Microstructural transformations of heat affected zones in duplex steel welded joints

The influence of the welding thermal conditions exemplified by heat input and heat treatment after welding on the structure of the heat affected zone (HAZ) UNS S31803 has been analysed. The post weld treatment was used to create the precisely defined thermal conditions for the decomposition of primary phases in the HAZ, by a multi-layer welding thermal cycle stimulation. Detailed analyses of the microstructure and chemical composition of the phases in the different post welded conditions were performed by scanning electron microscopy (SEM) combined with energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM). Three types of secondary precipitates have been observed: secondary austenite (γ₂), carbides: M₂₃C₆ and M₇C₃. The dependence of the secondary austenite volume fraction and morphology in the HAZ on thermal cycle have been interpreted. The eutectoid decomposition of the primary phases in the analysed thermal conditions was confirmed.     

NEURAL NETS SPEED FLOW CALCULATION

Neural Nets Successfully Solve Complex Fluid Flow Problem. Much research is being done in the area of neural networks, and industry is actively seeking successful application to real world problems. We describe here a successful application. We have used neural networks to model complex coolant flow patterns, such as those encountered in design of hypersonic aircraft. Previous calculation methods, while reasonably accurate, are iterative and extremely time consuming. Our new approach uses a hierarchical neural network architecture to model coolant flow distribution in multiple heat exchanger panels. This method is direct, fast, and accurate.     

Process heat integration of a heavy crude hydrotreatment plant

The present paper focuses on the study of process alternatives for heat integration of a heavy crude oil hydrotreatment plant. Experimental information obtained from a pilot scale, kinetics and reactor modeling tools, and a commercial process simulator were employed to develop mass and energy balances. Four study cases, which employ a combination of quenching and heat exchangers, were identified and evaluated. The results indicated that the case with two quenches with hydrogen and three heat exchangers is the best process heat integration (PHI) option from an energetic point of view.     

Thermal Generation of Residual Stress Fields for Purpose of Distortion Minimization

Thermal treatments of steel components with the goal of hardening often result in distortion by releasing the residual stresses which were brought into the specimen during the preceding processing steps. The goal of the presented work is the minimization of this distortion. By generating definite residual stress fields and investigating the resulting distortion, the distortion mechanism can be observed in detail. A flexible and reproducible way to generate such residual stress fields inside a specimen is by means of local thermal treatment with a laser beam. Computer simulations as well as experiments were carried out using an idealized tooth of a gearwheel (finger sample) as a model system. The deformation of the samples due to the laser heat treatment and the stress fields generated inside the samples were determined with respect to different process parameters.     

Heat transfer and flow of He II in narrow channels

Heat transfer and fluid flow of He II in a long, narrow channel connected to a bath that supplies a constant supply of heat have been investigated by numerical simulations by using the simplified model of Kitamura et al. [Cryogenics 37 (1) (1997) 1]. Such channels are used to cool compact, stable, low-temperature magnets. The fluid flow is driven by natural convection and the mutual friction between the normal fluid and the superfluid.In this model, the thermomechanical effect and the Goter-Mellink mutual friction balance each other. A consequence of this balance is that the velocity and temperature distributions of He II can be characterized by a dimensionless, dependent parameter equal to the ratio of the fluid speeds of internal convection to the total fluid flow. After a sudden application of heat flux, the internal convection dominates over the total fluid flow until the establishment of steady-state temperature gradients. This predicts that the time required to set up the steady-state total fluid flow is proportional to the total heat capacity in the channel.     

现场总线技术的特点及其在热电站的应用

阐述了现场总线技术的含义、主要特点和优点,对比了现场总线控制系统与DCS系统的区别,介绍了现场总线技术在洛阳石化分公司热电站的典型应用及其发展前景。     

Tribological behavior of PTFE nanocomposite films reinforced with carbon nanoparticles

Carbon-based nanoparticles synthesized by heat treatment of nanodiamond in the temperature range of 1000–1900 °C were added to PTFE film to investigate the structural effect of the carbon particles on the tribological properties of PTFE composite film. Carbon-based nanoparticles were prepared by milling with micron sized beads in chemically treated water before their addition to PTFE film. The wear and frictional properties of PTFE nanocomposite film were measured by the ball on plate type wear test. The wear resistance of PTFE film was found to be enhanced by the addition of 2 wt% of carbon nanoparticles. The wear coefficient of PTFE film was decreased from 16.2 to 3.5 × 10⁻⁶ mm³/N m by the addition of carbon-based nanoparticles heat-treated at 1000 °C. Increasing the heating temperature of the nanodiamonds caused the extent of aggregation and particle size to increase. The wear resistance of PTFE nanocomposite film was enhanced by the addition of nanodiamonds heat-treated at 1000 °C, but decreased when the heat treatment temperature of carbon nanoparticles was further increased. Tribological behavior of PTFE nanocomposite films depending on the types of carbon nanoparticles were explained based on the structural, physical and chemical modification of carbon nanoparticles.     

Pulsating Jet Impingement Heat Transfer Enhancement

This article presents results from a numerical study of pulsating jet impingement heat transfer. The motivation is to seek conditions offering a significant enhancement compared to steady flow impingement drying. The CFD software package FLUENT was used for simulating slot-type pulsating jet impingement flows with confinement. The parameter study included velocity amplitude ratio, mean jet velocity, and pulsation frequency. The distance from nozzle exit to surface was three times the hydraulic diameter of the nozzle. The Reynolds number based on the nozzle hydraulic diameter and jet temperature was 2,460 with a mean jet velocity of 30 m/s, which is the base case of the numerical experiments. Results showed that time-averaged surface heat transfer increased with increasing velocity amplitude for the same mean jet velocity. Large velocity amplitudes helped enhance heat transfer by two mechanisms: high jet velocity during the positive cycle and strong recirculating flows during the negative cycle. For the cases with different mean jet velocities but the same maximum velocity, time-averaged surface heat flux decreased with decreasing mean jet velocity. As for the effects of pulsation frequency, with high-velocity amplitude ratio, time-averaged surface heat fluxes were at the same level regardless of frequency. However, at low-velocity amplitude ratio, high frequency caused stronger recirculating flows resulting in greater heat transfer compared to the cases with a lower frequency.     

二高炉4号热风炉烘炉实践

介绍了二高炉4号热风炉烘炉的特点、前期准备工作、具体操作过程中的注意事项及烘炉后的相关作业。此次生产实践对今后类似情况的热风炉烘炉具有参考价值。     

Convective cooling of supercritical carbon dioxide inside tubes: heat transfer analysis through neural networks

In a previous work, convective heating of carbon dioxide was studied with neural networks (NN), obtaining a totally heuristical heat transfer equation from the direct regression of experimental data. In the present work, the analysis focuses on the cooling process, which has a technical relevance in various applications, as for example in transcritical refrigeration cycles. Heat transfer around the critical zone presents a marked enhancement, that follows the peaks in thermophysical properties like thermal conductivity and heat capacity. Similarly, other properties like density and enthalpy, present a strong variation in narrow temperature intervals around the critical point.This constitutes then a highly non-linear phenomenon, for which it is advisable to use a very flexible function approximator like the NNs. NN models were applied both in terms of dimensionless numbers and of physical quantities, obtaining the two corresponding NN architectures. The choice of the optimal number of neurons in the NN hidden layer is discussed. The NN models are then compared with a recent correlation from literature, for which the validation results present an AAD of 27% and a bias of −26% with an evident prediction shifting. On the other hand the NN models in terms of dimensionless numbers and of physical quantities have AAD and bias of 14% and −4%, and of 7% and −2%, respectively, showing a largely better performance.