超压气球驻空过程热力学特性分析

Analysis on Thermal Characteristic of Super-pressure Balloons at Float Conditions

超压气球具有结构简单、载荷量大、驻空时间长等突出优点,可以应用于侦察、通信、运输补给等各个方面,实现与空天地的衔接和中继。由于飞行原理和工作环境特殊,在其设计过程中必须重点考虑热力学特性的影响。文章详细分析了临近空间热环境,包括太阳辐射、长波辐射、对流换热等。在此基础上建立了超压气球三维瞬态热力学模型,编制了仿真程序,对超压气球驻空过程进行了研究;得到了蒙皮温度、氦气温度以及气球超压等随时间的变化规律,并分析了充气量、驻空季节纬度以及蒙皮物性对氦气温度的影响。结果表明:驻空过程气球蒙皮温度分布不均匀,随太阳方位变化而变化,最大温差达65K;考虑氦气中杂质的辐射吸收作用时,白天氦气的平均温度高于蒙皮的平均温度;氦气的"超热"会引起气球的超压,在不同季节和纬度飞行时应选择不同的充气量,将超压控制在合理范围内;为减小超压量,可以选择可见光吸收率小而红外发射率大的蒙皮材料。

Super-pressure balloons, which have inherent capabilities of simple structure, large load and long duration flight, which can be used in reconnaissance, communication and transportation, and achieve relaying with Space-Air-Ground. Due to special principles of flight and working environment, the design of super-pressure balloons must focus on the influence of thermodynamic characteristics. In this paper, the thermal environment near space is analyzed in detail, including the solar radiation, the infrared radiation and the convection heat transfer. Based on analysis above, a three-dimensional transient thermodynamic model of super-pressure balloon is established. By compiling simulation program, the float condition of super-pressure balloons is studied. And the variations of skin temperatures, gas temperatures and gas overpressure are obtained. The influence of aeration quality, season, latitude and skin radiation property on balloon thermal behaviors are discussed in detail. The results indicate that the temperature distribution of the film during the floating process is nonuniform and varies with the solar azimuth, and the maximum temperature difference is 65 K. Considering the radiative absorption of impurities in helium, the mean temperature of helium in daytime is higher than that of the skin. The ＂superheat＂ of helium can cause the over pressure of the balloon. Different helium mass should be filled in different seasons and latitudes, and the overpressure should be controlled within a reasonable range. In order to reduce the overpressure, skin materials with small solar absorptivity and high infrared emissivity can be chose for design.