5 replies to this topic

[LotusG]

So i have a question regarding the heating time of a substance with a high heating capacity. if the melting point is around 20 degrees celsius, the start temperature is 12 degrees celsius, density is 1700 kg/m3 and the Entalpy of the substance is 200 kJ/kg, how long does it take before one big cube of 330 L is melted in a styrofoam box when the box is heated with a 2000 W heater?

[Pilesar]

Is this a school problem? What is the assignment? Is this a professor's imagination at work to try and teach problem solving?

[LotusG]

It's for a project, the substance needs to be liquid to use for another application. When I calculated it, it would probably take 50 hours but don't know if that's correct. Any ideas on how to approach this?

[Pilesar]

Well, the solid substance is not metal... some sort of grease maybe? Is it a true solid or just a very viscous liquid? Pellets or a large block? If a large block, then the solid that contacts the surface of the heater will probably melt quickly. If the liquid then separates from the solid, the solid will have no contact with the heater or the hot liquid and will stay a solid for a long time. Several days later there will still be some solid left. I would not expect 'theoretical calculation' to get an accurate prediction. An experiment might help. There is not enough info in the problem statement to give a good answer. Consider just leaving the solid in a warm room for a week or so outside of the styrofoam box.

[latexman]

I think the best path forward is for you to attach your complete work.

 

In "Reply to this topic", click "More Reply Options".  Use the "Attach Files" functions to browse to, upload, and attach your work.

 

Remember, more details = better replies.

[MrShorty]

When I think about this, I would start here: https://www.khanacad...-vaporization-2

This is a high school level physics tutorial about heat that ends up walking through the problem of heating H2O from ice at -40 C to steam at 160 C, including sensible heat between phase changes and the latent heat needed to change phases. Even if your fluid is more complex (as others have asked) than a pure component like H2O, it still seems like the same basic ideas are there. How much heat will you need to change the temperature? How much heat will you need to "melt" the solid (or whatever heat is needed to change the phase)? Once you know how much heat is needed, then the time needed should be straightforward, given your constant rate heat source.