--- title: "Diesel cooling methods and cooling tower" subject: "Power Plant Equipment" chapter: 5 key: "semester_7/power_plant_equipment:diesel-cooling-tower" source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/diesel-cooling-tower site: BCT Engineering --- # Diesel cooling methods and cooling tower Power Plant Equipment · Chapter 5: Diesel Power Plant - Asked in: 2072 Kartik, 6 marks - Video: [Cooling Systems in Diesel Engines](https://www.youtube.com/watch?v=5NT2VrXBzb0) — Prof. Dr. Suresh D Mane - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/diesel-cooling-tower - Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-5 ## Question What are the different methods used for cooling diesel engines? Explain the function of cooling tower. ## Short answer Methods: air cooling (fins, fan) for small engines; water cooling (open, thermosiphon, forced circulation, closed double-circuit) for power plants; oil cooling of pistons in large engines. A cooling tower cools hot water from the engine by evaporative cooling, allowing water reuse with minimal consumption. ## Answer Diesel engines are cooled to remove the heat (about 25–35 % of fuel energy) that flows into cylinder walls, head and pistons, so that metal and lubricating oil stay within safe temperatures. #### Methods of cooling diesel engines 1. **Air cooling:** fins on the cylinder and head increase surface area; air from a fan or vehicle motion carries heat away. Used only for small engines (a few kW) because air has low heat capacity. 2. **Liquid (water) cooling:** water circulates through jackets; used for all power-plant engines. Types: - **Open (once-through) system** – raw water used once and discharged. - **Natural (thermosiphon) circulation** – circulation by density difference, no pump; small engines. - **Forced circulation** – pump drives water through jackets and radiator/cooling tower. - **Closed (double-circuit) system** – soft water in a closed loop through jackets and a heat exchanger; raw water in the secondary loop goes to a cooling tower or spray pond. - **Evaporative cooling** – water allowed to boil in jackets, steam condensed and returned. 3. **Oil cooling** of pistons in large engines (oil sprayed under the piston crown). #### Function of a cooling tower A **cooling tower** cools the hot water coming from the engine jackets or heat exchanger so the **same water can be reused**, which saves water where a river or lake is not available. ```text Air + vapour out ^ ^ ^ +----------------+ | Spray nozzles | <-- hot water in | ~~~~~~~~~~~~ | | Fill/packing | | ~~~~~~~~~~~~ | ->| air in air in|<- +----------------+ | Cold water | --> pump -> engine/HX +----------------+ ``` - Hot water (about 50–60 °C) is sprayed at the top and trickles down over **fill/packing** that breaks it into thin films and drops. - Air flows upward (by natural draught or fans – induced or forced draught) through the falling water. - A small part of the water **evaporates**; the latent heat for evaporation is taken from the rest of the water, which cools by 8–12 °C. Some sensible heat also passes to the air. - Cold water collects in the basin and is pumped back. Make-up water replaces evaporation, drift and blow-down losses (about 1–3 %). Thus the cooling tower rejects engine heat to the atmosphere with very small water consumption. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is air cooling used only for small engines? A. Air has low heat capacity B. Air is expensive C. Fins are heavy D. Water is free Answer: A. Fins and a fan suit only engines of a few kW because air carries little heat. (Key point: Air cooling limits) 2. What is oil cooling of pistons? A. Oil sprayed under the piston crown in large engines B. Oil mixed with fuel C. Oil in the jacket D. Oil in the radiator Answer: A. It is a supplementary method for large engine pistons. (Key point: Oil cooling) 3. What is the function of a cooling tower? A. Cool the hot water so the same water can be reused B. Heat the water C. Filter fuel D. Store water Answer: A. It saves water where a river or lake is unavailable. (Key point: Cooling tower function) 4. How does the water cool in the tower? A. A small part evaporates, taking latent heat from the rest, which cools by 8-12 deg C B. By freezing C. By chemical reaction D. By radiation only Answer: A. Air flows through falling water over fill; evaporation provides the cooling. (Key point: Cooling mechanism) 5. What does make-up water replace? A. Evaporation, drift and blow-down losses (about 1-3%) B. Fuel C. Oil D. Nothing Answer: A. Only a small consumption, so heat is rejected with little water use. 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