A Numerical Analysis on the Optimum Distribution of an Air-Conditioning Duct with Multiple Outlets in a Medium Bus

The air distribution duct with multiple outlets is an essential part of the automotive air-conditioning system in a bus. The estimation of airflow rate in an automotive air-conditioning duct is typically very complicated due to large variations in cross-sectional area and abrupt changes in flow direction, as well as unbalanced distribution of the flow. This paper describes numerical simulations performed for two simplified air conditioning ducts used in a medium bus. The three dimensional Navier-Stokes code was used to evaluate the overall pressure, velocity field, and distribution rate at each diffuser according to the change of cross-sectional duct area and diffuser area. In addition, a one-dimensional program based on the Bernoulli equation was developed to obtain the optimum diffuser area required to equalize discharge flow rate at each outlet. The results of this analysis were compared to the results obtained from experimental measurement and CFD simulation. This experimental analysis confirmed that a duct constructed in accordance with the optimized design produced equally distributed flow at each outlet, within a range of +/-9%. The simple and convenient one-dimensional analysis technique developed in this study can be applied as a practical and useful tool for designing air-conditioning ducts.