The local stability of a non-endoreversible Carnot refrigerator with Newton’s heat transfer law working at the maximum
ecological function is analyzed, the general expressions of the relaxation times with heat capacity C, overall heat transfer
surface area F, heat reservoirs’ temperature ratio s, the degree / of internal irreversibility, heat transfer coefficients a and
b are obtained. According to numerical calculations, the effects of / and b/a on relaxation times are discussed, and the phase
portrait of the system is analyzed. It is shown that any perturbation decays exponentially with time to the steady state, and
the steady state of the system working at the maximum ecological function is steady. It is noted that the internal irreversibility
/ has little influence on the stability of the system, and the stability of the system is improved as s increases. The
relaxation times t1 and t2 decrease as b/a (or a and b) increase(s). And thus, the local stability of the system is improved.
There are two different linear trajectories named fast eigendirection and slow eigendirection, respectively. The phase portraits
show that any perturbation on x and y values tend to approach the origin (steady-state point ðx; yÞ). The results can
provide some theoretical guidelines for the designs of practical refrigerator.