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Blood takes about 1.65 s to pass through a 2.00 mm long capillary. If the diameter of the capillary is 5.00 μm and the pressure drop is 2.85 kPa , calculate the viscosity of blood. Assume laminar flow.

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Answer:

Viscosity of blood will be [tex]918.54\times 10^{-6}Pa-sec[/tex]

Explanation:

We have given time to pass the capillary = 1.65 sec

Length of capillary L = 2 mm = 0.002 m

Pressure drop [tex]\Delta P=2.85kPa=2.85\times 10^3Pa[/tex]

Diameter [tex]d=5\mu m=5\times 10^{-6}m[/tex]

So radius [tex]r=\frac{5\times 10^{-6}}{2}=2.5\times 10^{-6}m[/tex]

Velocity will be [tex]v=\frac{L}{t}=\frac{0.002}{1.65}=1.212\times 10^{-3}m/sec[/tex]

We know that viscosity is given by [tex]\eta =\frac{r^2\Delta P}{8Lv}=\frac{(2.5\times 10^{-6})^2\times 2.85\times 10^3}{8\times 0.002\times 1.212\times 10^{-3}}=918.54\times 10^{-6}Pa-sec[/tex]

Viscosity of blood will be [tex]918.54\times 10^{-6}Pa-sec[/tex]

The viscosity of the blood flowing in the given capillary is [tex]9.27 \times 10^{-4} \ Pa.s[/tex]

The given parameters;

  • time taken for the blood to pass, t = 1.65 s
  • diameter of the capillary, d = 5 μm
  • length of the capillary, l = 2.00 mm
  • pressure drop, ΔP = 2.85 kPa

The velocity of the blood is calculated as follows;

[tex]v = \frac{L}{t} = \frac{2\times 10^{-3} \ m}{1.65 \ s} = 0.0012 \ m/s[/tex]

The radius of the capillary is calculated as follows;

[tex]r = \frac{d}{2} \\\\r = \frac{5\times 10^{-6}}{2} = 2.5 \times 10^{-6} \ m[/tex]

Assuming laminar flow, the viscosity of the blood is calculated as;

[tex]\mu = \frac{r^2 \times \Delta P}{8lv} \\\\\mu = \frac{(2.5\times 10^{-6})^2 \times 2850}{8 \times 2\times 10^{-3} \times 0.0012} \\\\\mu= 9.27 \times 10^{-4} \ Pa.s[/tex]

Thus, the viscosity of the blood flowing in the given capillary is [tex]9.27 \times 10^{-4} \ Pa.s[/tex]

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