Capillary rise inside International Space Station

CAPILLARY RISE INSIDE INTERNATIONAL SPACE STATION

INTRODUCTION

Capillarity or capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces. When a capillary tube is inserted into a beaker containing liquid, the level of liquid in the capillary tend to rise or fall depending on the angle of contact between liquid and the tube wall. We intend to study only the rise of liquid in a capillary tube. Since the liquid rises against gravity, the extent to which it can rise also directly depends on the local acceleration due to gravity. We thus intend to determine the extent of capillary rise by a liquid inside the International Space Station (ISS).

ASSUMPTIONS

1. The angle of contact is always acute

2. The liquid is free from impurities

3. Temperature of the liquid is constant

4. The capillary tube is indestructible

CALCULATION

Consider a liquid [pure water] of density ‘ρ’ in a glass beaker with an inverted glass capillary tube inserted in a beaker as shown in figure.1. Let ‘r’ be the radius of the capillary tube, ‘θ’ be the angle of contact between pure water and the wall of capillary tube and ‘T’ be the surface tension of water. The ISS is orbiting the Earth hence always in a state of free fall. This means that objects inside will not experience any acceleration and hence safe to assume that gravity is zero.

Fig .1 Capillarity

The equation for capillary rise ‘h’ in the tube is given by,

h – Capillary rise in the tube (m)

T – Surface tension of water [T = 7.28*10^-2 N/m]

θ – Angle of contact between pure water and glass tube [θ = 0°]

ρ – Density of water [ρ = 1000 Kg/m³]

r – Radius of capillary tube [r = 1.5 *10^-3 m]

g – Acceleration due to gravity on ISS [g = 0 m/s²]

Substituting the constants in equation (1),

Since gravitational acceleration is not present inside the space station due to free fall, the capillary rise would be infinite. This implies that as soon as water comes in contact with the capillary tube, it will be ejected out of the tube like a jet.

CONCLUSION

We thus determined the capillary rise of water inside the ISS. It is interesting to note that the capillary rise does not depend on the length of the capillary tube.