Design and evaluation of a Laval-type supersonic atomizer for low-pressure gas atomization of molten metals

A Laval-type supersonic gas atomizer was designed for low-pressure gas atomization of molten metals. The principal design ob-jectives were to produce small-particle uniform powders at lower operating pressures by improving the gas inlet and outlet structures and op-timizing structural parameters. A computational fluid flow model was developed to study the flow field characteristics of the designed atom-izer. Simulation results show that the maximum gas velocity in the atomization zone can reach 440 m＆#183;s-1;this value is independent of the atomization gas pressure P0 when P0〉0.7 MPa. When P0=1.1 MPa, the aspiration pressure at the tip of the delivery tube reaches a mini-mum, indicating that the atomizer can attain the best atomization efficiency at a relatively low atomization pressure. In addition, atomization experiments with pure tin at P0=1.0 MPa and with 7055Al alloy at P0=0.8 and 0.4 MPa were conducted to evaluate the atomization capa-bility of the designed atomizer. Nearly spherical powders were obtained with the mass median diameters of 28.6, 43.4, and 63.5μm, respec-tively. Compared with commonly used atomizers, the designed Laval-type atomizer has a better low-pressure gas atomization capability.

Design and Atomization Characteristic of Laval-style Annular Slot Nozzle

Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.

Experimental Research of Electronic Devices Thermal Control Using Metallic Phase Change Materials

A Phase-change thermal control unit( PTCU) filled with metallic phase change material( PCM) Bismuth alloy for electric devices thermal protection was developed and investigated experimentally. The PTCU filled with PCM was designed and manufactured. Resistance heating components( RCHs) produced 1 W,3 W, 5 W,7W,and 10 W for simulating heat generation of electronic devices. At various heating power levels,the performance of PTCU were tested during heating period and one duty cycle period. The experimental results show that the PTCU delays RCH reaching the maximum operating temperature. Also,a numerical model was developed to enable interpretation of experimental results and to perform parametric studies. The results confirmed that the PTCU is suitable for electric devices thermal control.

Effect of general anesthesia combined with epidural anesthesia on stress response, inflammatory reaction and coagulation in patients with colon cancer

Objective: To investigate the effects of general anesthesia combined with epidural anesthesia on stress response, inflammation level and coagulation function in patients undergoing laparoscopic colon cancer resection during intraoperative and postoperative. Methods: A total of 98 patients undergoing colon cancer radical surgery in our hospital from August 2015 to August 2017 were randomly divided into control group and observation group with 49 cases in each group. In the control group, systemic intravenous anesthesia was used;and in the observation group, a systemic intravenous anesthesia combined epidural anesthesia was used. Serum of venous blood was collected from patients before anaesthesia, 30 min after anesthesia, and two hours after operation to detect stress response indexes, such as adreno-cortico-tropic-hormone (ACTH), adrenaline (AD), norepinephrine (NE) and cortisol (Cor), and inflammatory response indexes, such as tumor necrosis factor-α (TNF-α), procalcitonin (PCT) and C-reaction protein (CRP). Venous blood was collected at the same time points for coagulation testing. Functional indicators such as prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT) and fibrinogen (FBG) were detected. Results: There was no significant difference in the level of each index between the two groups before anesthesia. At 30 minutes after anesthesia and at 2 hours after operation, the stress response indicators and inflammatory response indicators in the observation group were lower than those in the control group at the same time points;apart of the blood coagulation function indexes (PT, APTT and TT) in the observation group were higher than the corresponding indicators of the control group at the same time points, but the FBG content in the observation group was lower than that of the control group at the same time points, and these differences were significant. Conclusion: The method of general anesthesia combined with epidural anesthesia can effectively reduce the stress and inflammatory reaction during and after operation of laparoscopic colon cancer resection, and reduce the abnormal coagulation function as well as the blood hypercoagulability.