Experimental Research On Condensation Heat Transfer Characteristics Of Steam On Metal Foam Tubes Under Sloshing Conditions

Due to the limited space and sloshing conditions of offshore platforms,the thermal system on the platforms(such as FLNG)is required to adopt a condenser with both "high compactness" and "high stability".Metal foam tube has a large specific surface area,which can enhance heat exchange efficiency.Meanwhile,it can increase the mechanical strength of the heat exchange tube and reduce the negative impact of offshore sloshing conditions.However,the complex skeleton structure of metal foam is easy to accumulate liquid,which inhibits its positive effect on the condensation heat transfer.Under the offshore sloshing conditions,the condensation heat transfer characteristics of the metal foam tube is different from that under the static conditions.In order to clarify the condensation mechanism,an experimental research is conducted to investigate the condensation heat transfer of steam outside the metal foam tube under sloshing conditions,and a correlation is developed to reflect the effect of sloshing and surface modification.This research provides a reference for the design of marine high-efficiency condensers.The main results and findings are summarized as follows.1)An experimental rig is designed for testing the condensation heat transfer performance outside the metal foam tube under sloshing conditions.The metal foam tubes with different pore densities are manufactured.They are then treated with surface modification to get hydrophilic or hydrophobic surfaces.A visualization device is adopted to observe the condensation phenomenon in real-time.A direct wall temperature measurement method is realized to achieve accurate measurement of the test results.2)An experimental research on condensation heat transfer outside the foam tube is conducted and the condensation phenomenon is observed.The working conditions in the experiment include pore density,inclination angle and sloshing conditions.The results show that,the 10 PPI foam tube has the best condensation heat transfer performance;with the increase of the inclination angle and sloshing amplitude,the condensation performance outside tubes is increased up to 13% compared to that of horizontal metal foam wrapped tubes in static state;with the increase of the sloshing frequency,the condensation performance outside tubes is decreased up to10%.A correlation of heat flux outside the foam tube under sloshing conditions is developed based on the Nusselt’s model.The results predicted from the proposed correlation is consistent with 94% of the experimental results,and the prediction deviation is within ±5%.3)An experimental research on condensation heat transfer outside the surface modified foam tubes is conducted and the condensation phenomenon is observed.The same working conditions as the unmodified experiment are investigated.The results show that,the hydrophobic modification enhances the condensation heat transfer outside the foam tube;with the increase of the inclination angle and sloshing amplitude,the condensation performance outside hydrophobic foam tubes is increased up to 14% compared to that of horizontal hydrophobic metal foam wrapped tubes in static state;with the increase of the sloshing frequency,the condensation performance outside hydrophobic foam tubes is decreased up to 10%.A correlation of heat flux outside hydrophobic foam tubes under sloshing conditions is developed based on the correlation of heat flux outside unmodified foam tubes.The correlation predicted from the proposed correlation is consistent with 98% of the experimental results,and the prediction deviation is within ±5%.