A New Type Of Ventilation--2DPIV Studies Of Air Curtain Ventilation In A Slot-ventilated Encnclosure: Non-isthermal Conditon

The indoor air distribution characteristic is essential to the design of a ventilation system and the control of room thermal and air quality conditions.It also determinates the distribution of thermal energy,moisture,and fresh air into a room.Airflow characteristics,which have been investigated by many researchers,are dominated by the behavior of inlet air-jet.Air distribution is mainly composed of two types,one is conventional mixing ventilation based on dilute principle,and the other is neoteric displacement ventilation using buoyancy control as driving force.Air curtain ventilation, which is investigated in an enclosure,is "the mix-up" of both displacement ventilation and mixing ventilation.The mechanism of air curtain ventilation is that the Coanda effect of air curtain supply is used by controlling reasonable physical parameters(e.g. air supply velocity,supply air temperature,the size of slot inlet and so on).When the air supply would attach itself along the attached wall and only move down at a distance from its starting point,and then may spread over the floor to create an "air lake" or "air pool" phenomenon,the air distribution of air curtain ventilation,which is similar to displacement ventilation,is then achieved.Firstly,2DPIV,which is an ideal and highly promising technology to capture unsteady flow field,is used to visualize the airflow performance of air curtain from ceiling slot-inlet into an enclosure in non-isothermal condition.The test chamber is made by 5mm thickness of the Plexiglas with a size of 600 mm×300 mm×340 mm (L×W×H) enclosure.After completing the 2DPIV experiments,air temperature difference in the air lake zone is measured by the auto data acquisition system(Isolated Measurement Pods).Whole flow field airflow patterns characteristics and air temperature difference in the occupied zone are analyzed under different air supply velocities,different panel heat flows and the size and location of slot opening, respectively.Airflow patterns characteristics along the attached wall and along the air lake zone are observed and analyzed in detail.The vertical penetration distances of non-isothermal enclosure versus Archimedes number are showed by Origin software. The expression of air temperature difference in the air lake zone is also presented.The conclusion of this paper show that,the supply air velocity,which effects airflow patterns characteristics and air temperature differences in the air lake zones. When the air supply velocity is gradually varied at 1.00m/s and 1.50m/s,respectively, the velocity profile along the enclosure length at a distance of 170mm downstream of the slot displays a similarity character,which is presented in the air lake zones.When a panel heat source is adjusted,the velocity profile and air temperature profile are obviously different.When a panel heat source and air supply velocity are given,the velocity profiles along the enclosure length at a distance of 170mm downstream of the slot show that a decrease for s/b=5 results in a slower decay of the velocity than that of s/b=8 and s/b=10,respectively.According to the visualization and measurement of air curtain ventilation trajectory,the vertical penetration length of air curtain jet traveled through the attached wall are about H_p = 0.79～0.82H(L/H=2).At the same time, the air temperature profiles near the floor zone and in the air lake zones are dominantly affected by the air supply velocity,and the effect of the air temperature profiles near the floor zone and in the air lake zones by a panel heat source is negligible,to some extent. The influence of the dimensionless distance between the slot inlet and the attached wall presents the similarity character for the air supply velocity 1.00m/s and 1.50m/s, respectively.Results also shows that the increasing supply velocity and the decreasing size and location of slot opening is advantageous for air curtain ventilation to form the Coanda effect,in order to improve the physical behavior of indoor air,air exchange and thermal comfort.The physical behavior of air flow and air temperature difference of the test chamber have provided lots of initial materials to understanding the mechanism and principle for designing air curtain ventilation from ceiling slot-inlet into an enclosure in non-isothermal condition.