Shi Wei Zhang

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.

A Novel Fiber-Optic Liquid Level Sensor with Adjustable Light Path Based on Principle of Light Refraction

Considering the difficulty to precisely indicate the specified height for transparent or semitransparent thin liquid column, a novel fiber-optic liquid level sensor is reported which remarkably enhances the sensitivity by regulating the external light path based on the principle of light refraction. The structure and working principle of this sensor is introduced. A light path model is developed on the condition that the incident light ray obliquely penetrates the medium in the liquid level indicator. The formulae of deflection angle are deduced. Factors affecting the precision of the sensor are analyzed by means of an example. Finally the feasibility of this novel design is verified by experiments.

Freeze-Drying Investigations of Antlers

In this paper, the vacuum freeze-drying experiments of both antler slices and whole antlers are reported in details. The moisture content and the eutectic temperature of antler were measured. A 22 h process curve of antler slice freeze drying was obtained. The freeze drying process of whole antler was also investigated. The microscopic tissue structure was observed and chemical compositions were analyzed for those freeze-dried whole antlers in comparison with the traditional water boiling and hot air drying method. More nutrients were retained for freeze drying in addition to the better physical properties than traditional drying.

Investigation on the Strength Analysis of Vacuum Tank

A strength analysis on a large-scale horizontal vacuum tank, a dry equipment of the “ two million” large transformers, will be done in this article. Using the means of finite element analysis and two different unit-setting models, we compare the two results getting from the two units. Different lengthen styles of vacuum tank’s reinforced bead will be discussed, as well as different processing styles of welding parts model-setting in ANSYS.

Study on Evacuating Process of Vacuum Glazing

Vacuum glazing is a very choice in building energy efficiency. Therefore, it is necessary to study on evacuating process of vacuum glazing. Based on fundamental pumping equation of vacuum technique and simplified the existing pumping system for vacuum glazing, a mathematical model, which is described evacuating process of vacuum glazing, is established. An exact mathematical solution is obtained by solving the model. According to the solution, an example from a practical evacuating system is solved and analyzed, and two conclusions are summed up as follows: First, the evacuating time needed for vacuum glazing is mainly depended on the flow conductance at vacuum glazing’s bleeding point; Secondly, the ultimate pressure of vacuum chamber should two orders of magnitude lower than the required pressure in the vacuum glazing. Above model, solution and conclusions have a certain guiding significance in the actual production of vacuum glazing.

Study on the Film Coating Methods on Inner Surface of Long-Straight Tubes

In this paper, a variety of previous coating methods are reviewed for the film coating on the inner surface of long-straight tubes. A new magnetron sputtering method is introduced for the film coating in the thin and long tubes made by the conductive and non-magnetic material. The coating process of this method is as follow: the long rod target connecting the cathode is penetrated in center of the coated tube connecting the anode; a solenoid coil with DC exciting current is set outside of the tube so the steady axial magnetic field is generated in the ring discharge area between target and the tube; the working gas flows through the tube from one end to the other, the gas discharge and the magnetron sputtering coating occures in the region corresponding to the solenoid coil; the homogeneous film is obtained on the whole inner surface of the tube when the solenoid coil moves along the tube. The principle and structure of the coating system are analyzed. The distribution of electromagnetic field and electron trajectory in the electromagnetic field are calculated within the discharge region. And distribution of the magnetic field is simulated by COMSOL multiphysicsn software.

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.

Study on the Calculation Method of Gas Flow in Vacuum System Based on the Fluent Software

In order to improve the calculation method of the vacuum system design, the research focus on the way applying the Fluent software to calculation of gas flow in vacuum system in this paper. It is proved that the permission pressure lower limit is 1Pa for meeting the continuity hypothesis. The applicable flow patterns include turbulent flow, laminar flow and transitional flow between turbulent and laminar flow, which are totally defined as the viscous flow in the traditional vacuum field. By means of user define function (UDF), a layer mesh cell of negative quality source is defined to simulate the constant volume flow rate at the inlet of positive displacement vacuum pump, which makes up for the lack of compressible fluid velocity outlet boundary conditions in Fluent. The usability of Fluent in vacuum system is confirmed by a successful calculating example of gas flow in an ice condenser of vacuum freeze dryer.