Research On Stirling Cycle Analysis Models, Heat Transfer Of Oscillating Flows And Performance Of A Self-designed Stirling Engine

In this study, a thermodynamic model called Improved Simple Analysis Model was proposed, carefully considering heat and power losses in Stirling engines, including heat conduction loss, regenerator returning heat loss, shuttle heat loss of the displacer, flow resistance loss, gas spring hysteresis loss in the compression and expansion spaces and seal leakage loss. The error is less than 20% when the speed is less than 2500r/min. As the speed grows, the characteristics of oscillating flow and heat transfer become increasingly complex, which cause bigger error. The experimental study of Stirling engine heater tubes indicated that the oscillating flow heat transfer was greater than the steady flow especially in high Reynolds number. The heat transfer correlation of oscillating flow was expressed by:A 100 W β-type Stirling engine was built and tested with helium and nitrogen when pressure and revolving speed ranging from 1.6 MPa to 3 MPa and 260 r/min to 1380 r/min, respectively. Experimental information on performance, such as PV diagrams and temperatures of the heater and cooler, was systematically measured. Generally, the Improved Simple Analysis Model agrees well with the experimental data with a relative error of 4.3% to 13.4% for helium and 1% to 7.1% for nitrogen.Increased revolving speed caused imperfect compression and expansion processes and made the PV diagram "thin". Shaft power reached the maximum value of 30.1 W for helium and 21.0 W for nitrogen at revolving speeds of 1000 r/min and 650 r/min, respectively. Improving the mean pressure of gas increased the indicated power, cycle efficiency, shaft power, and electrical power. The maximum indicated power and cycle efficiency were 165 W and 16.5% for helium and 139 Wand 12.2% for nitrogen in the same working conditions of 2.96 MPa and 1120 r/min. Analysis of energy losses with ISAM indicated that helium had larger shuttle and seal leakage losses and smaller flow resistance and regenerator returning heat losses than nitrogen under the same working conditions. Flow resistance and regenerator returning heat losses, which increased much more rapidly than seal leakage or shuttle heat losses with the increase in revolving speed and pressure, played an important role and resulted in different performances with the two working gases. This study provides comprehensive understanding of the second-order model and the real Stirling cycle and recommends that more work (e.g., mechanisms of heat and power losses and PV diagrams) should be performed to improve the precision of second-order models.