Numerical Investigations of the Response of a Simplified Burner-heat exchanger System to Inlet Velocity Excitations

Transcription

1 Numerical Investigations of the Response of a Simplified Burner-heat exchanger System to Inlet Velocity Excitations Naseh Hosseini, Viktor Kornilov, Joan Teerling, Ines Lopez Arteaga and Philip de Goey COMBURA '14 Combustion Research and Application Kontakt der Kontinenten, Soesterberg, The Netherlands 8-9 October 2014

2 Introduction - Thermoacoustics 2

3 Introduction - Challenges Thermoacoustic noise is currently an issue in domestic heating systems Closer burner and heat exchanger in compact condensing boilers The industry s need for design rules to make thermoacoustically stable systems 3

4 Introduction - Goal The physics of the interactions between a burner and a heat exchanger from a hydrodynamic and thermoacoustic point of view In this presentation the method of modelling, implementation of CFD setup, validation of the simulations and first illustrative results will be discussed 4

5 Introduction - Numerical domain Flat multi-slit burner Plane 2D symmetric Dimensions in mm 5

6 Introduction - The model ANSYS Fluent CFD code Laminar flow with energy equation Species conservation t Y. vy. J R S i i i i i Single step reaction CH 2 O 3.76N CO 2H O 7.52N Arrhenius formulation k r r A T e r E r RT Modified to get the correct laminar flame speed 6

7 SL (CM/S) Introduction - Verifications Pseudo-1D model ( mm) Grid independency SQR SQR SQR SQR ELEMENT SIZE AND TYPE (MM) 7

8 Sl (cm/s) Introduction - Verifications Pseudo-1D model ( mm) Grid independency Equivalence ratio sensitivity This Study Lange (1992) Dyakov (2001) Kishore (2008) Equivalence Ratio 8

9 Sl (cm/s) Introduction - Verifications Pseudo-1D model ( mm) Grid independency Equivalence ratio sensitivity Unburnt temperature sensitivity This Study Sharma (1981) Brown (2003) Unburnt Temperature (K) 9

10 Introduction - 2D grid, using 1D conclusions, 165,000 elements 10

11 Introduction - Flame transfer function Velocity perturbation as input and heat release rate as output Step increase of 5% with assumed linearity, 40ms relaxation time The (complex) flame transfer function defined as relative flame response divided by the relative upstream velocity perturbation, in frequency domain TF f q f q u f u 11

12 Distance between Burner Deck and Heat Exchanger (mm) Introduction - Case studies Inlet Velocity (cm/s) Hex05-V25 Hex05-V50 10 Hex10-V25 Hex10-V50 15 Hex15-V25 Hex15-V50 N/A NoHex-V25 NoHex-V50 12

13 Introduction - Left: inlet velocity 25cm/s - Right: inlet velocity 50cm/s Reaction rate (kmol/m 3 s) Temperature (K) 17

14 Introduction - Flow field through flame and around heat exchanger 18

15 Heat Release Rate (kw) Normalized Heat Release Rate Introduction V50-NoHex V50-Hex15 V50-Hex10 V50-Hex05 V25-NoHex V25-Hex15 V25-Hex10 V25-Hex05 V50 V Flow Time (ms) V50 V Flow Time (ms) 19

16 Normalized Heat Release Introduction - Offset for Hex05V NoHex Hex15 Hex10 Hex Time (ms) 20

17 Normalized Heat Release Introduction - Response to square excitation Time (ms) 21

18 Element Heat Transfer Rate (kw) Introduction Deck Hex Flame HEX05 HEX10 HEX15 HEX05 HEX10 HEX15 V25 Case Studies with Heat Exchanger V50 22

19 Phase/ (rad) Introduction Phase ReacTF - V25 23

20 Phase/ (rad) Introduction Phase ReacTF - V25 24

21 Phase/ (rad) Introduction Phase ReacTF - V50 25

22 Phase/ (rad) Normalized Heat Exchanger Heat Flux Introduction Hex15 Hex10 Hex05 1 Hex15 Hex10 Hex Hex15 Hex10 Hex05 Hex15 Hex10 Hex Phase HexTF V Time (ms) Time 26

23 Phase/ (rad) Normalized Heat Exchanger Heat Flux Introduction Hex15 Hex10 Hex05 1 Hex15 Hex10 Hex Hex15 Hex10 Hex05 Hex15 Hex10 Hex Phase HexTF - V Time (ms) Time 27

24 Phase/ (rad) Burner Deck Heat Flux (W) Normalized Burner Deck Heat Flux Introduction DeckTF V NoHex NoHex Hex15 Hex10 Hex15 Hex05 Hex10 Hex Phase Time Flow Time (ms) Flow Time (ms) 28

25 Phase/ (rad) Burner Deck Heat Flux (W) Normalized Burner Deck Heat Flux Introduction DeckTF - V Hex15 Hex10 Hex05 Phase Time Flow Time (ms) Flow Time (ms) 29

26 Introduction - The possibility of calculating a total transfer function Q Q Q TF TF TF Q Q Q flame hex deck flame hex deck input input input TF flame Q Q hex flame TF hex Q TF TF TF hex total flame hex Qflame Transfer Function - Comparison with transfer matrix Total Hex Flame Deck 30

27 Introduction - The possibility of calculating a total transfer function Hex Total Flame Deck 31

28 Introduction - Experimental setup 32

29 Introduction - The model accurately predicts combustion properties - Absolute heat release changes with approaching hex, but normalized values and flame transfer function don t - Impingement causes intense flame cooling, counter phase behavior, and in special cases some degree of offset - Decoupling elements transfer function in order to construct a total transfer function enables better system identification and thermoacoustic design posibilities 33

30 Introduction The presented work is part of the Marie Curie Initial Training Network Thermo-acoustic and Aero-acoustic Nonlinearities in Green Combustors with Orifice Structures (TANGO). We gratefully acknowledge the financial support from the European Commission under call FP7-PEOPLE-ITN