  We start with a revision study of two coupled spin-$1/2$ under the influence
of Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interaction and a magnetic
field. We first show the role of idle levels, i.e., levels that do not couple
to the external magnetic field, when the system is working as a heat engine as
well as when it is a refrigerator. Then we extend the results reported in [PRE.
92, (2015) 022142] by showing that it is not necessary to change both the
magnetic field as well as the coupling parameters to break the extensive
property of the work extracted globally from two coupled spin-$1/2$ as has been
demonstrated there. Then we study the role of increasing the number of coupled
spins on efficiency, extractable work, and coefficient of performance (COP).
First, we consider two- and three-coupled spin-$1/2$ Heisenberg
$\mathrm{XXX}$-chain. We prove that the latter can outperform the former in
terms of efficiency, extractable work, and COP. Then we consider the Ising
model, where the number of interacting spins ranges from two to six. We show
that only when the number of interacting spins is odd the system can work as a
heat engine in the strong coupling regime. The enhancements in efficiency and
COP are explored in detail. Finally, this model confirms the idea that
entanglement and quantum correlations are not the reasons behind the
enhancements observed in efficiency, extracatable work, and COP, but only due
to the structure of the energy levels of the Hamiltonian of the working
substance. In addition to this, the extensive property of global work as well,
is not affected by entanglement and quantum correlations.
