Prediction of Temperature and Contaminant Concentration Profiles in a Room withImpinging Jet Ventilation System by Zonal Model

The impinging jet ventilation (IJV) system has been proposed as a new air distribution strategy and is expected to overcome the disadvantages of the mixing ventilation system (MV), which is the most widely used system, and displacement ventilation, which provides better air quality than MV.The present study aims to predict the temperature and contaminant distribution by a simple calculation model that is applicable for IJV with multiple heating elements inside the room. The present calculation model is based on the zonal model and turbulence jet theory. The concept and theory of the calculation model are introduced, and the calculation results are compared to that of CFD analysis.The correlation between the thickness of the jet along the floor and the radial coordinate is obtained by the results of CFD analysis under isothermal conditions and adapted to the model as the height of the first zone from the floor. The turbulent diffusion coefficient of heat in the vertical direction is identified by the CFD results of the vertical temperature profile, whereas the turbulent diffusion coefficient of heat in the horizontal direction is obtained by the function of the number of heating elements in the present paper. It has to be noted that the turbulent diffusion coefficient of heat and contaminant is treated to be equal, due to the assumption in the present paper that the turbulent Prandtl number and the turbulent Schmidt number are the same.Finally, the turbulent diffusion coefficient of vertical direction is expressed as the function of the Archimedes number (balance between buoyancy and inertial force of supply flow) defined in the present paper. The correlation was expressed by the equation from the previous study and also by the newly developed equation. It was shown that although some limitations exist, the calculation model developed in the present paper can predict the temperature and contaminant gradient in the room.The calculation results of temperature gradient fitted that of CFD well except for the cases with large supply velocity. However, those cases are not practically applicable, thus, the accuracy of the model is more important in the cases with supply velocity lower than those cases. Although the calculation results of contaminant concentration fitted that of CFD analysis well in some cases, the prediction accuracy of contaminant concentration is generally lower than that of temperature. It is assumed to be because of the assumption in the present calculation model that the thermal and material turbulent diffusion coefficients are equal. Moreover, it is assumed that the modelling of the flow along the wall and the thermal plume from heating elements also need to be improved to increase the accuracy of the calculation model