Numerical Simulation Studies On Heat And Mass Transfer Law Of Steam Condensation On Shell Side Of Atmospheric Condenser

The atmospheric condenser is mainly used in the ship steam system for the recovery of the secondary steam and the excess steam of the boiler.It is an important equipment that can ensure the stable and economic running of the ship steam system.The flow and heat transfer process on its shell side are affected by many factors,mainly including pipe bundle arrangement,tube spacing and non-condensed gas,which may lead to the deterioration of heat transfer and vibration of pipe bundle and bring many difficulties to the design and maintenance of condensers.This paper has studied the flow field on the shell side of atmospheric condensers and analyzed the influence of the above factors on the condensing process,which is of great significance to the design and maintenance of atmospheric condensers.In this paper,the mathematical model of steam condensation process has been established based on ANSYS FLUENT for the verification on the accuracy and accuracy of the model by the experimental data of steam condensation outside the horizontal one-pipe mentioned in references.Then,the non-uniformity of circumferential flow and heat transfer outside the pipe has been analyzed,and the effect of steam velocity and pipe diameter on the condensation process has been studied.Besides,the numerical simulation scheme of the steam condensation process on the shell side of the atmospheric condenser has been determined based on the horizontal one-pipe numerical simulation scheme.The characteristics of flow,heat transfer and pressure drop in the condensation process on the shell side of the atmospheric condenser are studied,and the influence of pipe bundle arrangement,tube spacing and non-condensed gas on the condensation process is analyzed.In the horizontal one-pipe model,the separation of steam boundary layer is captured and the relationship between the separation angle of the boundary layer and Reynolds number is analyzed,and the distribution law of circumferential heat transfer outside the horizontal pipe is explained by the distribution law of two-phase velocity outside the horizontal pipe.The coefficient fluctuation of circumferential heat transfer is about 2 kW/(m~2·K)and the fluctuation of the circumferential wall temperature is about 4.5 K.The heat transfer coefficient decreases gradually with the increase of heat flux and pipe diameter and increases with the increase of steam velocity.The two-phase velocity on the shell side of the atmospheric condenser decreases row by row under the two bundle arrangements of aligned pipes and staggered pipes;and the heat transfer coefficient and pressure drop of each row are reduced under both arrangements,and the heat transfer coefficient and pressure drop of each row under staggered pipe arrangement are higher than that under aligned pipe arrangement.And the difference between the heat transfer coefficient and pressure drops under two arrangements decreases gradually with the increase of the number of pipe-row.The average coefficient of heat transfer on the shell side of the atmospheric condenser decreases with the increase of the pipe spacing.When there is air in the steam,the coefficient of heat transfer decreases obviously.And when the mass fraction of air is1%,the average heat transfer coefficient of the pipe-bundle under aligned arrangement is only 49.34%of the heat transfer coefficient for the condensation of pure steam under the same parameters,and the average heat transfer coefficient of pipe-bundle under staggered arrangement is only 50.27%of that under the same parameters.Further more,when the air content continues to increase,the heat transfer coefficient will keep decreasing and fluctuates more sharply with the reduction of the air content.