Study on the parameter optimization of air-drying system in large continuous transonic wind tunnel
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摘要: 在跨声速风洞中，试验段水汽凝结会使气流变为非等熵流动并产生凝结波，严重破坏流场均匀性并对测试数据产生影响。因此，试验前需对气流进行干燥使其含湿量低于1.5 g/kg。大型连续式跨声速风洞经济、高效的气流干燥途径是设置循环干燥系统。针对连续式跨声速风洞干燥要求及运行特点，确定了转轮联合冷却除湿的总体技术方案，提出了基于均匀掺混假设的洞内气流干燥仿真计算模型，对系统总体参数进行了设计和优化。研究发现：当循环次数在2次以上时，模型可有效评估洞内气流平均含湿量变化情况，与试验偏差在8.3%以内；充分利用具有较高除湿能力的前4次循环和所选配转轮的除湿能力，可将前、后表冷器最大冷却负荷分别降低约41.9%和27.8%，提高设备使用效率。Abstract: In the transonic wind tunnel, the flow of wet air can turn into non-isentropic flow due to water vapor condensation in the test section, followed by the formation of condensation wave, seriously destroying the uniformity of the flow field and the accuracy of the test data. Therefore, the air should be dried ahead of test to ensure its moisture content less than 1.5 g/kg. The circulation drying system is an economical and efficient air-drying way in the large continuous transonic wind tunnel. In this paper, a rotary and cooling dehumidification drying system is designed for the wind tunnel, and an air-drying calculation model based on the assumption of uniform mixing is proposed and validated by experiment. According to the proposed model, the optimized parameters of the air-drying system are obtained. The results show that the model can effectively estimate the change of the average moisture content in the tunnel, and the deviation from the test is within 8.3% when the number of cycles is more than 2; the maximum cooling load of the front and rear heat exchanger can be reduced by about 41.9% and 27.8% respectively in this system by making full use of the dehumidification capacity of the first four cycles and the selected rotary dehumidifier.
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Key words:
- continuous wind tunnel /
- drying system /
- rotary dehumidifier /
- calculation model /
- performance analysis
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图 3 气流除湿过程焓湿变化过程
Figure 3. Change of enthalpy and humidity in air dehumidification process
图 5 0.6 m风洞干燥过程试验及仿真结果
Figure 5. Test and simulation results of drying process in 0.6 m wind tunnel
图 6 初步设计参数下的干燥过程结果
Figure 6. Drying process results under preliminary design parameter
表 1 空气除湿方法比较
Table 1. Comparison of air dehumidification methods
除湿方法 除湿原理 一般出风常压露点 加强措施 最低出风露点 冷却除湿 湿空气被冷却至露点以下而液化/固化 出风经济露点约为5℃，
常压下可到–10℃气流加压 –23℃左右 溶液除湿 利用氯化钙、氯化锂、二甘醇等溶液与空气中的水蒸气分压差 较容易实现–10℃露点 气流加压、多级溶液除湿、优化除湿溶液等 –26℃左右 吸附除湿 利用吸附剂和吸附质分子之间由范德华力引起的可逆吸附 硅胶及分子筛转轮除湿露点可分别达到–50℃和–75℃ 配合冷却除湿等 –80℃左右 膜除湿 利用水蒸气透过膜的速率比其他组分高两个量级以上的特性及膜两侧水蒸气浓度差 须采用吹扫气法、压差法、真空法以及膜/
吸收剂法等在膜的两侧维持水蒸气浓度差–65℃左右 
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表 2 计算模型主要控制方程
Table 2. Main governing equations of the calculation model
过程 主要控制方程 A-B前表冷器 除湿量：$\Delta {d}_{ {A} }=q\cdot \rho \cdot \left({d}_{ {A} }-{d}_{ {B} }\right)-{q}_{m}\cdot {d}_{\text{环境} }；$ 冷却负荷：${Q}_{ {A} }=q\cdot \rho \cdot \left({h}_{ {A} }-{h}_{ {B} }\right)=q\cdot \rho \cdot {f}_{h}({d}_{ {A} },{d}_{ {B} },{T}_{ {A} },{T}_{ {B} })$ B-C后表冷器 除湿量：$\Delta {d}_{ {B} }=q\cdot \rho \cdot \left({d}_{ {B} }-{d}_{ {C} }\right)；$ 冷却负荷：${Q}_{ {B} }=q\cdot \rho \cdot ({h}_{ {B} }-{h}_{ {C} }) =q\cdot \rho \cdot {f}_{h}({d}_{ {B} },{d}_{ {C} },{T}_{ {B} },{T}_{ {C} })$ C-E转轮 除湿量：$\Delta {d}_{ {C} }=q\cdot \rho \cdot \left({d}_{ {C} }-{d}_{ {E} }\right)=q\cdot \rho \cdot f\left({d}_{ {C} }\right)$ E-Aa 洞内气流平均含湿量：${d}_{ {\rm A} }=\dfrac{ {V\cdot \rho \cdot d}_{\mathrm{初}\mathrm{始} }-\displaystyle\sum _{1}^{i}(\Delta {d}_{ {A} }+\Delta {d}_{ {B} }+\Delta {d}_{ {C} })\cdot \Delta {t} }{V\cdot \rho }$ 注：Δ$ {d}$为气流经过前、后表冷器及转轮的除湿量，g/s；$ q $为系统处理风量，m3/s；$ \rho $为气体密度，kg/m3；${d}$为相应位置气流含湿量，g/kg；$ {q}_{\rm m} $为环境空气漏入量，kg/s；${Q}$为前、后表冷器冷负荷，kW；${h}$为前、后表冷器入口气流焓值，与含湿量和温度有关，kJ/kg；$ V $为风洞容积，m3；$\Delta {t}$为时间步长。
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表 3 系统初步设计参数
Table 3. System preliminary design parameters
气流参数 干球温度/
℃相对湿度/
%含湿量/（g·kg–1) A处 32.6 75.00 25.10 B处前表冷器出口 15.0 95.00 10.68 C处后表冷器出口 5.0 100.00 5.70 E处系统送风口 32.6 1.25 0.40
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表 4 不同风量下的干燥时间
Table 4. Drying time under different air volume
每小时处理风量/
（m3·h–1）1.83V 2V 2.2V 2.3V 2.5V 干燥用时/
s8276 7552 6933 6392 5907
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