| Heat exchanger is a vital device used in the industrial heat transfer process. Itsapplication includes power engineering, chemical engineering, food engineering etc. With thetechnological development and the urgency of resource and energy saving, some novel heatexchangers were developed and used in the sewage treatment. Thus, it is greatly significantthat new heat exchangers are developed to increase the heat transfer rate and energyutilization. Under these circumstances, this paper presents some novel surface structures toenhance heat transfer in rectangular channel by experimental and numerical methods with themicroscopic analysis of turbulent kinetic energy, velocity profiles, streamlines and pressure.Meanwhile, temperature and local Nusselt number distribution are also analyzed bysimulation. Additionally, overall Nusselt number and friction factor are compared andanalyzed by field synergy principle and overall thermal enhancement factor. The mechanismof heat transfer enhancement in rectangular channel with different geometrical protrusionsand cavity surfaces and the effect of vertical flow on heat transfer enhancement weresummarized. The aim of this paper is to modify the traditional surface structures with thepurpose of overall performance maximization.Transversal ribs are widely used in heat exchanger, reactor and mass transfer equipment.This paper presents a deflector which transports the fluid in the mainstream to the near-wallregion between two ribs, inducing the flow disturbance in this region and increasing the heattransfer rate. Compared with the ribbed channel, the overall Nusselt number is enhanced by14.8%~22.7%. In spite of higher flow resistance, the old devices are modified with low costand installation convenience. Moreover, four kinds of deflector and the locations of deflectorare investigated, finding that inclined flat deflector indicates superior heat transfer rate toother cases.Discrete inclined ribs and grooves with crossed arrangement and parallel arrangementare presented to study the fluid flow and heat transfer by experiment and simulations,showing that overall performance of discrete inclined ribs and groove with crossedarrangement is about10%~13.6%higher than that of parallel arrangement. The effects of inclined angle and rib pitch on the heat transfer are also investigated, finding that the best ofinclined angle is45°.A pair of longitudinal vortices is formed by trapezoidal static mixer, enhancing the heattransfer with less pressure loss. A trapezoidal vortex generator with clearance is presented toincrease overall thermal enhancement factor. Flow mode and the location of clearance areconsidered as parameters which influence heat transfer and flow resistance. The results showthat the Nusselt number with case of full size tab and flow forward is higher than thetraditional trapezoidal vortex generator. At lower Reynolds number, the case of backwardflow is better than that of forward flow. At higher Reynolds number, the case is reverse.Therefore, the tab with clearance can increase heat transfer efficiency.Spheric protrusion or dimple is a novel surface structure of heat transfer enhancementwhich attracts much interest all over the world. This paper presents a hemispheric protrusionwith imprinted dimple or dimple with imprinted protrusion and the studies on heat transferand flow characteristics are conducted by numerical method. The results show that the overallthermal enhancement factor of novel structure can be enhanced by10%compared to generalprotrusion due to the unique flow characteristic such as flow separation, vortex impingementand horseshoe vortices. The analysis of flow pattern shows that drag reduction of dimpledchannel with imprinted protrusion is attributed to the separation and suppression ofre-circulating vortices in the cavity, leading to the reduction of pressure drop betweenupstream region and downstream region. In conclusion, the combination of protrusion andcavity in the present way can increase the heat transfer efficiency.
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