using commands (APDL), how can we select all the nodes on the exterior surfaces of a volume like a block? I want to impose constant temperatures as BCs but I don't want to choose them one by one.
I'm not terribly familiar with the ADPL, but you can replicate this procedure for the GUI, and then look in the log to see what the specific commands were for your geometries.
Select your volume, select the areas of interest, then select nodes->attached to->areas, all
that will select all nodes attached only to the surface of your volume!
oops I just noticed, using the allsel command if you are using volume elements you would get all the nodes in the volume. Apologies. You will have to also use nsla as suggested in the first reply.