Question

It is desired to draw blood 3 cm up a capillary tube. Assuming a contact angle of 0 degrees and a blood density of 1060 kg/m3, what tube diameter should be used?

Answer 1

Answer:

If we assume a temperature of 20ºc and the blood interfacial surface tension is similar to water interfacial surface tension, the diameter of the capillary tube should be 0.933mm.

Step-by-step explanation:

The Jurin law describes the height a fluid can reach in a capillary tube. This law can be written as:

$H=\displaystyle\frac{2\gamma cos(\theta)}{\rho gr}$

where γ is the interfacial surface tension, θ is the contact angle with the fluid, ρ is the fluid density, g is the gravity acceleration and r is the tube radius.

If we assume that the interfacial surface tension of blood and water are almost the same, γ=0,0728 N/m at 20ºc. Therefore the diameter of the tube will be:

$D=2r=\displaystyle\frac{4\gamma cos(\theta)}{\rho gH}=0.933\cdot 10^{-3}m$