Enhancement of Forced Convection Heat TransferRongzhen YouClass 1202 of Power EngineeringIn my College Students Innovative Project, we are supposed to adopt some methods to enhance the forced convection heat transfer on the plain surface. Although we have taken several technical methods into consideration, most of them are too difficult for us to apply in our project. Therefore, I would like to make an introduction to these methods here.Firstly, machining some grooves or dimples on the plain plates is one of important methods to enhance the convection heat transfer. The grooves or dimples can change the flow field of the fluid near the surface, for which the fluid would be turbulent than before. In this way, the Nusselt number of the near surface fluid would be raised, and than the convection heat-transfer coefficient would increase. This method can enhance the convection heat transfer on the plain plate to some extent, but it’s still ineffective for the reason that the improvement of heat-transfer coefficient of the fluid in the near wall region can not enhance the heat-transfer of the mainstream.Secondly, some researchers come up with an idea that using spiral fine ribs (SFRs) in plate channel to enhance the convection heat transfer. They equally placed the SFRs in the channel, which can form a packing layer resembling a kind of quasi-porous media with large porosity and can produce efficient disturbance both to the boundary layer and the mainstream. The operation principle of SFRs is that the multi-longitudinal vortices induced by SFRs can significantly increase the tangential velocity components in the cross section, which is helpful to promote the micro-fluctuation in the fluid. What’s more, the transport action caused by the longitudinal vortices can improve the mass exchange between the boundary layer and the mainstream. These two factors can not only speed up the heat migration from the channel walls, but also enhance the heat diffusion in the mainstream. This improves the temperature distribution uniformity in channel.Thirdly, the most efficient way to enhance the convection heat transfer is installing fins on the plain plate. Base on this thought, some researchers have fabricated many different types of fins, such as columned pin fins, conical pin fins, elliptical pin fins, cross-cut pin fins and longitudinal vortex generator arrays (LVG). Nowadays, fins with geometric shape pins have been commonly used to in the engineering. As for the vortex generator, it can disturb the flow field by the vortex and generate vortex after the generator, which can break the boundary lay on the surface and transfer the heat into mainstream quickly. Nowadays, many researchers have proved that the LVG effect is much better than the straight fins within a certain limit of Reynolds number, as well as that the multi rows LVG can improve the whole heat transfer effect.The methods mentioned above sounds pretty advanced, but it’s quiet difficult for us, regular college students, to apply these methods in our project. Because we couldn’t analysis the complex flow field in these special structure, unless we use the FLUENT software to build up their mathematic model. As the advanced usage of FLUENT is out of our ability, we have no choices but to install the straight fins on the heat transfer surface. Some researchers have found that the overall thermal resistance of straight fins is lower than other geometric pin fins, due to the combination effect of enhanced later conduction along the fins and the lower flow bypass characteristics. At last, our experiment also proved that the straight fin can meet the requirement of the enhancement of forced convection heat transfer.References1. Christopher L. Chapman, and Seri Lee, Thermal Performance of an Elliptical Pin Fin Heat Sink, Silicon Graphics Computer Systems Mountainview, California, 940392. Pradeep Salapakkam, Ri Li, Mehmet Arik, Bill Gerstler, Augmenting Forced Convection Heat Transfer Coupled with an Aerodynamic Surface and a Synthetic Jet, One Research Circle, Niskayuna, NY 123093. Zhang Xiang, Research on Forced Convection Heat Transfer of Parallel Plate with Grooves, China Academic Journal Electronic Publishing House, TK 1234. Tang Yufeng, Research on Heat Transfer Enhancement Mechanism and Heat Transfer Characteristic of Spiral Fine Ribs in Plate Channel, China Academic Journal Electronic Publishing House, TK1245. K.W. Low, and C. Yap,The Enhanced Cooling of IC Chip Arrays On Printed Circuit Boards, Electronics Packaging Technology Conference, Singapore, 1192606. Gaowen Liu, Peng zhao, Zongwei zhang, Tao Liu, Transient Infrared Heat Transfer Measurements and Surface Flow Visualization on a Single Dimpled Wall, Journal of Propulsion Technology, Feb. 2009, V ol.30 No.11.。