I get the impression that our reluctance to speak of heat "flow" is
motivated by a
"caloric-phobia" and our fear of being counted a secret believer in
caloric.
If physics had always appreciated the molecular basis of "thermal
energy", so that caloric had
NEVER been proposed, we would feel free to speak of the flow of heat
just as glibly as we
now speak of the flow (or transport, or velocity, or propagation) of so
many other non-
substantial (and even purely mathematical) entities without outcries of
"heresy!" from
our colleagues.
I strongly recommend the (laborious) reading of Bridgman's "The Nature
of Thermodynamics"
(Harper Torchbooks, 1961) in which the "flow" of all sorts of things is
examined. This
includes the flow of heat, the flow of mechanical energy within
stressed, moving structures
(a highly useful - perhaps indispensable - model in mechanical
engineering), the flow of entropy
(which can even increase in total quatity as it "flows"!), etc. He also
examines the block sliding
over the plate! Also criticized is the notion of describing entropy as a
measure of "disorder"!
Something for everyone, but it is slow, philosophicaly pedantic reading.