EXPERIMENTAL STUDY ON AIR FLOW FIELD CHARACTERISTICS OF SUCTION METERING DEVICE

The vacuum seed metering device absorbs seeds by using the negative pressure generated by vacuum air flow. Therefore, it is of great significance to study the variation law of pyrolysis gas flow field to improve its seed metering performance. In this paper, the common disc and composite disc were selected as the research objects and tested on the indoor test-bed. The negative pressure was measured by U-type barometer, and the effects of fan speed, suction hole size, seed hole structure and air chamber thickness on the air flow field were studied. Firstly, the influence of fan rotation frequency on vacuum chamber negative pressure is studied, and the variation law of negative pressure in vacuum chamber and fan port of common disc and composite disc under the same frequency is compared. Secondly, the suction holes in the vacuum chamber were numbered, the negative pressure distribution of the suction holes was measured, and the influence of the number and diameter of the suction holes on the negative pressure of the vacuum chamber was studied. Finally, the negative pressure was measured at the distance of 0 to 10 mm from the suction hole to study the effect of seed hole structure on the air flow field. Moreover, increase the additional thickness of the vacuum chamber from 0 to 40 mm to study the influence of the chamber thickness on the distribution of the gas flow field. This paper makes a comprehensive experimental analysis on the influencing factors of air flow field of air suction seed metering device, necessary for future design of air suction seed metering device.

Flow field optimizing study of low temperature economizer in a coal-fired boiler

The complex structure of double inlet gas flue has a significant influence on gas flow field distribution in a 1000MW coal-fired boiler’s low temperature economizer. In order to optimize gas flow field of the low temperature economizer with double inlet gas flues and reduce its failure rate, this paper presents a flow field simulation of the low temperature economizer based on the computational fluid dynamics (CFD). This numerical simulation was operated by using porous media model instead of the complex structure inside heat exchanger and the standard k-epsilon model. Velocity contours of a same vertical cross-section inside of inlet gas flue of the heat exchange zone in different numerical simulations were evaluated by the evaluation standard of RSM. The results of numerical simulation show that the main reasons for uneven distribution of flow field in economizer and its inlet gas flues are unequal diameter of flue elbow and straight flue, unreasonable setting of guide plate and diffusion flue elbow. After making structural optimization of the low temperature economizer such as equalizing elbow to the straight flue diameter and setting the guide plate reasonably, the flow field in the low temperature economizer and its flues are obviously improved.

Finite Element Analysis and Experimental Study of Atomized Gas Flow Field in Spray Forming

<p align="justify">During the spray forming process of die steel, the gas flow field of nozzle atomizer has an important influence on the atomization effect of metal solution and the shape and performance of deposited billet. In this paper, the finite element analysis method was used to study the flow field distribution of the annular slot type restricted nozzle. The results showed that the negative pressure area was formed at the front of the atomizing gas outlet of the nozzle; the negative pressure area was enlarged and the negative pressure value was increased with the increase of the extending position of the liquid guide pipe and the atomizing pressure; when the atomizing pressure was 0.5MPa and the extending position of the liquid guide pipe was 7mm, the negative pressure value of the front of the liquid guide pipe could reach-38650Pa and the gas flow rate could reach 191.4m/s; the back-injection could be effectively avoided by optimizing the appropriate process parameters. And the damage of atomizing nozzle could be reduced.</p><p align="justify"> </p>