Discussion Forum

Hello Guys, This is nicknamed by Johnny and i would like ask and have a little disccusion about Heat transfer model with respect to convective coefficient.

My goal is to compare numerical analysis results with field test results which are both time-dependent.

Briefly explaning the geometry in my model, i have Soil, Rocks, Concrete. If you see my attached file please(i will send it by email if anyone can really feel into it), you can easily find out how they are aligned and designed.

Inside the concrete box, there lies Line heat Source with a 1.5W/m which creates the temperature change throughout the whole sections.

Details :
1. I have given a out-temperature at the boundary of top and slope side
2. I have read an average temperature inside the concrete box in order to spread out through the concrete box.

Two details above deal with convective coefficient and i have given 15.4W/m^2K and 3.0W/m^2K, respectively. These values are obtained by trial and error many times.

Value 15.4 for out-temperature condition is free-convective heat coefficient and 3.0 for concrete box is i guess forced-convective heat coefficient. (i believe)

Regarding the results, the time range is about 10 months, starting from winter to summer. When i compare the results with field test data, both results were almost close at the very beginning up to 4 months but it starts to have a big temperature difference after 4 months which the weather (out temperature) starts to increase. ( the difference is up to 2~2.5 celcius).

And when i plot a graph, it seems like there is a bit time lag in my model and i cannot find exactly what the reasons are.

Will you guys please find why it happens ?

Summary :

1. Is it because the heat coefficient is wrong ? then how should i start with?
2. or do i need to consider a convection? because my model seems considering only conduction.

Thankyou guys