How Does Evaporative Cooling Keep Beverages Cold?

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Homework Help Overview

The discussion revolves around the concept of evaporative cooling, specifically how a porous ceramic container soaked in water can keep a beverage cold despite a warmer environment. The scenario includes specific temperatures and dimensions, and participants are examining the energy exchanges involved in this process.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster questions whether the heat transfer required to raise the temperature of water to 100 degrees C should be considered in the context of evaporation. Other participants discuss the nature of evaporation occurring at room temperature without a temperature change.

Discussion Status

The discussion is ongoing, with participants exploring different aspects of the problem. Some guidance has been offered regarding the nature of evaporation, but there is no explicit consensus on the assumptions being made about heat transfer.

Contextual Notes

Participants are working with specific assumptions about emissivity and energy exchanges, while also addressing the limitations of the provided solution from the manual. There is a focus on the conditions under which evaporation occurs and the implications for the problem at hand.

laksate
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A cold beverage can be kep cold even on a warm day if it is slipped into a porous ceramic container that has been soaked in water. Assume that energy lost to evaporation matches the net energy gained via the radiation exchange through the top and side surfaces. The container and beverage have temperatures of 15 degrees C, the environment has temperature of 32 degrees C and the container is a cylinder with radius of 2.2cm and height of 10cm. Approximate the emissivity as 1 and neglect other energy exchanges. At what rate dm/dt is the container losing water mass.

Now I have attached the solution from the solutions manual. However my problem with the solution is shouldn't it be considered that heat must be transferred to bring the temperature of the water up to 100 degrees C?
 

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can you guys access the attachment or is it still pending approval
 


laksate said:
can you guys access the attachment or is it still pending approval

Generally it's better to put in a link to the picture if you can.
 


Well I only have the file, it is not available anywhere on the internet. The picture has been approved and now you guys can view the picture.

Can anyone help me with this problem?
 
Welcome to PF!

Hi laksate ! Welcome to PF! :smile:
laksate said:
Now I have attached the solution from the solutions manual. However my problem with the solution is shouldn't it be considered that heat must be transferred to bring the temperature of the water up to 100 degrees C?

No … evaporation happens without any change in temperature …

even at "room temperature", some of the molecules are going fast enough to get away! :biggrin:

For some more detail, se http://en.wikipedia.org/wiki/Thermal_radiation :wink:
 

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