Study on Liquid Volume in a Tank under micro-gravity space

航天工程对人类来说非常重要，许多国家都在按计划进行空间站工程。空间站内的模块处于微重力状态。在地球重力条件下效果良好的测量方法在微重力条件下并不一定有效。目前广泛应用于测量重力作用下罐内液量的液位计就是这样一个例子。在微重力条件下，需要用液位计以外的方法来测量罐内的液体含量。本文论述了在微重力条件下用气动法测量密闭罐内液体含量时出现的问题。气动法测量罐内压力的周期性变化，罐内压力受容积周期性小位移的影响。该方法(1)首先利用理想气体定律的关系，根据测得的压力和体积位移，估算出罐内残存气体的体积；(2)用罐容减去残存气体，计算出液体含量。该方法不同于液位计，可以测量微重力条件下的液体含量。然而，在微重力条件下测量压力变化的基本问题没有得到研究。当液体中存在许多气泡时会发生什么？(2)当压力传感器浸入液体时会发生什么？(3)汽化液体对压力有何影响？(4)水箱热时间常数对测量有何影响？我们从理论上研究了这些问题。通过飞机抛物线飞行实现微重力条件下的实验，验证了气动方法的有效性。

The space project are important for human beings and the space station projects are on schedule in many countries.Modules in the the space stations are under the micro-gravity condition. Measurement methods worked well under the earth gravity condition does not always work in such the micro-gravity conditions. The level meters employed widely to measure the liquid quantity in the tank under the earth gravity is one of such the examples. Methods other than level meters are required to measure the liquid content in the tank under the micro-gravity.This paper treats the problems occurred when the pneumatic method is applied to measure the liquid content in a closed tank under the micro-gravity condition.The pneumatic method measures the periodic change in the pressure in the tank which is subjected to the periodic small displacement of the volume. The method (1) first estimates the volume of the ullage gas in the tank from the measured pressure and the volume displacement by applying the relation of ideal gas law, and (2) calculates the liquid content by subtracting the ullage gas from the tank capacity. This method is different from the level meters and thus can measure the liquid content in the micro-gravity conditions. However the following essential problems for the measurement of the pressure change were not investigated when applied under the micro-gravity condition.(1) What happen when many bubbles exist in the liquid?(2) What happen when pressure sensor immerses in the liquid?(3) How does the vaporized liquid influence to the pressure?(4) How does the thermal time constant of the tank influence to the measurement?We investigated these problems theoretically. The validity of the pneui-natic method was examined by experiments under the micro-gravity conditions realized by tlie parabolic flight of an airplane.