往复振荡对活塞冷却油腔内纳米流体传热及流动特性的影响

内燃机工作过程中,燃烧产生的部分热能传给活塞。当活塞功率密度超过0.3 kW/cm~2时,必须采用冷却油腔进行冷却。为揭示纳米流体在冷却油腔内的传热及流动特性,对不同种类纳米流体在随活塞冷却油腔同步往复振荡状态下的传热和流动特性进行了对流换热和可视化实验。研究发现:最优传热充液率为53.4%;往复振荡频率、颗粒的水力半径与活塞冷却油腔内的对流换热系数成正比;转子转动角度在180°~270°范围时,工作流体混合效果最佳;纳米流体的流动紊乱度在整个往复振荡周期内均好于纯净水。

Heat transfer and flow characteristics of nanofluid at a cooling chamber of a piston under reciprocating vibration

Part of heat energy produced by burning oil is transferred to the piston in a combustion engine.When the power density of the piston exceeds 0.3 kW/cm2,the piston must be cooled with a cooling chamber.In order to reveal heat transfer and flow characteristics of nanofluid in the cooling chamber,heat transfer and visualization tests with different types of nanofluid were performed in a straight circular pipe under reciprocating vibration.The test results showed that the optimal filling rate for heat transfer is 53.4%; the frequency of reciprocating vibration and the hydraulic radius of particles are all proportional to the convection heat transfer coefficient of the cooling chamber; the fluid mixure effect is the best when the rotation angle of rotor is with in 180° to 270°; the flowing disord level of nanofluid is better than that of pure water in a reciprocating vibration cycle.