| In order to study the effect of low pressure and water content on the flammable liquid fire risk,this paper first established some flash point prediction models under the influence of water content and ambient pressure.After that,flash point determination experiments for methanol,ethanol,and n-decane at different mole fractions were conducted at 35 kPa,45 kPa,55 kPa,65 kPa,75 kPa,85 kPa,95 kPa,and 101 kPa based on high and low temperature low pressure test chamber.And compared with the prediction model.To further deepen understanding of the effect of water content on the risk of flammable liquid fire hazards,and strengthen the practical significance.In this paper,ethanol water solution and white liquor of Yanghe Winery are taken as the research object,and the study of flash point of different ethanol volume fraction and cone combustion test under normal pressure is carried out,and the fire hazard classification is discussed in conjunction with national standards.Finally,the experiments on boilover of diesel oil and aviation kerosene under normal pressure and low pressure environment were carried out to deepen the understanding of the industrial boilover induced by the water content in the low pressure environment.At the same time,the predictive models of the onset time of the boilover precursor stage and the onset time of the boilover stage were proposed.The main conclusions of this paper are as follows:(1)A number of flash point prediction models have been established through theoretical analysis.Including the theoretical prediction model of flammable liquid flash point under normal pressure environment,the flash point prediction model established based on the boiling point value under standard pressure environment,and the flash point prediction model based on the flash point value under standard pressure environment,different water content.Flash point predictive model for liquids under flammable liquids and prediction model for flash point of flammable liquids with different water content in low pressure environment.(2)Based on the theoretical analysis in Chapter 3,experimental studies were carried out to study the influence of different pressures and different water contents on the flash point of closed cups and open cups of methanol,ethanol and n-decane.As the pressure drops,both the closed cup flash point and the open cup flash point for a given mole fraction of methanol,ethanol,and n-decane water solutions drop.Moreover,as the pressure decreases,the flash point of the aqueous solution of the substance decreases more and more,and the flash point of the open cup is more pronounced.The reciprocal of flash point has a linear relationship with the natural logarithm of pressure,and the fitting result is consistent with the theoretical derivation.The water content has no effect on the flash point of n-decane,but for methanol and ethanol,as the molar fraction of the aqueous solution decreases,their flash point will increase,regardless of the flash point of the closed cup or the flash point of the open cup.Moreover,the relationship between water content and the flash point of methanol and ethanol is also non-linear.The experimental results are fitted according to the theoretical prediction model in the analysis process,which verifies the correctness of the theoretical derivation.(3)As the pressure decreases,the fire hazard levels of methanol,ethanol and n-decane pure substances and their aqueous solutions will increase.For methanol and ethanol aqueous solutions,the higher their molar fraction,the higher the fire risk at the same pressure.This paper proposes the concept of the critical pressure of fire hazard and deduces the critical pressure prediction formula for flammable liquid pure material and flammable liquid aqueous solution.Provide guidance on fire prevention and rescue of flammable liquids in high altitude or high altitude environments.At the same time,this critical pressure can be applied to all the world's standard specifications based on the fire risk classification of flash point as flammable liquid.(4)Ethanol water solution and liquor of Yanghe Winery were used as the research object to carry out the cone burning test.The results showed that the mass loss rate per unit area,heat release rate,flame height,combustion efficiency and fire hazard level increased with increasing ethanol volume fraction in both liquor and aqueous ethanol solutions.In addition,for the combustion time,the maximum unit heat release rate,the total heat release per unit area and the average effective combustion heat and other fire parameters,the two values are very similar.Since liquor contains about 1%of oxygen-rich organics such as acids and esters,the flash point of liquor is lower than the flash point of ethanol solution at the same volume fraction,and the flame height of white spirit is lower than the flame height of ethanol solution.The combustion efficiency is higher than the combustion efficiency of ethanol.In this paper,a formula for calculating the critical volume fraction for white spirits and ethanol aqueous solutions is proposed,which is applicable to the classification of flash points in various countries.According to GB50016-2014,the critical volume fraction between ethanol grade ? and grade ? is 38.9 vol.%,and the critical volume fraction between liquor grade ? and grade ? is 34.8 vol.%.(5)Using diesel and aviation kerosene as experimental samples,15cm oil pan and 18cm oil pan boilover experiments were conducted in Hefei and Lhasa respectively.In the standard pressure environment and the low pressure environment,the boilover can be divided into four stages:quasi-steady state combustion stage,boilover precursor stage,boilover stage and boilover decline stage.In addition to the analysis of the boilover by the change of the flame morphology,it is also possible to characterize the stages of the boilover by the change of the bubble at the oil-water interface.In the normal pressure environment,the temperature at the critical oil-water interface at the boilover precursor stage is 100?,and the temperature at the critical oil-water interface at the boilover stage is 120?.In Lhasa,the critical temperature changes,which are reduced to 87.6? and 110?,respectively.The experiment further shows that the boiling point is the critical temperature at which the boilover precursor occurs,and changes with pressure.For the critical temperature of boilover,this chapter analyzes it based on the pool boiling theory and explains the reason why the critical boilover temperature decreases after the pressure is reduced.(6)Predictive models for the occurrence of boilover precursors and boilover times were proposed.When PL>10kPa,the boilover precursor precursor tp is an increasing function of the ambient pressure PL.When PL<10kPa,the start time of the boilover precursor tp is a function of a decreasing relationship with the ambient pressure PL.At the same ambient pressure,the boil start time tp ?.boilover start time tb ?,is negatively correlated with P_L. |
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