Which surface does the dropwise condensation occurs on?
Dropwise condensation of steam has been observed on chromium and gold surfaces which are very smooth, without use of a promoting agent.
Can condensation occur on hydrophobic surfaces?
On hydrophobic surfaces, condensation forms in droplets [9] . During the condensation of water vapor, heat is released, causing an increase in temperature at the point of condensation. …
Why is there condensation in dropwise?
Under certain conditions, dropwise condensation provides for much higher heat transfer rates than filmwise condensation. Although a drop has a larger surface area than a film occupying the same surface area, this difference is relatively small.
What is dropwise and Filmwise condensation?
In filmwise condensation a laminar film of vapour is created upon a surface. This film can then flow downwards, increasing in thickness as additional vapour is picked up along the way . In dropwise con- densation vapour droplets form at an acute angle to a surface .
Which surface does the drop wise condensation occur on * 1 point?
Explanation: It generally occurs on oily surface.
What is film condensation process?
Film condensation occurs when the temperature of a vertical, impermeable, and wettable wall next to a porous medium saturated with vapor falls below saturation temperature (Fig. 8.29). The latter will create a two-phase region between the liquid film and the vapor region, where both condensate and vapor are present.
How do you get dropwise condensation?
Dropwise condensation is achieved by adding a promoter chemical into the vapor, and/or roughened surfaces and surface and surface coated with hydrophobic impurities like fatty acids and organic compounds, known as dropwise promoters.
How do I increase dropwise condensation?
Jumping droplets have been shown to enhance dropwise condensation through accelerating surface refreshing and reducing time-averaged droplet thermal resistance on the surface [22, 66, 86, 87].
Is dropwise condensation stable?
The heat transfer coefficient was found to increase with increasing steam pressure and decrease with increasing surface subcooling. The stability of dropwise condensation was maintained for 8 months. The measured condensation heat transfer coefficient was found to be 5.5 times larger than that for film condensation.
How can we convert dropwise to Filmwise condensation?
Dropwise condensation can be sustained for a long time by the combined effects of surface coating and periodic injection of the promoter into the vapor. When dropwise surfaces degrade, they convert to filmwise condensation.
How does dropwise condensation differ from film condensation which mode of condensation is characterized by larger heat transfer rates?
The drops form cracks, pits, and cavities on the surface and may grow and coalesce through continued condensation. Which mode of condensation is characterized by larger heat transfer rates? Dropwise condensation heat transfer rates are more than an order of magnitude larger than those associated with film condensation.
How can the rate of heat transfer from dropwise condensation?
During the condensation process, a continuous liquid film flowing downward will be formed and the steam must pass through this film to exchange heat of the surface. It will increase the thermal resistance of heat transfer, and thus the heat transfer capability is limited.