Numerical Simulation Of Operating Characteristics Of Indirect Air Cooling System

Energy is an indispensable material foundation for human existence,and an engine of economic growth and social progress.Thermal power generation units occupy an important position in the energy supply in our country.In recent years,the indirect air cooling technology in thermal power generation has been widely used in those areas in northern China where coal is scarce because of its water saving advantages and obtains good economic benefits.The influence of ambient wind on the operation characteristics of indirect air cooling system will have a significant impact.Therefore,the influence of ambient air on the air flow inside and outside the air cooling tower and the performance of the radiator is studied,which provides a reference for the optimal design of indirect air cooing system.This paper addresses that for the air-cooled radiator vertical arrangement outside the tower and horizontal arrangement inside the tower of indirect air cooling system.Firstly,a three-dimensional numerical model is established and the correctness of the numerical model is verified.Secondly,on the basis of the model,the heat rejection and the air mass flow rate of the air-cooled tower are simulated under different ambient wind speeds for vertical arrangement outside the tower and horizontal arrangement inside the tower respectively;and when the design wind speed is 4m/s,the influence of the air inlet of the non-operation radiator during the half-tower operation on the flow and heat transfer performance of the indirect air-cooled radiator is studied under different wind directions.The results show that the indirect air cooling system with the air-cooled radiator vertical arrangement outside the tower and horizontal arrangement inside has no spatial characteristics in the heat transfer flow field under the no-wind condition.Under windy conditions,the heat transfer characteristics of the radiator show obvious spatial differences.The heat transfer performance of the upwind radiator is the best and increases with the increase of ambient wind speed.The heat transfer performance of the leeward radiator is second only to the upwind and less affected by the ambient wind speed at low wind speed,but the performance are deteriorated seriously with the increase of the ambient wind speed.The heat transfer performance of the crosswind radiator is the worst,and with the increase of ambient wind speed,the heat transfer performance is worsened,but when the wind speed is more than 12m/s,the heat transfer performance is slightly improved.During the whole calculation of the ambient wind speed,when the ambient wind speed is 12 m/s,the heat rejection and air mass flow rate of the air cooling tower reach the minimum value,which indicates that the heat transfer characteristics of the indirect air cooling system are the worst in this wind speed.For two arrangements of the indirect air cooling system,there is no significant difference in the heat transfer characteristics when the wind speed is slow.However,with the increase of wind speed,the heat transfer characteristics of the two arrangements are more and more different.Overall,the heat transfer characteristics of the indirect air cooling system with vertically arranged outside the tower of the air-cooled radiator are better than that horizontally arranged inside.In the half-tower operation,the non-operating side air-cooled radiator can’t meet the design conditions of the unit when it is not tight;and even when the wind direction is opposite to the radiator on the operating side,the heat transfer performance can’t be achieved.However,when the rest part air cooled radiator inlet side is tight,the air mass flow rate of the air cooling tower and the heat rejection of the radiator can reach the design condition of the unit.Therefore,when the half-tower is running,the rest part air cooling radiator inlet side must be tight to ensure the safe operation of indirect air-cooled unit.