Experimental Study On Convective Heat Transfer Enhancement And Water Collection By Corona Discharge

Currently,the environmental impact of wet plume emission caused by coal combustion in thermal power units and industrial boilers has attracted widespread attention.Although the current wet plume control technology has certain effects,the recovery efficiency of waste heat and water is low.In the current environment of energy saving and emission reduction,how to efficiently recover heat and water in wet flue gas becomes a new idea for wet plume treatment.In this dissertation,based on the ionic wind enhanced heat transfer technology and electric mist elimination technology,the experimental study on the heat transfer enhancement and water collection of corona discharge in the dry and wet air atmosphere is carried out by a wire cylinder corona discharge structure and a self-designed cased heat exchanger with water as the cooling medium.The effects of primary flow rate,initial temperature,particles and other conditions on the heat transfer enhancement of corona discharge are investigated comprehensively,and its process and mechanism.are analysised.The main contents and conclusions are summarized as follows:(1)In the dry air atmosphere,the heat transfer enhancement effect of corona discharge decreases rapidly with the increase of air flow rate,with a maximum increase of 271%in total heat transfer coefficient at 0.15 m/s and-16 kV.With the increase of air temperature,the current at the same voltage and the heat transfer enhancement effect of the discharge increase.The presence of particles can improve the effect of heat transfer enhancement to a certain extent.(2)The heat transfer enhancement coefficient(K/K0)of corona discharge in dry air is positively correlated with I1/4.Discharge energy injection leads to the increase of air temperature.Combining the both effects,it is feasible and necessary to achieve low voltage and high current discharge conditions to reduce the negative effects of energy injection.(3)In the wet air atmosphere,K/K0 increases linearly with the increase of voltage and gradually decreases with the increase of flow rate.At the same voltage,the heat transfer enhancement effect of corona discharge in wet air is significantly higher,compared with the dry air discharge atmosphere.Corona discharge has a significant effect on water collection.The water collection rate gradually increases with the increase of discharge voltage but the energy efficiency gradually decreases.At 0.72 m/s,the total heat transfer coefficient increases by 144%at-20 kV and the energy efficiency reaches a maximum of 659 kg/kWh at-12 kV.The decrease in inlet temperature causes a decrease in the enhanced heat transfer coefficient and an increase in the water collection effect at a certain humidity level.(4)In wet air atmosphere,corona discharge enhances heat transfer by generating ionic wind and electric mist elimination:the ionic wind lowers the gas phase temperature and increases the condensation of supersaturated water vapor,while the fog droplets are charged and collected on the wall by electric field,and transfer heat to the cooling water.When voltage is less than-10 kV or so,corona discharge is mainly in the form of ion wind disturbing the flow field to achieve heat transfer enhancement;at high flow rate and high voltage,the effect of electrostatic mist elimination gradually dominate the role.