12-07-2013, 03:38 PM
A SEMINAR REPORT ON SOLAR POWERED STIRLING ENGINE
SOLAR POWERED STIRLING.docx (Size: 507.26 KB / Downloads: 111)
ABSTRACT:
The performance of Stirling engines meets the demands of the efficient use of energy and environmental security and therefore they are the subject of much current interest. Hence, the development and investigation of Stirling engine have come to the attention of many scientific institutes and commercial companies. The Stirling engine is both practically and theoretically a significant device, its practical virtue is simple, reliable and safe which was recognized for a full century following its invention by Robert Stirling in 1816. The engine operates on a closed thermodynamic cycle, which is reversible. The objective of this report is to provide fundamental information and present a detailed review of the Stirling cycle engine. Stirling engine concept is attached to the solar and the implementations are reported .Different types of stirling engines, their working, advantages and disadvantages are presented.
.INTRODUCTION:
A Stirling cycle machine is a device, which operates on a closed regenerative thermodynamic cycle, with cyclic compression and expansion of the working fluid at different temperature levels. The flow is controlled by volume changes so that there is a net conversion of heat to work or vice versa. The Stirling engines are frequently called by other names, including hot-air or hot-gas engines.
Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work. The stirling engine is associated with solar power to generate electrical energy since solar power is abundant source of energy.
HISTORY OF STIRLING ENGINE:
On September 27, 1816, Robert Stirling applied for a patent for his Economizer at the Chancery in Edinburgh, Scotland. By trade, Robert Stirling was actually a minister in the Church of Scotland and he continued to give services until he was eighty-six years old. But, in his spare time, he built heat engines in his home workshop. Lord Kelvin, who is best known for his work in the field of electricity, especially submarine telegraphy, used one of the working models during some of his university classes.
In 1850, Professor McQuorne Rankine first explained the simple and elegant dynamics of the engine. Approximately one hundred years later, Rolf Meijer coined the term “Stirling engine” in order to describe all types of closed cycle regenerative gas engines.
BASIC STIRLING ENGINE:
The engine is designed so that the working gas is generally compressed in the colder portion of the engine and expanded in the hotter portion resulting in a net conversion of heat into work. An internal Regenerative heat exchanger increases the Stirling engine's thermal efficiency compared to simpler hot air engines lacking this feature. Key components:
OPERATION OF STIRLING ENGINE:
Since the Stirling engine is a closed cycle, it contains a fixed mass of gas called the "working fluid", most commonly air, hydrogen or helium. In normal operation, the engine is sealed and no gas enters or leaves the engine. The Stirling engine, like most heat engines, cycles through four main processes: cooling, compression, heating and expansion. This is accomplished by moving the gas back and forth between hot and cold heat exchangers, often with a regenerator between the heater and cooler. The hot heat exchanger is in thermal contact with an external heat source, such as a fuel burner, and the cold heat exchanger being in thermal contact with an external heat sink, such as air fins. A change in gas temperature will cause a corresponding change in gas pressure, while the motion of the piston causes the gas to be alternately expanded and compressed.
STIRLING ENGINE WITH SOLAR:
Solar energy is one of the more attractive renewable energy sources that can be used as an input energy source for heat engines. In fact, any heat energy source can be used with the Stirling engine. The solar radiation can be focused onto the displacer hot-end of the Stirling engine, thereby creating a solar-powered prime mover. The direct conversion of solar power into mechanical power reduces both the cost and complexity of the prime mover. In theory, the principal advantages of Stirling engines are their use of an external heat source and their high efficiency. Stirling engines are able to use solar energy that is a cheap source of energy.
A solar powered stirling engine was patented by Roelf J. Meijer in 1987. His invention relates a heat engine, such as a Stirling cycle engine, with a solar dish collector in order to produce electricity .This apparatus consists of a large dish aimed at the sun to reflect the rays into the focus point, which is located at the center of the dish. Solar energy is now collected in the form of heat to fuel a Stirling cycle engine . which operates by letting heat flow from a hot source to a cold sink in order to do work. The work output of the stirling cycle is then used to drive a generator and create electric power.
CONCENTRATING SOLAR PLANTS:
Concentrating solar power plants uses parabolic trough collectors or central tower concentration arrangement. In parabolic trough system a parabolic shaped concentrator of aluminium is used. In the centre the receiver is placed. The temperatures at the centre point are of 232degree celcius. In the central tower system many number of heliostates are arranged in pattern such that the entire reflection of each heliostat towards a central tower. The central tower acts as a receiver. Generally molten salt is used as a working fuel to exchange the heat.