都采用了基于木材制浆的技术,包括TwinRollTM压榨、氧脱木素和无元素氯（ECF）漂白。但近2年的调查发现非木浆生产停滞,其中一个主要原因就是大量非木浆厂没有蒸煮废液回收系统,或极少量有蒸煮废液回收的小型工厂已被关闭。同时,非木材制浆的最大问题仍有待解决,即溶解在蒸煮液中的高浓硅化合物会给蒸发和新鲜蒸煮液再制备带来一系列问题。一个新的工艺概念FreeFiberTM是通过限制硅在蒸煮液中的溶解解决硅干扰问题。FreeFiberTM蒸煮中以气相乙醇作为加热介质;以碳酸钠作为碱源,无需苛化;纸浆可以漂到非常高的白度,而且纸浆强度性能可以与传统碱法纸浆相媲美。     

Generalized-α scheme in the PFEM for velocity-pressure and displacement-pressure formulations of the incompressible Navier–Stokes equations

Despite the increasing use of the particle finite element method (PFEM) in fluid flow simulation and the outstanding success of the Generalized-$\alpha$ (GA) time integration method, very little discussion has been devoted to their combined performance. This work aims to contribute in this regard by addressing three main aspects. First, it includes a detailed implementation analysis of the GA method in PFEM. The work recognizes and compares different implementation approaches from the literature, which differ mainly in the terms that are $\alpha$-interpolated (state variables or forces of momentum equation) and the type of treatment for the pressure in the time integration scheme. Second, the work compares the performance of the GA method against the Backward Euler and Newmark schemes for the solution of the incompressible Navier–Stokes equations. Third, the study is enriched by considering not only the classical velocity-pressure formulation but also the displacement-pressure formulation that is gaining interest in the fluid-structure interaction field. The work is carried out using various 2D and 3D benchmark problems such as the fluid sloshing, the solitary wave propagation, the flow around a cylinder, and the collapse of a cylindrical water column.