Analysis of makeup air in a natural smoke vent system in a tall space using numerical simulation and Schlieren technique

Purpose The purpose of this paper is to analyze the phenomenon of makeup effect using numerical simulation and model experiments on seven different natural smoke extraction patterns of tall space. Airflow distribution and heat accumulation phenomenon in different cases are compared. The natural smoke exhaust system for tall spaces has many advantages, including low cost, no power and low maintenance cost. It is more advantageous than the mechanical type of exhaust. However, the internal air distribution is complicated since the large span spatial character. Effective and correct verification method is very important for the analysis of flow fields in tall spaces. Design/methodology/approach This study used fire dynamics simulator (FDS) software to simulate the fire scene. The model experiments are conducted to determine if the numerical simulation results are reasonable. A single-mirror Schlieren system, including an 838 (H) × 736 mm (W) square concave mirror, as well as the focal length of 3,100 mm was adopted to record the dynamic flow of hot gas. Six smokeless candles were burned in a 1/12.5 model in experiments to record the distribution of inflow, accumulation and outflow of airflow in the space. In addition, the thermocouple lines were mounted in the model for temperature measurement. Findings The results of numerical simulation and model experiments have proved that makeup air has a significant effect on the effectiveness of a natural smoke vent system. Larger areas of smoke vents will produce more heat accumulation phenomenon. In this study, the air inlet and vent installed on the same side have a better heat removal effect. Moreover, Schlieren photography technique is proved to be an accurate measurement method to record the dynamic flow of hot air immediately, directly and accurately. The dynamic flow behavior of hot gas in the model has been visualized in this paper. Originality/value At present, there is no examination method other than checking the smoke vent area to validate the effectiveness of a natural smoke vent system in Taiwan, as well as no requirements regarding the makeup inlet. The effect of makeup air in generating the effective push-pull phenomenon of airflow has been analyzed. In addition, the post-combustion hot gas distributions were visualized by using Schlieren photography technology in the model space, compared with the FDS simulation result and thermocouple recorded temperature. A verification method in the model experiments is established to determine if the numerical simulation results are reasonable.

Organize Method on Platform of Machine Automation Control System

In the process of mechanical automation, due to the development of drive equipment in diversification, miniaturization, digitalization, intellectualization and the development of sensor in miniaturization, digitalization, visualization, on the one hand, automation mechanical structure become simple, on the other hand, with the increase of the dependence on control equipment for automation machinery, an automated machinery needs many kinds of control mode and means to complete the production. With the improvement of mechanical motion complexity, there will appear accumulation phenomenon of control equipment, in addition, in order to complete the data transfer between all kinds of control equipments, each control equipment need to build all kinds of communication protocol and special cables to connect. In order to solve the "accumulation" phenomenon, control equipment manufacturers competing to launch the new scheme. In this paper, a control project based on the control products of Mitsubishi electric company was proposed, which illustrates the change of the control way of mechanical automation. Once you master the control platform of these companies, will be able to build or integrate corresponding control system.

Simulation on Stress Relaxation of DD3 Nickel-Based Single Crystal Superalloy Based on Micro-Cell Model

Tension-torsion experiments at 680°C and 850°C on thin-wall tube specimens of DD3 nickel-based single crystal superalloys were successfully completed. It shows that specimens have stress relaxation obviously and inelastic deformation accumulation phenomenon with different crystal orientation under asymmetric cyclic loadings. Based on the microstructure characteristics of nickel-based single crystal superalloys, a two-phase multi-cell microscopic mechanical model was established by finite element method to simulate the test with displacement. Numerical simulation studies showed that the matrix phase appeared plastic deformation accumulation at first and resulted in low cycle fatigue damage, but stress distortion occurred on the boundary with a single cell model under tension-torsion displacement loading, which is not consistent with experimental results. While using multi-cell model can avoid this phenomenon, it could be better to simulate stress relaxation behavior under asymmetric cyclic loading at elevated temperature and to study on stress weaken damage for single crystal superalloys.

Research on Technology of Gas Drainage in Highly Gassy and Thin Coal Seams with Long Wall Coal Face on the Strike

Based on the Feng Huang Coalmine 1402# coalface, applying the vertical three zones of overlying strata theory and O-ring theory, this paper discusses the migration paths of pressure-relieved gas in stope and the abundant gas region. By means of optimizing the roof crossing borehole method and high-position borehole in gob method, the gas drainage efficiency and extraction concentration have been improved, the gas emission arising from coalface has been reduced, and the gas accumulation phenomenon has been eliminated, which verifies the accuracy of this research and realizes the safe and efficient gas extraction goal as well.