  Microscopic mechanisms of externally controlled reversable heat flow through
the carbon nanotube junctions (NJ) are studied theoretically. Our model
suggests that the heat is transfered along the tube section ${\cal T}$ by
electrons ($e$) and holes ($h$) moving ballistically in either in parallel or
in opposite directions and accelerated by the bias source-drain voltage $V_{\rm
SD}$ (Peltier effect). We compute the Seebeck coefficient $\alpha $, electric
$\sigma$ and thermal $\kappa$ conductivities and find that their magnitudes
strongly depend on $V_{\rm SD}$ and $V_{\rm G}$. The sign reversal of $\alpha$
versus the sign of $V_{\rm G}$ formerly observed experimentally is interpreted
in this work in terms of so-called chiral tunneling phenomena (Klein paradox).
