两种喷嘴结构对冲击式速冻机流场及换热特征的影响

摘要

以速冻机中 V 型条缝喷嘴与平直条缝孔板为研究对象,探索了两种喷嘴结构在相同送风条件下,改变喷嘴与钢带表面间距 H 对速冻机内部冻结区域流场与压力场的影响,以及钢带表面的换热特征.结果表明:与平直条缝孔板相比V型条缝喷嘴沿横流方向流体流动阻力更小,当钢带与条缝出口间距H 与条缝宽度S 之比即Hs 较小时,横流方向压力极差明显小于平直条缝孔板,此时V型条缝喷嘴出口流速均匀性高于平直条缝孔板;平直条缝孔板横流方向气流流速较大,冻品易被吹飞,不利于冻品安全有效的加工;沿横流方向,平直条缝孔板的钢带表面Nu数存在较大差异性,其平均Nu数较低,而V型条缝喷嘴的差异性较小,平均Nu数高于平直条缝孔板,因此,使用 V 型条缝喷嘴在钢带表面的换热均匀性更强,且换热均匀性优于平直条缝孔板.%In this study,V type slit nozzle and straight seam hole plate in a quick freezer was used to invetigatethe effect by the change of distance (H)between the nozzle and the plate surface on the in-ternal flow field and the pressure field in a freezer with these two kinds of nozzle structures under the same air condition.Moreover, the metal surface heat transfer characteristics were also studied.The results showed that the flow resistance of the straight slot seam orifice was smaller than that of the V type slot nozzle along the cross-flow direction.The pressure range along cross flow direction of the V slot nozzle was significantly less than that of the flat nozzle,when the jet-to-plate spacing Hs(Hs=H/s)was at the small value,and the V slot nozzle outlet velocity uniformity was higher than that of straight slotted orifice.The velocity along cross-flow direction in flat nozzle was higher than that of the V slot nozzle,which was not good to safe and effective production for an air impact freezer.Compared with the flat nozzle quick freezer,the difference of the Nu number on the surface of the steel strip of the V slot nozzle was obviously smal-ler,and the average Nu number of the V slot nozzle was greater than that of the flat nozzle.The overall flow and heat transfer characteris-tics of the V slot nozzle was better than those of flat nozzle,and the heat transfer uniformity of metal surface of the V slot nozzle was also better than that of flat nozzle.