Numerical Analysis On The Heat Transfer And Flow Characteristics Of Condensation In Special Type Heat Exchange Tube About The Mixed Gas

Condensation in presence of non-condensable gas is common in many industrial industried including nuclear power generation,heat recovering and petrochemicals.Due to the exists of non-condensable gas,the condensing heat transfer process is significantly deteriorated.So it has become a hot topic in the area of vapor condensation to deeply investigate the flow and heat transfer characteristics of mixed gas condensation with different influencing factors.A study on the influence of the angle of inclination of tube,tube shape,tube diameter and flow velocity on the condensation heat transfer and flow process with mixed gas of vapor and air in a special type heat exchange tube was performed through numerical simulation.A two-dimension numerical simulation was carried out to discuss the heat transfer and flow characteristics of mixed gas in tube with angle of inclination.The results of numerical analysis show that the pressure of mixed gas inside tube decreases along the tube and the condensation heat transfer coefficient first increases and then decreases with the tube diameter decreasing;The angle of inclination of tube has little influence on the condensation heat transfer coefficient of mixed gas with a small tube diameter,and the pressure of the points inside tube decreases with the increases of the angle of inclination of tube with small diameter.Within the range of the parameters studied in this paper,the condensation heat transfer coefficient increases with the increases of the angle of inclination of the tube with big tube diameter,and the maximum is in the angle of 90;With the increases of the flow velocity,the influence of the angle of inclination of the tube on mixed gas pressure was weakened.A flow and heat transfer math model in heat exchange tube with three cross-sectional shapes,namely circlr,square and equilateral triangle,was established and a three-dimension numerical simulation was carried out to discuss the heat transfer and flow characteristics of mixed gas in these tubes.The numerical simulation discussed the comprehensive influence of the tube equivalent diameter and flow velocity.The results of numerical analysis show that the condensation heat transfer coefficient of mixed gas in square tube was the highest,in circlr tube was the second,and in equilateral triangle tube was the smallest.In the square corner area,the content of air is bigger while the air film in the perimeter of the square is smaller,the thermal resistance of the air film becomes thinner.In addition,because the Angle of the Angle area is relatively large,the deterioration degree of the square section heat exchange tube is relatively small,and the condensation heat transfer coefficient is the highest.With the increases of the tube equivalent diameter,the pressure of mixed gas in equilateral triangle was the highest,which was the same in circlr and square tube;The condensation heat transfer coefficient of mixed gas in square tubes was the highest.A numerical simulation was carried out to study the condensation heat transfer and flow characteristics of mixed gas in corrugated tube,and was compared to the circlr tube under the same condition.The comprehensive influence of the wave structure,content of non-condensable gas and Reynolds number was discussed.The wall average heat transfer coefficient was higher than that of smooth tube.The heat transfer coefficient and flow velocity in the corrugated tubes show an overall oscillation trend.The wall average heat transfer coefficient in downstream of the crest was three times higher than that in upstream of crest.It was because that a counterclockwise vortex would generated when the fluid passes through each node,and this vortex would drive part of the fluid out of the mainstream at the downstream of the node and into the entire nodal region,where it would be cooled by the wall and break the gas film at the downstream of the node.After staying for a period of time,this part of fluid was sucked back to the mainstream in upstream of crest.However,the upstream of crest formed a reflux zone due to vortexes.So the upstream of crest in corrugated tube plays a decisive role in the enhancement of heat transfer process.the wall average heat transfer coefficient in the corrugated tube increases with the decreases of the pitch spacing and the increases of the width of the wave node.Within the range of the parameters studied in this paper,the influence of wave height on the wall average heat transfer coefficient and skin friction coefficient was maximum,which followed by the width of the wave node and the pitch spacing.The results of numerical analysis show that the reduction of wall average heat transfer coefficient in smooth tube was higher than that of corrugated.tube with the content of non-condensable gas increases.Due to the action of nodules,corrugated tubes have a remarkable effect of enhancing heat transfer.The research results above play a certain guiding role for the heat transfer and flow characteristics of mixed gas condensation in the special type heat exchange tube.