Investigation Of Ventilation And Bifurcation Phenomenon In Space Station Cabin

The objective of this study is to investigate air ventilation and its influence on heat and mass transfer in space station cabins, so as to provide useful information for the design of Thermal Control System (TCS) and Environment Control and Life Support System (ECLSS) in space stations. The flow pattern visualization experiments were first carried out and it was observed that, slot inlets with 45-degree angle to horizontal direction produced asymmetric flow patterns in symmetric geometry configuration at certain flow rates, depending on the initial conditions. This phenomenon is called bifurcation. The flow turns to be symmetric and no bifurcation is found when the air comes into the cabin with 60-degree or the inlet was blocked in interval. Flow bifurcation phenomenon was then successfully simulated with numerical schemes. The influences of flow rate and initial calculation velocity field on air flow patterns were investigated. It is found that flow rate, inlet angle and width are main factors of flow bifurcation in the cabin. At very low value of these factors, no bifurcation exists. There are critical values for these parameters where bifurcation occurs.Qualitative and quantitative factors were put forward to assess the characteristics of carbon dioxide removal in space station cabins. Compared with other inlet patterns, the interleaving 45-degree oblique one was proved to excel in the all-round characteristics of flow, heat and mass transfer by numerical simulation of carbon dioxide removal. The influence of ventilation on dew condensation in the inner wall of space station cabins was also investigated in this study. The characteristics of dew condensation in the inner wall and their influence factors were analyzed based on the establishment of physical and mathematical models. Dew condensation will be enhanced or prohibited by ventilation when the thermal conductivity of thermal insulation layer is relatively small. With ventilation, dew condensation will disappear when the thermal conductivity increases to some extent. Condensation in inner wall can be effectively prohibited by measures of both ventilation and thermal insulation.Furthermore, the mass constitutes of condensation-free walls were analyzed and it was found that minimum mass of the cabin walls exists. Lowering the thermal conductivity of the thermal insulation layer and the emissivity of outer surface, increasing the emissivity of inner surface with suitable ventilation flow rate are expected to benefit to the reduction of wall mass increase of space stations.After the analysis of thermal scale method and pressure reduction method, based with the combination of these two methods, Scale and Pressure Reduction technology is presented for the first time in this study to simulate the micro-gravity flow and heat transfer on the ground. This technology is proved to be effective for ground-based simulation after theoretical analysis and numerical validation. Correlation convection in space station cabins under micro-gravity and terrestrial gravity was suggested and evaluated by numerical simulations. The combination of this method and Scale and Pressure Reduction technology will offer convection correlation in use of the ground-based experimental results. Low Reynolds number k-e turbulent model was applied to numerically simulate the flow and heat transfer with vertical inlet pattern. The simulation results agreed well with the available experimental data.