[teguhtf]

Dear all,

I am simulating dimple effect on coil ground heat exchanger in transient in Ansys FLUENT 17.2. This is my first time I do transient simulation.

I have done simulation on the dimple effect on the coil but I just observe steady state heat transfer the water side only. On my steady state shows that there is noticeable increase of heat transfer.

So, now I simulate the dimple coil and ground in transient condition. Then, I compare with the similar condition to plain coil. For initial temperature distribution inside ground, I use experimental data. The boundary condition of top surface is constant temperature, bottom is constant heat flux, and vertical wall is constant temperature (Similar with temperature distribution in transient condition).

My first attempt I use k-omega SST, and residual graph of energy is 10^-6, time step size is 60 seconds for 24 hour flow simulation.. I find the transient heat transfer value of dimple coil is realistic however this heat transfer is overlapping each other. It seems that there is no effect of using dimple.

Then, my second attempt I change convergence criteria for energy 10^-7, time step size 30 seconds for 24 hours flow simulation. I find there noticeable different between dimple coil and plain coil. However, both heat transfer rate value is not realistic. The value is too big compared to experiment results.

Both case use similar settings such as 1st order upwind for all parameters except pressure equation the other settings are defaults.

Do you have any suggestion?

Thank you
Best regards
Teguh