圆形自由水射流冲击换热及喷嘴布置

引言水射流冲击冷却由于具有较高的换热能力,广泛应用于机械和化工行业,以实现工件的快速冷却和控制工件的温度变化.在大型轴类工件(工件直径D=1000～3000 mm)喷水冷却装置中,多喷嘴圆孔自由水射流以特定阵列布置冲击至工件表面,相对短暂的沸腾换热结束后,阵列自由水射流即以强制对流方式实现工件冷却.因此,自由水射流冲击换热特性及多喷嘴布置形式对喷水冷却装置的结构设计至关重要.

Free surface circular water jet impingement heat transfer and nozzle arrangement

Mathematical models for flow and heat transfer combined with theoretical analysis and numerical solution are developed to predict the free surface water jet impingement heat transfer for design of water jet cooling equipment with large axles.The stagnation region, boundary layer region and similarity region are numerically solved separately by differential method.Heat transfer characteristics are obtained and validated by comparison with experimental data.Effects and contributions of key parameters on the free surface water jet heat transfer are analyzed and the arrangement for nozzles is discussed.The results show that the Reynolds number based on the nozzle diameter is a dominant parameter in local Nu-r/d distribution.The area-averaged Nusselt number increases with nozzle diameter at a constant Re and the same impinging areas, and with nozzle flow rate.At a constant flow rate, Re and nozzle diameter exhibit comparable heat transfer capacities in small impinging areas, while the combination of larger nozzle diameter and smaller Re presents a better heat transfer effect in larger impinging areas.The area-averaged Nu has a small decrease with the aspect ratio decreasing from 1∶1 to 1∶4.The staggered arrangement for nozzles is better than in-line arrangement for uniform heat transfer though the area-averaged Nu values are nearly the same.