Q.1 What Is The Purpose Of Main Engine Fresh Water Cooling System?
Ans: Main Engine Fresh Water Cooling System Has Very Significant Functions As Combustion Of Fuels And Friction Between Moving Parts Gives Rise To The Temperature Of Components Of The Engine.
Q.2 Descibe The Components Of Fresh Water Cooling System?
Ans Here Is A Pictorial Representation Of Fresh Water Cooling System.
As You Can See In The Diagram Above, The Primary Components Are As Follows:
i) Header Tank/ Expansion Tank: The Expansion Tank Is A Water Storage Tank, Provided At Maximum Height Possible Such That A Constant Head Is Maintained On The System. Any Loss Of Water Through Leakage Etc Are Maintained By This Tank. It Is Also Known As Make Up Water Tank.
iii) Cooler: The Water Which Enters The Main Engine To Cool It, In Return Becomes Hot. Thus A Cooler Is Required To Cool it And Make It Ready For Use Again. The Cooler Can Be Sea Water Cooler Or Fresh Water Cooler, Depending On The Medium Used As Cooling System On Ship. Most Of The New Ships Are Central Cooling Systems And Use Fresh Water As A Cooling Medium.
iii) Circulating Pump: The Circulating Pump Is A Centrifugal Pump, Generally Called As Jacket Water Circulating Pump Onboard. This Pumps The Water Cooled From Cooler Into The System Towards Main Engine. Generally The Discharge Pressure Is 2-3 Bar.
iv) Pre-Heater: A Pre-Heater Is Provided Such That Water Is Maintained At Around 60-65 Deg Celsius. If Temperature Is Found To Be More, Cooling Water Is Bypassed Through The Pre Heater. It Happens Generally In The Colder Regions Or When The Ship Is In Port, Main Engine Is Not Getting Heated Up And Fresh Water Generator Is Also Not Working. Hence The Water Coming From Cooler Is Colder And Needs To Be Heated Up. So When At Port, Engine Staff Opens The Pre Heat Steam, To Maintain The Main Engine Jacket Temperature Around 80-85 Deg Celcius.
v) Air Separator/ De-Aearator: It Is An Important Component In The System As It Removes The Air Formed/ Accumulated In The System, This Happens Due To Heating Up Of Water. Oxygen Tends To Evolve From The Boiling Process, If It Is Not Removed, An Air Lock In Then System Is Likely To Happen.
vi) Fresh Water Generator: Fresh Water Generator Acts A Cooling Component, Which Cools The Heated Up Water From Main Engine Through Its Evaporator, Which Basically Is A Plate Type Heat Exchanger. The Cooling Medium Which Is Sea Water Takes Up The Heat And In Turn Gets Heated Up.
Q.3 What Are The Conditions Which Arise Due To Lack Of Cooling?
Ans: Following Are The Conditions Which Arise Due To Lack Of Cooling,
I) Expansion Of Components Reduces Clearance Between Moving Parts Causing The Following.
Ii) Restriction To The Flow Of Lubricating Oil:
Reduction In Cooling Effect, And Increase In Frictional Drag Due To Loss Of Lubricant Film. The Above In Turn Lead To Further Rise In Temperatures And Further Expansion Of Components Thereby Worsening The Operating Conditions.
Iii) Chances Of Seizure Due To Reduction In Working Clearances, And Due To Changes In Shape Of Components With Limited Allowances For Expansion. Changes In The Shape Of Components, Such As, Pistons And Cylinder Liners Lead To A Loss Of Sealing Between Parts For Compression And For Retention Of Exhaust Products With The Combustion Space.
Iv) Stresses Increase When Components, Such As, Cylinder Heads, Cylinder Blocks Cannot Expand Freely.
Q.4 Why And Where Water Is Prefered As A Coolant Instead Of Lubricating Oil?
Ans: As Compared To Lubricating Oils, Water Has Negligible Effect On Frictional Drag Between Two Components In Contact And It Does Not, On Its Own, Prevent Corrosion Of Components.
Thus, Water Is Used Where Only Cooling Is Desired And Lubricating Oil Is Used Where Cooling, Reduction In Frictional Drag, And Prevention Against Corrosion Is Required.
Cooling Water Is Used For Cooling Cylinders Liners, Cylinder Cover, Exhaust Valve And In Some Cases Pistons Of The Engine.