GB2073402A - Cooling means for waterborne vessels - Google Patents

Abstract

A ship's engine is cooled by fresh water circulated in contact with the hull skin 2 in the manner of a falling-film heat exchanger, thereby transferring heat to the water 1 in which the ship floats, without bringing such water aboard. The fresh water is drawn up from a tank in the bottom of the hull by a pump 4, 12 and circulated through the engine jacket via an atmospheric break/surge tank 5 or tundish 11 to an inlet header 7, 14 of a falling-film heat exchanger formed by the hull skin 2. After flowing down the hull skin, the water returns to the tank for recirculation. <IMAGE>

Description

SPECIFICATION Cooling means for waterborne vessels This invention relates to waterborne vessels and in particular to means for disposing of heat generated by equipment on the vessel, for example propulsion machinery.

At present, diesel engines and other marine propulsion equipment are cooled by pumping inboard the surrounding water, transferring heat to this water, and then discharging the water. The pumping power required can be substantial. Furthermore, the water inlets complicate the whole design and can increase drag. As the water is untreated, and in most cases is sea water, the risk of corrosion is severe and it may be necessary for the cooling circuit to incorporate expensive corrosion-resistant materials.

According to the present invention, cooling is effected by indirect heat exchange with the surrounding water, which is not brought inboard.

This has numerous advantages, including the elimination of inlets and outlets for cooling water and associated pipework and other equipment, reduction in pumping power, and the possibility of using relatively non-corrosive coolant.

The invention is particularly but not exclusively concerned with vessels having displacement hulls, in which case the heat can be dissipated by heat transfer through the hull itself to the water in which the vessel floats.

In a particularly simple and convenient arrangement, the skin of the hull forms part of a falling-film heat exchanger, a coolant being passed over the internal surface of the skin to transfer heat from propulsion machinery or other heat-producing equipment to the surrounding water in which the vessel floats.

One embodiment of the invention will be described, by way of example, with reference to the accompanying diagrammatic drawing which shows the hull of a vessel in crosssection, a diesel engine and cooling circuits.

The illustrated system has separate cooling circuits for the cylinder jackets and the pistons of the engine, which need to be cooled to different temperatures. The piston and jacket cooling circuits are shown respectively on the right and left hand sides of the drawing. Most of the heat to be dissipated is derived from the jackets and may be several MW.

The velocity of sea water at the ship's side, for a conventional vessel at full power, is likely to exceed the velocity of sea water that would provide acceptable performance flowing through a conventional heat exchanger connected to the engine. Acceptable performance can be obtained if a falling-film heat exchanger is used incorporating an immersed region of the hull, particularly if this is aft where flow is more turbulent; the engine room will usually be aft.

In the case of a typical diesel engine developing 25,000 BHP, the amount of heat to be dissipated is, typically, 5.5 MW, of which about 4.2 MW is to be dissipated from the cylinder jackets. For jacket inlet and outlet temperatures of 54 "C and 68 "C respectively, and taking the sea water temperature to be 32 "C, a surface area of steel skin of about 100 m2 should provide adequate heat dissipation.

In the case of a vessel with a 25,000 BHP engine, the minimum draught associated with maximum power (indicated by the line 1) is, typically, 4.5 m. The length of a falling-film of cooling water to provide sufficient heat dissipation therefore be 20 to 25 m.

As shown in the drawing, the skin 2 of the hull in the selected region is fitted with internal coffer-dams 3 to define the skin area which is to operate as a falling-film heat exchanger. Between the coffer-dams, baffles may be provided, and the heat exchanger may be subdivided by internal coffer-dams to provide different cooling regions for different parts of the engine or other pieces of equipment, for example bearings.

A coolant tank is formed in a part of the double bottom and it contains treated water.

The jacket cooling system, shown on the left, includes a tank-mounted pump 4 which pumps the cooling water into the jackets and thence to an atmospheric break/surge tank 5 provided with a vent 6, from which the water flows to an inlet header of the falling-film heat exchanger formed by the outer skin of the hull. After flowing down the hull skin, the thus cooled water returns to the tank for recirculation.

We envisage a film thickness of about 3 mm.

The falling-film type of heat exchanger requires an atmospheric break and this is provided at the tank 5. This tank and vent also serve to maintain the required jacket pressure and to avoid any possibility of a siphon.

A thermostatic bypass 8, responsive to the cooling water inlet temperature, is provided to bypass the falling-film heat exchanger to maintain the required coolant temperature.

The pump operates against a head which compared with a conventional system, is increased by the provision of the atmospheric break. However, friction losses are low in a falling-film heat exchanger, compared with a conventional heat exchanger and associated fittings, and we therefore envisage that the pump power required will not be significantly different from that of a conventional closedcircular heat exchange system. No sea water pump is required and therefore the power needed for this is saved.

The hull has an inner skin 9 enclosing the heat-exchanger at least, and a double bottom forming the coolant tank. The heat exchanger has vents 10. The double skinning may be extended up to the full load line.

The possibility of collision damage should be taken into account when the position of the heat exchanger is chosen, as it can contribute to the safety of the vessel.

The piston cooling system, shown on the right, is similar but has a simple atmospheric break 11 using a tundish instead of a tank. A second tank-mounted pump 12, a thermostatic bypass 1 3 and a coolant header 14 are provided, as in the jacket cooling system. This system will provide a reduction in pumping energy compared with a conventional cooling system, owing to the elimination of conventional coolers and associated fittings.

Further cooling circuits can be provided for example for cooling bearing lubricating oil, the heat exchanger being divided by cofferdams to form separate cooling areas for the separate cooling systems.

The falling-film heat exchanger is cheap and simple, and does not impede periodic inspection of the interior of the skin of the hull. The inner skin 9 will require insulation dependent upon climate and removable portions may be advantageous.

The falling-film type of heat exchange also has the advantage of requiring a relatively small tonnage of fresh water for cooling.

The cooling system described has a number of advantages in addition to the reduced pumping power compared with conventional systems using sea water. Since sea water is not brought aboard for cooling, the risk of corrosion is eliminated inside the hull. Capital cost is also reduced because it is no longer necessary to use expensive corrosion-resistant materials such as bronze, cupronickel and titanium. Furthermore, construction or complications such as sea inlet boxes, strainers, valves, sea water pipework and pumps, mechanical seals and heat exchangers are eliminated, and the size of the ship's alternator can be reduced. Running costs are reduced and reliability is increased because the system uses few components and fewer replacements will be needed because of corrosion and wear; for example, mechanical seal replacement is eliminated. Weight is reduced, leading to increased cargo or bunker capacity.

The elimination of sea inlet boxes reduces hull drag and therefore reduces energy consumption or allows higher speeds. The bilges will need less frequent pumping, reducing energy cost and the risk of pollution.

It may still be necessary to allow sea water within the hull for ballast, fire fighting and production of fresh water. However, these needs are intermittent and of relatively small volume. The necessary sea water inlets can have fairings to reduce drag.

Claims (6)

1. A waterborne vessel having heat-producing equipment and cooling means therefor comprising indirect heat-exchange means arranged to transfer heat from said equipment to water in which the vessel is borne.

2. A vessel as claimed in claim 1 in which the vessel has a displacement hull and the cooling means comprise at least one coolant circuit in which the immersed hull forms a heat sink.

3. A vessel as claimed in claim 2 in which the coolant circuit includes means for passing the coolant in contact with the interior surface of the hull.

4. A vessel as claimed in claim 3 in which the coolant in operation flows down the said surface in the manner of a falling film heat exchanger.

5. A vessel as claimed in any preceding claim in which the said equipment is propulsion machinery.

6. A vessel substantially as herein described with reference to the accompanying drawing.