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5517 results in Thermal-fluids engineering

Page 187 of 276

  • 2 - Mechanism Effectiveness and Mechanical Efficiency

  • James R. Senft, University of Wisconsin, River Falls
  • Book:
    Mechanical Efficiency of Heat Engines
    Published online:
    15 October 2009
    Print publication:
    13 August 2007, pp 12-19

  • Summary

    In a cyclic heat engine, the mechanism plays a key and complicated role. Its main objective is to transport energy from the working substance to the output shaft. But it also functions to constrain and effect the movement of the piston in order that it carry out a certain thermodynamic cycle. This requires that the mechanism work in a bidirectional fashion. It must transport work from the piston to the flywheel and output shaft during some parts of the cycle, and from the flywheel to the piston in other parts. In practice, it is sometimes even more complex. For example, just after dead center in some engines, both the piston and the flywheel supply work to the mechanism, which is consumed by friction.

    For analytic treatment, a comprehensive model of machines that reflects in detail all of the modes in which a mechanism is called upon to function in an engine is the natural first thought. However, such a model quickly becomes exceedingly complex, as the development in Appendix A shows. Rather, the main text of this monograph employs only very basic principles and examines best possible cases. As will be seen as the chapters unfold, a surprising number of interesting and practical insights about ultimate engine performance can be easily deduced through this simple approach.

  • Appendix B - An Ultra Low Temperature Differential Stirling Engine

  • James R. Senft, University of Wisconsin, River Falls
  • Book:
    Mechanical Efficiency of Heat Engines
    Published online:
    15 October 2009
    Print publication:
    13 August 2007, pp 153-162

  • Summary

    Although the analysis presented in Chapter 7 is highly idealized, it is quite appropriate for providing some insight into the geometrical requirements of the ultra low temperature differential Stirling engine illustrated in Figures B.1–B.3. Nicknamed the P-19, this engine has proven itself capable of operating down to a temperature difference of just 0.5 °C (less than 1 °F) between its warm and cool sides. The P-19 was the first to run from heat absorbed while resting on the palm of a human hand. The P-19 was first publicly demonstrated at the 25th Intersociety Energy Conversion Engineering Conference held in Reno, Nevada, in August 1990.

    BACKGROUND

    A low temperature differential (LTD) Stirling engine may be characterized as one that operates more or less optimally with a temperature difference of less than 100 °C between its hot and cold end. Ivo Kolin was the first to design and build such an engine. At the Inter-University Center in Dubrovnik in 1983 he demonstrated the first of his engines operating with hot water as the heat source and cold water as the heat sink (Kolin, 1983). The engine continued to run until the temperature difference between the source and sink dropped to 15 °C.

    Kolin's first engine inspired a number of research projects over the next decade to further develop LTD Stirling engines (Senft, 1996).

Page 187 of 276