Multi-scale simulation and analysis of gas evacuation processes in a microcavity
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摘要: 基于适用于整个克努森数范围的流动理论，建立了去除惯性约束聚变实验中靶丸内空气的理论模型，并设计实验验证了此模型的可靠性。物理实验要求靶丸内空气浓度低于10×10−6，数值模拟了去除靶丸内空气的过程，重点分析了靶丸内空气浓度、压力与除气时间的关系。计算并比较了单管路一次抽气法、单管路循环抽气法与双管路流洗法三种去除靶丸内空气方法的时间成本。数值计算结果表明：单管路一次抽气法中，靶丸上的微通道的存在对去除靶丸内空气所需时间的影响不可忽略，在考虑靶丸上微通道与充气管的情况下，需要1961.77 h才能使靶丸内的空气浓度达到标准。单管路循环抽气法中，抽气次数与单次抽气程度会影响去除靶丸内空气所需总时间，在单次抽气程度值取最优的情况下，采用充三次，抽四次的方案可使达标总时间减少至1 h左右，此方案下单次充气和抽气时间分别为6 min和10 min。而采用双管路流洗法则仅需11 min便可使靶丸内空气浓度达标。Abstract: Based on the flow theory applicable to the whole Knudsen number range, a theoretical model for removing air from the target shot in inertial confinement fusion was established, and the reliability of the model was verified by designed experiments. The physical experiment requires the air concentration in the target shot to be lower than 10×10−6, the process of removing air in the target shot was simulated numerically, and the relationship between the air concentration in the target shot, the pressure in the target shot and time was emphatically analyzed. The time cost of three methods for removing the air in the target shot, namely the single-pipe one-time gas evacuation method, the single-pipe circulation gas evacuation method and the double-pipe flow washing method, were calculated and compared. Numerical calculation results show that: in the single-pipe one-time gas evacuation method, the existence of the micro-channel on the target shot has a non-negligible effect on the time required to remove the air in the target shot, and it takes 1961.77 h to make the air concentration in the target shot reach the standard when the micro-channel on the target shot and the gas-filling pipe is considered. In the single-pipe cycle gas evacuation method, the number of evacuation times and the degree of single gas evacuation will affect the total time required to remove the air in the target shot. When the single gas evacuation degree is at the optimal value, the plan that filling three times and evacuation four times can reduce the total time to reach the standard to about 1 h, while the single gas filling and gas evacuation times under this plan are 6 min and 10 min, respectively. However, it only takes 11 minutes to make the air concentration in the target shot reach the standard by using the double-pipe flow washing method.
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Key words:
- filling /
- evacuation /
- microcapillary tube /
- free molecular flow /
- numerical simulation
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图 3 真空罐抽气过程的模拟与实验数据
Figure 3. Simulation and experimental data of the gas evacuation process invacuum tank
图 4 充气过程中ICF腔内外压差变化
Figure 4. Differential pressure changes inside and outside the ICF cavity during the gas filling process
图 5 三种情况下靶丸内空气浓度及压力与时间的关系
Figure 5. The relationship between theair concentration in the target shot，the pressure in the target shot and time under three conditions
图 6 第一次抽气程度X的值对第一次抽气时间（t1）、第一次充气时间（t2）、第二次抽气时间（t3）、与总时间（tall）的影响
Figure 6. Influence of the values of the first gas evacuation degree X on the first gas evacuation time (t1), the first gas filling time (t2), the second gas evacuation time (t3), and the total time (tall)
图 7 充气一次和抽气两次时的气体流动（a）靶丸内压力与时间的关系（b）靶丸内空气浓度与时间的关系
Figure 7. Gas flow underfilling one timeandevacuationtwo times (a) relationship between the pressure in the target shot and time; (b) relationship between the air concentration in the target shot and time
图 8 充气两次和抽气三次时的气体流动（a）靶丸内压力与时间的关系（b）靶丸内空气浓度与时间的关系
Figure 8. Gas flow underfilling two times and evacuationthree times (a) relationship between the pressure in the target shot and time; (b) relationship between the air concentration in the target shot and time
图 9 充气三次和抽气四次时的气体流动情况
Figure 9. Gas flow under filling three times and evacuation four times
图 10 不同管径下的充气和抽气时间
Figure 10. Time of gas filling and gas evacuation under different pipe diameters
表 1 情况B不同阶段的抽气时间
Table 1. Evacuation time at different stages of Case B
stage the initial pressure/Pa the final pressure/Pa extraction time/h the proportion/% I 101325 10132.5 0.17 0.01 II 10132.5 1013.25 1.77 0.09 III 1013.25 101.325 17.66 0.90 IV 101.325 10.1325 176.56 9.00 V 10.1325 1.01325 1765.61 90.00 
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