A dynamic model for the efficiency optimization of an oscillatory low grade heat engine

A simple approach is presented for the modeling of complex oscillatory thermal-fluid systems capable of converting low grade heat into useful work. This approach is applied to the NIFTE, a novel low temperature difference heat utilization technology currently under development. Starting from a first-order linear dynamic model of the NIFTE that consists of a network of interconnected spatially lumped components, the effects of various device parameters (geometric and other) on the thermodynamic efficiencies of the device are investigated parametrically. Critical components are highlighted that require careful design for the optimization of the device, namely the feedback valve, the power cylinder, the adiabatic volume and the thermal resistance in the heat exchangers. An efficient NIFTE design would feature a lower feedback valve resistance, with a shorter connection length and larger connection diameter; a smaller diameter but taller power cylinder; a larger (time-mean) combined vapor volume at the top part of the device; as well as improved heat transfer behavior (i.e. reduced thermal resistance) in the hot and cold heat exchanger blocks. These modifications have the potential of increasing the relevant form of the second law efficiency of the device by 50% points, corresponding to a 3.8% point increase in thermal efficiency.

[1]  D M Berchowitz,et al.  Linear Dynamics of Free-Piston Stirling Engines , 1985 .

[2]  Thomas C. B. Smith,et al.  Power Dense Thermofluidic Oscillators for High Load Applications , 2004 .

[3]  Graham Walker,et al.  Free piston Stirling engines , 1985 .

[4]  Christos N. Markides,et al.  Dynamic modelling of a two-phase thermofluidic oscillator for efficient low grade heat utilization: Effect of fluid inertia , 2012 .

[5]  Franz Durst,et al.  Pulsating laminar pipe flows with sinusoidal mass flux variations , 2005 .

[6]  Graham Walker,et al.  Small Free-Piston Stirling Engine: Power Systems for the Artificial Heart , 1985 .

[7]  J. A. C. Kentfield.  Thermodynamics of Airbreathing Pulse-Detonation Engines , 2002 .

[8]  Peter H. Ceperley,et al.  A pistonless Stirling engine—The traveling wave heat engine , 1979 .

[9]  David Cottrell Mosby.  The Fluidyne Heat Engine. , 1978 .

[10]  G. Swift,et al.  A thermoacoustic-Stirling heat engine: detailed study , 2000, The Journal of the Acoustical Society of America.

[11]  Thomas Charles Brannam Smith.  Thermally driven oscillations in dynamic applications , 2006 .

[12]  J. A. C. Kentfield.  Fundamentals of Idealized Airbreathing Pulse-Detonation Engines , 2002 .

[13]  C. D. West,et al.  Laboratory prototype fluidyne water pump , 1981 .

[14]  L. F. Goldberg,et al.  A prototype liquid-piston free-displacer Stirling engine , 1979 .

[15]  G. Swift,et al.  Experiments with an Intrinsically Irreversible Acoustic Heat Engine , 1983 .

[16]  G. W. Swift,et al.  An intrinsically irreversible thermoacoustic heat engine , 1983 .

[17]  Bin-Juine Huang,et al.  System design of orifice pulse-tube refrigerator using linear flow network analysis , 1996 .

[18]  Charles W. Stammers,et al.  The operation of the Fluidyne heat engine at low differential temperatures , 1979 .

[19]  J. A. C. Kenté.  Thermodynamics of Airbreathing Pulse-Detonation Engines , 2002 .

[20]  D. Jones.  Free Piston Stirling Engine Scaling Study , 1990, Proceedings of the 25th Intersociety Energy Conversion Engineering Conference.

[21]  C. D. West.  Dynamic analysis of the fluidyne , 1983 .