- Email: [email protected]
Coanda flames for development of flat burners
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Energyonline Procedia 00 (2018) 000–000 Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energy Procedia 00 (2018) 000–000
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy Procedia 158 Energy Procedia 00(2019) (2017)1885–1890 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Coanda flames for development of flat burners Coanda flames for development flat burners The 15th International Symposium on Districtof Heating and Cooling Victor Castaneda, Agustin Valera-Medina*
Victor Castaneda,ofAgustin Assessing the feasibility usingValera-Medina* the heat demand-outdoor School of Engineering, Cardiff Univeristy, Queen’s Building, The Parade, Cardiff, Wales, CF24 3AA, United Kingdom School of Engineering, Cardiff Univeristy, Building, The Parade, Cardiff, Wales, CF24demand 3AA, United Kingdom temperature function for Queen’s a long-term district heat forecast
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
Abstract a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b Veolia Recherche 291 Avenue Dreyfous Daniel,Since 78520itsLimay, Franceseveral applications have The Coanda effect is the tendency of a fluid &toInnovation, stay attached to a nearby surface. discovery, c Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, Franceunexplored, The effect the tendency heat of a fluid to stay a nearby Since its discovery, several applications have beenCoanda developed in isaerodynamics, transfer and attached medical to fields usingsurface. this concept. A potential, and currently been developed aerodynamics, transfer and medical fields using this and currently application of theinCoanda effect is heat its use in heating equipment. However, few concept. research A haspotential, been conducted on the unexplored, behavior of application Coanda effect is its use in Thus, heating However, few research has been on the behavior of flames underofathe Coanda flow pattern regime. theequipment. present study uses a generic swirl burner to conducted analyze influence of the flow flames a Coanda patternstability. regime. The Thus, the present usesdifferences a generic swirl to analyze influence of Open the flow rate andunder fuel mixture onflow the flame objective is tostudy identify in theburner behavior of a flame under an jet Abstract rate fuel mixture on the The will objective is to identify differencesofin novel the behavior of a flame underinanthe Open jet flowand pattern and Coanda jetflame flow stability. pattern that lead to further development flat burners. Changes burner flow pattern and flow pattern thattwo willflow leadpatterns. to further development of as novel flatand burners. Changes in Both the burner configuration wereCoanda made tojetinduce one of the Methane was used a fuel air as an oxidizer. gases District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the configuration to at induce the twoatmospheric flow patterns. Methane was used as aregulated fuel and using air as variable an oxidizer. gases were supplied were to themade burner ~20°Cone andofalmost pressure. Flow rates were area Both flowmeter. greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat were supplied to the burner atmospheric pressure. Flow rates were using area flowmeter. Gas flow was increased fromat3~20°C L/minand to aalmost maximum of 12 L/min with incremental stepsregulated of 1 L/min. Forvariable each gas flow rate, the sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, Gas flowflow was rate increased from 3 L/min to flame a maximum of 12 L/min with of Coanda 1 L/min.flame For each flow the oxidizer was increased, and the behavior recorded. It wasincremental found that asteps stable couldgas only be rate, induced prolonging the investment return period. oxidizer increased, flame behavior It was that a stable Coanda be induced when an flow Openrate jet was flame existed. and It is the theorized that this recorded. behavior is due found to a coherent structure thatflame breakscould downonly when a stable The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand when flame existed. It isflame. theorized this behavior is due to aascoherent thatdevelopment breaks downofwhen a stable Open an jet Open flamejet changes to Coanda Thethat concept is now presented a novel structure option for novel, large forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Open jet flame flame. The concept is nowsize presented a novel for development industrial deviceschanges capableto of Coanda stabilizing the flame while reducing for theirasuse in highoption temperature processes. of novel, large buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district industrial devices capable of stabilizing the flame while reducing size for their use in high temperature processes. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Copyright © 2018 Elsevier Ltd. All rights reserved. compared with results from a dynamic heatLtd. demand model, previously developed and validated by the authors. © 2019 The Published by Elsevier Copyright ©Authors. 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee of the 10th International Conference on Applied Theisresults showed when onlythe weather change is license considered, the margin of error could be acceptable for some applications This an open accessthat article under CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International Conference on Applied Selection and peer-review under responsibility of the scientific committee of the 10 Energy (ICAE2018). Peer-review responsibility of lower the scientific committee of ICAE2018 – Theconsidered). 10th International Conference on Appliedrenovation Energy. (the error inunder annual demand was than 20% for all weather scenarios However, after introducing Energy (ICAE2018). scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). Keywords: Coanda; Swirling flow; Flat flame The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Keywords: Coanda; Swirling flow; Flat flame decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +44-(0)29-2087-5948.
address:author. [email protected] * E-mail Corresponding Tel.: +44-(0)29-2087-5948. Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected] 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection peer-review under responsibility the scientific 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.436
Victor Castaneda et al. / Energy Procedia 158 (2019) 1885–1890 Author name / Energy Procedia 00 (2018) 000–000
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Nomenclature CFJ D NTP OJF PVC VAFM X
Coanda Jet Flow Nozzle diameter Normal temperature and pressure (1 atm & 20°C) Open Jet Flow Precessing Vortex Core Variable Area Flow Meters Distance between the flat plate and the tip of the nozzle outlet Equivalence ratio (fuel-air)
1. Introduction The Coanda effect is the tendency of a fluid to stay attached to a nearby surface and remain attached even when the surface curves away from the initial jet direction. The first time it was observed was in 1800 by Thomas Young. The effect takes its name from Henri Coanda, who in 1910, used it in the first practical application by building the world’s first jet propelled aircraft [1]. In the last 25 years, the Coanda effect has resurfaced in several applications. Some examples are: in aeronautics, where it has been used to increase the lift and thrust vectoring; in industry, where it has been used in reaction turbines, swirl atomizers, galvanizing techniques, cooling of cylinders and waste-gas flares; some applications in medicine also exist. A compilation of the applications has been made by Reba [2], with a more recent review made by Lubert [3]. The bulk of the available research was conducted in the 1960s. Ongoing research in the phenomena now focuses on noise levels [4], effect of wall temperature on the flow [5] and supersonic jets [6-7]. Energy related applications of the Coanda effect in industry seem to be limited to waste gas flares. As described by Desty [8] the advantages of having a Coanda effect on these type of flares is a smokeless combustion with increased combustion efficiency and decreased thermal radiation, when compared to other types of flare devices. Therefore, it is believed that potential applications exist that take advantage of the flat flow profile that the Coanda effect produces and are yet to be explored, especially on industrial processes that involve the heat treating of flat surfaces. One such application could be the use of this flat flame, wall attached, burners on annealing furnaces in the steel industry to substitute current technologies, i.e. radiant tubes. Expected benefits would include the reduction of volume furnace due to increased proximity of burner to strip, emission reduction and energy usage due to reduced fuel consumption. However, to develop new industrial combustion applications that take advantage of the Coanda effect, a better understanding of the behavior of a Coanda flame is needed. Research has been conducted on the stability of an isothermal Coanda flow. Vanierschot [9] described a change in the flow pattern that was dependent on the inlet swirl as well as a hysteresis pattern when increasing and subsequently decreasing the swirl. Valera-Medina [10] conducted research on transition of a Coanda Jet Flame to/from an Open Jet Flame and found that it was dependent on the geometry and step size of a flat plate fitted to the nozzle. Therefore, the present study aims to increase the understanding of the stability of a Coanda flame by looking into different flow patterns that occur as the flow rate and equivalence ratio are varied during the experiment. 2. Experimental setup A generic swirl burner was used to examine the flame stability under a Coanda Jet Flow (CJF) and an Open Jet Flow (OJF) pattern. The burner was fitted with a tangential swirl generator providing a geometrical swirl number of 1.04. The nozzle diameter was D=28mm and had an angle of 45 degrees. A schematic of the generic swirl burner is presented in Figure 1 and detailed elsewhere [11]. A flat plate was fitted to the nozzle. Two different normalized plate heights were chosen, X/D=0.36 and X/D=0.00, being X the distance between the flat plate and the tip of the nozzle outlet. A set of experiments was performed for each normalized height. Previous isothermal studies have
Victor Castaneda et al. / Energy Procedia 158 (2019) 1885–1890 Author name / Energy Procedia 00 (2018) 000–000
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shown that a normalized plate height of the plate height X/D=0.00 allowed the existence of a Coanda Jet Flow pattern, whereas a normalized height of X/D=0.36 made it impossible to obtain [10]. Methane was used as fuel and air as oxidizer. Both gases were supplied to the system through flexible hoses. Inlet gas temperature was ~20°C and pressure was close to atmospheric. Three variable area flow meters (VAFM) with ranges of 1-12 L/min, 6-50 L/min and 40-440 L/min for air at NTP were used to regulate the air flow. Air was split between the VAFM in a way such that operating at the limits of each flow meter was avoided. A single VAFM with range of 1-18 L/min for methane at NTP was used to regulate the methane flow. After passing through the VAFM, methane and air combine into a single stream ~1 meter upstream from the burner inlet. The mixed flow then enters the burner and is furtherly mixed at the swirl chamber. The flow gains additional swirl by going through the swirl generator. Finally, the gas mixture goes out through the nozzle burner and is ignited by a pilot burner located ~0.3 m downstream the nozzle exit. A schematic of the experimental setup is presented in Figure 2. Gas flow rate was varied from 3 L/min (~2 g/s) to a maximum of 12 L/min (~8 g/s) in incremental steps of 1 L/min (~0.7 g/s). For each incremental step of methane, the air flow rate was increased, and the flow pattern was recorded. All experiments where performed without confinement.
Fig. 1. Swirl burner
Fig. 2. Experimental setup
3. Results and discussion With the flat plate set at position X/D=0.36, four different states of the open jet flame were identified. For each gas flow rate with a low inlet air flow, the flame started as a stable, nozzle attached flame (Figure 3A). From this state, an increase in air flow could start the transition to one of two states: (1) flashback and (2) lifted flame. The transition to flashback occurred when the total mass flow rate was less than ~0.75 g/s. In this situation, as the air flow was increased, the outer part of the flame continued attached to the nozzle but the central part of the flame started going into the nozzle. A point was reached when full flashback occurred, and combustion was taking place inside the burner (Figure 3D). This flashback behavior has been previously described in the literature as combustion induced vortex breakdown [12]. The transition to a lifted flame occurred when the total mass flow rate was more than ~0.75 g/s. An increase of the air flow detached the flame from the nozzle and went into a lifted flame state (Figure 3B). From this point, the lifted flame can take two paths as air flow is increased. The first one is flashback (Figure 3D). The second one being a lifted flame that ends up being blown off. Figure 5 shows the different transition points for each state. The overall behavior of the Open jet flame is known and widely reported in the literature [13-14].
Victor Castaneda et al. / Energy Procedia 158 (2019) 1885–1890 Author name / Energy Procedia 00 (2018) 000–000
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(A)
(B)
(C)
(D)
Fig. 3. Flow patterns in an Open Jet Flow flame. A) Stable Open Jet Flame B) Lifted Flame C) Transition Lifted Flame – Flashback D) Flashback
With the flat plate at position X/D=0.00, the four previously described flame states were also possible. As with the previous configuration, the flame started as a stable, nozzle attached flame (Figure 3A), and transitioned to either a lifted flame or to flashback with an increase in the inlet air. By increasing gas and air flow, an attempt was made to induce the Coanda flame by using a steel rod to spread the flame. It was observed that a Coanda flame was possible when a lifted flame occurred. Thus, the lifted flame turned into a Coanda flame and remained like this until physically disturbed (Figure 4A and 4B). If the attempt was made to spread the OJF nozzle attached flame with the steel rod, the flame immediately returned to its nozzle attached state and the Coanda state could not be induced. This behavior was consistent at every combination of mass flow rates and equivalence ratios. Once the Coanda flame was established, and when the air flow rate was increased, the flame gradually retreated to the nozzle and the combustion zone became smaller (Figure 4C and 4D). This behavior continued until a point where the Coanda flame spontaneously detached from the plate and turned into a lifted flame that was close to a flashback condition (Figure 3C). Figure 6 shows the different transition point for each flame state. (A)
(C)
(B)
(D)
Fig. 4. Flow patterns in a Coanda Jet Flow flame. A) Stable Coanda Flame B) Stable Coanda Flame side view C) Transition Coanda Flame – Flashback D) Transition Coanda Flame – Flashback side view
Victor Castaneda et al. / Energy Procedia 158 (2019) 1885–1890 Author name / Energy Procedia 00 (2018) 000–000
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By comparing the set of measurements with the flat plate at position X/D=0.36 (Figure 5) and with the plate at position X/D=0.00 (Figure 6) it can be observed that the flame stability patterns follow a close resemblance between each case. Moreover, the operating region corresponding to a lifted flame in Figure 5 is practically a mirror image to the region in Figure 6 where the Coanda flame existed. Previous experiments on this swirl burner suggest the presence of a Precessing Vortex Core (PVC) on an OJF regime [9]. It has been shown that the PVC plays an important part on the stability of swirling flames by anchoring the flame [15-16]. It is speculated that the reason that the transition to a Coanda flame is only possible when the flame detaches is because once the flame detaches from the nozzle, the PVC breaks down and can no longer contribute to the flame stabilization, allowing the possibility for the Coanda flame to exist. Additional evidence from new results (unpublished) on isothermal experiments performed in this same burner seem to confirm this hypothesis, where a PVC was observed on the Open Jet cold flow [17] and another similar structure was observed in the Coanda Jet cold flow in the region between the nozzle and the jet. This suggests that this structure is responsible for anchoring the jet to the flat plate. However further experimentation is needed to confirm the presence of this structure in a reacting flow.
Fig. 5. Burner flow patterns with plate set to X/D=0.36.
Fig. 6. Burner flow patterns with plate set to X/D=0.00.
4. Conclusion The flame stability under two flow patterns, Open Jet Flow and Coanda Jet Flow, were investigated using a generic swirl burner. The swirl burner was fitted with a flat plate and the distance between the plate and the tip of the nozzle was changed to induce one of the two flow patterns. It was found that a stable Coanda flame could only be induced when the flame was previously in a lifted condition. It is theorized that this behavior is due to the breakdown of the PVC when the stable Open jet flame transitions to a lifted flame. The breakdown of the PVC allows the change to a Coanda flame. The results denote the need of reaching this lifted state before the flame can be flatted up by the Coanda effect, thus suggesting that further development to create new flat burners will need to consider this aspect. Acknowledgements Mr Castaneda gratefully acknowledges a PhD scholarship from CONACYT and stipend support from TATA Steel.
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Victor Castaneda et al. / Energy Procedia 158 (2019) 1885–1890 Author name / Energy Procedia 00 (2018) 000–000
References [1] R. Wille and H. Fernholz. Report on the first European Mechanics Colloquium, on the Coanda effect. Journal of Fluid Mechanics. 1965;23(4):801. [2] I. Reba. Applications of the Coanda Effect. Scientific American. 1966;214:84–93. [3] C. Lubert. On some recent applications of the coanda effect. International Journal of Acoustics and Vibrations. 2011;16(3):144–153. [4] C. P. Lubert, C. R. Schwantes, and R. J. Shafer. An investigation of initial shock cell formation in turbulent Coanda Wall Jets. International Journal of Acoustics and Vibrations. 2016;45(2):199–208. [5] 4. Dumas A, Subhash M, Trancossi M, Marques J. The Influence of Surface Temperature on Coanda Effect. Energy Procedia. 2014;45:626634. [6] P. Carpenter and C. Smith, “The Aeroacoustics and Aerodynamics of High-Speed Coanda Devices, Part 2: Effects of Modifications for Flow Control and Noise Reduction,” Journal of Sound and Vibration. 1997;208(5):803-822. [7] Carpenter P, Green P. The Aeroacoustics and Aerodynamics of High-Speed Coanda Devices, Part 1: Conventional arrangement of exit nozzle and surface. Journal of Sound and Vibration. 1997;208(5):777-801. [8] Desty D.H., Boden J.C., Witheridge R.E. The origination, development and application of novel premixed flare burners employing the Coanda effect. 85th Nat. AIChE meeting; 1978; Philadelphia. [9] Vanierschot M, Van den Bulck E. Hysteresis in flow patterns in annular swirling jets. Experimental Thermal and Fluid Science. 2007;31(6):513-524. [10] Valera-Medina A, Baej H. Hydrodynamics During the Transient Evolution of Open Jet Flows from/to Wall Attached Jets. Flow, Turbulence and Combustion. 2016;97(3):743-760. [11] Abdulsada M, Syred N, Bowen P, O'Doherty T, Griffiths A, Marsh R et al. Effect of exhaust confinement and fuel type upon the blowoff limits and fuel switching ability of swirl combustors. Applied Thermal Engineering. 2012;48:426-435. [12] Sommerer Y, Galley D, Poinsot T, Ducruix S, Lacas F, Veynante D. Large eddy simulation and experimental study of flashback and blowoff in a lean partially premixed swirled burner. Journal of Turbulence. 2004;5. [13] Lewis B, Von Elbe G. Combustion, Flames and Explosions of Gases. Burlington: Elsevier Science; 2012. [14] Turns S. An introduction to combustion. New York: McGraw-Hill; 2012. [15] Syred N, Beér J. Combustion in swirling flows: A review. Combustion and Flame. 1974;23(2):143-201. [16] Gupta, A.K., Lilley, D.J., Syred, N. Swirl flows. Tunbridge: Abacus Press; 1984. [17] Castaneda V, Ogus G, Valera-Medina A, Vanierschot M. Identification of the complex nature of coherent structures in Open and Coanda Jet flows via 2D3C-PIV. Paper to be presented at: 19th International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics; 2018 Jun 16-19; Lisbon.
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Energyonline Procedia 00 (2018) 000–000 Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energy Procedia 00 (2018) 000–000
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy Procedia 158 Energy Procedia 00(2019) (2017)1885–1890 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Coanda flames for development of flat burners Coanda flames for development flat burners The 15th International Symposium on Districtof Heating and Cooling Victor Castaneda, Agustin Valera-Medina*
Victor Castaneda,ofAgustin Assessing the feasibility usingValera-Medina* the heat demand-outdoor School of Engineering, Cardiff Univeristy, Queen’s Building, The Parade, Cardiff, Wales, CF24 3AA, United Kingdom School of Engineering, Cardiff Univeristy, Building, The Parade, Cardiff, Wales, CF24demand 3AA, United Kingdom temperature function for Queen’s a long-term district heat forecast
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
Abstract a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b Veolia Recherche 291 Avenue Dreyfous Daniel,Since 78520itsLimay, Franceseveral applications have The Coanda effect is the tendency of a fluid &toInnovation, stay attached to a nearby surface. discovery, c Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, Franceunexplored, The effect the tendency heat of a fluid to stay a nearby Since its discovery, several applications have beenCoanda developed in isaerodynamics, transfer and attached medical to fields usingsurface. this concept. A potential, and currently been developed aerodynamics, transfer and medical fields using this and currently application of theinCoanda effect is heat its use in heating equipment. However, few concept. research A haspotential, been conducted on the unexplored, behavior of application Coanda effect is its use in Thus, heating However, few research has been on the behavior of flames underofathe Coanda flow pattern regime. theequipment. present study uses a generic swirl burner to conducted analyze influence of the flow flames a Coanda patternstability. regime. The Thus, the present usesdifferences a generic swirl to analyze influence of Open the flow rate andunder fuel mixture onflow the flame objective is tostudy identify in theburner behavior of a flame under an jet Abstract rate fuel mixture on the The will objective is to identify differencesofin novel the behavior of a flame underinanthe Open jet flowand pattern and Coanda jetflame flow stability. pattern that lead to further development flat burners. Changes burner flow pattern and flow pattern thattwo willflow leadpatterns. to further development of as novel flatand burners. Changes in Both the burner configuration wereCoanda made tojetinduce one of the Methane was used a fuel air as an oxidizer. gases District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the configuration to at induce the twoatmospheric flow patterns. Methane was used as aregulated fuel and using air as variable an oxidizer. gases were supplied were to themade burner ~20°Cone andofalmost pressure. Flow rates were area Both flowmeter. greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat were supplied to the burner atmospheric pressure. Flow rates were using area flowmeter. Gas flow was increased fromat3~20°C L/minand to aalmost maximum of 12 L/min with incremental stepsregulated of 1 L/min. Forvariable each gas flow rate, the sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, Gas flowflow was rate increased from 3 L/min to flame a maximum of 12 L/min with of Coanda 1 L/min.flame For each flow the oxidizer was increased, and the behavior recorded. It wasincremental found that asteps stable couldgas only be rate, induced prolonging the investment return period. oxidizer increased, flame behavior It was that a stable Coanda be induced when an flow Openrate jet was flame existed. and It is the theorized that this recorded. behavior is due found to a coherent structure thatflame breakscould downonly when a stable The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand when flame existed. It isflame. theorized this behavior is due to aascoherent thatdevelopment breaks downofwhen a stable Open an jet Open flamejet changes to Coanda Thethat concept is now presented a novel structure option for novel, large forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Open jet flame flame. The concept is nowsize presented a novel for development industrial deviceschanges capableto of Coanda stabilizing the flame while reducing for theirasuse in highoption temperature processes. of novel, large buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district industrial devices capable of stabilizing the flame while reducing size for their use in high temperature processes. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Copyright © 2018 Elsevier Ltd. All rights reserved. compared with results from a dynamic heatLtd. demand model, previously developed and validated by the authors. © 2019 The Published by Elsevier Copyright ©Authors. 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee of the 10th International Conference on Applied Theisresults showed when onlythe weather change is license considered, the margin of error could be acceptable for some applications This an open accessthat article under CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International Conference on Applied Selection and peer-review under responsibility of the scientific committee of the 10 Energy (ICAE2018). Peer-review responsibility of lower the scientific committee of ICAE2018 – Theconsidered). 10th International Conference on Appliedrenovation Energy. (the error inunder annual demand was than 20% for all weather scenarios However, after introducing Energy (ICAE2018). scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). Keywords: Coanda; Swirling flow; Flat flame The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Keywords: Coanda; Swirling flow; Flat flame decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +44-(0)29-2087-5948.
address:author. [email protected] * E-mail Corresponding Tel.: +44-(0)29-2087-5948. Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected] 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection peer-review under responsibility the scientific 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.436
Victor Castaneda et al. / Energy Procedia 158 (2019) 1885–1890 Author name / Energy Procedia 00 (2018) 000–000
1886 2
Nomenclature CFJ D NTP OJF PVC VAFM X
Coanda Jet Flow Nozzle diameter Normal temperature and pressure (1 atm & 20°C) Open Jet Flow Precessing Vortex Core Variable Area Flow Meters Distance between the flat plate and the tip of the nozzle outlet Equivalence ratio (fuel-air)
1. Introduction The Coanda effect is the tendency of a fluid to stay attached to a nearby surface and remain attached even when the surface curves away from the initial jet direction. The first time it was observed was in 1800 by Thomas Young. The effect takes its name from Henri Coanda, who in 1910, used it in the first practical application by building the world’s first jet propelled aircraft [1]. In the last 25 years, the Coanda effect has resurfaced in several applications. Some examples are: in aeronautics, where it has been used to increase the lift and thrust vectoring; in industry, where it has been used in reaction turbines, swirl atomizers, galvanizing techniques, cooling of cylinders and waste-gas flares; some applications in medicine also exist. A compilation of the applications has been made by Reba [2], with a more recent review made by Lubert [3]. The bulk of the available research was conducted in the 1960s. Ongoing research in the phenomena now focuses on noise levels [4], effect of wall temperature on the flow [5] and supersonic jets [6-7]. Energy related applications of the Coanda effect in industry seem to be limited to waste gas flares. As described by Desty [8] the advantages of having a Coanda effect on these type of flares is a smokeless combustion with increased combustion efficiency and decreased thermal radiation, when compared to other types of flare devices. Therefore, it is believed that potential applications exist that take advantage of the flat flow profile that the Coanda effect produces and are yet to be explored, especially on industrial processes that involve the heat treating of flat surfaces. One such application could be the use of this flat flame, wall attached, burners on annealing furnaces in the steel industry to substitute current technologies, i.e. radiant tubes. Expected benefits would include the reduction of volume furnace due to increased proximity of burner to strip, emission reduction and energy usage due to reduced fuel consumption. However, to develop new industrial combustion applications that take advantage of the Coanda effect, a better understanding of the behavior of a Coanda flame is needed. Research has been conducted on the stability of an isothermal Coanda flow. Vanierschot [9] described a change in the flow pattern that was dependent on the inlet swirl as well as a hysteresis pattern when increasing and subsequently decreasing the swirl. Valera-Medina [10] conducted research on transition of a Coanda Jet Flame to/from an Open Jet Flame and found that it was dependent on the geometry and step size of a flat plate fitted to the nozzle. Therefore, the present study aims to increase the understanding of the stability of a Coanda flame by looking into different flow patterns that occur as the flow rate and equivalence ratio are varied during the experiment. 2. Experimental setup A generic swirl burner was used to examine the flame stability under a Coanda Jet Flow (CJF) and an Open Jet Flow (OJF) pattern. The burner was fitted with a tangential swirl generator providing a geometrical swirl number of 1.04. The nozzle diameter was D=28mm and had an angle of 45 degrees. A schematic of the generic swirl burner is presented in Figure 1 and detailed elsewhere [11]. A flat plate was fitted to the nozzle. Two different normalized plate heights were chosen, X/D=0.36 and X/D=0.00, being X the distance between the flat plate and the tip of the nozzle outlet. A set of experiments was performed for each normalized height. Previous isothermal studies have
Victor Castaneda et al. / Energy Procedia 158 (2019) 1885–1890 Author name / Energy Procedia 00 (2018) 000–000
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shown that a normalized plate height of the plate height X/D=0.00 allowed the existence of a Coanda Jet Flow pattern, whereas a normalized height of X/D=0.36 made it impossible to obtain [10]. Methane was used as fuel and air as oxidizer. Both gases were supplied to the system through flexible hoses. Inlet gas temperature was ~20°C and pressure was close to atmospheric. Three variable area flow meters (VAFM) with ranges of 1-12 L/min, 6-50 L/min and 40-440 L/min for air at NTP were used to regulate the air flow. Air was split between the VAFM in a way such that operating at the limits of each flow meter was avoided. A single VAFM with range of 1-18 L/min for methane at NTP was used to regulate the methane flow. After passing through the VAFM, methane and air combine into a single stream ~1 meter upstream from the burner inlet. The mixed flow then enters the burner and is furtherly mixed at the swirl chamber. The flow gains additional swirl by going through the swirl generator. Finally, the gas mixture goes out through the nozzle burner and is ignited by a pilot burner located ~0.3 m downstream the nozzle exit. A schematic of the experimental setup is presented in Figure 2. Gas flow rate was varied from 3 L/min (~2 g/s) to a maximum of 12 L/min (~8 g/s) in incremental steps of 1 L/min (~0.7 g/s). For each incremental step of methane, the air flow rate was increased, and the flow pattern was recorded. All experiments where performed without confinement.
Fig. 1. Swirl burner
Fig. 2. Experimental setup
3. Results and discussion With the flat plate set at position X/D=0.36, four different states of the open jet flame were identified. For each gas flow rate with a low inlet air flow, the flame started as a stable, nozzle attached flame (Figure 3A). From this state, an increase in air flow could start the transition to one of two states: (1) flashback and (2) lifted flame. The transition to flashback occurred when the total mass flow rate was less than ~0.75 g/s. In this situation, as the air flow was increased, the outer part of the flame continued attached to the nozzle but the central part of the flame started going into the nozzle. A point was reached when full flashback occurred, and combustion was taking place inside the burner (Figure 3D). This flashback behavior has been previously described in the literature as combustion induced vortex breakdown [12]. The transition to a lifted flame occurred when the total mass flow rate was more than ~0.75 g/s. An increase of the air flow detached the flame from the nozzle and went into a lifted flame state (Figure 3B). From this point, the lifted flame can take two paths as air flow is increased. The first one is flashback (Figure 3D). The second one being a lifted flame that ends up being blown off. Figure 5 shows the different transition points for each state. The overall behavior of the Open jet flame is known and widely reported in the literature [13-14].
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(A)
(B)
(C)
(D)
Fig. 3. Flow patterns in an Open Jet Flow flame. A) Stable Open Jet Flame B) Lifted Flame C) Transition Lifted Flame – Flashback D) Flashback
With the flat plate at position X/D=0.00, the four previously described flame states were also possible. As with the previous configuration, the flame started as a stable, nozzle attached flame (Figure 3A), and transitioned to either a lifted flame or to flashback with an increase in the inlet air. By increasing gas and air flow, an attempt was made to induce the Coanda flame by using a steel rod to spread the flame. It was observed that a Coanda flame was possible when a lifted flame occurred. Thus, the lifted flame turned into a Coanda flame and remained like this until physically disturbed (Figure 4A and 4B). If the attempt was made to spread the OJF nozzle attached flame with the steel rod, the flame immediately returned to its nozzle attached state and the Coanda state could not be induced. This behavior was consistent at every combination of mass flow rates and equivalence ratios. Once the Coanda flame was established, and when the air flow rate was increased, the flame gradually retreated to the nozzle and the combustion zone became smaller (Figure 4C and 4D). This behavior continued until a point where the Coanda flame spontaneously detached from the plate and turned into a lifted flame that was close to a flashback condition (Figure 3C). Figure 6 shows the different transition point for each flame state. (A)
(C)
(B)
(D)
Fig. 4. Flow patterns in a Coanda Jet Flow flame. A) Stable Coanda Flame B) Stable Coanda Flame side view C) Transition Coanda Flame – Flashback D) Transition Coanda Flame – Flashback side view
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By comparing the set of measurements with the flat plate at position X/D=0.36 (Figure 5) and with the plate at position X/D=0.00 (Figure 6) it can be observed that the flame stability patterns follow a close resemblance between each case. Moreover, the operating region corresponding to a lifted flame in Figure 5 is practically a mirror image to the region in Figure 6 where the Coanda flame existed. Previous experiments on this swirl burner suggest the presence of a Precessing Vortex Core (PVC) on an OJF regime [9]. It has been shown that the PVC plays an important part on the stability of swirling flames by anchoring the flame [15-16]. It is speculated that the reason that the transition to a Coanda flame is only possible when the flame detaches is because once the flame detaches from the nozzle, the PVC breaks down and can no longer contribute to the flame stabilization, allowing the possibility for the Coanda flame to exist. Additional evidence from new results (unpublished) on isothermal experiments performed in this same burner seem to confirm this hypothesis, where a PVC was observed on the Open Jet cold flow [17] and another similar structure was observed in the Coanda Jet cold flow in the region between the nozzle and the jet. This suggests that this structure is responsible for anchoring the jet to the flat plate. However further experimentation is needed to confirm the presence of this structure in a reacting flow.
Fig. 5. Burner flow patterns with plate set to X/D=0.36.
Fig. 6. Burner flow patterns with plate set to X/D=0.00.
4. Conclusion The flame stability under two flow patterns, Open Jet Flow and Coanda Jet Flow, were investigated using a generic swirl burner. The swirl burner was fitted with a flat plate and the distance between the plate and the tip of the nozzle was changed to induce one of the two flow patterns. It was found that a stable Coanda flame could only be induced when the flame was previously in a lifted condition. It is theorized that this behavior is due to the breakdown of the PVC when the stable Open jet flame transitions to a lifted flame. The breakdown of the PVC allows the change to a Coanda flame. The results denote the need of reaching this lifted state before the flame can be flatted up by the Coanda effect, thus suggesting that further development to create new flat burners will need to consider this aspect. Acknowledgements Mr Castaneda gratefully acknowledges a PhD scholarship from CONACYT and stipend support from TATA Steel.
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Victor Castaneda et al. / Energy Procedia 158 (2019) 1885–1890 Author name / Energy Procedia 00 (2018) 000–000
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