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Questions and Answers
Why are higher heat-transfer rates experienced in dropwise condensation compared to film condensation?
Why are higher heat-transfer rates experienced in dropwise condensation compared to film condensation?
- Increased thickness of the condensation layer in dropwise condensation
- Reduced surface area exposed to vapor in dropwise condensation
- Higher pressure in the vapor phase during dropwise condensation
- Lack of film barrier in dropwise condensation (correct)
Why is dropwise condensation preferred over film condensation?
Why is dropwise condensation preferred over film condensation?
- It experiences lower heat-transfer rates
- It requires a thicker condensation layer
- It is easier to maintain over extended periods of time
- It experiences higher heat-transfer rates (correct)
What makes maintaining dropwise condensation difficult over time?
What makes maintaining dropwise condensation difficult over time?
- Low heat-transfer rates
- Increased surface area exposed to vapor
- High pressure in the vapor phase
- Wetting of most surfaces after exposure to condensing vapor (correct)
Which method has not been successful in maintaining dropwise condensation according to the passage?
Which method has not been successful in maintaining dropwise condensation according to the passage?
What effect does cupric oleate coating have on the condensation process?
What effect does cupric oleate coating have on the condensation process?
What influence does a thermocouple probe have on the steam condensation process depicted in Figure 2?
What influence does a thermocouple probe have on the steam condensation process depicted in Figure 2?
What is the main difference between film condensation and dropwise condensation?
What is the main difference between film condensation and dropwise condensation?
What happens if the temperature of the plate is below the saturation temperature of the vapor in condensation heat transfer?
What happens if the temperature of the plate is below the saturation temperature of the vapor in condensation heat transfer?
What does dropwise condensation refer to?
What does dropwise condensation refer to?
How can film condensation be described in terms of thermal resistance?
How can film condensation be described in terms of thermal resistance?
Why is it important for a chemical engineer to understand boiling and condensation processes?
Why is it important for a chemical engineer to understand boiling and condensation processes?
What is characteristic of film condensation on a vertical flat plate?
What is characteristic of film condensation on a vertical flat plate?
What does the equation 𝛿𝑀𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 = න 𝜌 𝑢 𝑑𝑦 represent?
What does the equation 𝛿𝑀𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 = න 𝜌 𝑢 𝑑𝑦 represent?
By using the boundary condition that u=0 at y=0, what value was determined?
By using the boundary condition that u=0 at y=0, what value was determined?
What is a key result of integrating the equation 𝜌𝑙 − 𝜌𝑣 𝑔 𝑦2 𝑢= 𝛿𝑦− +𝐶 𝜇 2?
What is a key result of integrating the equation 𝜌𝑙 − 𝜌𝑣 𝑔 𝑦2 𝑢= 𝛿𝑦− +𝐶 𝜇 2?
What does the equation 𝛿 𝑚ሶ = න 𝜌𝑙 0 𝜌𝑙 − 𝜌𝑣 𝑔 𝑦2 𝛿𝑦− 𝜇 2 𝑑𝑦 represent?
What does the equation 𝛿 𝑚ሶ = න 𝜌𝑙 0 𝜌𝑙 − 𝜌𝑣 𝑔 𝑦2 𝛿𝑦− 𝜇 2 𝑑𝑦 represent?
What is the derivative with respect to x of the function m(x) = 3𝜇𝑙?
What is the derivative with respect to x of the function m(x) = 3𝜇𝑙?
What does the formula $m(0)$ represent in the context of condensation process?
What does the formula $m(0)$ represent in the context of condensation process?
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Study Notes
Condensation Types
- There are two types of condensation: film condensation and dropwise condensation.
- In film condensation, a smooth film is formed on the surface, and the process is characterized by a temperature gradient in the film.
- In dropwise condensation, droplets are formed that fall down the surface in a random fashion.
Dropwise Condensation
- Dropwise condensation has higher heat-transfer rates, up to 10 times higher than film condensation.
- However, it is extremely difficult to maintain due to surface wetting over time.
Film Condensation
- In film condensation, the surface is blanketed by the film, which grows in thickness as it moves down the plate.
- The film represents a thermal resistance to heat transfer.
Plate Coating Effect
- The effect of plate coating on the condensation process can be seen in Figure 2, where the right side of the plate is clean copper and the left side has a coating of cupric oleate.
- The coating promotes dropwise condensation.
Heat Transfer and Condensation
- Boiling and condensation are classified as forms of the convection mode of heat transfer.
- Condensation heat-transfer phenomena involve the change of a vapor to a liquid or a liquid to a vapor.
- The chemical engineer must understand the processes involved to design the appropriate heat transfer equipment.
Mass Flow of Condensate
- The mass flow of condensate through any x position of the film is given by the equation: 𝛿 𝑚ሶ = 𝑚ሶ = න 𝜌 𝑢 𝑑𝑦.
- The equation can be integrated and solved using the boundary condition u=0 at y=0.
Rate of Condensation
- The rate of condensation of vapor over a vertical distance dx is given by the equation: 𝑑𝑚ሶ 𝑔𝜌𝑙 𝜌𝑙 − 𝜌𝜈 𝛿 2 𝑑𝛿 = 𝑑𝑥 𝜇𝑙 𝑑𝑥.
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