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| 2. |
- Hosseini, N., et al.
(författare)
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Evaluating thermoacoustic properties of heating appliances considering the burner and heat exchanger as acoustically active elements
- 2018
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Ingår i: Combustion and Flame. - : Elsevier. - 0010-2180 .- 1556-2921. ; 191, s. 486-495
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Tidskriftsartikel (refereegranskat)abstract
- Heat exchangers are an essential constituent part of many combustion systems. The thermoacoustic instability in such systems is a common problem and it has been studied extensively. However, the heat exchanger has not gained much attention in the field of combustion thermoacoustics, leading to a lack of knowledge about the thermoacoustic interactions between the burner and the heat exchanger. In this paper, a modeling approach is introduced to study these interactions in an academic representation of a heating appliance, comprised of a perforated slit burner and a tube heat exchanger. Both elements are considered thermally and acoustically active. A CFD model is used in a two-dimensional domain to simulate the response of the system to small amplitude broadband velocity perturbations. The thermochemical and acoustic coupling between the burner and the heat exchanger is investigated and a method is introduced to decouple their effects and study them separately. The extents to which this method is valid are addressed by varying the distance between the elements. Results show that as long as the flames do not impinge on the heat exchanger surface, a linear network modeling approach can be applied to construct the acoustic response of the composed configuration from the responses of its constituting elements. This approach requires registering the average velocity on a properly chosen intermediate plane between the burner and heat exchanger. Choosing this plane may be to some point difficult, i.e. when the burner and heat exchanger are close and cannot be considered independent. Moreover, when flame impingement occurs, the interactions between the flame and heat exchanger affect their individual thermoacoustic behaviors and the burner plus heat exchanger assembly needs to be considered as one coupled acoustic element. Particularly, flame impingement changes the phase of the heat absorption response of the heat exchanger and it may significantly alter the acoustic properties of the coupled assembly. The physics lying behind the effects of such interactions on the thermoacoustics of the system is discussed. The obtained results signify that a correct stability prediction of an appliance with burner and heat exchangers requires considering active thermoacoustic behavior of both elements as well as their interactions.
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| 3. |
- Hosseini, N., et al.
(författare)
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Intrinsic thermoacoustic modes and their interplay with acoustic modes in a Rijke burner
- 2018
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Ingår i: International Journal of Spray and Combustion Dynamics. - : Sage Publications. - 1756-8277 .- 1756-8285. ; 10:4, s. 315-325
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Tidskriftsartikel (refereegranskat)abstract
- The interplays between acoustic and intrinsic modes in a model of a Rijke burner are revealed and their influence on the prediction of thermoacoustic instabilities is demonstrated. To this end, the system is examined for a range of time delays, temperature ratios and reflection coefficients as adjustable parameters. A linear acoustic network model is used and all modes with frequency below the cut-on frequency for non-planar acoustic waves are considered. The results show that when reflection coefficients are reduced, the presence of a pure ITA mode limits the reduction in the growth rate that usually results from a reduction of the reflection coefficients. In certain conditions, the growth rates can even increase by decreasing reflections. As the time delay of the flame and thus the ITA frequency decreases, the acoustic modes couple to and subsequently decouple from the pure ITA modes. These effects cause the maximum growth rate to alternate between the modes. This investigation draws a broad picture of acoustic and intrinsic modes, which is crucial to accurate prediction and interpretation of thermoacoustic instabilities.
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| 4. |
- Konnov, Alexander, et al.
(författare)
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2D effects in laminar premixed flames stabilized on a flat flame burner
- 2013
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 1879-2286 .- 0894-1777. ; 47, s. 213-223
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Tidskriftsartikel (refereegranskat)abstract
- In the present work non-idealities of flat burner-stabilized flames at atmospheric and low pressures are examined using PIV measurements, which are supported by and analyzed with the help of CFD modeling. Radial and axial velocity profiles measured in the cold flow and in the flames at atmospheric and at lower pressures are presented. Two possible reasons for the drop in the apparent laminar burning velocity at low pressures (below 20 kPa) were considered: the non-uniformity of the velocity profile issuing from the burner mouth and diffusion of the gas mixture from the original gas flow. At very low pressures an outward velocity at the edge of the burner plate is detected. A part of the fuel-air mixture therefore seems to escape the flow at the edge of the burner. Further experiments, however, revealed that diffusion of the fuel from the fresh mixture and of the ambient atmosphere into the flame is less important as compared to the diffusive loss of H atoms from the flame at low pressures. This was substantiated by the numerical analysis and assessment of the earlier observations from the literature. A critical relation between the size of the burner and the lowest pressure for ensuring the stabilization of a flat flame is demonstrated. (C) 2013 Elsevier Inc. All rights reserved.
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| 5. |
- van den Boom, J.D.B.J, et al.
(författare)
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Active control of oscillations in a Rijke tube-like flat flame configurations
- 2007
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Ingår i: Proceeding of the European Combustion Meeting.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of low NOx premixed surface burners with a large modulation range in modern central heating systemsoften to noise problems. In order to make any further advance in the development of these systems the noise problemhas to be solved. Therefore, the possibility of suppression (and stabilization) of these instabilities is in investigatedusing active model-based control strategies. A model for the condensing gas-fired boiler is derived first. based on anacoustic network approach. Special attention is paid to the flame dynamics. Second, a H1 controller is synthesized,where also modelling uncertainties are taken into account. In the end the performance and the robustness of thecontroller is validated during experiments.
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