Design and Development of a Liquid Piston Stirling Engine E90 Senior Design Project Report May 2 2006. BY: FRANK KYEI-MANU ALOYSIUS OBODOAKO Advisor: Professor Carr Everbach 1 Abstract An alpha-type Liquid Piston Stirling engine with a maximum power output of 23W and an efficiency of 3.4% was designed, built and instrumented for demonstration purposes. Based on in-depth research and design optimization, engine parameters were determined and a particular design was drafted. All the engine parts were manufactured in the Engineering Department’s machine shop. The design was modified following initial testing and modified to improve performance. During the final two weeks of the project different sensor types were added to enable real-time data collection and processing. Furthermore, sufficient data was taken to characterize the fluidyne system. There is still a lot of work to be done in order to realize our initial project goals and it is our hope that the engine will be improved upon extensively in the coming years. 2 Acknowledgements We owe Professor Carr Everbach a great deal of gratitude for his expertise, support and advice during the entire process but more especially during the initial stages of the project in getting us onto the right track. Secondly, we would like to thank Mr. Grant Smith ‘Smitty’ for his help in machining several system components, in ordering several system parts and directing us when it came to using the machines in the departmental shop. Professor Fred Orthlieb was also very invaluable in moving the project forward and his help in machining some of the system pieces when Smitty was away is very much appreciated. To our E14 students, Paul Agyiri ’07 and Lauren ’07, we say thank you for testing the regenerative materials in order suggest what the best material is for the purposes of our project. Finally to our peers, engineering faculty members and friends who kept pushing us on, we say thank you. 3 Table of Contents 1. Introduction …………………………………………………………….. 6 1.1 Background Information …………………………………………….. 6 1.2 Project Objectives & Goals …………………….…………………….. 6 1.3 Why a Liquid Piston Stirling Engine……………………………………8 1.4 Liquid Piston Stirling Engines- A Historical Overview ..........................8 1.5 Basic Operation of a Stirling Engine……………………………………9 1.6 Basic Operation of the liquid piston Fluidyne Engine………………….13 1.7 Effects of Evaporation and Mean Pressure……………………………...14 1.8 Applications……………………………………………………………...15 1.9 Report Organization……………………………………………………..16 2. Theory …………………………………………………………………….. 16 2.1 Working Fluid and Pressure …………………………………….. 16 2.2. Operating Temperatures ........................…………………………….. 16 2.3 Displacer Frequencies……………………………………………….. 17 2.3.1. Derivation of Operating Frequencies…................................ 17 2.4 Tuning of Liquid Columns…………………….…………………….. 18 2.4.1. Derivation of Tuning Column length given Frequency………18 2.5 Power Output…………………………………………………………...21 2.6 Losses…………………………………………………………………...22 2.6.1. Viscous Losses………………………………………………..22 2.6.2. Power Losses in Fluid Flow…………………………………..23 2.6.3. Kinetic Flow Losses…………………………………………..23 2.6.4. Heat Losses……………………………………………………24 2.6.5 Shuttle Losses………………………………………………….25 2.6.6 Other Losses that could affect System………………………...25 2.7 The Regenerator and its Operation……………………………………...26 3. Design Process …………………………………………………………………...28 3.1 Our Design……………………………………………………………….28 3.1.1 Engine System Parameters………………………………………30 3.2 Components of the System………………………………………………32 4 3.2.1 Heat Exchanger…………………………………………………32 3.2.2 PVC…………………………………………………………….33 3.3.3 Displacer………………………………………………………..33 3.3.4 Pumping Column……………………………………………….34 3.3.5 Regenerator……………………………………………………..34 3.3.6 Connections…………………………………………………….34 3.3.7 Tuning Column…………………………………………………36 3.3.8 Unistrut Structure………………………………………………36 3.3.9 Summary of Design and Parameter sizes……………………....36 4. Construction and Assembly …………………………………………….. 38 4.1. Introduction …………………………………………………….. 38 4.2. Machine Shop Work Details …………………………………….. 38 4.2.1. Displacer……………..…………………………………….. 39 4.2.2. Six inch to three quarter inch end caps………………….........40 4.2.3. The Tuning Column …………………………………….. 40 4.2.4. The Regenerator …………………………………….. 40 4.2.5. The Heat Exchanger……………………….. ………………. 42 4.2.6. Carbide Silicate/Fibre Funnels……………………………… 43 4.2.7 Unistrut………………………………………………………..43 4.2.8 Insulating Float………………………………………………..44 4.2.9 Modifications…………………………………………………45 4.3. Data Acquisition System…………………………………………….. ..46 4.3.1. The Pressure Transducer……………………………...……...46 4.3.2 Thermocouples. .……………………………………..............47 4.3.3 Proximity Sensor……………………………………………..47 5. Results and Discussion…………………………………………………………47 6. Conclusions……………………………………………………………………..57 7. Further Work…………………………………………………………………...58 8. References………………………………………………………………………62 5 1. INTRODUCTION 1.1 Background Information There is an ongoing campaign for the need for alternative energy sources to meet the demands of today’s world. The abundance of solar energy especially in sub-Saharan African is a resource that cannot be overlooked. This ever-present energy source is however underutilized despite the many uses to which it can be put. It is with this in mind that we intend to address one of the pressing needs in developing countries. Residents in developing countries often cannot count on the availability of clean drinking water due to the pollution of surface water sources such as rivers and lakes. (see fig 1.1 overleaf). Thousands of deaths occur every year from water-borne diseases alone. In countries with plentiful sunlight, heat energy powered by a constant supply of solar energy could be used to pump well water. In addition, the water that is pumped could be boiled by the same focused sunlight, thereby providing a continuous source of clean water. The purpose of this project is to design and implement a liquid piston Stirling engine that outputs enough power to pump water from a depth of at least 7 feet. We also intend to include a parabolic collecting mirror that will focus the sun’s energy to heat the system. The system we plan to implement will use fluidyne technology, which is currently underappreciated. 1.2 Project Objectives & Goals The primary objectives of the project are: • To build a liquid piston Stirling engine with a power output of at least 5W, capable of pumping water to a height of at least 7 feet. • To boil the water that has been pumped using focused sunlight. • To choose a suitable design that incorporates mechanical simplicity with sustainability within the limitations of a third-world society. • To raise awareness about fluidyne technology as an alternative, low cost energy source. 6 Fig 1.1 below shows the crude methods most rural folks in Africa obtain their water and attempt to purify them. As is evident for one or more of these images, water supply is generally unhygienic and the means of accessing water is not as efficient as it could be. Slow flowing pond as source of water Village water source. Girl with bucket in a ditch, fetching her water. Woman pouring water into pot to be purified/sterilized by sunlight Women standing next to a well, typically 20-30 feet in depth Fig 1.1: Pictures of rural water supply and storage 1.3 Why a Liquid Piston Stirling Engine 7 A very important objective of this project, as was mentioned in the goals section in this report, is to design and develop a system that can easily be constructed given the limitations of a developing society. With this in mind, there is the need to choose a design that incorporates constructional simplicity; a fluidyne system provides this. It can be constructed using relatively simple and inexpensive materials. In our case, PVC tubing, which are primarily cheap and also come in different standard sizes, can sufficiently accommodate the needs of a Fluidyne System. A liquid piston Stirling engine can therefore be built without the need for sophisticated machining which is definitely a plus. A second major advantage of liquid piston Stirling engines is that they are silent during operation. Compared to mechanical-piston Stirling engines as well as other pumps, fluidynes are extremely silent during operation which is an added benefit. One does not have to concern themselves with losses as a result of moving parts (mechanical pistons). In fact the only predominant losses that lower the efficiencies considerably of fluidyne systems are viscous losses. The oscillating liquid must be viscous enough to be able to sustain oscillations got a long period of time. The engines’ efficiency ranges from 3-6%. Despite the low efficiency, the constant supply of solar energy all year round will be enough to power the engine to serve the needs of villages in a typical rural setting. 1.4 Liquid Piston Engines: A Historical Overview Internal-combustion liquid pistons have been built and sold since the early 1900’s. The first of these, popularly referred to as the Humphrey pump, is more-or-less an internal combustion engine, using either a two- or four-stroke cycle in which the conventional solid pistons are replaced with a liquid column. Inlet and outlet valves for the water, as well as a high-grade fuel to provide the energy to power the engine - usually petroleum – are used. The major advantage of liquid pistons is clearly depicted by the aforementioned engine: its simplicity. Liquid pistons do not require accurately dimensioned cylinders and they permit great flexibility in mechanical design with relatively simple