--- title: "Types of water cooling systems" subject: "Power Plant Equipment" chapter: 5 key: "semester_7/power_plant_equipment:water-cooling-types" source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/water-cooling-types site: BCT Engineering --- # Types of water cooling systems Power Plant Equipment · Chapter 5: Diesel Power Plant - Asked in: 2076 Asoj, 6 marks - Video: [Cooling water systems' Types, Open recirculating/Closed and Once through](https://www.youtube.com/watch?v=1jRGxANoOAI) — Learning for Knowledge - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/water-cooling-types - Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-5 ## Question Explain the different types of water cooling system with their advantages and disadvantages. ## Short answer Types are open once-through, natural thermosiphon, forced circulation, closed double-circuit, and evaporative. Open is simplest but causes scaling; thermosiphon needs no pump but is slow; forced suits all sizes but needs a pump; closed prevents scaling but costs more; evaporative uses little water but runs hot. ## Answer In **water (liquid) cooling**, water circulates through jackets around the cylinders and cylinder head, absorbs the heat conducted through the walls and gives it up in a cooler. The main types used in diesel power plants are: #### 1. Open (once-through) cooling system Water is taken from a river, lake or well, pumped through the engine jackets once and then discharged to waste. - **Advantages:** simplest and cheapest; no cooling tower or heat exchanger. - **Disadvantages:** needs a large, continuous water supply; raw water causes scale and corrosion in jackets; temperature control is poor. Used only where plenty of clean water is available. #### 2. Natural (thermosiphon) circulation system Hot water, being lighter, rises from the jackets to the top of a tank/radiator, cools and falls back to the engine. No pump is used. - **Advantages:** no pump, simple, no power for circulation. - **Disadvantages:** slow circulation, so suitable only for small engines; radiator must be above the engine; cooling depends on load. #### 3. Forced circulation system A pump forces water through the jackets and then through a radiator or cooling tower. A thermostat controls the flow. - **Advantages:** fast, uniform cooling; suitable for all sizes; good temperature control. - **Disadvantages:** pump consumes power; cooling stops if the pump fails. #### 4. Closed (double-circuit) cooling system Soft treated water circulates in a closed primary circuit through jackets and a heat exchanger; raw water in a secondary circuit removes the heat and is cooled in a cooling tower or pond. - **Advantages:** no scale or corrosion in jackets, very low water loss, accurate temperature control, long engine life. - **Disadvantages:** higher cost, more pumps and piping, heat-exchanger maintenance. #### 5. Evaporative cooling Water is allowed to boil in the jackets; the steam is condensed and returned. Large heat removal per kg of water. - **Advantage:** low water requirement. - **Disadvantage:** engine runs hot; local hot spots; rarely used in power plants. ```text Closed system: ENGINE -> Heat exch -> Pump -> ENGINE (soft water) ^ | raw water in out -> Cooling tower -> back ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main drawback of open (once-through) cooling? A. Needs a cooling tower B. Needs large continuous water supply and raw water causes scale and corrosion C. Needs a heat exchanger D. It cannot be used at all Answer: B. Water is used once and discharged; raw water scales the jackets and temperature control is poor. (Key point: Open cooling) 2. How does natural (thermosiphon) circulation work? A. A pump drives the water B. Hot, lighter water rises to a tank/radiator, cools and falls back C. Steam is condensed D. Air is forced through Answer: B. Density difference drives circulation without a pump, so it suits only small engines. (Key point: Thermosiphon) 3. What is a disadvantage of forced circulation? A. Slow cooling B. Pump consumes power and cooling stops if the pump fails C. Not suitable for large engines D. No temperature control Answer: B. It gives fast, uniform cooling but depends on the pump. (Key point: Forced circulation) 4. What characterises evaporative cooling? A. Water boils in the jackets and the steam is condensed and returned B. Water is circulated by a pump only C. Air passes over fins D. Oil sprays pistons Answer: A. Boiling removes large heat per kg of water, but the engine runs hot with local hot spots. (Key point: Evaporative cooling) 5. Which type gives no scale in jackets, low water loss and accurate temperature control? A. Open system B. Thermosiphon C. Closed double-circuit system D. Evaporative system Answer: C. Soft water in a closed primary circuit avoids scale; the cost is higher. (Key point: Best for scale-free) ## Related in Power Plant Equipment - [Diesel plant lubrication and cooling systems](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-lubrication-cooling) — Power Plant Equipment, chapter 5, asked 2× - [Closed cooling system: advantages and disadvantages](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aclosed-cooling-system) — Power Plant Equipment, chapter 5 - [Need for cooling and cooling types in diesel engines](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-cooling-need-types) — Power Plant Equipment, chapter 5, asked 2× - [Diesel components, lubricating and cooling functions](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-components-lube-cooling) — Power Plant Equipment, chapter 5 - [Diesel noise, vibration reduction and cooling](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-noise-vibration-cooling) — Power Plant Equipment, chapter 5 - [Diesel layout with its five systems](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-layout-five-systems) — Power Plant Equipment, chapter 5 ## Related in other subjects - [Water cooling systems and components](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Awater-cooling-systems-components) — Internal Combustion Engines, chapter 7 - [Need of cooling; air versus water cooling](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Aengine-cooling-need-air-water-comparison) — Internal Combustion Engines, chapter 7 - [Newton's law of cooling: water to 40°C](https://www.bctengineer.com/question.md?key=semester_1%2Fmathematics_i%3Aapp-newton-cooling-water-40) — Mathematics I, chapter 4, asked 3× - [Cooling water and radiator air flow calculation](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Aengine-coolant-flow-radiator-numerical) — Internal Combustion Engines, chapter 7