Preliminary Study On Air Supply Mode Of Vortex Ring

People spend most of their time indoors every day,which makes indoor air quality an important factor affecting the health of indoor personnel.At the same time,the energy consumption of the heating,ventilation and air conditioning system(HVAC)accounts for 10-20% of the total primary energy,which requires the ventilation system to face great challenges in improving indoor air quality and energy saving.Therefore,personalized ventilation systems(PV)have been extensively studied.However,the actual application of personalized ventilation systems is not satisfactory,which is mainly due to the limitations of the existing personalized ventilation systems that often require the provision of the air terminal device(ATD)near the breathing zone(BZ).Therefore,it is necessary to propose a new type of personalized air supply method,which can realize the long-distance and directional delivery of fresh air to the breathing zone.Based on the above requirements,this thesis proposes a personalized air supply method based on the vortex ring principle: vortex ring personalized ventilation(VRPV).As we all know,the vortex ring is a common flow form in nature.Its characteristic is that it can maintain its own structure during movement and realize long-distance transportation with lower energy consumption.The flow characteristics of the vortex ring can better wrap the fresh air in its own volume,and transport the fresh air to the breathing zone with less energy dissipation,so as to achieve the air supply to the local area.Therefore,when the air vortex ring is used for air supply,it can not only achieve a higher fresh air ratio,but also improve the flexibility of the system.So is a form of air distribution has potential applications.Based on the above discussion,this thesis has studied the vortex ring ventilation through theoretical analysis and experimental methods.The specific content includes the following aspects:Firstly,by analyzing the analytical solution of the thin-core vortex ring kinematics model under viscous conditions,the whole life cycle of the vortex ring motion is clarified,and the corresponding relationship between the factor effects is summarized,which is suitable for the new air vortex ring generating device designed in this thesis.It provides a theoretical basis for further research on the formation and evolution characteristics and application of air vortex rings.Secondly,an air vortex ring generating device suitable for air supply was designed to explore the formation and shedding of air vortex rings,the migration and distribution of air vortex ring groups,and the air supply performance of vortex rings.Third,an experimental investigation was conducted on the formation and shedding of the air vortex ring to determine two key parameters that affect the volume of the vortex ring: the diameter of the vortex ring and the diameter of the vortex core.The changing rules of volume and translational velocity during the formation of vortex ring were explored according to different working conditions.Studies have shown that the entire formation process of the vortex ring can be subdivided into three states:(a)the entrainment of the jet before the vortex ring sheds;(b)the vortex ring sheds;(c)the dissipation and entrainment of environmental fluid after the vortex ring sheds.In addition,under different extending strokes,the vortex ring itself has three states:(a)the vortex ring is under-saturated;(b)the vortex ring is near-saturated;and(c)the vortex ring is oversaturated.Finally,it is found that the translational velocity of the vortex ring is determined by the translational velocity of the piston.Under the same pressure level of the air compressor,the excess stroke cannot increase the translational velocity of the piston,nor can it increase the translational velocity of the vortex ring.Fourthly,based on the conclusion of the formation stage of vortex ring,the migration and distribution of vortex ring group are investigated experimentally.The results show that the relation between the translational velocity and the dimensionless transport distance of vortex ring is similar to hyperbolic curve.When the vortex ring is generated,it is interfered by equipment factors and influenced by environmental factors in the process of transportation,so the additional deviation of the centroid position of the vortex ring group is generated,and the distribution boundary of the vortex ring group is nonlinear.With the increase of the transport distance,the distribution range of vortex ring group is larger and larger,which means that when the vortex ring is used for air supply,the air supply distance and distribution range of vortex ring should be fully considered to ensure that the distribution range of vortex ring air supply covers the air supply area.Finally,based on the above study on the basic characteristics of the vortex ring,the experimental study on the air supply performance of the vortex ring is carried out.Research shows that in the commonly used personalized ventilation/local supply(0-1 m),and centralized ventilation(1-4 m)under the different scales of vortex ring air supply air rate were significantly higher than that of the traditional symmetrical round jets,the fresh air ratio increased by 37.6% on average,maximum in 0.89 m to achieve 159.3%,thus,vortex ring has great application potential in the field of ventilation.