Research On Matching Of Water-splashing Noise And Thermal Performance For Natural Draft Wet Cooling Towers

Natural draft wet cooling tower(NDWCTs)are the important cooling equipment in the fossil-fuel power plants.Currently,the volume of NDWCTs is getting big to comply with the increasing unit load,so the water-splashing noise is also getting large,which seriously affects residents' health and life.As a result,the theoretical calculation model is proposed in this paper to predict the water-splashing noise of NDWCTs,and the thermal performance of NDWCTs is also studied.This paper will lay a foundation for the parallel study of the water-splashing noise and the thermal performance for NDWCTs.Firstly,based on the distribution law of droplet size in rain zone and the theory of the droplet impact noise,the theoretical calculation model was established to predict the water-splashing noise for NDWCTs.And the noise distribution and noise influencing factors of cooling towers for 300 MW,600 MW and 1000 MW units are studied.Then,combined with the principle of the heat and mass transfer between air and water inside tower,the UDF calculation program of heat and mass transfer process was written,and a three-dimensional numerical model of cooling tower used for 1000 MW units was established.Finally,by mean of the two calculation models,under the condition of partition water distribution model(2/5,1/3 and 1/2 partition radius)and variable droplet size distribution(1 mm,2 mm,3 mm and 4 mm droplet size distribution)in rain zone,the optimal matching between the water-splashing noise and the thermal performance was studied.The main conclusions are as follows,Model verification results show that,according to the water-splashing noise in the field test,the mean error between the theoretical calculation value and the measured value is 0.58 dB,which verifies the accuracy of the theoretical calculation model.Then,when the outlet water temperature is used as the evaluation index of thermal performance,the maximum relative error between the simulation value and the design value is 3.26%,which verifies the accuracy of the numerical calculation model.The results based on the theoretical calculation model show that the SPL of noise increases logarithmically with the increase of water-spraying density.When the water-spraying density is doubled compared with the design condition,the SPL of noise increases by about 3.0 dB.Additionally,under the condition of constant water circulating rate,the SPL produced by small droplets is small,and the attenuation amplitude is large with the propagation distance.Within 0 m to 5 m from noise source,the SPL of 2 mm and 3 mm droplets reduces by 15.75 dB and 5.34 dB respectively.In order to optimize the layout of water-splashing noise reduction devices,when the proportion of sound energy reaches 80%in measuring point,the noise reduction devices should be installed in the outer distance at least 21 m for 1000 MW units cooling tower.The results based on the partition water distribution show that,reducing the water circulating rate is beneficial to the outlet water temperature,but it increases the water-splashing noise of the cooling tower.Combined with the water-splashing noise and the thermal performance,when the ratio of inner radius is 2/5,the outlet water temperature is lower,and the change of water-splashing noise is smaller.At this point,compared with the uniform water-splashing pattern,the maximum water temperature can be reduced by 0.16?,while the SPL of water-splashing noise only increases by 0.28 dB.The results based on the different droplets distribution in rain zone show that,reducing the proportion of small water droplets is beneficial to the thermal performance,but it also increases the water-splashing noise.Hence,under the condition of changeable proportion of 3 mm droplets,the maximum outlet water temperature reduces by 0.22?at most,and the variation of the water-splashing noise is relatively small.This paper established the theoretical calculation model of noise,and proposed the active noise reduction method based on droplet size distribution in rain zone,which can provide a new idea for the subsequent noise reduction measures.Meanwhile,the matching relation between the water-splashing noise and the thermal performance for NDWCTs was revealed,which can provide guidance for the parallel study of water-splashing noise reduction and thermal performance improvement.This has an important theoretical meaning and engineering project value.