Heat transfer, fluid flow characteristics and entropy generation of water-Al₂O₃ nanofluid for cylindrical heat sinks with helical minichannels that have secondary branches are investigated experimentally. The minichannels helix angles are 45, 60 and 90 degrees; the volume fraction of nanoparticles variation is 0.05% – 0.1%; the Reynolds number range is between 113 to 478. The effects of the helix angle of minichannels, Reynolds number and nanoparticle volume fraction are studied. The heat transfer enhances with increasing Reynolds number, decreasing helix angle and increasing volume fraction of nanoparticles. However, with increasing Reynolds number, increasing helix angle and decreasing nanoparticles volume fraction, the friction factor decreases. The experimental results show that the secondary branches decreased the friction factor and Nusselt number. The maximum enhancement of Nusselt number in helix angle 60 and 45 for pure water are 31.1% and 51.3% greater in comparing with the straight minichannel, respectively; moreover, maximum enhancement of the Nusselt number of nanofluid compared with the pure water was about 14.3% for 0.1% vol. The thermal entropy generation rate decreases and, the frictional entropy generation rate increases with increasing the nanoparticles volume fraction and decreasing the helix angle. Furthermore, two new correlations are obtained for the Nusselt number and friction factor.

水-Al ₂ O _3的传热，流体流动特性和熵产生实验研究了具有螺旋形微通道，具有次级分支的圆柱形散热器的纳米流体。小通道螺旋角分别为45度，60度和90度；纳米颗粒变化的体积分数为0.05％– 0.1％；雷诺数范围为113至478。研究了微通道螺旋角，雷诺数和纳米粒子体积分数的影响。随着雷诺数的增加，螺旋角的减小和纳米颗粒的体积分数的增加，传热增强。然而，随着雷诺数的增加，螺旋角的增加和纳米颗粒体积分数的减小，摩擦系数减小。实验结果表明，次级分支降低了摩擦系数和努塞尔数。纯水的螺旋角60和45中的Nusselt数最大增加量分别比直线小通道大31.1％和51.3％。此外，与纯水相比，纳米流体的努塞尔特数最大增加量为0.1％（体积）约14.3％。随着纳米粒子体积分数的增加和螺旋角的减小，热熵的产生速率降低，摩擦熵的产生速率增大。此外，针对努塞尔数和摩擦系数获得了两个新的相关性。摩擦熵的产生速率随着纳米颗粒体积分数的增加和螺旋角的减小而增加。此外，针对努塞尔数和摩擦系数获得了两个新的相关性。摩擦熵的产生速率随着纳米颗粒体积分数的增加和螺旋角的减小而增加。此外，针对努塞尔数和摩擦系数获得了两个新的相关性。