Marine Engineering Study Materials

What is the purpose of charge air cooler on ships ?

1. To reduce air temperature & increase density of charge air.
2. More fuel can be burnt and more power can be obtained.
3. Reduce exhaust temperature and engine thermal load.
4. Increase scavenging efficiency, safe working temperature.

What are the cooler maintenance carried out for optimum efficiency ?

1. Cooler should be checked any deposit of lime, scale or oil sludge may be present in cooler; it should be cleaned.
2. Cooler of water side can be done with soft tube brush and oil side with carbon tetra chloride solution in reverse direction to normal flow with hand pump for about 4 hours.
3. After cleaning the cooler are hydraulically pressure tested normally 1.5 times the working pressure.
4. If 10% of the tubes have been leaked retubing in necessary. Normal leaking tubes may be stopped by plugging.
5. Corrosion can be protected by means of preservative coating (Anti corrosive paints) inside the shell and water boxes and by means of anodes such as zinc fitting inside water boxes.
6. Essential cooler for optimum efficiency can be maintained by controlling of temperature of fluid or sea water.

What is the purpose of division plate in cooler ?

1. Provided to increase numbers of pass.
2. This increase the cooling efficiency.

What do you know L.O cooler leakage ? How to do L.O cooler leakage occur on ships ?

When engine run,

1. Oil comes out at the cooling water overboard.
2. Sump tank oil level will fall down.
3. L.O pressure will drop
4. If L.O cooler leaks the engine should be stopped with permission from bridge.
5. The leakage can be detected by carrying out a hydraulic pressure test to the oil side.
6. After cooling down the engine stop main circulating L.O pump and main S.W cooling pump.
7. Close necessary valve of them
8. Open water box covers cooler both side.
9. Blank off discharge pipe of cooler oil side.
10. Connect hydraulic pump to inlet of cooler.
11. Apply oil pressure normally 1.5 times the working pressure. Then check the leakage at cooler both sides 
12. Normally leaking tubes may be stopped by plugging 
13. If 10% of the tubes have been leaked retubing is necessary.
14. Then the engine is put back normal running.

How do you know main engine air cooler water leakage ?

1. Check water level insight glass fitted at cooler drain pipe.
2. Drain the cooler / taste the water
3. If the water continuous comes out, the cooler is leakage. Also in the funnel white & dense smoke.
4. Small amount of water leakage is detected by the shore lab analysis carried out on scrape down samples.
5. Then the engine should be stopped with permission from bridge.
6. Normal leaking tubes can be stopped by plugging.
7. Then the engine is put back normal running.

How to check cooler efficiency ?

1. Check sea water in/out temperature difference. Less difference means poor efficiency of cooler (must be high)
2. Check coolant medium in / out pressure (Pressure drop across the cooler: should be low)
3. Feel over cooler shell, upper hot, middle  warm, down cool is normal.
4. Check pump and by pass valve.

What is the purpose of baffle plate in coolers ?

1. To support the tube stack.
2. To guide the flow of fluid
3. To increase cooling surface area
4. To minimize the tube vibration 

What are the causes of loss of vacuum in fresh water generator ?

1. Failure of ejector pump
2. Failure of ejector nozzle (fouling, erosion)
3. Malfunction of check valve (at ejector nozzle)
4. Defective vacuum breaker
5. Any air leakage into the system (At joint)

What will happen when vacuum reach 100% in fresh water generator ?

1. Increase the salinity because of agitation. At that time boiling rate is very high.
2. To control this condition, open the vacuum breaker to maintain 93% vacuum.

Why fresh water generator is fitted on ships ?

1. To produce the high purity distilled water from sea water
2. To provide make up water for boiler and portable water for drinking and domestic use. So can save cost.

What are the treatments for drinking purposes ?

• Chlorination.
• Ultra violet light sterilization.
• Liberation of silver ions to the water.

What is meant by Osmosis ?

• When different concentration solutions are separated by a semi-permeable membrane, water from less concentrated solution pass to the other solution through the membrane to equalize the concentration of the two solution.
• It create hydraulic pressure gradient across the membrane as the volume and level of weaker solution fall and those of the stronger solution rise.

What is meant by Reverse Osmosis ?

• The pressure greater than the osmotic pressure is applied to the side of higher concentration solution, the osmosis process is reversed.
• Water from the stronger solution is forced back through the semi-permeable membrane to dilute the initially weak solution on the other side and further increase the concentration of the strong solution. 
• The total pressure required for this process consists of the osmotic pressure (between 4 bar for brackish water up to 28 bar for sea water) plus the system pressure losses and net driving pressures (around 25 bar).

What are the semi permeable membranes used on ships ?

1. Hollow fine fiber (aromatic polyamide or cellulose acetate spurn to form hollow fiber)
2. Spirally wound (cellulose acetate for backish water and polymide or polysulphonate for sea water)

Reference:

Oral Guide by – MIN ZAR TAR