内置双螺旋结构换热管金属氢化物反应器的传热性能

Heat Transfer Performance of Metal Hydride Reactor Incorporating a Heat Exchange Tube with Double Helix Structure

针对金属氢化物反应器传热性能较差的问题,提出了更紧凑高效的单进–出口的双螺旋结构换热管。建立了内置螺旋管的金属氢化物反应器的3维数学模型,并采用COMSOL Multiphysics 5.2a软件进行求解。首先,通过热阻分析发现,在不同换热流体入口平均流速(0.5~3.0 m/s)下,导程为15 mm的单螺旋换热管管内对流传热热阻占总热阻的百分比为8.5%~45.2%,这表明管内对流传热热阻对反应器的传热性能有很大影响。然后,研究了换热流体入口平均流速对反应器传热性能的影响,确定了模拟中换热流体入口平均流速的范围,对比分析了单、双螺旋结构对反应器性能的影响。结果表明:当换热流体入口平均流速大于0.5 m/s时,能达到较好的换热效果,换热流体的平均真实温升趋于稳定。减小螺旋导程可以明显提高换热流体的平均真实温升及反应器的传热和输出性能。对于导程为60 mm的单、双螺旋结构管,床层平均温度降至300 K所用时间分别为7000 s和3000 s。导程为30 mm的双螺旋结构管的单位重量输出㶲功率比导程为15 mm的单螺旋结构管更高,可见双螺旋结构管反应器的传热和输出性能均优于单螺旋结构管反应器。双螺旋结构管具有更大的换热面积,在反应器床层内的位置分布更加均匀,从而提升了反应器的传热和输出性能。

Given unsatisfactory heat transfer performance of the metal hydride reactors,a more compact and efficient single inlet-outlet heat exchanger tube with double helix structure was proposed.A three-dimensional model was established for the metal hydride reactors incorporating helical-coiled tubes,and was solved utilizing the commercial software package COMSOL Multiphysics 5.2a.Firstly,the thermal resistance analysis showed that for the helical-coiled tube with a 15 mm helical pitch,the percentage of the convection heat resistance inside the tube to the total thermal resistance is between 8.5%and 45.2%under different inlet flow velocities of the heat transfer fluid(0.5~3.0 m/s).The result indicated that the convection heat resistance inside the tube had a great influence on the heat transfer performance for the reactor.Then,the influences of the inlet flow velocity of the heat transfer fluid on the heat transfer performance of the reactors were investigated,and the range of the inlet flow velocity of the heat transfer fluid in the simulation was determined.Furthermore,the effects of the single and double helix structures were analyzed.The results show that when the inlet flow velocity of the heat transfer fluid is greater than 0.5 m/s,the heat transfer performance reaches a desirable level,and the average true temperature boost of the heat transfer fluid tends to stabilize.Besides,the average true temperature boost of the heat transfer fluid and the heat transfer and output performance of the reactors are significantly improved by reducing the helical pitch.For the single and double helix tubes with a 60 mm helical pitch,the time for reducing the average bed temperature to 300 K is shortened from 7000 s to 3000 s.In addition,the double helix tube with a 30 mm helical pitch has the higher gravimetric exergy-output rate than the single helix tube with a 15 mm helical pitch.These results suggest that the reactor with double helix tube has better heat transfer and output performance than the reactor with single helix tube.The double helix tube has a larger heat transfer area and a more uniform distribution in the metal hydride beds,thus improving the heat transfer and output performance of the reactors.