Experimental Study Of Steam Condensation Heat Transfer In Vertical Tube With/Without Mesh Tube Insert

Condensation is an efficient phase change heat transfer process.Enhancing condensation heat transfer can realize the miniaturization and cost reduction of the seawater desalination system,and reduce the cold end parameters of the heat conversion system,improving energy conversion efficiency to meet carbon Peak and carbon neutral demand.The existing enhanced technology mainly follows the idea of single-phase heat transfer enhancement.The research group proposed the flow pattern modulation,that is,the idea of "phase separation".We inserted a wire mesh tube into the condenser tube,developing a new phase separation condenser.The previous research mainly focused on the enhancement of the condensation heat transfer of the organic working fluid in the ORC system.The visualization and condensation heat transfer experiments in the horizontal tube under normal pressure and medium and high pressure were performed.This article mainly focuses on the condensation system in thermal power plants.The steam condensation in vertical tube is studied under vacuum.It not only discusses the influence of wire mesh tube on heat transfer performance,but also pays attention to the effect of wire mesh tube on vapor-liquid two-phase flow Influence of resistance and instability of two-phase flow.The condensation heat transfer experiment of steam is performed in a vertical tube.The inner diameter of the tube is 14.83 mm,and the length of the tube is 1000 mm.The inlet vapor pressure is in the range of 7～25 kPa,the corresponding saturation temperature is 40～65℃.The vapor mass flow rate G=5～20 kg/m2s,the inlet vapor mass qualities xin=0.5～0.8,and the mass flow rate of cooling water mc=50～300 kg/h.The experimental runs are divided into two conditions:the flooding flow and the annular flow.For flooding flow,the steam-liquid flooded under the action of interfacial shear force,friction force and gravity.Periodic fluctuations of the entrance temperature and tube wall temperature of the test section occurred,resulting in heat transfer deterioration and larger pressure drop.For annular flow,the temperature distribution in the heat transfer tube is uniform,and the heat transfer coefficient increases with the increase of G and xin.For improving the condensation heat transfer performance,we inserts three stainless steel mesh tubes with mesh pore size of 15 μm,200 μm,350 μm into tube,respectively.Among them,the mesh tube with pore size of 200 μm insert has the best overall performance of heat transfer and pressure drop.The mesh tube divides the flow region in heat transfer tube into two regions:annular region and the core region.For flooding flow,the steam slug was squeezed into the annular region with the capillary force the mesh tube,which improves the vapor quality and makes the liquid film thin.Due to the pressure difference between the two regions,the long steam slug will break at the entrance of the mesh tube.More condensate is sucked into the core region,reducing condensate accumulation and avoiding slug reversal.So flooding is eliminated.The effects for flooding flow with a mesh tube insert are:(1)the flooding is suppressed,and the temperature fluctuation is reduced by 79.17%,(2)the steam condensation heat transfer is enhanced,up to 7.47 times,(3)the friction pressure drop is reduced effectively,and the maximum reduction is 48%.For annular flow,under the "attractive" effect of the mesh micropores,the condensate in annular region is sucked into core region,the liquid film becomes thinner and the condensation heat transfer is enhanced,and the maximum is 1.77 times.The insert reduces the two-phase flow area,leading to the friction pressure drop increase.In a word,the comprehensive factor PEC>1,which indicates that the heat transfer performance is improved with mesh tube insert.This paper confirms the modulation of mesh tube on the slug flow pattern and the annular flow pattern in the vertical tube.The condensation heat transfer was enhanced with mesh tube insert.The energy conversion rate of the condensation heat transfer equipment was improved,which is significance for practical industrial applications.