用于低温风洞的新颖制冷方法

描述了用于低温风洞的新颖制冷系统,利用热交换器回收排气冷量预冷压缩空气,然后再用热分离器将其降至深低温作风洞气源．原理性实验结果证实新制冷方法的可行性．讨论了新制冷方法产生的有一定压力的低温空气作引射气源,引射驱动回流型风洞的特性．其制冷方法与现有低温风洞喷雾液氮制冷相比,由于仅需压缩空气而无需液氮,造价更便宜．更由于能量利用合理,效率高,因而运行成本可显著降低．

NOVEL COOLING MEANS FOR A CRYOGENICWIND TUNNEL

Existing cryogenic wind tunnels with cooling accomplished by spraying liquid nitrogendirectly into the tunnel circuit must equally discharge cryogenic gaseous nitrogen for keeping thesteadiness of the test flow. The tremendous "cool energy" carried away not only leads to heavydemands on liquid nitrogen and hence refrigerating power but also causes pollution of the localatmosphere.An alternative means of cooling air to cryogenic temperature by relying alone on the compres-sion energy of the air is presented. A bi-directional heat exchanger is installed at the exhaust exitof a wind tunnel. After the cryogenic exhaust and the compressed air pass in opposite directionsthrough which in the meantime, the former is heated to near ambient temperature and the latteris cooled deeply. By means of a thermal separator, the precooled compressed air is cooled furtherto the required cryogenic temperature and then to supply the wind tunnel.For cooling air from 320K to 100K, the thermal separator inlet pressure needs to be 2.5, 3.5or 8.2 times of the exit pressure, if the heat exchanger efficiency is assumed to be 90% and thethermal separator efficiency assumed to be 80%, 60% or 40% respectively.An experimental device for concept studies was set up in the lab. The experimental data areas follows: The pressure and temperature of compressed air at the inlet of the heat exchanger arel.162 MPa and 293.5 K respectively. The temperature and pressure at the inlet and the exit of thethermal separator are 140K, 118.5K and 1.119MPa, 0.13MPa respectively. In test section, theMach number and the temperature of the test flow are approximately one and 100K. The exhausttemperature at the exit of the heat exchanger is 283.9 K. The pressure loss of airflow through thetunnel circuit except the thermal separator is lower than 0.1 MPa. On the basis of the measureddata, it can be calculated that the efficiency of the heat exchanger and the thermal separator areequal to 90% and 33.4% respectively. The abnormal low efficiency of the thermal separator inuse is attributed to bad manufacturing. Otherwise the temperature of test gas and the requiredpressure of compressed air would be lower.The particular virtues of the novel cooling means for a wind tunnel are to save refrigeratingenergy and to protect environment in comparison with existing one by liquid nitrogen.