Assertion (A): Even though dropwise condensation is more efficient,sur...
Ans. (b) A and R are true. R is not correct reason for A.
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Assertion (A): Even though dropwise condensation is more efficient,sur...
Assertion (A): Even though dropwise condensation is more efficient, surface condensers are designed on the assumption of filmwise condensation as a matter of practice.
Reason (R): Dropwise condensation can be maintained with the use of promoters like oleic acid.
The correct answer is option B - Both A and R are individually true, and R is the correct explanation of A.
Explanation:
Surface Condensation:
Surface condensation is a process that occurs when a vapor comes into contact with a cooler surface and undergoes a phase change to become a liquid. In surface condensers, the vapor is condensed on the surface of a solid material, typically a metal, which acts as a heat exchanger. The condensed liquid is then collected and removed from the system.
Filmwise Condensation:
In filmwise condensation, the liquid film flows smoothly and uniformly over the surface without any drops or discontinuities. This type of condensation is commonly assumed in the design of surface condensers because it provides a predictable and uniform condensation rate. The design calculations for surface condensers are based on this assumption of filmwise condensation.
Dropwise Condensation:
Dropwise condensation, on the other hand, occurs when the condensed liquid forms discrete droplets on the surface. This type of condensation is more efficient than filmwise condensation because the droplets have a smaller contact area with the surface, reducing the resistance to heat transfer. However, dropwise condensation is not commonly observed in practice due to the tendency of the liquid film to wet the surface, leading to the formation of continuous films instead of discrete droplets.
Use of Promoters:
The use of promoters, such as oleic acid, can help maintain dropwise condensation by reducing the surface tension and promoting the formation of discrete droplets. These promoters work by altering the surface properties of the condensing surface, preventing the formation of continuous films and promoting dropwise condensation.
Explanation of the Assertion and Reason:
The Assertion states that surface condensers are designed on the assumption of filmwise condensation, even though dropwise condensation is more efficient. This is because dropwise condensation is not commonly observed in practice. The Reason states that dropwise condensation can be maintained with the use of promoters like oleic acid. This provides the correct explanation for the Assertion, as the use of promoters can help overcome the limitations of dropwise condensation and promote its occurrence.
In conclusion, both the Assertion and Reason are individually true, and the Reason correctly explains the Assertion.
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