| Cooling tower is one of the most important cold end equipment in power plant,and its outlet water temperature directly affects the thermal economy of the unit.There is almost no water loss in the operation of dry cooling tower,which has a good application prospect in arid areas.However,the cooling efficiency of dry-cooling tower is lower than that of wet-cooling tower,especially in the high temperature period in summer.At this time,the peak of electricity consumption seriously affects the economic benefits of power plants.For this reason,scholars put forward the solar enhanced natural draft dry cooling tower(SENDDCT),aiming at using solar energy to reheat the air after the heat exchanger,so as to increase the temperature difference between the inside and outside of the tower,enhance the natural buoyancy of the cooling tower,increase the ventilation in the tower,and achieve the purpose of enhancing the heat transfer of the dry cooling tower.Literature review found that SENDDCT is at the exploratory research stage,and there are the following problems to be explored urgently:(1)the influence of environmental factors on the cooling performance of solar energy synergistic air cooling tower;(2)the optimization measures of heat exchanger layout of SENDDCT.In view of the above problems,this paper is an exploratory study.The analysis process does not take into account the actual changes of solar radiation intensity with time,season and azimuth.The follow-up study will be comprehensive analysis combined with the actual situation.Firstly,a three-dimensional numerical model of 140 m high SENDDCT was established.The heat exchangers were arranged in a circle along the entrance of the collector shed.The model was solved and verified by Fluent.Based on the validated model,the influence of environmental factors(temperature,solar radiation intensity,cross wind,etc.)on the cooling performance of SENDDCT was studied.Secondly,in order to improve the tower performance,a new model was proposed.A three-dimensional numerical model of the tower with sawtooth heat exchangers was established.The influence of cross-wind on the tower with sawtooth heat exchangers was then studied.Finally,the cooling performance of the cooling tower with circular and sawtooth arrangement of heat exchangers was compared.It was found that SENDDCT with circle heat exchanger had the following conclusions:(1)with the increase of ambient temperature,the heat dissipation rate and ventilation of the cooling tower decreased,the water temperature of the outlet tower rose by 2.5℃ for every 5℃ of ambient temperature;(2)with the increase of solar radiation intensity,the heat dissipation rate of the heat storage layer in the solar collector shed increased,which helped heat the air after heat exchanger,increase the density difference between inside and outside of the tower(i.e.natural ventilation buoyancy),thereby improving the ventilation and heat transfer performance of the tower;(3)the presence of environmental cross-wind could have a great impact on the flow field in the tower,and the circumstance cross-wind with a certain wind speed would destroy the axisymmetric air flow field under the condition of no wind,leading to the intake air.The distribution of outlet air velocity was not uniform,which reduced the ventilation of tower and weakened the heat transfer intensity in the tower;the ventilation of solar energy synergistic air cooling tower took the cross-wind speed of 3 m/s as turning point,showing a trend of slight rise and then sharp decline;when the maximum cross-wind speed was 6 m/s,the dimensionless mass flow maw/ma decreased to the lowest 0.79,and the dimensionless heat dissipation rate Qw/Q reached the lowest value 0.94.Comparing the cooling performance of SENDDCT with circular and sawtooth heat exchangers,the following conclusions could be drawn:(1)Under the condition of no cross-wind,the sawtooth arrangement increased the airflow velocity in all parts of SENDDCT,i.e.the sawtooth heat exchangers could increase the ventilation in the towers compared with circular arrangement.(2)In the cross-wind speed range of 1-6 m/s,the sawtooth heat exchanger was less affected by the cross-wind than the circular one,and the ventilation and heat dissipation rate in SENDDCT were higher than that in the circular arrangement.Through the study of the influence of environmental factors on SENDDCT and the comparative study of the circular and sawtooth arrangement of heat exchangers,this paper reveals the influence of environmental factors on SENDDCT,and obtains the effect of the sawtooth heat exchangers on the cooling performance of SENDDCT,which provides a reference for the performance optimization of the tower.This study can be used in areas with abundant solar energy resources and water shortage,such as Northwest China,to provide reference for energy saving and efficiency enhancement of air cooling towers.This paper belongs to exploratory research,and the parameters selected in the calculation model are not comprehensive enough.The follow-up study will further explore the feasibility of applying SENDDCT to engineering practice. |
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