Condensation Flow Characteristics Under Synergetic Control Of Surface Wettability And Gravity

Steam condensation widely applied in various industrial production, such as air conditioning systems, refrigeration technology, automotive industry and many other process industries. How to utilize energy efficiently and enhance heat transfer efficiency is the long-term concern and research problems by researchers. Generally speaking, enhancing condensation heat transfer can be considered from two perspectives:Firstly, increasing extended surface, that is making structural changes on the surface of the tube, the most common is finned tubes, spiral tube, corrugated tube and so on. The second is to change the surface wettability, it can usually be achieved by treatment on the solid surface, increasing the contact angle of steam condensation droplets on the solid wall, so as to form droplet condensation and thereby enhance the heat transfer performance.In this paper, combining the surface modification method to change the surface wettability, the impact of inclination angle and non-condensable gas on the condensation heat transfer is explored, which provides a reference for enhancing steam condensation of different angles of tube and data support for the practical project application.Experimental device of vapor condensation out of inclined tube is set up firstly, and verifying the thermal balance of the experimental setup. Hydrophobic and superhydrophobic surface on the copper tube by octadecanethiol can be prepared by the molecular self-assembly method. The experiment studied on condensation flow and heat transfer characteristics of the different inclined angles of the hydrophobic and super-hydrophobic surfaces under the condition of pure steam and mixed steam with 10% of non-condensable gas. Temperature and pressure can be real-time monitored and recorded, at the same time computing condensation heat transfer data. Also, droplets forming and flowing characteristics can be observed and analyzed by CCD screening from different position.Experimental data show that:droplets on the different locations of the tube have varying contact angle hysteresis, and have a greater impact. For mixed steam conditions with 10% of non-condensable gas, the contact angle hysteresis of droplets of hydrophobic surfaces at different locations are less than pure steam conditions. For different inclined angles of the tube, the contact angle hysteresis has the trend, which decreases with the inclination angle increasing. In the condition of hydrophobic surface, drop diameter decreases with the inclined angle increasing. In the condition of superhydrophobic surface, drop diameter increases with inclined angle increasing. Scouring cycle on the superhydrophobic surface is longer than hydrophobic surface. With the same surface wettability, scouring cycle in the condition of mixed steam is longer than the condition of pure steam.For different inclined angles of hydrophobic surface, at the same surface subcooling, heat transfer coefficient is approximate equality and has the trend, which decreases with the inclined angle increasing. In the condition of pure steam and superhydrophobic surface, when the inclined angle reaches 0°,30° and 45°, its heat transfer performance is approximately equal, and the heat transfer performance reaches the better value at 60°...