| Jet heat exchanger of radiant tube has been widely used in waste heat recovery because of its excellent performance.Because of the complexity of the structure of the jet flow field,the heat transfer phenomenon and mechanism are still not fully explained.The calculation of the heat transfer of the jet can not be given in theory.At present,the calculation of the heat transfer of the jet heat exchanger is mainly based on the empirical formula.However,different design data or scholars have given different formulas,and the difference of heat transfer coefficient is very large.Therefore,it is important to explore the reasonable calculation method of the jet heat transfer of the jet heat exchanger,which has important guiding significance for the design and calculation of the jet heat exchanger.First,the calculation formula of the jet heat transfer given by different design materials and scholars is discussed,and a relatively reasonable calculation formula is obtained.However,the formula does not fully consider the effects of the physical parameters of the gas,the radius of the impact surface curvature and the influence of the transverse flow on the heat transfer of the jet.The influence of the three on the heat transfer of the jet is discussed through numerical simulation,and the correction factor of the curvature radius and transverse airflow is obtained.By using the established mathematical model of the jet heat transfer,the performance differences of the heat exchangers with equal and unequal spacing in the air jet section are studied and compared with the experimental results.In the end,the structure parameters of the air side and the flue gas side are optimized for the air side jet section with better comprehensive heat transfer performance by using a non equidistant heat exchanger.The main conclusions are as follows:(1)In the calculation of jet heat transfer in jet heat exchangers,the Martin formula in document [58] is recommended.(2)The gas physical parameters and the transverse flow have great influence on the heat transfer of the jet,and the design and calculation of the jet heat exchanger can not be ignored.The radii tube jet heat exchanger with a smaller curvature radius will make the calculation of the jet heat transfer more significant if the impact surface is not considered as the surface.(3)Compared with the air side jet section,the heat transfer performance of the heat exchanger with non equidistant layout is better and the preheating temperature of air is higher.Under the same air flow condition,the air side resistance loss is smaller and the heat transfer surface temperature is lower.The distribution of the length of each section of the jet stream affects the comprehensive heat transfer performance of the whole jet.(4)Along the direction of air flow,the diameter of the nozzle and the distance between the jet holes are gradually increased.On the one hand,the flow resistance and the anti scouring capacity of the air flow can be reduced.The heat load uniformity of the nozzle in the heat exchange process can be improved,the interference between the adjacent jet holes is reduced,the efficiency of heat exchange and the service life of the nozzle can be improved.Life.The optimal air side structure is scheme 1.(5)Under the condition of the metal consumption of the fin,the optimum fin structure parameters are as follows: the number of ring fin is 24,the thickness of the fin is 5mm,that is,the optimal scheme is scheme 4. |
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