Chapter 5 - Stirling Engine Simple Analysis

Once we have done an Ideal Adiabatic analysis on a specific Stirling engine, we would like to evaluate the heat transfer and flow-friction effects of the three heat exchangers on the performance of the engine. This will enable us to do a parametric sensitivity analysis as required for design optimization.

Forced convection heat transfer is fundamental to Stirling engine operation. Heat is transferred from the external heat source to the working fluid in the heater section, cyclicly stored and recovered in the regenerator, and rejected by the working fluid to the external heat sink in the cooler section. All of this is done in compact heat exchangers (large wetted area to void volume ratio) so as to limit the "dead space" to an acceptable value and thus allow for a reasonable specific power output of the engine. We find that effective heat exchange comes at a price of increased flow friction, resulting in the so-called "pumping loss". This loss refers to the mechanical power required to "pump" the working fluid through the heat exchangers, and thus reducing the net power output of the engine.

The theory and analysis of these effects is extremely complex, and we find that we can only rely on the plethora of documented experimental and empirical studies ( e.g. Kays & London ,"Compact Heat Exchangers"). Almost all of this vast body of work is based on steady flow conditions and is thus not directly applicable to the oscillating flow conditions that apply to Stirling engines. In this section we adopt a "Quasi-Steady Flow" approach, in that we assume that at each instant of the cycle the fluid behaves as though it is in steady flow. Thus we have called this analysis a "Simple" analysis because it is a gross simplification of an extremely complex process. At this stage there is still a major controversy about this approach, and we need to treat the results of this analysis with a healthy measure of skepticism. An alternative for design is the recent "Similarity and Scaling" approach which has been developed by Allan Organ and is presented in his book "The Regenerator and the Stirling Engine".

On to Scaling Parameters (Flow Friction and Convective Heat Transfer)

On to Regenerator Simple analysis

On to Heater and Cooler Simple analysis

On to Pumping Loss Simple analysis

On to Function set 'simple'

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Stirling Cycle Machine Analysis by Israel Urieli is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License