If I interpret the help file of OpenLoop version 1.6 correctly, this is possible:
"2. A nodal reference distribution with the name 'OpenLoop' is created to identify participating nodes for a temperature differential. For single-species mass transport, the distribution is called 'OpenLoop Mass', for multi-species transport 'OpenLoop Mass 1' for species 1, 'OpenLoop Mass 2' for species 2, etc..In these reference distributions, all nodes belonging to a specific group (injection and extraction nodes) are assigned a value equal to the number of the time-varying power function containing the corresponding temperature or concentration differential. All other nodes need to be given values less than or equal to 0 (default in FEFLOW is -99999 = nodata). Be careful with mesh refinement: In case of refining the mesh after assigning the power function number, the data interpolation will lead to a number of nodes with non-zero values around the wells, too. "
For heat transport, this would then be OpenLoop Heat 1 etc. The citation is from the last version that we have very recently received from DHI WASY.
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I apologize, I was completely wrong here, misreading the help file - now I checked again. The OpenLoop Mass 1 etc. are for multiple species, not for multiple groups of wells. Groups of wells with separate temperature differentials are simply assigned different values in the User Data distribution, corresponding to the time series id to be used for the temperature differential. So if the temperature differential of the first pair of wells is in time series 50, the two (or more) well nodes get the value 50 in the User Data Distribution OpenLoop. Assuming the second pair has time series 60, those nodes need to get 60 as their value.
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