| The coal mine hot air unit is mainly used for heating mines in winter.It has the advantages of low thermal inertia,high thermal efficiency,energy saving and environmental protection.Due to the lack of relevant research on the heat exchange process of the hot air unit,the product design is relatively extensive,and the structure of the hot air stove and the arrangement of the heating pipes have many unreasonable points.At the same time,in order to save space,the furnace body often adopts a U-shaped design,which results in stagnant zones in the flow channel and overheating of the heating tube surface,which affects the life of the hot blast stove.This paper uses the CFD method and takes an actual hot air unit as a prototype to explore the heat transfer effect of the furnace body under different working conditions and different structure conditions,and obtain some laws.Through research,it is found that due to the U-shaped setting,the upper layer of air will directly impact the bottom of the furnace body when passing through the U-shaped opening.At the same time,the bottom heating tube forms a barrier to block,so that the air cannot rise to exchange heat with other layers of heating tubes.It flows out through the outlet,forming a large amount of escape flow.The eccentric design of the outlet of the furnace body causes the non-eccentric side air to be impacted by the eccentric side air at the outlet and return to the heating tube area for secondary heating,which improves the convective heat exchange between the air and the heating tube.Therefore,the high-temperature air at the outlet mainly comes from this part of the backflow.In addition,the influence of the three operating parameters of ambient temperature,flow and power on the heat transfer of the hot blast stove is studied.Among them,because the power is constant,the ambient temperature has no significant effect on the temperature rise of the working fluid.Flow and power affect the temperature rise together,where the temperature rise increases approximately linearly with the increase of power,and with the increase of flow,the rate of temperature rise decreases first and then becomes faster.Furthermore,the influence of two structural parameters of outlet eccentricity and tube pitch on temperature rise is studied.It is found that when the eccentricity is increased,the temperature rise and pressure difference of the furnace body are first reduced and then increased,the temperature rise can be increased by up to 7.5%;the maximum fluid temperature can be reduced by 8.7%.In addition,the heat transfer efficiency can be improved by increasing the tube pitch.The longitudinal pitch is increased from 17 mm to 25 mm,the convective heat transfer coefficient of the heating tube is increased by 11%,the temperature rise is increased by 7.2%,the maximum fluid temperature is decreased by 14%,and the maximum wall temperature is decreased by 7.9%;the horizontal pitch is increased from 45% to 65 %,the convective heat transfer coefficient of the heating tube is increased by 12.6%,the air temperature rise is increased by 16%,the maximum air temperature is decreased by16.3%,and the maximum wall temperature is decreased by 15.6%.Based on the above research,optimize the design of the furnace body,and set up baffles at the U-shaped opening,bottom and both sides.Finally,the optimal solution was adopted for the design.Compared with the original solution,the heat transfer coefficient of the heating tube wall increased by 44.5%,the air temperature increased by 8.5%,the pressure difference increased by 3.1%,the maximum air temperature decreased by32%,and the maximum wall temperature decreased by 24.1%.,The heat exchange effect of the furnace body has been significantly improved,effectively avoiding the phenomenon of over-temperature,and improving the life of the heating furnace. |
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