This article presents the fluid mechanics of a ventilation system formed by a momentum source and buoyancy sources. We investigate the interaction between plumes and a non-isothermal air jet for separate sources of buoyancy produced by the plume and the momentum of the air jet. The mathematical model represents the situation in which a plume rises from two heat sources causing buoyancy. The model is used to discuss the interactions involved. The effects of parameters such as the power of the source and the air-flow volume used in the mathematical-physical model are also discussed. An expression is deduced for the trajectory of the non-isothermal air jet penetrated by plumes. Experiments were also carried out to illustrate the effect on the flow of the air jet and to validate the theoretical work. The results show that the buoyancy source's efforts to baffle the descent of the cold air have even been effective in reversing the direction of the trajectory. However, increasing the distance between the plumes can reduce the effect of the plumes on the jet curve. And it is apparent that when the velocity of the air supply increases, the interference caused by the plumes can be reduced.

No abstract

The thermal environment of large space building with stratified air distribution is characterized by its obvious gradient of vertical temperature, and the stratified air conditioning load (SACL) is closely related to the thermal environment. The Block-Gebhart (B-G) model in summer is established for an actual large space building which has two stratified air distribution (STRAD) systems. One system is the air supply nozzles (ASN) arranged at middle sidewall, the other is the half-cylinder diffusers (HCD) arranged at low sidewall. In order to quickly calculate the air temperature of unoccupied zone (ATUZ), two regression equations for the air temperature gradient under the conditions of two STRAD systems were proposed. Considering six factors, the B-G model was used to calculate 648 cases and the two equations were obtained by multiple regression analysis. Through the field measurement in summer, in three cases of ASN system, the mean absolute error (MAE) between predicted and experimental values of ATUZ was 1.4°C, and the mean absolute percentage error (MAPE) was 4.5%; in three cases of HCD system, the MAE was 1.0°C and the MAPE was 3.0%. The results of this study establish the foundation for the calculation of SACL.