3D CFD analysis of exhaust fan system in paper mill for energy saving.

The purpose of this study is to conduct computational fluid dynamic (CFD) simulations for the paper mills in China. To prevent the accumulation of water vapor for causing condensation on the interior surfaces of the building’s rooftop, this research explored a solution to implement exhaust fans for capturing and exhausting vapor to outdoor environments. The simulation results were based the ventilation system design configuration and the measurements of vapor mass flow rates around the paper machine. The mass conservation check indicated that the differences between the inflow mass flow rate and exhausted mass flow rate were less than 1.2% for each case. The percentages of water vapor expelled by exhaust fans were 81.1%, respectively, in summer. The water vapor concentration distribution showed that the vapor pressure over the ceiling surface was higher than the corresponding saturated vapor pressure at the same temperature, causing the condensing phenomenon. Based on the covering region of condensed water vapor, the predictions also indicated that turning off 18 exhaust fans can not only prevent the occurrence of vapor condensation but also effectively save up to 25% of energy consumption.

本研究旨在针对中国境内的造纸厂开展计算流体动力学（CFD）模拟研究。为防止水蒸气积聚导致建筑屋顶内表面结露，本研究探索了通过安装排风机以捕捉并将水蒸气排放至室外环境的解决方案。本次模拟结果基于造纸机周边的通风系统设计配置与水蒸气质量流量实测数据。质量守恒校验结果显示，各工况下流入质量流量与排出质量流量的差值均小于1.2%。夏季时，排风机排出的水蒸气占比可达81.1%。水蒸气浓度分布结果表明，屋顶表面的水蒸气压力高于同温度下的饱和蒸气压，从而引发结露现象。基于结露水蒸气的覆盖区域，本次预测还显示，关停18台排风机不仅可避免水蒸气结露问题，还能有效节省最高达25%的能源消耗。