微槽板内的对流换热和流动特性

在单相强迫对流情况下,对刻有水力直径为0.133mm～0.367mm微矩形槽的微槽结构进行了换热和流动特性实验研究。研究发现,层流换热受槽道高宽比、水力直径与槽间距比值影响,而紊流换热则与水力直径、槽间距和无量纲参数Z有关,对紊流换热而言Z=0.5是最佳参数.实验表明Z对流动阻力因子亦有很大影响,层流情况下当Z为0.5时,摩擦因子或流动阻力都可达最小值;紊流流动阻力比经典理论预示值小,流动向充分发展紊流过渡的临界Re数也比常规值小。文中给出了计算换热和阻力降的经验公式。

Convective Heat Transfer and Flow Friction in MicroChannel Structures

The single-phase forced convective heat transfer and flow characteristics of water in microchannel structures/plates with small rectangular channels having hydraulic diameters of 0. 133mm to 0. 367mm and distinct geometrical configurations were investigated experimentally. The experimental results indicated that the geometrical configuration of the microchannel plate and the individual microchannels had a significant effect on the single phase convective heat transfer and flow characteristics. The laminar heat transfer was found to depend on the aspect ratio, the ratio of the hydraulic diameter and the center-to-center distance of the microchannels, while the turbulent convection was associated with the hydraulic diameter and the center-to-center distance and a new dimensionless variable, Z . It was shown that Z = 0. 5 is the optimum configuration for turbulent heat transfer and the heat transfer process cannot be described properly with the groove aspect ratio. The experimental results also illustrated that the geometrical parameters, including the hydraulic diameter, the aspect ratio, and Z, had important influence on the friction factor. For the laminar flow, the friction factor or flow resistance reaches a minimum value as Z approaches to 0. 5. The turbulent flow resistance is usually smaller than the value predicted by chassical relationships and the Reynolds number becomes lower than the Reynolds number at which the flow transiting to turbulent flow in a conventional conduit. Empirical correlations were suggested for calculating both the heat transfer and pressure drop.