Simultaneous investigation of boiling heat transfer and power output in ORC

Transcription

1 Simultaneous investigation of boiling heat 4th International Seminar on ORC Power Systems, Sep. 2017, Milano

2 ORC geothermal binary power plants Shell-and-tube evaporator HC: Flammability ORC turbine HFC: GWP Replacements? Simultaneous experimental investigation of nucleate boiling heat transfer and power output 2/14

3 Low GWP replacement R245 fa R1233 zd(e) Refrigerant group GWP Safety classification Sat. pressure (T sat = 100 C) Vapour density (T sat = 100 C) HFC 1030 B bar 72.8 kg/m³ HCFO 5 A bar 56.3 kg/m³ 3/14

4 Flowsheet scroll expander evaporator throttle condenser preheater pump tank 4/14

5 Evaporator Pool boiling Heating element Calculation of nucleate pool boiling HTC q α nb = T w T sat T w = T i qd o ln D o 2λ t D i 5/14

6 Scroll expander and generator Scroll expander Manufacturer: Air Squared Nominal power: 1 kw Max. speed: /min Volume ratio: 3.5 Generator Manufacturer: Voltmaster Type: Self-excited AC Nominal power: 2.4 kw Nominal speed: /min Variable electronic load Type: Phase angle control Nominal power: 1.5 kw Frequency range: Hz 6/14

7 Operating parameters Q evap (kw) n scroll (1/min) T sat ( C) Equal saturation temperatures Optimization of applications with limited heat source temperatures variable Equal rotational speeds Comparison at equal heat fluxes and similar mass flow rates variable Scroll expander at idle operation Evaluation of thermal and generator losses variable variable 7/14

8 Heat Transfer and Power Output Equal saturation temperatures R1233zd(E): Heat flux and mass flow rate lower Influence of rotational speed low 8/14

9 Heat Transfer and Power Output Equal saturation temperatures -23 % to -30% R1233zd(E): Lower HTC due to lower pressure and heat flux R1233zd(E): Lower power due to lower thermal input power and mass flow rate 9/14

10 Heat Transfer and Power Output Equal saturation temperatures R1233zd(E): Lower filling factor causes lower volume flow rate and higher volume ratio Low electrical isentropic efficiency indicates poor generator efficiency 10/14

11 Heat Transfer and Power Output Equal rotational speeds q = const. n 12 % - 19 % n R245fa R1233zd(E): Reduced pressure compensates effect of thermophysical properties Decreasing electrical power due to lower thermal input power and higher internal consumption of generator 11/14

12 Summary + R1233zd(E) + R245fa GWP 99.6 % HTC 30 % Filling factor 5 % R1233 zd(e) vs. R245 fa Power output 100 W Volume ratio 6 % Isentropic efficiency 12/14

13 Further work and acknowledgments Further work Comparison of measured HTC to common pool boiling correlations Scroll expander High efficiency generator Torque measurement Evaporator Stainless steel tube Bundle evaporator Acknowledgments Funding from the Bavarian State Ministry of Education, Science and the Arts in the framework of the project Geothermie-Allianz Bayern is gratefully acknowledged. 13/14

14 Thank you Matthias Welzl, Florian Heberle and Dieter Brüggemann

15 Heat Transfer and Power Output Idle operation 15/14