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

[StillDumb]

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.

 

[Mech_Engineer]

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 into 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 textbook 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

 

[sophiecentaur]

Also, the thermal conductivity of the material of the object itself is very relevant. Even with 'forced cooling', keeping the outside of the object very cold, the core could be maintaining a high temperature until the heat has had time to transfer to the surface. (Think of cooking the Christmas turkey - same thing but the other way round).

 

[BilPrestonEsq]

There is a site that has a lot of useful information. Search: engineering toolbox. There is a lot of information on properties of many different materials. The work being done in creating insulating ceramic coatings should be interesting to you also.

 

[alphy]

The time it takes to heat up a material depends on a variety of factors, including the type of material, the amount of heat being applied, and the method of heating. In the case of solar energy, the time it takes to heat up a material also depends on the intensity of the sunlight and the efficiency of the solar collector.

In terms of thermal energy storage, the time it takes to heat up a substance such as molten salts will depend on the amount of sunlight hitting the collector and the surface area of the collector. The larger the surface area, the more sunlight can be absorbed and the faster the substance will heat up. As for calculating the amount of energy being radiated away while heating the substance, this can be done by using the Stefan-Boltzmann law, which relates the energy radiated by an object to its temperature and surface area.

The duration for which a substance can hold its energy also depends on various factors, such as the insulation of the storage container and the ambient temperature. In general, the higher the insulation and lower the ambient temperature, the longer the substance will hold its energy.

Specific heat values do change with temperature, but for most materials, this change is relatively small. To get accurate results, it is best to use specific heat values that are specific to the temperature range you are working with. These values can be found in tables or calculated using thermodynamic equations.

Overall, the time it takes to heat up a material and the duration for which it can hold its energy will vary depending on the specific conditions and variables involved. It is important to consider all these factors when designing and conducting experiments involving solar energy and thermal energy storage.