  We formulate an endoreversible finite-time Carnot cycle model based on the
assumptions of local equilibrium and constant energy flux, where the efficiency
and the power are expressed in terms of the thermodynamic variables of the
working substance. By analyzing the entropy production rate caused by the heat
transfer in each isothermal process during the cycle, and using an
endoreversible condition applied to the linear response regime, we identify the
thermodynamic flux and force of the present system and obtain a linear relation
that connects them. We calculate the efficiency at maximum power in the linear
response regime by using the linear relation, which agrees with the
Curzon-Ahlborn efficiency known as the upper bound in this regime. This reason
is also elucidated by rewriting our model into the form of the Onsager
relations, where our model turns out to satisfy the tight-coupling condition
leading to the Curzon-Ahlborn efficiency.
