Numerical Simulation And Experimental Research On Characteristics Of Heat Transfer Elements In Cold-end Of Air Preheater

The cold-end of rotary air preheater generally uses enamel heat transfer elements in order to alleviate plugging ash and low-temperature corrosion problems after SC R denitration. Compared with the conventional low-carbon steel elements, enamel heat transfer elements' physical parameters change, such as density, specific heat, coefficient of thermal conductivity, general low-carbon steel heat transfer elements' heat transfer and fluid flow resistance calculation standard does not necessarily apply on enamel's. Researching on the heat transfer and fluid flow characteristics of enamel heat transfer elements with different structural parameters can provide a reference for the thermodynamic calculation of heat transfer elements in rotary air preheaters' cold-end as well as centralized control of power plants operation.This paper sums up experience of domestic and foreign scholars' research achievement on heat transfer elements in rotary air preheater with different wave type, design a optimized project of heat transfer element in rotary air preheaters' cold-end, and analyze its heat transfer and fluid flow characteristics by three-dimensional numerical simulation method. The author test heat transfer and fluid flow characteristics of optimized element and another three commonly used enamel elements by the simulation test experimental platform, which is built based on the working principle of the rotary air preheater in power plant and change cold or hot airflow to achieve the purpose of variable condition, comparing their comprehensive performance factor G, the optimized element's G>1 and its heat transfer and fluid flow characteristics parameters conform to the requirements of engineering. Then analyze optimized element's structure parameters, comprehensive performance and the relationship between Nusselt number and Reynolds number under different rotational speed ? before and after enamel retro fit. The result shows that, equivalent diameter de increase, void fraction n and surface density C decrease after plating enamel on elements' surface, and enamel retrofit decreases pressure loss of per unit length ?P by 40% and convection heat transfer coefficient h by 5%. The Nu increases with the increase of Re when changing ?; and reduce ? appropriately can obtain high thermal efficiency in low Re condition, but conversely in high Re condition.