(a) Keel Cooling System: Main Components
A keel cooling system is a closed-circuit system utilized for cooling marine engines by transferring heat to seawater. Here are the main components:
- Heat Exchanger (Keel Cooler): This is the heart of the system, typically mounted externally on the vessel’s hull below the waterline. Engine coolant circulates through tubes or channels within the heat exchanger, transferring heat to the surrounding seawater flowing over the outside.
- Circulation Pump: An engine-driven or electrically powered pump is responsible for circulating the coolant through the closed loop within the system.
- Thermostat: This valve regulates the coolant temperature by controlling the flow of coolant through the heat exchanger. When the coolant reaches a set temperature, the thermostat opens, allowing coolant to flow through the heat exchanger for cooling.
- Expansion Tank: This tank accommodates the volume changes of the coolant due to temperature fluctuations. It also serves as a reservoir for any trapped air within the system.
- Seawater Inlet and Outlet: These connections allow seawater to enter the system, flow past the heat exchanger, and exit back into the sea after absorbing heat from the coolant.
- Shut-Off Valves: Valves positioned at strategic points in the system allow for isolation of sections for maintenance or repairs.
- Strainers: These filters placed on the seawater inlet line prevent debris and marine growth from entering the system and potentially clogging the heat exchanger.
(b) Purpose of Specific Components:
(i) Header Tanks:
There might be one or two header tanks depending on the system design. Here’s a breakdown of their functions:
- Coolant Reservoir and Expansion Space: The header tank acts as a reservoir for the coolant and provides space for coolant expansion due to temperature changes. This expansion space prevents excessive pressure buildup within the closed loop.
- Additional Functions: The header tank may also incorporate features like:
- Overflow Outlet: This allows excess coolant to escape the system and prevent overfilling in case of a coolant mix error or expansion beyond the tank’s capacity.
- Fill Point: This allows for refilling or topping up the coolant level in the system.
- Level Indicator: This helps visually monitor the coolant level within the system.
(ii) Vent Lines:
Vent lines play a crucial role in removing trapped air from the system. Air pockets within the system can impede proper coolant circulation and reduce heat transfer efficiency.
- Location: Vent lines are typically located at high points in the system, such as the top of the header tank or at high points in the piping circuit.
- Function: These lines allow trapped air to escape the system as the coolant fills the cavities during initial system filling or after topping up the coolant level. They might also be equipped with one-way valves that allow air to escape but prevent seawater ingress.