Dirichlet BC for heat transport

Dear all,
I am working on simulating the coupled process of groundwater flow and heat transport by OGS5 recently. I’m confused about the set of model. In the simulation, I set a Dirichlet BC for heat transport(known temperature of the injected water) and a Neumann flow rate for source term of groundwater flow. How can this kind of setting ensure that the total energy injected in is related to the amount of the inflow? Or is there any way to set a source term for heat transport as well?
Best,
Haoyue