问答题 6分

The lubrication system of an engine provides a supply of lubricating oil to the various moving parts...

The lubrication system of an engine provides a supply of lubricating oil to the various moving parts in
an engine. Its main function is to enable the formation of a film of oil between the moving parts, which
reduces friction and wear. The lubricating oil is also used as a cleaner and in some engines as a coolant. The
usual method of bearing lubrication is by forced feed system, which supplies oil to all bearings, so that a
film of oil is maintained on the journal and bearing surfaces.
(The following 2 questions are based on the passage above.)

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5 问答题 6分
For a certain provision cooling plant, the capacity regulator is generally controlled depending on
pressure, temperature or relative humidity. The pulse emitter is therefore either a pressostat(压力继电器),
thermostat or hygrostat. The switching difference of the control units should be rated as large as possible.
This applies in particular to control by means of the pressure, because change to the load in the
refrigeration circuit results in relatively quick pressure changes compared to temperature, which can in turn
lead to inadmissible oscillation of the regulator.

Under partial load, the suction volume and thus the gas speed can undergo marked changes depending on the
regulation stage. For this reason, the rating and routing of the suction line must be given particular attention.
In order to guarantee sufficient oil return, neither full load nor partial load operation may allow the gas speed
to fall below a minimum level: 4 m/s in horizontal pipe sections; 8 m/s in vertical pipes.

For this reason we recommend that vertical pipes bestaggered into two separate sections (as illustration).
As a result of the falling suction gas speed velocity in partial load operation, the pipe elbow B is
blocked by an accumulation of oil. This increases the gas velocity in pipe section A. In order to guarantee adequate
oil return, both cross sections must be rated so large that the velocity does not fall below the minimum level
in full and partial load operation. In plants with extensive pipe systems it is recommended at least for R22 and NH3
to install an additional oil separator. This reduces the oil circulation period and can have positive effects above
all for cold starts with relatively high oil ejection.