医用大型蒸汽灭菌器蒸汽“冷点”分布特性研究

医用大型灭菌器承担着医疗器械的消毒灭菌工作,关系到患者的生命安全。医疗器械灭菌过程内部的温度,尤其是局部的“冷点”温度的监测对灭菌质量有着决定性的影响。本文采用实验和数值模拟方法对医用大型灭菌器内内部冷点分布情况进行研究,为医用大型蒸汽灭菌器的计量校准和溯源提供技术依据。研究发现高温灭菌室内温度并非全部均匀分布,以点盖全的监测手段在医院灭菌监控中存在不足,单靠某一测点温度来维持除菌时间并不可靠。灭菌过程中蒸汽的流速对灭菌室内“冷点”分布极其重要,随着入口蒸汽速度的增加,温度的最大值与最小值之差逐渐减小,局部低温区域将逐渐消失;对于非满载工况,室内温度变化相差较大,传统冷点测试方法不适用。

A Perspective on Rheological Studies of Gas Hydrate Slurry Properties

Gas hydrates are solid inclusion compounds that are composed of a three-dimensional hydrogen-bonded network of water cages that can trap small gas molecules, such as methane and carbon dioxide. Understanding the rheological properties of gas hydrate crystals in solution can he critical in a number of energy applications, including the transportation of natural gas in suhsea and onshore operations, as well as technological applications for gas separation, desalination, or sequestration. A number of exper- imental and modeling studies have been done on hydrate slurry rheology; however, the link between theory and experiment is not well-defined. This article provides a review on the current state of the art of hydrate slurry viscosity measurements from high- and low-pressure rheometer studies and high-pressure flowloops over a range of different sub-cooling （ATsub = TequiI Texp） and fluid conditions, including for water and oil continuous systems. The theoretical models that have been developed to describe the gas hydrate slurry relative viscosity are also reviewed. Perspectives＇ linkage between the experiments and theory is also discussed.

Rheological characterization of A201 aluminum alloy

The thermodynamic characterization as well as the rheological characterization of the A201 alloy were conducted.Thermodynamic simulations (CALPHAD method) and calorimetric experiments were performed to determine the solidus and liquidus temperatures, the melting range and the sensitivity of the solid fraction at the thixoforming temperatures.The rheology of aluminium alloy A201 was examined using a high temperature Searle rheometer.The flow behaviour was analyzed with concentric cylinders of graphite to avoid chemical interactions with the liquid or semi-solid aluminium.The rotational body was grooved to prevent a phenomenon called wall slippage.Continuous cooling experiment was used to observe the shear rate effects on the flow behaviour.It can be seen that the viscosity level decreases at higher shear rates.Shear rate jump experiment was carried out to evaluate the steady state flow curve within the analyzed shear rate range from 60 s-1 to 260 s-1.It is found that the power law indexes are-1.35 and-1.49 for 35% and 45% solid fraction, respectively.Finally, some mechanical property data of as-cast and as-thixoformed A201 alloy are included indicating the potential for high strength applications.

Computational Study on Interaction Between Swimming Fish and Drifting Vortices Behind the Cylinder

To predict the flow evolution of fish swimming problems,a flow solver based on the immersed boundary lattice Boltzmann method is developed.A flexible iterative algorithm based on the framework of implicit boundary force correction is used to save the computational cost and memory,and the momentum forcing is described by a simple direct force formula without complicated integral calculation when the velocity correction at the boundary node is determined.With the presented flow solver,the hydrodynamic interaction between the fish-induced dynamic stall vortices and the incoming vortices in unsteady flow is analyzed.Numerical simulation results unveil the mechanism of fish exploiting vortices to enhance their own hydrodynamic performances.The superior swimming performances originate from the relative movement between the“merged vortex”and the locomotion of the fishtail,which is controlled by the phase difference.Formation conditions of the“merged vortex”become the key factor for fish to exploit vortices to improve their swimming performance.We further discuss the effect of the principal components of locomotion.From the results,we conclude that lateral translation plays a crucial role in propulsion while body undulation in tandem with rotation and head motion reduce the locomotor cost.

Simplified Correlation Equations of Heat Transfer Coefficient during Phase Change for Flow inside Tubes

In this work, the easy to use, simple and direct equations were formulated and tested. These equations can be used to calculate the mean values of the heat transfer coefficients of inside tube flow during phase change. Analytical and experimental methods were used to correlate these equations. Two different forms were used, one for evaporation case and the other for condensation case. Carbon dioxide, CO2, was used as case study. Correlated values of the mean heat transfer coefficients （hcor,.） were compared with the experimental results （he^e） and with other published result, a good agreement was noticed. The resulted correlations can be used to simplify the design and performance studies of both condensers and evaporators.

Probability analysis of contact forces in quasi-solid-liquid phase transition of granular shear flow

The quasi-solid-liquid phase transition exists widely in different fields,and attracts more attention due to its instinctive mechanism.The structure of force chains is an important factor to describe the phase transition properties.In this study,the discrete element model(DEM) is adopted to simulate a simple granular shear flow with period boundary condition on micro scale.The quasi-solid-liquid phase transition is obtained under various volume fractions and shear rates.Based on the DEM results,the probability distribution functions of the inter-particle contact force are obtained in different shear flow phases.The normal,tangential and total contact forces have the same distributions.The distribution can be fitted as the exponential function for the liquid-like phase,and as the Weibull function for the solid-like phase.To describe the progressive evolution of the force distribution in phase transition,we use the Weibull function and Corwin-Ngan function,respectively.Both of them can determine the probability distributions in different phases and the Weibull function shows more reasonable results.Finally,the force distributions are discussed to explain the characteristics of the force chain in the phase transition of granular shear flow.The distribution of the contact force is an indicator to determine the flow phase of granular materials.With the discussions on the statistical properties of the force chain,the phase transition of granular matter can be well understood.