A system including a primary evaporator facilitating heat transfer by evaporating liquid to obtain vapor is disclosed. The asymmetric axle shafts are asymmetrically selected such that the relative torsional stiffness therebetween is different by a ratio substantially between about 1. The user has the option to allow incoming callers to bypass voicemail for emergency calls by pressing a predetermined button on the caller’s phone in order for the user’s phone to ring. Therefore, it is possible to continuously drive the motor generator while preventing increase in the current passing through the short-circuited phase, without adding a new device structure.