不同桨型的搅拌槽中非稳态温度场分布的研究

Study on the Unsteady Temperature Profiles in an Agitated Tank Equipped with Different Types of Impeller

在搅拌槽中,由于搅拌桨型式的不同,会导致流体温度分布的不同。本文在直径为0.5m的搅拌槽中分别使用CBY、带副叶CBY以及PBT三种桨进行研究。三种桨的搅拌雷诺数分别为267,251和203。在搅拌槽中设置了四组加热列管(兼作挡板)进行加热。将热色液晶均匀地分散在甘油中,以显示温度的分布。实验研究了相同功率下三种桨的瞬时温度分布。结果表明,搅拌槽中的温度分布取决于搅拌桨产生的流型。当流体被加热时,流场内漩涡中温度梯度通常大于其它区域,漩涡的存在不利于槽内温度分布的均一性。在三种桨中,PBT 桨的轴向温差最小。

The temperature profile in an agitated tank is greatly affected by impeller抯 type. Heat transfer experiments were carried out in a cylindrical stirred vessel of 0.5 m diameter with four sets of vertical heating pipes. The effect of impeller types (CBY, CBY-D and PBT) on the temperature profile in transition region was examined when the power input was kept the same. Reynolds numbers (Re) were 267, 251 and 203, respectively. A mixture of cholesteric liquid crystals dispersed homogeneously in glycerol was used to visualize the temperature field of fluid in the stirred tank. The experimental results showed that the effect of flow pattern on temperature profile is significant in the stirred tank. The highest temperature gradient is located in the vortices when fluid is heated. The vortices in flow field will enlarge the temperature gradient in the stirred tank. The lowest temperature is either near the bottom of the tank or the surface of fluid. Among three types of impeller, the axial temperature difference for PBT is the smallest.