Cheng Hai Xu

Virtual Design and Structural Optimization of Dry Twin Screw Vacuum Pump with a New Rotor Profile

Twin screw vacuum pump is an important kind of dry vacuum pump, which is widely used in the oil-free vacuum system. The design of the screw rotor profile directly influences the working performance and manufacture cost of the screw pumps. In this paper, a new rotor profile for twin screw vacuum pump is introduced which is comprised of the cycloid curve, the dedendum circle arc, the involute curve and the addendum circle arc. The processes of three-dimensional modeling, motion simulation, interference checking and structural optimization for twin screw vacuum pumps are studied by means of Solidworks software. The works provide theoretical basis for optimal designing and reference for test prototype manufacturing. The results showed the performance of the vacuum pump according with the designer’s intention.

Effects of Substrate Temperature on ZAO Thin Film Prepared by DC Reactive Magnetron Sputtering

The effects of substrate temperature on the resistivity and transmittance of ZAO thin films prepared by DC magnetron reactive sputtering have been investigated. The properties of the samples have been analyzed through Hall effect, X-ray diffraction and SEM. The results show that carrier concentration, Hall mobility and crystallinity of the films depend obviously on the deposition temperature. The film deposited at the range 200-250°C has lower resistivity and higher transmittance.

Properties of Al Doped ZnO Thin films by DC Reaction Magnetron Sputtering

The high quality ZAO thin films were successfully produced by DC reaction magnetron sputtering technology. The XRD，electrical and optical properties of films are particular investigated. The results show that ZAO films are polycrystalline hexagonal wurtzite structure，and Al2O3 crystal phase are not found. At the same time，the high quality ZAO films with the minimum resistivity of 4.5x10-4Ω•㎝, the transmittance in visible region above 80% and the reflectivity in IR region above 70% are gained.

Performance Study of Storage-Type Domestic Electrical Water-Heaters with Wedged Inlet: Unsteady Water Discharge Rate

The unsteady water discharge rate on performance of storage-type domestic electrical water-heaters with wedged inlet was studied by computer fluid dynamics simulation (CFD). The results were compared with those of conventional design EWHs having the same tank size. The heater performance is characterized the discharge efficiency, extraction efficiency and fraction of heat recoverable. The water draw-off temperature profile of steady and unsteady water discharge rate has nothing difference for wedged inlet structure, both curve was overlapped. The almost the same energy utility efficiency was gotten both steady and unsteady discharge rate for wedged inlet structure. The obviously difference of water draw-off temperature profile was shown for conventional inlet structure. Water draw-off temperature profile of unsteady discharge rate was decreased faster than steady discharge rate. The energy utility efficiency of unsteady discharge rate was also lower than steady discharge rate. The results were shown that the wedged inlet structure heater has excellent performance for energy utility efficiency under unsteady discharge rate.

Performance Estimate for Design of Storage-Type Domestic Electrical Water-Heaters Based on the CFD Simulation

The 3D physical model of the electrical water heater was built. The water-heater performance of two kind structures was resolved by computer fluid dynamics simulation (CFD). The heater performance is characterized by a new method rather than that the discharge efficiency, extraction efficiency and fraction of heat recoverable. The new method is based on the constant discharge water temperature and rate for end user, 5L/min and 43°C that include the hot water from EWH and cold water from outside EWH. But the water discharge rate from EWH was variable as the water temperature discharge from EWH was variable. The discharge efficiency of conventional EWH was 79.312%, and the discharge efficiency of improved EWH was 84.97%. Compared with the traditional method, it is more close to the user using reality condition.

The Simulation Study on 3D Gas Flow Field and Structure Improvement with Tower Continuous Vacuum Dryer

The 3D gas flow field, including the gas pressure and gas velocity was studied by computer fluid dynamics simulation (CFD). The tower continuous vacuum dryer’s structure was improved and the pumping gas sketch was also optimized. The model was resoled by standard turbulence model. The porous medium zone was adopted to the material zone. The Darcy law, Ergun equation and porous medium interface jump boundary condition was applied. The effect of the drying intensity, vacuum pumping pipes setting and vacuum degree of gas outlet was analyzed. The result shows that the pressure of gas outlet should be maintained lower at 8000 Pa, and the pressure of grain inlet and outlet should be maintained at 9000 Pa. The vacuum pumping pipes should be set at the bottom of last drying stage of the drying room in order to improve the gas flowing direction, and to improve vacuum performance. The pressure and velocity of gas along height of dryer is not the main effect factor of drying quality. On the top of each drying stage of the vacuum dryer, two horny pumping pipelines were set. It has good velocity uniformity, but more simple compared with three horny pumping pipelines.

The Profile and Structure Design on Trochoidal Vacuum Pump

Vacuum pump plays an important role in vacuum applications. The rotor and stator profile is one of the key factors for improving pump performance. In this paper, the traditional trochoidal vacuum pump that the rotor and stator profile both are trochoidal equation was introduced. The profile of trochoidal vacuum pump with two angle rotor was studied. In order to simply the design and manufacture, the rotor profile was substituted by the arc curve. The design parameter and performance was deducted on slenderness ratio. The slenderness ratio should larger than 4, otherwise the down part of the stator profile would be dent to upper. When slenderness ratio is 4, the utilization ratio of volume would be getting the maximum value, 0.5851942. The utilization ratio of volume was decreased with the slenderness ratio increased.

The Strength Analysis of Tower Vacuum Dryer Structural

Tower vacuum dryer room is the key device for continuous vacuum dryer. In order to lower the cost of manufacture, the wall of dryer should be thinner. But as the pressure container, it must have the well intensity while operating. Because its complex structure, the simple calculation is not enough, the finite element analysis in intensity control was carried out. The model of vacuum dryer was built, the intensity of general primary membrane stress and the intensity of primary bending stress was picked-up on the max stress intensity point through the path of wall thickness. Accord with JB4732-1995, the structural strength was fulfilled the requirement.

Performance Study of Structure Improvement Design for Storage-Type Domestic Electrical Water-Heaters Based on the CFD Simulation

The 3D physical model with two different structure of the electrical water heater was built. The performance of water heater was studied by computer fluid dynamics simulation (CFD). The heater performance is characterized the discharge efficiency, extraction efficiency and fraction of heat recoverable. It was 73.7%, 45% and 49.8% respectively with conventional structure, and it was 81.1%, 54.1% and 59.6% respectively of improved structure with discharge rate was 5L/min when all initial hot water temperature was 90°C. The temperature distribution of different discharged stage was also disclosure. The water inner the water tank of improved structure has the better thermal stratification than traditional structure. It was also agreed with the water heat performance.

VACUUM DRYING CHARACTERISTICS OF MAIZE: KINETICS, CRACKING AND GERMINATION QUALITY

Drying kinetics of China maize dried in a laboratory scale vacuum dryer was studied. The effect of drying temperature, vacuum degree, bed height and initial moisture on maize cracking and germination rate was presented. Characteristic drying rate curves exhibited mainly falling rate period, with an induction periodic, but without the constant rate period. A custom-made light box was built to visually analyze the cracking on the surface of maize. Maize cracking was lower than 10% just after drying at 50 -90 . But the cracking at all temperature was higher after drying for 24h. The germination rate reduced with drying temperature increasing. The initial drying rate (induction period drying rate) at higher vacuum degree was higher, but the vacuum degree did not significantly affect the falling rate period. The total drying time and total drying rate almost was the same at different vacuum degree of the same temperature. Vacuum degree also did not significantly affect the cracking percent and germination rate. The cracking and germination rate of initial moisture25% were better than the initial moisture 37% after vacuum drying. The bed height has little effect on cracking.