海船船员考试
单选题Generating tubes in waste heat boilers are finned to （）.A reduce gas flow turbulenceB prevent exhaust gas corrosionC increase the rate of combustionD increase the rate of heat transfer
题目
reduce gas flow turbulence
prevent exhaust gas corrosion
increase the rate of combustion
increase the rate of heat transfer
相似问题和答案
第1题：
What is the most usual reason for the fresh water-sea water heat exchanger fouling in the sea side?
A.lube oil sludge accumulating in it
B.dirt and scale etc , formed on the surfaces
C.deformation of the tubes and the shell or the plates
D.lube oil leakage into sea-water side
第2题：
A bypass line provided around a waste heat auxiliary boiler in a diesel engine exhaust system, may be used to avoid boiler ______.
A.corrosion at low engine loads
B.erosion at high engine loads
C.overload at high engine loads
D.scaling at all exhaust temperatures
第3题：
5 The directors of Blaina Packaging Co (BPC), a well-established manufacturer of cardboard boxes, are currently
considering whether to enter the cardboard tube market. Cardboard tubes are purchased by customers whose
products are wound around tubes of various sizes ranging from large tubes on which carpets are wound, to small
tubes around which films and paper products are wound. The cardboard tubes are usually purchased in very large
quantities by customers. On average, the cardboard tubes comprise between 1% and 2% of the total cost of the
customers’ finished product.
The directors have gathered the following information:
(1) The cardboard tubes are manufactured on machines which vary in size and speed. The lowest cost machine is
priced at $30,000 and requires only one operative for its operation. A one-day training course is required in order
that an unskilled person can then operate such a machine in an efficient and effective manner.
(2) The cardboard tubes are made from specially formulated paper which, at times during recent years, has been in
short supply.
(3) At present, four major manufacturers of cardboard tubes have an aggregate market share of 80%. The current
market leader has a 26% market share. The market shares of the other three major manufacturers, one of which
is JOL Co, are equal in size. The product ranges offered by the four major manufacturers are similar in terms of
size and quality. The market has grown by 2% per annum during recent years.
(4) A recent report on the activities of a foreign-based multinational company revealed that consideration was being
given to expanding operations in their packaging division overseas. The division possesses large-scale automated
machinery for the manufacture of cardboard tubes of any size.
(5) Another company, Plastic Tubes Co (PTC) produces a narrow, but increasing, range of plastic tubes which are
capable of housing small products such as film and paper-based products. At present, these tubes are on average
30% more expensive than the equivalent sized cardboard tubes sold in the marketplace.
Required:
(a) Using Porter’s five forces model, assess the attractiveness of the option to enter the market for cardboard
tubes as a performance improvement strategy for BPC. (10 marks)
(a) In order to assess the attractiveness of the option to enter the market for spirally-wound paper tubes, the directors of BPC
could make use of Michael Porter’s ‘five forces model’.
In applying this model to the given scenario one might conclude that the relatively low cost of the machine together with the
fact that an unskilled person would only require one day’s training in order to be able to operate a machine, constitute
relatively low costs of entry to the market. Therefore one might reasonably conclude that the threat of new entrants might be
high. This is especially the case where the market is highly fragmented.
The fact that products are usually purchased in very large quantities by customers together with the fact that there is little real
difference between the products of alternative suppliers suggests that customer (buyer) power might well be very high. The
fact that the paper tubes on average only comprise between 1% and 2% of the total cost of the purchaser’s finished product
also suggests that buyer power may well be very high.
The threat from suppliers could be high due to the fact that the specially formulated paper from which the tubes are made is
sometimes in short supply. Hence suppliers might increase their prices with consequential diminution in gross margin of the
firms in the marketplace.
The threat from competitive rivals will be strong as the four major players in the market are of similar size and that the market
is a slow growing market. The market leader currently has 26% of the market and the three nearest competitors hold
approximately 18% of the market.
The fact that Plastic Tubes Co (PTC) produces a narrow range of plastic tubes constitutes a threat from a substitute product.
This threat will increase if the product range of PTC is extended and the price of plastic tubes is reduced.
The fact that a foreign-based multinational company is considering entering this market represents a significant threat from a
potential new entrant as it would appear that the multinational company might well be able to derive economies of scale from
large scale automated machinery and has manufacturing flexibility.
Low capital barriers to entry might appeal to BPC but they would also appeal to other potential entrants. The low growth
market, the ease of entry, the existence of established competitors, a credible threat of backward vertical integration by
suppliers, the imminent entry by a multi-national, a struggling established competitor and the difficulty of differentiating an
industrial commodity should call into question the potential of BPC to achieve any sort of competitive advantage. If BPC can
achieve the position of lowest cost producer within the industry then entry into the market might be a good move. In order
to assess whether this is possible BPC must consider any potential synergies that would exist between its cardboard business
and that of the tubes operation.
From the information available, the option to enter the market for cardboard tubes appears to be unattractive. The directors
of BPC should seek alternative performance improvement strategies.
第4题：
bypass exhaust gas at high loads to prevent excessive back pressure
bypass a portion of the exhaust gas at peak loads for better efficiency
recycle exhaust gas to the turbocharger
minimize moisture condensation in the boiler gas passages at low loads
第5题：
Control of evaporation
A separate means to prevent feed-water contamination
Power circulating pump
Super-heater
第6题：
The maximum pressure developed by a waste heat boiler is determined by the main engine exhaust ______.
A.gas composition
B.gas temperature
C.pressure
D.timing
第7题：
To prevent internal damage form local overheating
To ensure the fuel nozzles are flushed clean
To clear the smoke stack
To let the waste heat boiler reduce its rate of steam generation
第8题：
第二组
The only attention that heat exchanger should require is to ensure that the heat transfer surfaces remain substantially clean and the flow passages generally clear of obstruction. Indication that undue fouling is occurring is given by a progressive increase in the temperature difference between the two fluids, over a period of time, usually accompanied by a noticeable rise in pressure loss at a given flow.
Fouling on the sea-water side is the most usual cause of deterioration in performance. The method of cleaning the sea water-side surfaces depends on the type of heat exchanger. With shell-and-tube heat exchangers, the removal of the header covers or, m the case of the smaller heat exchangers, the headers themselves, will provide access to the tubes. Obstructions, dirt, scale etc., can then be removed, using the tools provided by the heat exchanger manufacturer. Flushing through with fresh water is recommended before a heat exchanger is returned to service. In some applications, such as piston oil cooling, progressive fouling may take place on the outside of the tubes. Most manufactures recommend a chemical flushing pr6cess to remove this in situ~ without dismantling the heat exchanger.
Plate heat exchangers may be cleaned by unclamping the stack of plates and mechanically cleaning the surface of each plate as recommended by the manufacturers. The plate seals may require replacement from time to time and here the manufacturers&39; instructions should be closely followed
By which of the following indication, can we conclude that the lube oil-sea water heat exchanger is unduly fouled?
A.the heat exchanger lube oil inlet temperature lowering
B.the heat exchanger sea-water outlet pressure rise
C.the heat exchanger temperature difference between lube oil and sea water increasing
D.the heat exchanger pressure difference between sea water inlet and outlet decreasing
第9题：
Internally finned liner
Externally finned liner
Wet liner
Integral water-jacket liner
第10题：
prevent engine back pressure at heavy loads
increase total engine efficiency at low loads
prevent boiler corrosion at low engine loads
improve engine fuel consumption at any load