Experimental study on the flow field and economic characteristics of parallel push-pull ventilation system

Push-pull ventilation systems provide excellent control of contaminants and harmful gases.However,since both a push inlet and a pull outlet are used in the push-pull ventilation system,the flow rate required by the system is large.In that case,the energy consumption of the system is large.The purpose of this paper is to study the flow field and economic characteristics of a parallel push-pull ventilation system by reducing the flow rate of the exhaust outlet,which will be achieved by reducing the size of the exhaust hood.The three commonly used push-pull ventilation systems were analyzed:a high velocity push-pull system with high air supply velocity,a low velocity push-pull system with wide airflow and small velocity,and a parallel push-pull system with wide airflow and uniform air supply velocity.Results showed that the parallel push-pull ventilation system was the only one in which the flow rate of the exhaust outlet could be reduced,reducing the overall energy consumption.Under conditions of the parallel air supply jet,the diffusion range of contaminants in the push-pull flow field was the smallest and reducing the exhaust air flow rate did not affect the capture efficiency of pollutants.These results may be useful in guiding the design of push-pull ventilation system and optimize economic constraints.

Characteristics of the recirculation zone in a cylindrical confined space and its suppression by an annular orifice plate

The accumulation of pollutants in the recirculation zone can worsen ventilation.It is critical to reduce recirculation zones to improve the ventilation efficiency of buildings.However,the variation rule of the recirculation zone in a cylindrical confined space(CCS)is unclear,and there are few solutions to suppress or eliminate the recirculation zone at present.In this paper,an annular deflector orifice plate for suppressing the recirculation zone was developed based on the structural characteristics of the CCS.This device is simple in structure and can be used flexibly.Through experiments and numerical simulations,the variation rule of the recirculation zone length and the influence of structural parameters of the device on the vortex suppression were explored.Firstly,empirical formulas for calculating the length of the recirculation zone in the CCS were obtained.In addition,it was proved that placing the annular orifice plate inside the CCS effectively reduced the recirculation zone and improved the ventilation efficiency.Compared to the system without the annular orifice plate,the dimensionless length of the recirculation zone was decreased by 76.3%,and the time to completely discharge the pollutants from the CCS was decreased by 16.7%.Finally,parameters of the annular orifice plate that form the best vortex suppression effect were proposed:the porosity range was 40%–50%,uniform in shape with equal ring spacing,and placed more than one inlet diameter away from the inlet.The results help guide the ventilation design of CCS.