Overview
My bachelor graduation project at Selcuk University (Mechanical Engineering) was carried out with four classmates. We studied water cooling systems together with water purification and filtration, and designed a cooling system to increase the efficiency of a Stirling engine.
Why cooling matters for a Stirling engine
A Stirling engine produces work from the temperature difference between its hot and cold ends. The lower the temperature of the cold side, the larger that difference and the higher the efficiency. Cooling the regenerator and the cold cylinder is therefore not an accessory: it is part of the thermodynamic cycle.
What we did
- Reviewed the principles behind Stirling cycles, refrigeration cycles, heat pumps and heat exchangers, including how exchangers are classified by construction, flow arrangement and heat-transfer mechanism.
- Adapted ideas from internal-combustion engine cooling (water channels, radiator, fan) to the Stirling engine.
- Designed an open-loop cooling circuit: water circulates around the regenerator walls, absorbs heat from the gas flowing between the pistons, and leaves the system instead of being recirculated.
- Added a treatment stage before the cooling channels to remove limescale, particles, heavy metals and microorganisms, which protects the components and extends their service life.
- Sized the circuit around the capacity of the selected treatment unit (800 L/h), which limits the working flow rate.
Outcome
The cooling circuit increased the temperature and density difference between the two pistons, which raises the pressure swing and therefore the efficiency of the engine. The open-loop design suits marine engines, where sea water is available, and stationary engines that can use mains water with a fan-assisted radiator.
The project report is 100 pages long and covers the theory, materials, method, results and recommendations.
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