轮机长
考试试题
[问答题]Basically, these units incorporate an evaporating section beneath a condensing or distilling section in a
common vessel of appropriate shape. A controlled flow of filtered feed, taken preferably from a salt
circulating outlet, enters the evaporating section and ascends through a battery of vertical tubes, surrounded
by steam or hot water, vaporizing as it goes, to the condensing section through a labyrinth or screen
(generally called a demister) which ensures that no droplets of salt water enter the condenser with the vapor.
The vapor, directed by suitably placed baffles, passes over the condenser tubes and falls as water to an
outlet duct, from which it is removed by a distillate pump, via a salinometer.
[问答题]Governing prime movers, particularly diesel engines, require careful consideration. The cyclic
variations of a diesel cycle can be passed into the governor drive if it is too "stiff". That is, the cyclic
vibrations will be imposed on the internal gearing etc. inside the governor housing. To prevent this, some
form of damper should be used on the drive into the governor. The mounting point for the governor should
be rigid; a vibration mounting would soon downgrade even the best of governors. Chain or belt drives
should be avoided as far as possible, as slapping of the belt or chain produces speed variations causing
malfunction of the governor. Similarly the drive from the end of the camshaft is subject to torsional
vibrations, and governors should not be located at that point. They should be located as close as practicable
to the fuel pumps, thereby limiting the mass/inertia of operating linkage. In all cases, the governor should
be matched to the engine requirements in terms of droop, load limiting, response time etc. On large engines
there is an inertial resistance to acceleration within the masses of reciprocating and rotating elements of the
engine, so that during acceleration fuel could be released to the cylinders at a faster rate than efficient
combustion can burn it. In an attempt to compensate for this, and to maintain acceptable combustion during
acceleration, a tapping from the scavenge space may be taken and the pressure used to regulate the rate of
fuel released to the engine. This process is incorporated into the governor operating system so that the
governor releases a quantity of fuel commensurate with the increase in air pressure in the scavenge space.
(during deceleration the problem is not so great, as excess air can be tolerated far more easily than can the
incomplete combustion associated with insufficient air.)
(The following questions are based on the passage above)
