energy2d power density heated concrete slab

[frankquietly]

Hello, I am new here, nice to meet you. Have been modelling a heated slab in Energy2d. I've come unstuck by "power density" (W/m^3). I am used to thinking of a heated slab in terms energy flux, say 50 W/m^2. My brains melts when I start thinking of how the power density is some relation to the energy input to the slab, the emissivity of concrete, a coefficient of temperature. Note I am keen to use power source  in Energy2d as can control those with a thermostat. Appreciate any advice or pointers to research.  

 

 

[Jenki]

I can't help direct..but suggest you look up @Terry H blogs he modelled his Slab and there may well be some helpful information in there.

[SteamyTea]

3 hours ago, frankquietly said:

I've come unstuck by "power density" (W/m^3)

Not seen expressed like that, and I am tired after work.

 

W [watt] can be expressed as J.s^-1 [joule per second].

 

J [joule] can be expressed as kg.m².s^-2 [kilogram times, metre squared, times second raised to the power minus 2]

 

I think you probably need to know the specific heat capacity of the floor material i.e. concrete ~0.8 J.kg^-1.K^-1, then convert it to a volumetric heat capacity with the material density i.e. concrete 2700 kg.m^-3.

 

Then cancel out what you can.

 

I tried to rearrange it all, but too tired.

All seems a bit complicated this late at night, but luckily we have a mathematician professor on here, so maybe @Garald will be along to finish off the sums.

 

It is starting to look very similar to the thermal effusively, or thermal inertia units.

W.s^0.5.m^-2.K^-1

https://en.wikipedia.org/wiki/Thermal_effusivity

Edited January 26, 2023 by SteamyTea

[frankquietly]

Thank you for your help, @Jenki assume you meant TerryE, found the Fortran model info, very helpful.

 

@SteamyTea as I was failing to model the concrete material as a power source, I decided to remodel it as a 3 layer onion. The inner core being water (this water layer being the thermostatically controlled power source), wrapped in PEX, wrapped in concrete. This has moved the power density problem to the water layer only, which at least makes it more searchable on the web, water heating being the defacto examples everywhere! I'll get into it again soon and see if can solve now it's a ?simpler? water problem.

 

 

 

[SteamyTea]

45 minutes ago, frankquietly said:

I'll get into it again soon and see if can solve now it's a ?simpler? water problem.

I shall have a ponder as well, but today is Comic Day, so shall be a bit occupied.

I last looked at these problems about 15 years ago, seem to remember that they were not that complicated, but time erodes the memory of the techniques.

 

[Jenki]

3 hours ago, frankquietly said:

Thank you for your help, @Jenki assume you meant TerryE, found the Fortran model info, very helpful.

Opps - yep TerryE