Ignition energy is one of tbe important parameters of flammable materials, and evaluating ignition energy precisely is essential to the safety of process industry and combustion science and technology. By using electr...Ignition energy is one of tbe important parameters of flammable materials, and evaluating ignition energy precisely is essential to the safety of process industry and combustion science and technology. By using electric spark discharge test system, a series of electric spark discharge experiments were conducted with the capacitor-stored energy in the range of 10 J, 100 J, and 1000 J, respectively. The evaluation method for energy consumed by electric spark, wire, and switch during capacitor discharge process has been studied respectively. The resistance of wire, switch, and plasma between electrodes has been evaluated by different methods and an optimized evaluation method has been obtained. The electric energy consumed by wire, electric switch, and electric spark-induced plasma between electrodes were obtained and the energy structure of capacitor-released energy was analyzed. The dynamic process and the characteristic parameters （the maximum power, duration of discharge process） of electric spark discharge process have been analyzed. Experimental results showed that, electric spark-consumed energy only accounts for 8%-14% of the capacitor-released energy. With the increase of capacitor-released energy, the duration of discharge process becomes longer, and the energy of plasma accounts for more in the capacitor-released energy. The power of electric spark varies with time as a damped sinusoids function and the period and the maximum value increase with the capacitor-released energy.展开更多
For further understanding of self-heating of coal, we tested the reactions of seven different ranks of coal under inert atmosphere. In the test, 50-gram of coal sample ranged from 0.18 mm to 0.38 mm was put into a spe...For further understanding of self-heating of coal, we tested the reactions of seven different ranks of coal under inert atmosphere. In the test, 50-gram of coal sample ranged from 0.18 mm to 0.38 mm was put into a special designed copper reaction vessel and let pure nitrogen to flow into the coal sample from the bottom at a rate of 100 mL/min. The programmed temperature enclosure was run at a programmed rate of 0.8 ~C/min. The concentration of the carbon oxides and the coal temperature were tested. The results show that the coal reactions under inert atmosphere can generate CO and C02. The reactions under inert atmosphere are affected by coal ranks, initial pore structure of coal and sulfur content. For low ranks of coal, the productions of carbon oxides are piecewise. The coal temperature is lower than the surrounding temperature throughout the reactions under inert atmosphere, but it rises quickly and reaches a crossing point temperature in the later stage under dry-air atmosphere. Based on the analysis, it indicates the self-reaction of initial active groups exists in the self-heating of coal besides the reactions in the two parallel reactions model. Spontaneous combustion of coal is due to both the oxidation heat accumulation and the chain reaction. A new reaction model of self-heating of coal was orooosed.展开更多
Oxalate was generally used as a precipitant for synthesis of MnZn ferrites during the co-precipitation process. However, the MnZn ferrite couldn’t be directly obtained and a calcination process was needed. In this re...Oxalate was generally used as a precipitant for synthesis of MnZn ferrites during the co-precipitation process. However, the MnZn ferrite couldn’t be directly obtained and a calcination process was needed. In this research, we reported a direct preparation of the MnZn ferrite nanoparticles by using co-precipitation method, together with refluxing process. XRD measurements proved that crystallite size of the obtained samples increased with an increase in pH value of the co-precipitation solution, and that the crystallite size of about 25 nm was obtained for the sample at a pH of 13. This sample showed the maximum Ms of 58.6 emu/g, which was about one times larger than that of 12 (pH value). Calcination to the obtained samples result in an enlargement in their crystal size and an improvement in their magnetic properties with an increase in temperatures. The samples calcinated in CO2 + H2 atmosphere presented good stability, and the maximum Ms value of 188.2 emu/g was obtained for the 1100。C-heated sample. Unfortunately, precipitation of some Fe2O3 at 800。C suggested poor stability of the nanocrystalline MnZn ferrite in N2 atmosphere.展开更多
In order to design the relief system size of di-tert-butyl peroxide(DTBP) storage tanks,the runaway re-action of DTBP was simulated by accelerating rate calorimeter(ARC).The results indicated that under adiabatic cond...In order to design the relief system size of di-tert-butyl peroxide(DTBP) storage tanks,the runaway re-action of DTBP was simulated by accelerating rate calorimeter(ARC).The results indicated that under adiabatic conditions the initial exothermic temperature was 102.6 ℃,the maximum self-heating rate was 3.095×107 ℃·min-1,the maximum self-heating temperature was 375.9 ℃,and the pressure produced by unit mass was 4.512 MPa·g-1.Judged by ARC test,the emergency relief system for DTBP was a hybrid system.Based on Design Institute for Emergency Relief System(DIERS) method,the releasing mass flow rate W was determined by Leung methods,and the mass velocity G was calculated by two modified Omega methods.The two relief sizes calculated by monograph Omega method and arithmetic Omega method are close,with only 0.63% relative error.The monograph Omega method is more convenient to apply.展开更多
Pressure-swirl atomizers are often employed to generate a water-mist spray,typically employed in fire suppression.In the present study,an experimental characterization of dispersion(velocity and cone angle)and atomiza...Pressure-swirl atomizers are often employed to generate a water-mist spray,typically employed in fire suppression.In the present study,an experimental characterization of dispersion(velocity and cone angle)and atomization(drop-size axial evolution)was carried out following a previously developed methodology,with specific reference to the initial region of the spray.Laser-based techniques were used to quantitatively evaluate the considered phenomena:velocity field was reconstructed through a Particle Image Velocimetry analysis;drop-size distribution was measured by a Malvern Spraytec device,highlighting secondary atomization and subsequent coalescence along the spray axis.Moreover,a comprehensive set of relations was validated as predictive of the involved parameters,following an inviscid-fluid approach.The proposed model pertains to early studies on pressure-swirl atomizers and primarily yields to determine both initial velocity and cone angle.The spray thickness is also predicted and a classic correlation for Sauter Mean Diameter is shown to provide good agreement with experimental results.The analysis was carried out at the operative pressure of 80 bar;two injectors were employed featuring different orifice diameters and flow numbers,as a sort of parametric approach to this spray typology.展开更多
In this paper,the influence of different opening ratios and different opening directions of the windows on the natural smoke exhaust was studied through a series of real fire experiments and simulation analysis.Increa...In this paper,the influence of different opening ratios and different opening directions of the windows on the natural smoke exhaust was studied through a series of real fire experiments and simulation analysis.Increasing the open area of the window could effectively improve the overall smoke exhaust effect.When the top windows were open and the opening ratio increased from 19.2%to 24.3%,the optical density was decreased by 12.4%.The average smoke exhaust rate per unit area of the window did not change significantly.Increasing the area of the natural smoke exhaust window could effectively increase the smoke exhaust rate and improve the overall effect of smoke extraction.When the top windows were open,the temperature rise on the top floor was 30.8%-47.5%lower while the visibility was 16.8%-21.9%higher than that when the side windows were open.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.11572044)the National Key Research and Development Program of China(Grant No.2017YFC0804705)
文摘Ignition energy is one of tbe important parameters of flammable materials, and evaluating ignition energy precisely is essential to the safety of process industry and combustion science and technology. By using electric spark discharge test system, a series of electric spark discharge experiments were conducted with the capacitor-stored energy in the range of 10 J, 100 J, and 1000 J, respectively. The evaluation method for energy consumed by electric spark, wire, and switch during capacitor discharge process has been studied respectively. The resistance of wire, switch, and plasma between electrodes has been evaluated by different methods and an optimized evaluation method has been obtained. The electric energy consumed by wire, electric switch, and electric spark-induced plasma between electrodes were obtained and the energy structure of capacitor-released energy was analyzed. The dynamic process and the characteristic parameters （the maximum power, duration of discharge process） of electric spark discharge process have been analyzed. Experimental results showed that, electric spark-consumed energy only accounts for 8%-14% of the capacitor-released energy. With the increase of capacitor-released energy, the duration of discharge process becomes longer, and the energy of plasma accounts for more in the capacitor-released energy. The power of electric spark varies with time as a damped sinusoids function and the period and the maximum value increase with the capacitor-released energy.
基金Financial supports for this research provided by the National Natural Science Foundation of China (No. 50927403)the Fundamental Research Funds for the Central Universities (No.2011RC06)the Jiangsu Natural Science Foundation (No.BK2009004)
文摘For further understanding of self-heating of coal, we tested the reactions of seven different ranks of coal under inert atmosphere. In the test, 50-gram of coal sample ranged from 0.18 mm to 0.38 mm was put into a special designed copper reaction vessel and let pure nitrogen to flow into the coal sample from the bottom at a rate of 100 mL/min. The programmed temperature enclosure was run at a programmed rate of 0.8 ~C/min. The concentration of the carbon oxides and the coal temperature were tested. The results show that the coal reactions under inert atmosphere can generate CO and C02. The reactions under inert atmosphere are affected by coal ranks, initial pore structure of coal and sulfur content. For low ranks of coal, the productions of carbon oxides are piecewise. The coal temperature is lower than the surrounding temperature throughout the reactions under inert atmosphere, but it rises quickly and reaches a crossing point temperature in the later stage under dry-air atmosphere. Based on the analysis, it indicates the self-reaction of initial active groups exists in the self-heating of coal besides the reactions in the two parallel reactions model. Spontaneous combustion of coal is due to both the oxidation heat accumulation and the chain reaction. A new reaction model of self-heating of coal was orooosed.
文摘Oxalate was generally used as a precipitant for synthesis of MnZn ferrites during the co-precipitation process. However, the MnZn ferrite couldn’t be directly obtained and a calcination process was needed. In this research, we reported a direct preparation of the MnZn ferrite nanoparticles by using co-precipitation method, together with refluxing process. XRD measurements proved that crystallite size of the obtained samples increased with an increase in pH value of the co-precipitation solution, and that the crystallite size of about 25 nm was obtained for the sample at a pH of 13. This sample showed the maximum Ms of 58.6 emu/g, which was about one times larger than that of 12 (pH value). Calcination to the obtained samples result in an enlargement in their crystal size and an improvement in their magnetic properties with an increase in temperatures. The samples calcinated in CO2 + H2 atmosphere presented good stability, and the maximum Ms value of 188.2 emu/g was obtained for the 1100。C-heated sample. Unfortunately, precipitation of some Fe2O3 at 800。C suggested poor stability of the nanocrystalline MnZn ferrite in N2 atmosphere.
文摘In order to design the relief system size of di-tert-butyl peroxide(DTBP) storage tanks,the runaway re-action of DTBP was simulated by accelerating rate calorimeter(ARC).The results indicated that under adiabatic conditions the initial exothermic temperature was 102.6 ℃,the maximum self-heating rate was 3.095×107 ℃·min-1,the maximum self-heating temperature was 375.9 ℃,and the pressure produced by unit mass was 4.512 MPa·g-1.Judged by ARC test,the emergency relief system for DTBP was a hybrid system.Based on Design Institute for Emergency Relief System(DIERS) method,the releasing mass flow rate W was determined by Leung methods,and the mass velocity G was calculated by two modified Omega methods.The two relief sizes calculated by monograph Omega method and arithmetic Omega method are close,with only 0.63% relative error.The monograph Omega method is more convenient to apply.
基金supported by Bettati Antincendio S.r.l. and Regione Emilia-Romagna
文摘Pressure-swirl atomizers are often employed to generate a water-mist spray,typically employed in fire suppression.In the present study,an experimental characterization of dispersion(velocity and cone angle)and atomization(drop-size axial evolution)was carried out following a previously developed methodology,with specific reference to the initial region of the spray.Laser-based techniques were used to quantitatively evaluate the considered phenomena:velocity field was reconstructed through a Particle Image Velocimetry analysis;drop-size distribution was measured by a Malvern Spraytec device,highlighting secondary atomization and subsequent coalescence along the spray axis.Moreover,a comprehensive set of relations was validated as predictive of the involved parameters,following an inviscid-fluid approach.The proposed model pertains to early studies on pressure-swirl atomizers and primarily yields to determine both initial velocity and cone angle.The spray thickness is also predicted and a classic correlation for Sauter Mean Diameter is shown to provide good agreement with experimental results.The analysis was carried out at the operative pressure of 80 bar;two injectors were employed featuring different orifice diameters and flow numbers,as a sort of parametric approach to this spray typology.
基金This work was supported by SCFRI research project(No.T2019881101,No.T2019880402).
文摘In this paper,the influence of different opening ratios and different opening directions of the windows on the natural smoke exhaust was studied through a series of real fire experiments and simulation analysis.Increasing the open area of the window could effectively improve the overall smoke exhaust effect.When the top windows were open and the opening ratio increased from 19.2%to 24.3%,the optical density was decreased by 12.4%.The average smoke exhaust rate per unit area of the window did not change significantly.Increasing the area of the natural smoke exhaust window could effectively increase the smoke exhaust rate and improve the overall effect of smoke extraction.When the top windows were open,the temperature rise on the top floor was 30.8%-47.5%lower while the visibility was 16.8%-21.9%higher than that when the side windows were open.
