Closed cooling system: advantages and disadvantages

A closed cooling system is a water (liquid) cooling system in which the same treated water (soft water or water + anti-freeze/inhibitor) circulates continuously through the engine jackets and a heat exchanger. The jacket water never comes in contact with air or raw water, so it stays clean; a separate raw-water circuit removes the heat from the heat exchanger.

Layout

        Primary (closed) circuit
   +--------------------------------+
   |                                |
 ENGINE  -->  Heat  ---> Pump  ---> +
 jackets      exchanger    ^
   ^            |  ^       |
   |            |  |    Expansion /
   +-- (return) |  |    surge tank
                v  |
       Raw water out  Raw water in
       (to cooling    (from river,
        tower/pond)    tower)
          Secondary (open) circuit

Working

1. A circulating pump forces soft water through the cylinder jackets and cylinder heads, where it absorbs heat (outlet about 70–85 °C).
2. Hot water flows to a heat exchanger (or radiator). In the heat exchanger, raw water from a river, pond or cooling tower passes through tubes and takes the heat away.
3. The cooled jacket water returns to the pump and engine, completing the closed loop.
4. A surge/expansion tank takes up volume changes and allows make-up water; a thermostat bypasses the heat exchanger when the engine is cold so that it warms up quickly.
5. The raw water is cooled in a cooling tower or spray pond and reused, or discharged.
6. Lubricating oil coolers are often placed in the same secondary circuit.

For small engines the heat exchanger is replaced by an air-cooled radiator with a fan (radiator cooling is also a closed system).

Advantages

• Jacket water is soft and clean, so there is no scale formation or corrosion in the jackets; heat transfer stays good.
• Water loss is very small; little make-up is needed.
• Engine temperature can be controlled accurately with a thermostat.
• Anti-freeze can be used in cold places.
• Raw water of poor quality (river water) can be used in the secondary circuit.
• Long life of engine parts and less maintenance of jackets.

Disadvantages

• Higher initial cost: heat exchanger, extra pumps, tanks and piping.
• More pumping power is needed (two circuits).
• Heat exchanger tubes on the raw-water side can still foul and need cleaning.
• More complicated than open (once-through) cooling; more space required.
• Leakage in the heat exchanger can contaminate the closed circuit.