Study On The Flow Characteristics Of Protective Gas In The Bell-type Annealing Furnace With HPH

The production capacity of cold rolled sheet in China has reached 32.773 million tons per year,ranking first in the world.The bell-type annealing furnace with HPH is the key equipment for the annealing treatment of strip steel.In practical production,the problems in the mechanical properties and surface quality of the steel coil are mainly due to the unreasonable annealing process,and the main factors affecting the annealing process are the flow field and the temperature field.Therefore,based on the previous research results,the flow characteristics and heat transfer of the protective gas within the enclosure of the bell-type annealing furnace with HPH are studied in this paper,which provides the basis for improving the annealing quality of the cold-rolled steel coil.First,the cold state test rig of the bell-type annealing furnace with 1:5 ratio to the furnace at production site is designed and set up by the similarity principle,and the numerical simulation is carried out.Particle Image Velocimetry(PIV)was used to test the annular channel of cold flow field in the bell-type annealing furnace,and the pressure and velocity were tested by aerodynamic probe and hot wire anemometer to verify the accuracy of numerical simulation.The results show that in the outer circumferential channel of steel coil,the average relative error is 10.1% between the measured value and the numerical simulation value of the flow velocity;the average relative error is 12.9% between PIV experimental value and numerical simulation value,and the error is within the allowable range;In the channel of the coil core,the average relative error is 8.68% between the hot-wire and numerical simulation values of the flow velocity.The error is within the allowable range,and the accuracy of the simulation is verified.Then,taking the actual production equipment of a cold rolling mill in a domestic iron and steel enterprise as the prototype,and adopting the numerical simulation method,the flow state of the protective gas in the bell-type annealing furnace was studied.The flow law of protective gas in the bell-type annealing furnace with HPH is analyzed,and the structure of diffuser is optimized.The rationality of spot right-lateraldiffuser and the rationality of upper and lower equal-length trapezoid blade convection plate are further proved.In order to optimize the structure of the convection plate,a new type of structure is proposed,in which the flow ratio of hydrogen between coil channels is optimized by adding a guide wing to the inner channel of the convection plate.Compared with the prototype,the flow distribution of the second layer convection plate is 11.97% more than that of the prototype,and the flow distribution of the third layer convection plate is 18.07% more than that of the prototype.The problem of heat transfer bottleneck on the second steel coil and the third steel coil is effectively solved.The flow of the top channel has been reduced by0.4%,so the heat transfer of other flow channels will also be improved.In the end,the numerical simulation of the flow field and the temperature field is carried out for the medium size the bell-type annealing furnace by using the dynamic grid technology and the fluid-solid coupling heat transfer technology.The results show that the velocity of protective gas decays along the direction of height,the attenuation speed of the core channel is faster than that of the outer channel,and there is a sudden change of the velocity at the convection plate.The temperature at the corner of the steel coil rises faster than that at the middle part;The heating rate on the outside of the coil is greater than the inside;At the end of heating,the cold point temperature of the fourth steel coil is the highest,which is 745 ?,and the cold point temperature of the other three steel coil is not much different.The cold point temperature of the third steel coil is the lowest,which is 659 ?.The location of the faster heating cold point is the first steel coil.Because of the heating on three sides,the heating speed of the top steel coil is also relatively fast.For radial heat transfer on the upper and lower surfaces of the coil,the heat transfer effect is: the fourth steel coil > the second steel coil >the first steel coil > the third steel coil.According to the distribution of the total heat flux on the outer surface of the coil,the total heat flux on the outer surface of the coil increases gradually alone the height direction of the bell-type annealing furnace.