轮机英语四篇阅读_在线真题试卷与模拟练习_轮机英语四篇阅读_考试宝

更新时间：试题数量：购买人数：提供作者：

有效期：个月

章节介绍：共有个章节

收藏

我的练习

我的错题
(0道)

我的收藏
(0道)

我的斩题
(0道)

我的笔记
(0道)

专项练习

顺序练习 0 / 0

随机练习 自定义设置练习量

题型乱序 按导入顺序练习

模拟考试 仿真模拟

题型练习 按题型分类练习

易错题 精选高频易错题

学习资料 考试学习相关信息

搜索

题库预览

A number of biological sewage treatment plant types are in use at sea but nearly all work on what is called the extended aeration process. Basically this consists of oxygenating the liquor either by bubbling air through it or by agitating the surface. By so doing a family of bacteria is propagated which thrives on the oxygen content and digests the sewage to produce an innocuous sludge. The imprison that bubbling air through the sewage serves to oxidize it thus reducing BOD is not strict case. It is the bacteria that reduce the BOD by converting the organic content of the sewage to a chemically and organically inert sludge.
In order to exist, the bacterial need air and nutrient. The nutrient is in the form of
Body and galley wastes. If the nutrient source is cut off, i.e. the plant shut down or
By-passed for say an extended ocean passage, the bacterial die and the plant cannot
Function correctly until a new bacteria colony is generated. This process can take from
7 to 14 days. Bacterial which live in the presence of oxygen are said to be aerobic.
When oxygen is not present, the aerobic bacterial cannot live but a different family of
Bacterial is generated. These bacterial are said to be anaerobic.
While they equally capable of producing an inert sludge, in so doing hydrogen sulfide,
Carbon dioxide and methane are formed.
Some sewage processes are designed to work anaerobically but they are not usually
Adopted for shipboard use.

The bacteria usually used in the sewage treatment process on board are ___.

If the treatment plant has been shut down for a long time, it can function again only
After___.

According to this passage, bubbling air through the sewage to oxidize it thus reducing
BOD___.

The biochemical oxygen demand of the sewage is reduced by___.

Displacement pumps are those where the volume of the pump chamber is alternately
Increased to draw the liquid in from the suction pipe and then decreased to force the
Liquid out into the delivery pipe. Centrifugal pumps are those wherein an impeller
Rotating at high speed throws the liquid by centrifugal force from the center to the
Periphery of the impeller where the liquid is discharged through the delivery outlet.
Gear pump consists of two or more meshing gears (spur, single or double helical teeth)
Enclosed m a close-fitted housing. These are used extensively for pumping fuel oil,
Lubricating oil and hydraulic oil. When gears are unmeshed on the inlet side, a
Pressure drop occurs that helps the atmospheric pressure acting on the surface of the
Oil in the reservoir to force it up the pipe to fill the void, the oil is then
Transferred around the periphery of the pump housing. As the gear teeth mesh again on
The outlet side, they form a seal that prevents oil from backing up to the inlet, the
Oil in the void is then be forced out into the discharge line.
All vane pumps have a rotor driven within a ring (cam ring) by a drive shaft coupled to
A prime mover. A cylindrical rotor with sliding vanes, generally in radial slots,
Rotates within the ring. The center of the rotor is offset from the center of the ring.
In a simple vane pump, as the rotor turns, the vanes are forced outward against the
Inner surface of the cam ring by centrifugal force. This outward radial movement of the
Vanes and turning of the rotor causes the chamber between the vanes to increase as the
Vanes pass further away from the inlet port. This increase in volume results in a
Lowering of pressure until the atmospheric pressure is sufficient to force oil from the
Reservoir into the inlet chamber. Oil from the inlet is swept away by the vanes toward
The outlet port through a decreasing series of chambers until it is forced through the
Outlet port. A vane pump of balanced design has an elliptical cam ring so that two
Pumping chambers are formed. This pump is in hydraulically balance, since the two
Intake and two outlet ports are diametrically opposed to each other. Therefore the side
Loads exerted on the rotor cancel out, thereby increasing bearing lift and permitting
High operating pressure.

According to the last sentence of paragraph 1, from where the liquid is discharged
Through the delivery outlet?

Which statement is NOT true?

Gear pumps are widely used to transfer any one of the following but_____.

Which statement is NOT true?

The jacket cooling system differs from that used on trunk piston engines only in the fact that LO cooler and the charge air cooler, which are seawater cooled, may be included in the same circuit.
An elevated expansion tank maintains a static head on the suction side of the system
And provides a convenient point for collecting vents, adding makeup feed, and adding
Chemicals to inhibit corrosion and formation of scale. Good venting is important: air
Carded with the coolant will enhance the potential for corrosion and can also
Accumulate at points to block coolant flow.
The jacket water circulating pumps are usually centrifugal pumps, and in larger plants
Are fitted in duplicate. Both pumps are motor driven in installations with low speed
Diesels, but medium and high speed engines are often fitted with an engine-driven pump,
Relaying on the motor driven pump for standby service.
The jacket water heater is used when the engine is idle. Maintaining the engine in a
Warm condition assists in minimizing corrosion.
Automation is likely to include alarms for low pressure, high temperature, and low
Level in the expansion tank; automatic changeover of the pumps; and thermostatic
Control of the three-way valve at the cooler.
While all trunk piston engines, as well as some crosshead engines, use oil to cool the
Pistons, a number of crosshead engines use a cooling water system separate from the
Jacket water system. The water reaches and leaves the piston through telescoping tubes
Enclosed within compartments inside the crankcase in order to avoid contamination of
The LO should a gland fail.
Because of the high temperature of water draining from the pistons and the resulting
Potential for flashing at the pump suction, some manufacturers recommend that deep well
Pumps immersed in the tank be used. Both pumps will be motor driven. Automation and
Other features will be similar to those described for the main engine jacket water
System.

All of the followings are the functions of the elevated expansion tank except_______.

According to the passage, which of the followings is TRUE?

Jacket cooling system is quite different from that used on trunk piston engines.
Jacket cooling system is just the same as that used on trunk piston engines.
LO cooler and the charge air cooler in trunk piston engines are freshwater
Jacket water circulating pumps are cannot be driven by the engine itself.
The abbreviation “LO” in this passage stands for ______.

The best title for this passage should be_______.

The field current supply in older machines comes from a lower voltage direct current generator or exciter on the same shaft as the alternator. Modern machines however are either statically excited or of the high-speed brush-less type. The exciter is required to operate to counter the effects of power factor for a given load. The power is a measure of the phase difference between voltage and current and is expressed as the cosine of the phase angle. With a purely resistance load the voltage and the current are in phase, giving a power factor of one. The power consumed is therefore the product of voltage and current. Inductive or capacitive loads, combined with resistance loads, produce lagging or leading power factors which have a value less than one. The power consumed is therefore the product of current, voltage and power factor. The alternating current generator supplying a load has a voltage drop resulting from the load. When the load has a lagging factor this voltage drop is considerable. Therefore the exciter, in maintaining the alternator voltage, must vary with load current and also the power factor. The speed change of the prime mover must also be taken into account.

The word “ machines” in the passage refers to ______.

Which of the following statements is true according to the passage?

When the load has a lagging power factor this voltage drop is considerable. This sentence means that_____.

The exciter must vary with:_______
1 load current2 the power factor3 speed change of the prime mover.

1

更多题库