Numerical Calculation Research On Impact Of Structural Parameters On Large-scale Cooling Tower Thermal Performance

The cooling performance of natural draft counterflow wet cooling tower (NDWCT) has a direct impact on performance of thermodynamic system and safe and economic operation of the power station unit. The cooling tower performance is influenced by many factors. Except circulating water parameters and environmental parameters which have been done a lot of research, structural parameters of cooling tower also have a nonnegligible influence on cooling tower perfprmance, while their specific influence rule is not clear enough. Thus, this article makes a deep discussion of the influence rule of tower structure parameters on cooling tower performance.Three-dimensional numerical model of cooling tower was built with FLUENT, and its applicability and accuracy were confirmed based on the measured data of real tower and previous research achievements. Then on the basis of the real tower, many new tower structures were built by changing RAUL (the ratio of inlet height to base diameter)、RAUZ (the ratio of tower height to base diameter)、Af/Ao (the ratio of area of water drenching to exit area)、RAUC (the ratio of throat diameter to base diameter)、 Hth/Ht (the ratio of throat height to base diameter) and area of water drenching Af, and influence rule of these six parameters on NDWCT performance were obtained under no crosswind condition and crosswind conditions by doing numerical calculation for these new tower structures. The summer average wind velocity of the place where the real tower is located in is3.2m/s, so the crosswind velocities of0m/s and3.2m/s are representative and have great research value. These two conditions were called typical conditions. Under these two typical conditions the interaction between RAUL, RAUZ and Af/Ao were studied. Based on the range analysis, the size of impact of RAUL, RAUZ and Af/Ao on circulating water temperature drop were quantified, at the same time the primary and secondary relations of these three factors were analyzed.From the single variable calculation results under the two typical conditions, a series of conclusions were drawn. Compared with RAUC and Hth/Ht, the influence of RAUL、RAUZ、Af and Af/Ao on cooling tower performance is relative larger. If the value of RAUL、RAUZ、Af increases or Af/Ao decreases, the cooling tower performance will improve. Within the scope of the study, RAUZ is lasting improvement and its effectiveness basically remains unchanged, while the influence of RAUL, Af and Af/Ao on cooling tower performance will decreases along with the increase of RAUL, the increase of Af and the decrease of Af/Ao. Both RAUC and Hth/Ht only have small impact on tower performance. Under the two typical conditions, if RAUC increases, the cooling tower thermal performance will increases first, but as RAUC increasing to some value the thermal performance begins to decrease. When there is no crosswind, the cooling tower performance will increase firstly and then decrease with the increase of Hth/Ht, as the crosswind velocity is3.2m/s, the change law is opposite. Through the calculation results of many crosswind conditions it can be seen that critical wind velocity mainly depends on the inlet height, tower height and area of water drenching.The research of multivariate combination calculation indicates that increasing RAUZ and decreasing Af/Ao can increase the effect degree of RAUL on outlet water temperature. The outlet water temperature variation caused by RAUZ and Af/Ao will increase with RAUL. The size of interaction between RAUZ and RAUL is different under the two typical conditions and it is smaller under no crosswind condition, however the interaction of RAUL and Af/Ao is bigger when there is no crosswind. The interaction between RAUZ and Af/Ao is very small that in practice we can regardless of it.By range analysis it is can be concluded that within the variable range RAUL influences circulating water temperature drop most, RAUZ take the second place and Af/Ao is the least significant factor. The combined action of RAUL, RAUZ and Af/Ao on circulating water temperature drop increases with Af under no crosswind condition, while under the other typical condition it decreases first and then increases. As long as the other structure size is large enough, the performance of cooling tower with small area of water drenching can as high as the tower with large area of water drenching. On the basis of these conclusions, suggestion is given that tower type rather than area of water drenching should be taken as cooling tower thermal performance indicators. All of the above research is based on dimensionless parameters, so it is universally applicable. It has certain theoretical research value and engineering applications value because it provides reference for future dedign and optimization of cooling tower structure.