| Under the background of national Marine power strategy and "dual carbon",the promulgating of far-reaching offshore oil and gas exploration and development and other related policy planning provides a huge opportunity for the development of crude oil transportation industry.Shipping is one of the most important ways of global crude oil transportation,so it is of great significance to fully understand the heat-flow coupling characteristics of crude oil heating for guiding engineering practice.In this thesis,a 27000 DWT tanker cargo tank was used as the prototype for theoretical modeling.Based on the computational fluid dynamics method,the heat transfer and flow characteristics of crude oil in the cargo tank under the swaying state were expounded and analyzed.The influence of the cargo tank under different liquid loading rate,heat flux,swaying amplitude and shaking period on the characteristics of temperature field and velocity field during the heating process was specifically studied.At the same time,the energy system of crude oil heating in cargo tank under swaying condition is evaluated and analyzed.Firstly,the influence of the density and viscosity of crude oil on the heat transfer and flow characteristics is analyzed and expounded.It is clear that the influence of the change of physical parameters on the physical field in the cargo oil tank cannot be ignored when the oil is heated in the cargo oil tank.This is the precondition to carry out follow-up research.Then,the distribution of temperature field and velocity field in the tank body under static and swaying state is compared,and the formation mechanism is explained and analyzed.Due to the natural convection caused by the heating of the bottom crude oil,the velocity vector of crude oil in the cargo tank in the static state rotates in the model domain.When the tanker is swaying,the fluid flow is guided by the swaying effect,which significantly changes the distribution of the flow field.Compared with the flow field in the static state,these vortex structures help to mix the fluids near the wall and in the center area of the cargo tank.So the temperature distribution is more uniform.Thirdly,the effects of different liquid loading rate,heat flux,swing amplitude and swing period on the thermal flow coupling characteristics of crude oil were investigated.Due to the difference in liquid loading rate,the oil temperature distribution and flow pattern in the tank will be different,and a vortex with the oil at the bottom as the main driving force is formed in the tank,which promotes the rapid mixing of hot and cold oil in the crude oil tank.When heated to the same moment,the top crude oil is most affected by the hot plume heated by the steam coil and has the highest temperature.The top oil temperature corresponding to the same monitoring point at different liquid levels is 59.86 ℃,44.21 ℃,39.68 ℃ and 37.74 ℃.At high heat flux,the heat transferred to bilge crude oil by the steam coil at the bottom of the tank will be more heat per unit time through heat conduction.When the heat flux of the steam coil is heated to the same time with different heat densities,the temperature at the same monitoring point in the bilge increases by 13.22℃,16.61℃,19.58℃ and 22.69℃ respectively.When the cargo oil tank swing amplitude is larger,stronger eddy currents can be generated in the bilge area,thus bringing stronger flow disturbance,which significantly increases the velocity gradient near the steam coil boundary layer and enhances the heat transfer effect.The forced convection caused by shaking drives the rapid heat diffusion of crude oil in the cargo tank.The shorter the rocking period,the more thoroughly the temperature stratification structure in the cabin will be destroyed,resulting in stronger convective heat transfer between hot and cold oil products.With the shortening of the swaying period,the fluctuation range of the crude oil flow velocity is larger.The crude oil flow velocity fluctuates between 0.002 m/s and 0.023 m/s in the short swaying period,while the crude oil flow velocity fluctuates between 0.003 m/s and 0.009m/s in the long swaying period.After that,the heating rate of crude oil and the unevenness of crude oil temperature field are considered as the evaluation of steam heating effect.When the oil storage level is high,the heating rate of crude oil is relatively slow,and the non-uniformity of crude oil gradually increases with the increase of liquid loading rate of cargo oil tank.At high heat flux,more heat can be input into the cargo tank,resulting in a higher rate of crude oil temperature rise.The average temperature difference of crude oil in the tank after heating is small.The variation of swaying amplitude and swaying period does not significantly change the heating rate of crude oil.The overall temperature rise rate tends to be slower and slower with the heating process,and has the maximum temperature rise rate at the initial stage of heating.The non-uniformity of cargo oil tank first increases and then decreases with the heating time,and then tends to be stable.Finally,thermal efficiency and exergy efficiency evaluation indexes were used to scientifically and completely analyze the energy utilization in the heating process of cargo oil tank.When the liquid carrying rate increases,the crude oil needs more heat for temperature rise,so the energy can be fully utilized.With the increase of heating heat flux,heat released by steam coil increased,so thermal efficiency and exergy efficiency would increase.Under the condition of small swing amplitude and long swing period,the crude oil in cargo tank is disturbed relatively small,the less energy is lost to the outside world per unit time,and the system has a high energy utilization rate. |
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