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Sewage treatment is one of the main contents of environmental protection, so it is very important to provide a theoretical basis for sewage treatment through the analysis of the mechanism. Based on the classical material conservation mathematical model of microorganism and substrate, this paper analyzed the existence and stability of each equilibrium point of the model by calculating the Jacobian matrix of the model, and gave the sufficient conditions to make the stability of the equilibrium point of the model. The numerical simulation method is used to effectively verify the analysis results. In order to improve the effect of sewage treatment, we put forward some suggestions on the setting of relevant parameters in the sewage treatment process from the perspective of mathematical analysis, and verified the correctness of the suggestions by numerical simulation method. [ABSTRACT FROM AUTHOR]

In this paper,a radiator for a low-speed electric vehicle is taken as the research object. Based on the computational fluid dynamics method?STAR-CCM+ is used to analyze the flow field of the two radiators ? and the results of the flow field distribution under idle speed and the maximum speed (45 km/h) are analyzed. The results show that the overall cooling air distribution of radiator in scheme 2 is worse than that in scheme 1，nd the cooling air dis tribution of corresponding condenser is also worse. In terms of cell relative velocity distribu-tion, the cell relative velocity distribution of radiator in scheme II is slightly worse than that in scheme land the cell relative velocity distribution of condenser is basically the same; the quantity of cooling air entering the engine room from above and below the air inlet grille is basically the same. Generally speaking? the cooling air distribution and cell relative velocity distribution of radiator in scheme I are better than that in scheme II，so it is suggested to use scheme I to carry the whole vehicle for road test; if scheme II is adopted? considering the structural layout and performance ? it is suggested to Improve the structural parameters of radiator or increase the fan speed to improve the air volume of radiator to achieve the corre-sponding cooling effect. The research results of this paper can provide simulation data sup-port and theoretical reference for the scheme selection of vehicle radiator. [ABSTRACT FROM AUTHOR]

In view of the problems of large temperature stratification and uneven cooling of grain piles in large warehouses, this paper is based on the theory of heat and mass transfer in porous media grain piles. This study incorporates methods from computational fluid dynamics coupled with the physics of heat transfer, fluid and moisture transport. A mathematical physical model for heat and moisture transfer in grain piles is established. The ventilation experiment of the one-story warehouse is simulated. The results from the experimental data and the results from the numerical simulations are compared. The temperature and moisture changes during actual ventilation and numerical simulation ventilation were explored. The results show that the model can predict the changes of airflow velocity, temperature and relative humidity inside the grain pile; when the initial average temperature of the grain pile is the same. When the inlet air temperature is increased from-17 ℃ to-4 ℃,the ventilation time is extended from 37 h to 108 h. When the speed is increased from 0.24 m/s to 0.31 m/s, the ventilation time is shortened from 228 h to 176 h. Changing the inlet air temperature or outlet wind speed will affect the required ventilation time. Economical ventilation time can be obtained by establishing the relationship between inlet air temperature and apparent wind speed, and outlet air speed and apparent wind speed. The fan with reasonable power can be selected based on this. Provide a reference for the ventilation operation of grain piles. [ABSTRACT FROM AUTHOR]

In order to solve the potential freezing problem caused by wind speed on heat exchange tube bundle of indirect air-cooling tower in winter environment, this paper simulates the flow heat exchange situation of a dual indirect air-cooling tower in a power plant in north China under different environmental wind speeds by utilizing user-defined function（UDF） on Fluent software. The results show that ambient wind speed leads to complex air flow and turbulent vortexes in the area inside and outside the tower. The air intake volume of each fan segment changes, which affects its heat transfer performance. When the ambient wind speed increases from 4 m/s to 15 m/s, the heat loss in the windward fan section increases, and the maximum outlet water temperature decreases by 10 ℃. The heat dissipation in the back fan section decreases, and the outlet water temperature at some fan sections exceeds 25 ℃. The heat transfer in the side fan section deteriorated the most, so the area of high temperature area and outlet water temperature were higher than those in the back fan section. The side fan section of the middle passage of the twin towers gradually shrinks, resulting in the loss of heat dissipation capacity, and the outlet water temperature is close to 43. 1 ℃. When the ambient temperature is-20 ℃ and the wind speed is 15 m/s, the heat pipe bundles in the windward and back fan sections are frozen. At this time, the indirect air-cooling towers must take some anti-freezing measures to ensure safe operation. [ABSTRACT FROM AUTHOR]

Cooling fan of a certain engine was taken as the research object in this paper and STAR-CCM +software was applied for constructing the numerical simulation model of cooling fan performance analysis according to the test model of cooling fan performance experiments; the method of Moving Reference Frame was used to conduct the internal flow field a-nalysis of cooling fan. The results show that the maximum airflow velocity is at the tip of the fan blade,the pressure in most areas of the suction surface of the cooling fan is negative,and the pressure in most areas of the hack surface of the cooling fan is positive. By comparing the simulation results with the experimental results,it was concluded that the wind quantity variation trend of cooling fan under different wind pressures was basically the same. The maximum error was about 4. 9%,and the overall average error was 2. 94%. The simulation accuracy was within acceptable range. It indicated that the simulation calculation model and simulation method of cooling fan performance built in this paper was reliable and can he used to predict cooling fan performance effectively. The research results of this paper can provide theoretical basis and data support for the early design and development of cooling fans.. [ABSTRACT FROM AUTHOR]

Muffler cover of general purpose engine was taken as the research object in this paper and the fluid dynamics analysis software STAR-CCM+ was applied for conducting the numerical simulation study on temperature field analysis of muffler cover. Simulation results showed that the radiation emissivity of materials, thermal boundary conditions and the number of prism layers had great influence on the temperature distribution of muffler cover;the temperature distributions and boundary radiosity distributions of muffler cover for different starter were basically the same, the temperature and boundary radiosity of the side which was far away from fan cooling device was quite high. The simulation value of muffler cover temperatures were basically in good agreement with the experimental values, which indicated that the numerical simulation result of muffler cover temperature had a good feasibility. The research results in this paper can provide a theoretical basis for the early-design and developing of muffler cover for general purpose engine. [ABSTRACT FROM AUTHOR]

After years of depletion and water flooding development, Jinnan complex faultblock tight oil reservoir is now facing problems, such as high water cut of production wells in water flooding block, se rious deple tion of formation energy in depletion block, low single-well oil production rate and low overall oil recovery degree in the block. To solve these problems, this paper takes the complex fault-block tight reservoir in Jinnan as the target, and studies the feasibility of CO2 flooding EOR and storage. Based on the reservoir development history matching and remaining oil analysis by the geologic modeling technology and reservoir numerical simulation technology, the development mode optimization, well pattern improvement analysis and gas injection parameter optimization are studied. The results show that CO2 WAG flooding can effectively improve oil re cover y in fault-block tight oil reservoirs. Perfect well pattern is the guarantee of gas injection development. Parameters such as injection pressure, slug ratio, shut-in gas-oil ratio and production fl owing bot tom-hole pressure are the key parameters of WAG flooding.WAG flooding can not only improve oil recovery in complex fault-block tight reservoirs, but also achieve effective CO2 storage, thus achieving both economic and environmental benefits. [ABSTRACT FROM AUTHOR]

There are some problems of serious blade wear, sediment accumulation near impeller ring and low efficiency in the process of transporting sand-water medium by the double suction pump. The traditional solution is to enhance the wear resistance of blade material. This paper proposes a new and improved double suction pump structure, which reduces the blade placement angle and opens wedge groove on the outer side of impeller cover plate, and analyzes the flow field of solid-liquid two-phase flow in the double suction pump before and after the improvement by FLUENT. The numerical simulation results show that the low-pressure area near the improved impeller inlet decreases and the cavitation erosion resistance of the impeller is enhanced. The impeller flow field is improved, and the vortex near the pressure surface of the impeller vanishes. The efficiency is increased by about 1. 5%. Decreasing the blade installation angle can effectively reduce the sand concentration at the inlet of the blade pressure surface and the outlet of the blade suction surface, and improve the sediment wear on the surface of the blade. The wedge-shaped groove can improve the fluid velocity near the impeller, which enhances the carrying capacity of the water flow on the sediment. In addition, it can greatly reduce the sand volume fraction near the impeller ring, slowing down impeller ring wear. [ABSTRACT FROM AUTHOR]

In this paper, the CFD method is used to establish the numerical model of plain fins, and the calculated results are compared with the relevant experimental data to verify the accuracy of the model. A new structure of cross-spoiler and cross-pins was presented. The new structure enhances the disturbance of the fluid in the flow channel and periodically hinders the development of the boundary layer,so that the temperature in the center of the fluid increases obviously, the heat transfer was enhanced. Compared with plain fins, the new structural fins have higher 7-factor and f-factor, but also higher pressure drop. The relationship between the j, f factor and reynolds number is obtained by fitting the experimental data. The correlation has a certain accuracy in predicting the heat transfer performance of the new structure in the low Reynolds number range. [ABSTRACT FROM AUTHOR]