The Flow Manipulation For Heat Transfer Enhancement And Drag Reduction In Typical Heat Transfer Enhancement Structures

Now,heat transfer and cooling problem is significant topic in resources and power field. Heat transfer enhancement structures are widely used in heat transfer exchangers, turbine blade cooling, electronic microchannel cooling and some medical instruments. The traditional heat transfer structures enhance heat transfer by directly-destroying boundary layer. At the same time, form drag and frictional frag are increased quickly and then work efficiency is decreased.Firstly, present work concentrates on the improvement on traditional continuous ribs by using truncated ribs. Four different truncation types are built to explore heat transfer and fluid flow details. The results show truncated ribs can improve vortex structures and induce transverse flow and better thermal performance is obtained by truncated ribs when compared with continuous ribs. After that, the attention is put on the influence of arrangement of mid-truncated ribs on heat transfer and fluid flow. Different arrangements, including parallel, staggered, inclined ribs, and V-shaped ribs are designed and compared. The staggered or inclined mid-truncated ribs can strengthen flow mixing which increase heat transfer coefficient.Then, the popular dimple heat transfer structures are investigated. The research shows the shapes of dimple structure have a significant influence on vortex structure inside dimple. When a smaller protrusion is located inside a primary dimple, the recirculation flows in the upstream of dimple is restricted and vortex structures form surround the protrusion. The fluid mixing is greatly improved and then heat transfer is increased. Second protrusions are also brought in dimple channel with different height ratios and relative locations in the upstream of primary dimple. Due to secondary protrusions, the attack angle of main stream is changed and recirculating flows shrink. In addition, different locations of secondary protrusion induce transverse flow which benefits the overall heat transfer.The improvement on traditional cylindrical groove is to add rounded corner on the boundary and move the deepest point of section to search for the optimal vortex structure and reattachment. The improved groove has better performance than traditional ribs considering both heat transfer enhancement and pressure drop. When the deepest point of groove section is displaced the downstream of groove, the heat transfer of adjacent flat area is also increased.At last, the research is put on the effect of oscillating flow on heat transfer of the cross flow of two cylinders. The results show that when the frequency of oscillating flow approaches the natural frequency of Karman vortex streets, the heat transfer of the cylinder is greatly improved. Also, the heat transfer is increased when the amplitude of oscillating flow is increased.