water. The outboard water is warmed up and rises by its lower density, thus causing a natural upward cir-
culation flow which removes the heat.
Box cooling has the advantage that no raw water system is needed, and box coolers are less sensitive for
fouling and therefor well suited for shallow or muddy waters.
9.3.9 Waste heat recovery
The waste heat in the HT cooling water can be used for fresh water production, central heating, tank heating
etc. The system should in such case be provided with a temperature control valve to avoid unnecessary
cooling, as shown in the example diagrams. With this arrangement the HT water flow through the heat re-
covery can be increased.
The heat available from HT cooling water is affected by ambient conditions. It should also be taken into
account that the recoverable heat is reduced by circulation to the expansion tank, radiation from piping
and leakages in temperature control valves.
9.3.10
Air venting
Air may be entrained in the system after an overhaul, or a leak may continuously add air or gas into the
system. The engine is equipped with vent pipes to evacuate air from the cooling water circuits. The vent
pipes should be drawn separately to the expansion tank from each connection on the engine, except for
the vent pipes from the charge air cooler on V-engines, which may be connected to the corresponding line
on the opposite cylinder bank.
Venting pipes to the expansion tank are to be installed at all high points in the piping system, where air or
gas can accumulate.
The vent pipes must be continuously rising.
9.3.11
Expansion tank (4T05)
The expansion tank compensates for thermal expansion of the coolant, serves for venting of the circuits
and provides a sufficient static pressure for the circulating pumps.
Design data:
70 - 150 kPa (0.7...1.5 bar)
Pressure from the expansion tank at pump inlet
min. 10% of the total system volume
Volume
NOTE!
The maximum pressure at the engine must not be exceeded in case an electrically driven pump
is installed significantly higher than the engine.
Concerning the water volume in the engine, see chapter Technical data.
The expansion tank should be equipped with an inspection hatch, a level gauge, a low level alarm and ne-
cessary means for dosing of cooling water additives.
The vent pipes should enter the tank below the water level. The vent pipes must be drawn separately to
the tank (see air venting) and the pipes should be provided with labels at the expansion tank.
Small amounts of fuel gas may enter the DF-engine cooling water system. The gas (just like air) is separated
in the cooling water system and will finally be released in the cooling water expansion tank. Therefore, the
cooling water expansion tank has to be of closed-top type, to prevent release of gas into open air.
The DF-engine cooling water expansion tank breathing has to be treated similarly to the gas pipe ventilation.
Openings into open air from the cooling water expansion tank other than the breather pipe have to be
normally either closed or of type that does not allow fuel gas to exit the tank (e.g. overflow pipe arrangement
with water lock). The cooling water expansion tank breathing pipes of engines located in same engine room
can be combined.
The structure and arrangement of cooling water expansion tank may need to be approved by Classification
Society project-specifically.
The balance pipe down from the expansion tank must be dimensioned for a flow velocity not exceeding
1.0...1.5 m/s in order to ensure the required pressure at the pump inlet with engines running. The flow
94
Product Guide Wärtsilä 34DF - 3/2012
Product Guide
9. Cooling Water System
