Query on Boiling of water placed on the surface of plate

[akhilsharma47]

Guys...I have a very simple doubt. I want to boil water placed on the surface of the plate using the hot air blower. Yes, we have to apply forced convective heat transfer equation but my doubt is whether I have to consider the heat transfer due to humidity separately or it is just included into the convective HT equation ?

 

[IRstuff]

What do you mean by humidity? If you are talking about evaporation, then no, the standard convective equation does not.

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[akhilsharma47]

By humidity I meant that if I want to evaporate water by blowing hot air on its surface then, should I use the simple convective heat transfer equation? or do I need to solve this problem by plotting it on psychometric chart and finding change in enthalpy corresponding to different relative humidity ?

 

[MintJulep]

Boiling and evaporating are not the same. You have used both terms, so it's not really clear what you are trying to accomplish.

Evaporation is driven largely by the difference in vapor pressure.

Depending on a lot of things, notably how much water, how big is the plate and how much air, and what temperature, this is not a trivial problem. So perhaps your doubt needs to be bigger.

 

[akhilsharma47]

Yeah sorry... I have used wrong term, its evaporation.

Basically my problem is to select a hand dryer necessary to blow hot air over an surface area A of water (at temperature T0) with thickness t placed over a plate, so that the water can be evaporated in time t.For that I may need to find the particular velocity and temperature of air at which the water evaporates.

My objective is to get the expression between these variables somehow so that I can then make some appropriate assumptions if needed to solve the problem.

Thanks

 

[chicopee]

It's also a mass transfer problem, so get a heat transfer book and that subject will be introduced.

 

[dvd]

Is the hot air blower the only possible choice? It may be worth considering radiant heat to evaporate/boil from above.

 

[dbill74]

What are you trying to accomplish? Is this some attempt to dry something?
This almost sounds like a homework assignment, which is not permitted in these forums. In which case, go ask your professor.

 

[akhilsharma47]

This is not a home assignment, it is a small part of my project.

 

[dbill74]

All good. Still not clear on the objectives of this part of your project. It sounds like you are trying to dry something that is flat. I wonder why though you need to dry with hot air. It will take a lot of energy to do that. Is there some reason you cannot dump or blow the water off? Using your example, a hand dryer blows water off your hands more than it evaporates the water. If the air from a hand dryer is hot enough to evaporate water off you hands, you will burn your hands.

If the object to be dried is coming out of a bath, would you not want to recycle as much water as possible?