Posted Fri, 31 Aug 2018 06:25:17 GMT by dazy

In the framework of my master's thesis I'm trying to model the influence of rainwater infiltration on the geothermal gradient (ground temperature).

As a first step, I made a simple unsaturated model with Hydraulic head BCs on two sides.
Heat BCs are:
- fixed Temperature BC on the bottom of the model
- Heat flux BC out of the model (on the top)
The simulation of hydraulic head and ground temperature works fine.

When I insert infiltration into the model (via In/Outflow on Top/Bottom), the change in ground temperature distribution is reasonable, but the Rate Budget for heat transport is way too high. It seems like all the heat (I'm trying to simulate different temperatures of infiltration) that comes into the model with infiltration, doesn't go out, whereas the Rate budget for Fluid is perfectly fine (what goes in - goes out).
I'm using convective transport equation.

Is there any better way of setting BCs to improve the model reliability and reduce the Heat imbalance? I would appreciate any suggestion, as my time with the licence is limited.

Thank you and best regards,
Posted Mon, 03 Sep 2018 11:42:44 GMT by Björn Kaiser
It's difficult to say anything about the reason for the high imbalance. In general, a groundwater flow model with a small imbalance for the fluid does not necesserily imply a small imbalance for the temperature. In most of the cases the large imbalance can be attributed to the spatial descrizitations. For more details, I suggest to contat the FEFLOW Support:

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