PHASE ANGLE EFFECT ON HEAT TRANSFER AND INDICATED POWER OF FREE PISTON STIRLING ENGINE

In this work, a transient CFD analysis is performed to analyze the effects posed by changing the phase angle between the displacer and power piston in a free piston Stirling engine. The numerical model that is used for analysis is axisymmetric which contains live engine spaces (expansion and compression space) and dead spaces (heater, regenerator, and cooler). The displacer and power piston movements are defined by a user defined function. The results showed that the compression ratio and pressure wave amplitude are strong function of phase angle and peaked at 120 degrees phase angle. The optimum phase angle is also changing with operating frequency. The suitable phase angle at 80 Hz is the range of 60-70 degrees, but at a lower frequency around 50 Hz, its range is 80-100 degrees. The results also showed that the heat transfer rate at the heater and cooler channels are influenced by the change ofphase angle. The heat exchange at the heater and cooler is peaked at 90 degrees and 100 degrees phase angle, respectively. The flow losses from the heater, regenerator and cooler showed a rising trend with phase angle increase. The optimum phase angle was obtained by making a balance between phase angle effects and found the optimum range to be between 60 degrees- 80 degrees for peak power and efficiency.