| Rain area is an important heat transfer area in cooling tower.The improvement of its cooling efficiency is of great significance to the improvement of overall heat transfer efficiency of power plant and the reduction of standard coal consumption rate.At present,the research on rain area of cooling tower has not been carried out comprehensively at home and abroad.The diameter of water droplets in rain area is limited to describe by equivalent diameter,and the resistance of import and export of rain area is limited to calculate roughly by empirical formula with dimensionless correction coefficient.All of these are due to the complexity of the internal environment and the excessive space in rain area.The rough description and calculation in the study of water droplets in rain area will inevitably bring a large error to the calculation of whole rain area.Therefore,accurate description of the raindrops size is necessary..Therefore.in this paper,the particle size of the water droplets and the pressure difference between the inlet and outlet of rain area in natural draft counter-flow wet cooling tower are taken as the research objects,mainly adopting the research method combining field test and medium tower experiment.And the paper mainly uses the experimental research method combining field test and medium-sized tower experiment.Firstly,the particle size of water droplet in the conventional wet cooling tower(CWCT)was tested on site.The OTT Parsivel2 was used to collect and analyze the velocity,particle size and total number of the water droplet in rain area,and the horizontal comparison analysis was carried out for the cooling towers of different units to further analyze the distribution of water droplet particle size.Secondly,the distribution of water droplet particle size in the wet cooling tower with water collecting devices(WCTWCDs)under different gas-water ratios was studied on a medium-sized tower.Finally,the pressure difference between the inlet and outlet of rain area in the WCTWCD is measured on the spot,and the proportion of the resistance in rain area of the WCTWCD is analyzed to further improve the corresponding study of resistance performance.Through the above analysis,the paper has carried out the following research:.(1)Comparison of droplet particle size of different units in CWCTs.For the 335MW.635MW,and 1000MW units,the overall particle size cumulative ratio charts are consistent,that is,the majority of raindrops have a particle size of 0～8mm,accounting for more than 85%.And in the range of 0～5mm.the cumulative proportion of the raindrops size is close to a straight line.After that.the growth rate of the raindrops size tends to slow down,and it is close to 100%after 10mm.that is.the raindrops size is basically below 10mm.The difference is that as the installed capacity increases from 335MW to 635MW.the number of small particle sizes increases,but the relative proportion decreases,and the proportion of medium particle size and large particle size increases.When the installed capacity continues to increase from 635MW to 1000MW.the overall trend is that the number of small particle sizes increases with the increase of power,and the proportion of small particle size decreases first and then increases with the increase of power.The change of the number of medium and large particle sizes is not very obvious as the power increases,but the ratio decreases relatively as the power increases.(2)Comparison of droplet particle size distribution in the case of variable gas-water ratio in WCTWCD:In this paper,two regulation modes of gas-water ratio,namely,constant water variable wind(which reflects the influence of ambient sidewind)and constant wind variable water(which reflects the influence of the operation mode of circulating water pump).are studied.Both of them will influence the distribution of raindrops size,and their influences are slightly different.When the water flow rate is fixed.as the gas-water ratio increases,within a certain range,the proportion of small particle size increases due to wind blowing,and after exceeding this range,the larger ventilation resistance makes the proportion of large particle size increases again;When the air flow rate is fixed.as the gas-water ratio decreases,within a certain range,the number of small particle sizes increases,and the proportion also increases.After the certain range,due to excessive water flow rate,the proportion of large particle size in the initial particle size range is increased.(3)The test of the pressure difference between the inlet and outlet of the rain area in WCTWCD,and the relationship between the droplet particle size distribution and the pressure difference:When the water flow rate is fixed,the pressure drop of the water collecting device in WCTWCD gradually increases with the increase of the inlet air flow rate,but the proportion of pressure drop of the water collecting device also gradually decreases from the 12.2%of the whole tower pressure drop to 10.5%.Combined with the particle size distribution,when the wind speed increases from 600 to 900.the total number of raindrops increases.and the proportion of small particle size increases significantly while the proportion of large particle size is significantly reduced.This is because the raindrops are broken into finer raindrops under the action of wind blowing.which increases the gas-water contact resistance.but the increase of the inlet air volume makes the pressure drop of the packing zone more obvious,which reduces the pressure drop of the water collecting device.When the wind speed continues to increase to 1300,the total number of raindrops gradually decreases,and the proportion of large particle size also increases again,and the overall particle size distribution is more uniform than before.This is because the wind speed is higher at this time,and more raindrops are wrapped into large-sized raindrops under the action of wind blowing.and the higher wind speed also increases the pressure drop of the water collecting device portion to some extent.When the air flow rate is fixed.with the increase of the amount of water entering the tower.the pressure drop of the water collecting device in WCTWCD is obviously increased,and the proportion of pressure drop also increased from 11.14%of the whole tower pressure drop to 1 6.89%.Combined with this part of the particle size distribution.when the inlet water volume increases from 500m3/h to 700m3/h.the total number of raindrops decreases,and the proportion of large-diameter raindrops decreases significantly.This is due to the increase of inlet water volume,which causes more raindrop movements during the raindrops to fall,resulting in a decrease in the proportion of large particle size,and the increase of inlet water volume also greatly increases the flow resistance,causing a significant increase in the partial pressure drop of the water collecting device.Compared with the adjustment of the gas-water ratio of the fixed water,it can be seen that the adjustment of the gas-water ratio of the fixed air is more obvious to the change of the resistance of the water collecting device in WCTWCD.The increase of the amount of water flow can significantlv increase the proportion of water collection device pressure drop.When the gas-water ratio adjustment mode of fixed,water is adopted,the pressure drop variation of each area in the cooling tower is relatively small and stable. |
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