Study On Influence Of Pressure And Boiling Point Of Water Layer On Boilover

Since the second industrial revolution,human beings have been using fossil fuels in large quantities all over the world,and they are applied to various tools,such as airplanes and cars.In addition,various types of fuel storage devices,such as oil depots and gas stations,inevitably increases the risk of oil fires.The research object of this article is boilover phenomenon,is a special phenomenon of oil fire.It is well known that our country has built a large number of pipeline transportation of crude oil resources.But water is inevitably mixed in the fossil fuels in the process of transportation.When the fuel is stored in the tank,water in this tank can form a water layer at the bottom of the form over a period of time.If fuel was ignited by accident,overheating and strong boiling would happen because complex heat transfer process.A lot of gas bubbles and burning fuel will splash out of the tank and will form the spitting fire.Some eyewitnesses of the fire described that the fire rose from the oil tank,and the spilled fuel would cause damage to other equipment,and ignite other combustible materials,resulting in the expansion of fire area,which will greatly increases the risk of oil tank fire.Because a lot of the Midwest of our country is located in plateau,in where many airports,pipelines and other infrastructures are constructed.Previous studies have confirmed that the fossil fuel combustion under low pressure is different from that in plain area,it is necessary to study the difference of boilover phenomenon between low pressure and the plain area so as to the prevention in the plateau.Due to the difficulty in operation and repetition of large size boilover test,this paper uses small scale test instead.Considering that viscosity boiling range and other parameters are in line with the conditions of boilover,diesel oil is used as a kind of fuel in the experiment,and aviation kerosene is used for the experiment in the hope that this study will have guiding significance for the fire prevention in the plateau airport environment.Because boilover phenomena is related to phase transformation,turbulence,and other physical and chemical phenomena.It is very difficult to clear the mechanism of boilover completely.This paper follows the predecessors' study of boilover,records multiple physical parameters in the boilover process,including the intensity of the sound,mass loss rate,radiation intensity,and arranges thermocouple on multiple locations in the water layer,interface,burning layer to study the temperature change rule in the process of boilover.In order to study the influence of different main heat transfer control factors on the boilover phenomenon,four sizes of oil pan were purchased for experiments in this paper,including 15cm,18cm,30cm and 40cm.The research in this paper includes two parts.The experiment in Chapter 3 is carried out under sub-atmospheric pressures,and the nature of the oil pool fire under sub-atmospheric pressure is analyzed.Since a large number of areas in Midwest China are located on the plateau,airports,pipelines and other facilities are also constructed these areas.Previous studies have confirmed that the combustion behavior of fossil fuels at low pressure is somewhat different from that in the plain area,so it is necessary to study the difference between the boilover characteristics under low pressure conditions and the plain areas.It is hoped that this research will have a guiding significance for fire prevention in the highland airport,and will be able to contribute to preventing and controlling boilover fires in the plateau in the future.In the experiment,it was observed that part of the experimental group had obvious boilover phenomenon,several groups of experimental groups with typical boilover phenomenon and those without boilover phenomenon are selected to analyze the physical quantity data of each group,and the conclusions are as follows:The obvious decrease in flame temperature is an important sign to enter the precursor stage of boilover.Bubbles start to be generated during the precursor stage of boilover.The latent heat of vaporization and the disturbance caused by bubble generation in the fluid enhance the heat transfer,resulting in a significant increase in the heat flux at the interface.While the average combustion rate of the quasi-steady combustion stage and the boilover precursor stage does not change and the fuel combustion heat production rate does not change,so the heat obtained from the flame decreases,resulting in a decrease in its temperature and radiation.The combustion behavior of the oil pool fire with a water layer can be divided into four categories:No boilover occurred,A typical boilover occurred,Multiple typical boilover occurred,and Continuous boilover occurred.When the pressure is reduced and the oil basin size is reduced,it is difficult for boilover to occur.At higher altitudes,the change in the boilover strength is not sensitive to the size of the oil basin.The rate of splash mass loss for continuous boilover is much lower than that of typical boilover.Similar to the influence of pressure on the combustion of oil pool fire,the influence of environmental pressure on the characteristics of boilover is reflected in the decrease of oxygen content and combustion rate at low pressure,and the increase of combustion rate at the quasi-steady stage at relatively high pressure.When boilover occurs earlier than the low pressure group,more fuel is left,and the interface temperature is higher than that at low pressure,resulting in the boilover intensity being greater than that at low pressure.The fourth chapter studies the influence of the change of the water layer's properties on the boilover characteristics.Adding salt to the water layer to get a salt-saturated fluid,changed the boiling point of the water layer.We measured physical parameters such as noise and temperature,and compared with the experimental groups with pure water layer.The comparative analysis of groups used saturated sodium chloride solution as the water layer and the pure water groups come to important conclusions:the addition of sodium chloride salt in the water layer changes the boiling point of it,resulting in the increase in the time for the interface to reach the critical super-heat temperature difference.Thus,completely inhibited the occurrence of boilover in the diesel experiment groups,and also limits the combustion rate of jet fuel.