# How long does it take to heat up a material? Solar Energy.

## Main Question or Discussion Point

I was wondering how long it takes to heat up materials. And how long will they hold their energy?

Say for like thermal energy storage, how long does it take to heat up molten salts or other substances with sunlight? I guess I could just use Q=mcT and divide by time and then solve for time, but how do you calculate how much energy is radiated away while you are heating the substance? And how do you calculate how long a substance will hold its energy, or how fast it will radiate away its energy?

Also, I'm using large temperature ranges and was wondering how the specific heat values change with temperature. I would like to get as accurate results as possible.

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Mech_Engineer
Gold Member
I was wondering how long it takes to heat up materials. And how long will they hold their energy?
The measure of how much energy is required to heat a material is called it's "specific heat capacity." Wikipedia Article: http://en.wikipedia.org/wiki/Heat_capacity

How long they hold their energy will depend on the heat transfer environment around them.

Say for like thermal energy storage, how long does it take to heat up molten salts or other substances with sunlight? I guess I could just use Q=mcT and divide by time and then solve for time,
On the first order it's basically a heat transfer calculation where you calculate the total thermal mass, and then use the amount of power in to solve time.

but how do you calculate how much energy is radiated away while you are heating the substance? And how do you calculate how long a substance will hold its energy, or how fast it will radiate away its energy?
That depends on a lot of other factors, all part of heat transfer. You need to know something about the air around it (convection), what it's attached to (conduction), and what it's surrounded by (radiation).

http://en.wikipedia.org/wiki/Heat_transfer

Also, I'm using large temperature ranges and was wondering how the specific heat values change with temperature. I would like to get as accurate results as possible.
Depending on the material, properties as a function of temperature are available in published literature (likely) or possibly free online (unlikely, unless it's a fluid). My heat transfer text book has a lot of temperature dependent material properties for common engineering materials like metals (aluminum, steel, titanium, copper, etc.) and building materials (cement, wood, etc.).

ASTM should have what you're looking for: www.astm.org

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