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Abstract: This work provides a review of n solar-powered Stirling engines devices. Previous works have focussed on the solar powered as well as low temperature differential engines. The aim of this work is to review working fluids for operation of this engine. Air was found to be a good alternative as a working medium for gamma type engines.
Keywords: Stirling Engines
(ProQuest: ... denotes formulae omitted.)
1. Introduction
In a Stirling engine the fluid is contained in a confined space, hence there are no problems of contamination. In order to reduce the heat losses, the mass flow rate must be low which can be maintained by low viscosity fluid or high working pressures. These engines are 30 to 40% efficient in a temperature range of 923-1073 K.[1].
A Stirling engine consists of following components:
1. Heat source-as fuel does not come in direct contact with the working fluid, Stirling engines can work on fluids which may damage parts of a conventional engine.
2. Regenerator-the function of regenerator is to use the waste heat from being lost to environment by storing it temporarily, thus helping to achieve high efficiencies close to an ideal Carnot cycle. A simple configuration consists of fine mesh of metallic wires. In an ideal Stirling cycle, the connecting space between hot and cold ends acts as regenerator.
3. Heat sink-typically the ambient environment acts as an ideal heat sink; otherwise the cold side can be maintained by iced water or cold fluids like liquid nitrogen.
4. Displacer piston-it causes the displacement of working gas between hot and cold regions so that expansion and contraction occurs alternatively for operation of engine.
5. Power piston- transmits the pressure to crankshaft.
In a Stirling engine, hot air expands when heated and contracts when cooled. This principle of operation was most properly understood by Irish scientist Robert Boyle from his results on experiments on air trapped in a J shaped glass tube. Boyle stated that pressure of a gas is inversely proportional to its volume and product of pressure and volume occupied is a constant depending on temperature of gas.
Hence PV=NRT
Various assumptions which are made in this cycle are [3]:
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