| 1. |
- Liberman, M. A., et al.
(författare)
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Deflagration-to-detonation transition in highly reactive combustible mixtures
- 2010
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Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765 .- 1879-2030. ; 67:7-8, s. 688-701
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents experimental, theoretical, and numerical studies of deflagration-to-detonation transition (DDT) in highly reactive hydrogen-oxygen and ethylene-oxygen mixtures. Two-dimensional reactive Navier-Stokes equations for a hydrogen-oxygen gaseous mixture including the effects of viscosity, thermal conduction, molecular diffusion, and a detailed chemical reaction mechanism are solved numerically. It is found that mechanism of DDT is entirely determined by the features of the flame acceleration in tubes with no-slip walls. The experiments and computations show three distinct stages of the process: (1) the flame accelerates exponentially producing shock waves far ahead from the flame, (2) the flame acceleration decreases and shocks are formed directly on the flame surface, and (3) the final third stage of the actual transition to a detonation. During the second stage a compressed and heated pocket of unreacted gas adjacent ahead to the flame the preheat zone is forming and the compressed unreacted mixture entering the flame produces large amplitude pressure pulse. The increase of pressure enhances reaction rate and due to a positive feedback between the pressure peak and the reaction the pressure peak grows exponentially, steepens into a strong shock that is coupled with the reaction zone forming the overdriven detonation wave. The proposed new physical mechanism of DDT highlights the features of flame acceleration in tubes with no-slip walls, which is the key factor of the DDT origin.
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| 2. |
- Liberman, M. A., et al.
(författare)
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On the mechanism of the deflagration-to-detonation transition in a hydrogen-oxygen mixture
- 2010
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Ingår i: Journal of Experimental and Theoretical Physics. - 1063-7761 .- 1090-6509. ; 111:4, s. 684-698
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Tidskriftsartikel (refereegranskat)abstract
- The flame acceleration and the physical mechanism underlying the deflagration-to-detonation transition (DDT) have been studied experimentally, theoretically, and using a two-dimensional gasdynamic model for a hydrogen-oxygen gas mixture by taking into account the chain chemical reaction kinetics for eight components. A flame accelerating in a tube is shown to generate shock waves that are formed directly at the flame front just before DDT occurred, producing a layer of compressed gas adjacent to the flame front. A mixture with a density higher than that of the initial gas enters the flame front, is heated, and enters into reaction. As a result, a high-amplitude pressure peak is formed at the flame front. An increase in pressure and density at the leading edge of the flame front accelerates the chemical reaction, causing amplification of the compression wave and an exponentially rapid growth of the pressure peak, which "drags" the flame behind. A high-amplitude compression wave produces a strong shock immediately ahead of the reaction zone, generating a detonation wave. The theory and numerical simulations of the flame acceleration and the new physical mechanism of DDT are in complete agreement with the experimentally observed flame acceleration, shock formation, and DDT in a hydrogen-oxygen gas mixture.
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| 3. |
- Gustafsson, U. O., et al.
(författare)
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Guidelines for perioperative care in elective colonic surgery : enhanced recovery after surgery (ERAS(®)) society recommendations
- 2013
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Ingår i: World Journal of Surgery. - : Springer. - 0364-2313 .- 1432-2323. ; 37:2, s. 259-284
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Forskningsöversikt (refereegranskat)abstract
- BACKGROUND: This review aims to present a consensus for optimal perioperative care in colonic surgery and to provide graded recommendations for items for an evidenced-based enhanced perioperative protocol.METHODS: Studies were selected with particular attention paid to meta-analyses, randomised controlled trials and large prospective cohorts. For each item of the perioperative treatment pathway, available English-language literature was examined, reviewed and graded. A consensus recommendation was reached after critical appraisal of the literature by the group.RESULTS: For most of the protocol items, recommendations are based on good-quality trials or meta-analyses of good-quality trials (quality of evidence and recommendations according to the GRADE system).CONCLUSIONS: Based on the evidence available for each item of the multimodal perioperative care pathway, the Enhanced Recovery After Surgery (ERAS) Society, International Association for Surgical Metabolism and Nutrition (IASMEN) and European Society for Clinical Nutrition and Metabolism (ESPEN) present a comprehensive evidence-based consensus review of perioperative care for colonic surgery.
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| 4. |
- Gustafsson, U. O., et al.
(författare)
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Guidelines for perioperative care in elective colonic surgery : enhanced recovery after surgery (ERAS®) society recommendations
- 2012
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Ingår i: Clinical Nutrition. - Amsterdam, Netherlands : Elsevier. - 0261-5614 .- 1532-1983. ; 31:6, s. 783-800
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Forskningsöversikt (refereegranskat)abstract
- Background: This review aims to present a consensus for optimal perioperative care in colonic surgery and to provide graded recommendations for items for an evidenced-based enhanced perioperative protocol.Methods: Studies were selected with particular attention paid to meta-analyses, randomised controlled trials and large prospective cohorts. For each item of the perioperative treatment pathway, available English-language literature was examined, reviewed and graded. A consensus recommendation was reached after critical appraisal of the literature by the group.Results: For most of the protocol items, recommendations are based on good-quality trials or meta-analyses of good-quality trials (quality of evidence and recommendations according to the GRADE system).Conclusions: Based on the evidence available for each item of the multimodal perioperative-care pathway, the Enhanced Recovery After Surgery (ERAS) Society, International Association for Surgical Metabolism and Nutrition (IASMEN) and European Society for Clinical Nutrition and Metabolism (ESPEN) present a comprehensive evidence-based consensus review of perioperative care for colonic surgery.
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| 5. |
- Kuznetsov, M., et al.
(författare)
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Experimental Study of the Preheat Zone Formation and Deflagration to Detonation Transition
- 2010
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 182:11-12, s. 1628-1644
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Tidskriftsartikel (refereegranskat)abstract
- The authors present experimental studies of the deflagration-to-detonation transition (DDT) in tubes with smooth and rough walls in stoichiometric hydrogen-oxygen and ethylene-oxygen mixtures. On the basis of experimental evidence, it is shown that formation of the preheat zone, where reaction is chemically frozen, promotes the transition to detonation if temperature and width of the preheat zone are above certain critical values. A sequence of high-speed Schlieren records permits an accurate determination of the minimal values of temperature and width of the preheat zone, leading to transition to detonation. The experimentally measured critical temperatures and widths of the preheat zone initiating restructuring of the flame and transition to detonation in hydrogen-oxygen and ethylene-oxygen mixtures are consistent with the developed theory.
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| 6. |
- Liberman, M. A., et al.
(författare)
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On detonation initiation by a temperature gradient for a detailed chemical reaction models
- 2011
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Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 375:17, s. 1803-1808
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Tidskriftsartikel (refereegranskat)abstract
- The evolution from a temperature gradient to a detonation is investigated for combustion mixture whose chemistry is governed by a detailed chemical kinetics. We show that a detailed chemical reaction model has a profound effect on the spontaneous wave concept for detonation initiation by a gradient of reactivity. The evolution to detonation due to a temperature gradient is considered for hydrogen-oxygen and hydrogen-air mixtures at different initial pressures. It is shown that the minimal length of the temperature gradient for which a detonation can be ignited is much larger than that predicted from a one-step chemical model.
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| 7. |
- Chukalovsky, A. A., et al.
(författare)
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Study of singlet delta oxygen O 2 ( 1 δg) impact on H 2-O 2 mixture ignition in flow reactor : 2D modeling
- 2012
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 184:10-11, s. 1768-1786
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Tidskriftsartikel (refereegranskat)abstract
- Influence of electron excited singlet delta oxygen (SDO) molecules produced in direct current (DC) glow discharged plasma on the induction length decrease in the H2-O2 mixture has been studied via comprehensive two-dimensional (2D) numerical simulations. The sensitivity analysis of the induction length on SDO mole fractions and residual mole fractions of odd oxygen was carried out. The influence of the reaction H 2+O 2( 1g)H+HO2 on the ignition length was found to be negligible due to the presence of residual odd oxygen in the oxidizer flow. Two stages specify the ignition time decrease for the studied conditions: (1) chain initiation in reactions with residual odd oxygen and (2) the following chain-branching enhancement due to reaction H 2+O 2( 1g)O+OH. The last reaction is the key process for studied conditions when the concentration of SDO exceeds 4%. The estimated rate constant of this reaction was found to be about 2.510 13cm 3/s at 780K. The quenching reaction H 2+O 2( 1g)H 2+O 2 does not affect the ignition length.
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| 8. |
- Ivanou, M. F., et al.
(författare)
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Flame acceleration and DDT of hydrogen-oxygen gaseous mixtures in channels with no-slip walls
- 2011
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 36:13, s. 7714-7727
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-oxygen flame acceleration and transition from deflagration to detonation (DDT) in channels with no-slip walls were studied theoretically and using high resolution simulations of 2D reactive Navier-Stokes equations, including the effects of viscosity, thermal conduction, molecular diffusion, real equation of state and a detailed chemical reaction mechanism. It is shown that in "wide" channels (D > 1 mm) there are three distinctive stages of the combustion wave propagation: the initial short stage of exponential acceleration; the second stage of slower flame acceleration; the third stage of the actual transition to detonation. In a thin channel (D < 1 mm) the flame exponential acceleration is not bounded till the transition to detonation. While velocity of the steady detonation waves formed in wider channels (10, 5, 3, 2 mm) is close to the Chapman Jouguet velocity, the oscillating detonation waves with velocities slightly below the CJ velocity are formed in thinner channels (D < 1.0 mm). We analyse applicability of the gradient mechanism of detonation ignition for a detailed chemical reaction model to be a mechanism of the deflagration-to-detonation transition. The results of high resolution simulations are fully consistent with experimental observations of flame acceleration and DDT in hydrogen-oxygen gaseous mixtures.
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| 9. |
- Ivanov, M. F., et al.
(författare)
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Hydrogen-oxygen flame acceleration and deflagration-to-detonation transition in three-dimensional rectangular channels with no-slip walls
- 2013
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 38:36, s. 16427-16440
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-oxygen flame acceleration and the transition from deflagration to detonation (DDT) in channels with no-slip walls are studied using high resolution simulations of 3D reactive Navier-Stokes equations, including the effects of viscosity, thermal conduction, molecular diffusion, real equation of state and detailed (reduced) chemical reaction mechanism. The acceleration of the flame propagating from the closed end of a channel, which is a key factor for understanding of the mechanism of DDT, is thoroughly studied. The three dimensional modeling of the flame acceleration and DDT in a semi-closed rectangular channel with cross section 10 x 10 mm and length 250 mm confirms validity of the mechanism of deflagration-to-detonation transition, which was proposed earlier theoretically and verified using 2D simulations. We show that 3D model contrary to 2D models allows to understand clearly the meaning of schlieren photos obtained in experimental studies. The numerical schlieren and numerical shadowgraph obtained using 3D calculations clarify the meaning of the experimental schlieren and shadow photos and some earlier misinterpretations of experimental data.
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| 10. |
- Ivanov, M. F., et al.
(författare)
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Hydrogen-oxygen flame acceleration and transition to detonation in channels with no-slip walls for a detailed chemical reaction model
- 2011
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Ingår i: Physical Review E - Statistical, Nonlinear and Soft Matter Physics. - 1539-3755. ; 83:5, s. 056313-
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Tidskriftsartikel (refereegranskat)abstract
- The features of flame acceleration in channels with wall friction and the deflagration to detonation transition (DDT) are investigated theoretically and using high resolution numerical simulations of two-dimensional reactive Navier-Stokes equations, including the effects of viscosity, thermal conduction, molecular diffusion, and a detailed chemical reaction mechanism for hydrogen-oxygen gaseous mixture. It is shown that in a wide channel, from the beginning, the flame velocity increases exponentially for a short time and then flame acceleration decreases, ending up with the abrupt increase of the combustion wave velocity and the actual transition to detonation. In a thin channel with a width smaller than the critical value, the exponential increase of the flame velocity is not bounded and ends up with the transition to detonation. The transition to detonation occurs due to the pressure pulse, which is formed at the tip of the accelerating flame. The amplitude of the pressure pulse grows exponentially due to a positive feedback coupling between the pressure pulse and the heat released in the reaction. Finally, large amplitude pressure pulse steepens into a strong shock coupled with the reaction zone forming the overdriven detonation. The evolution from a temperature gradient to a detonation via the Zeldovich gradient mechanism and its applicability to the deflagration-to-detonation transition is investigated for combustible materials whose chemistry is governed by chain-branching kinetics. The results of the high resolution simulations are fully consistent with experimental observations of the flame acceleration and DDT.
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