Research On Distribution Of Liquid Film And Heat Transfer Characteristics For Condensation In A Tube

Condensation heat transfer in a tube is widespread in industrial heat exchange process. Condensate film is the major resistance in condensation heat transfer process for condensation heat transfer in a tube, It is therefore significant to study the condensation heat transfer in a tube and improve its heat transfer efficiency for economic benefits and energy saving.In the condensation heat transfer process of steam in a tube, the liquid film formed by the condensation is the major factor affecting the effect of heat transfer, so a physical and a mathematical model of liquid film for the condensation of steam in a vertical tube on the basis of boundary layer theory considering the shear stress which is caused by steam flow were established. And the distribution of liquid film and the heat transfer performance for pure steam condensation in a vertical tube were investigated. Definitely, it is concluded that: First, the thickness and temperature distribution of liquid film in the condensation heat transfer process of pure steam in a tube have a great impact on the heat transfer. Second, the universal laws that the liquid film thickness and the heat transfer coefficient change along the heat transfer length were discovered. The liquid film thickness increases with the length of the heat exchanger and the gradient becomes smaller from the inlet. But the heat transfer coefficient and the gradient decrease with the length of the heat exchanger. Third, when other conditions are unchanged the liquid film thickness decreases with the decreasing of the steam flow in the same heat transfer location. And the difference of the liquid film thickness corresponds to different mass flows in the same heat transfer location is larger in the first half tube than that in the the second half tube. And the heat transfer coefficient increases with the increasing of the steam flow. Forth, when other conditions are unchanged the liquid film thickness increases and the heat transfer coefficient decreases with the increasing of the steam temperature in the same heat transfer location. The difference of the liquid film thickness corresponds to different steam temperatures increase along the flow direction of steam. Fifth, when other conditions are unchanged the liquid film thickness decreases with the decreasing of the wall temperature in the same heat transfer location. And the heat transfer coefficient increases with the increasing of the wall temperature. The difference of the liquid film thickness corresponds to different wall temperatures increase along the flow direction of steam. Sixth, when other conditions are unchanged the liquid film thickness increases with the increasing of the inner diameter in the same heat transfer location. And the difference of the liquid film thickness corresponds to different inner diameters in the same heat transfer location is larger in the first half tube than that in the the second half tube.The heat transfer performance for pure steam condensation in a inclined tube was investigated detailedly for steam condensation heat transfer characteristics of the tube through physical and mathematical modeling computing. Definitely, it is concluded that: First, when other conditions are unchanged the liquid film thickness decreases with the increasing of the steam temprature in the same heat transfer location. Second, when other conditions are unchanged the pond depth decreases and the heat transfer coefficient increases with increasing of the inner diameter of the tube in the same heat transfer location. Third, when other conditions are unchanged the heat transfer coefficient increases with increasing of the inclined angle in the same heat transfer location.