Study Of The Flow Field Characteristics Of The Push-pull Ventilation System Based On The Mass Transfer Method

With the rapid development of economy, industrial building indoor pollution control problem is increasingly prominent. The technology of highly efficient ventilation is an important way, which can achieve energy conservation and emissions reduction, improve the operating environment and reduce the air pollution. Push-pull ventilation system is an effective way of ventilation. Because of many different properties and types of the pollutant sources, equipment research and development of breathing ventilation system is not geared for a specific pollutant. We assume that pollutants move with jet flow, is transported to the pull hood and then absorbed by it. Hence, the performance of the push-pull ventilation system is the control of the flow field performance. The improvement of the equipment is based on the improvement of the flow field characteristics. Jet features, jet outflow conditions (Such as velocity distribution form) and turbulence parameters have a great influence on the flow field characteristics of push-pull ventilation. The building space form, obstacles and other limited conditions can have an important impact on the field in addition. For this parameters, the existing methods usually rely on experiment and numerical calculation for flow field, temperature field under different parameters, including optimize these parameters. And in order to improve energy efficiency, the results in physical mechanism theory should be deeply studied and discussed.The air around the environment is entrained when the jet is flowing. Generally the media of the push hood air and the environment air is the same. In order to reveal the flow field characteristics under the action of both of them, this paper proposes the methods of identifying different sources homogeneous fluid, which is named mass transfer method. And it is verified by using the classical experimental data and the analytic solution of jet. The results show that the mass transfer method for different sources of homogenous fluid is effective. Moreover, the application example is given.By the method of numerical simulation, we obtain the jet velocity, the velocity distribution and turbulent parameters, which can influence the jet mixing characteristics based on mass transfer method. We analysis these influencing factors through the field synergy theory, clarify the mechanism of the jet mixing and entrainment characteristics, reveal the strengthening or weakening direction of the jet flow field.The flow field characteristics of the push-pull ventilation system are required to be absorbed into the pull hood completely and try to decrease the entrainment of the surrounding air, reducing energy consumption at the same time. This paper proposes equipment performance coefficient index to evaluate the content of the jet in the pull hood. In order to reduce the entrainment of the ambient air, mass transfer of the jet flow of the push-pull flow field should be weaken. We adopt the method of numerical simulation to get the velocity distribution of the air supply outlet, turbulence parameters, the geometry size of the air supply outlet that influence the mixing characteristics of the jet fluid and the environment fluid, the capture efficiency of push-pull ventilation system and the energy consumption. We achieve the regular of the capture efficiency and energy consumption of the push-pull ventilation system through the field synergy principle to analysis this influencing factors. Besides, it provides the theory basis for engineering design of the push-pull ventilation system.Obstacles have a big influence on the flow field characteristics. The presence of the obstacles can make jet deflected, jet are all escaped when the phenomena is seriously, which influence the equipment performance coefficient of the system. In addition, the back flow zone will be produced around the obstacles when flow by pass the obstacles, which the pollutants are easily accumulated. In the practical application, we should avoid placing pollution sources in thereverse flow zone and operators should reduce working time in this area as far as possible. By using the experiment and numerical simulation method, we study the influence of the obstacles size and position to the flow field characteristics and get the rules of the position and size of the obstacles, which influence the equipment performance coefficient, low speed area after the obstacles andreverse flow area. Moreover, this paper proposes the fitting curves relation to the length of low velocity area and the length of reverse flow area, which can provide a certain reference for the engineering application.