What is the pressure drop (in mm Hg) in the blood as it passes through a capillary 1 mm long and 2μm in radius if the speed of the blood through the centre of the capillary is 0.66 mm/s ? (The viscosity of whole blood is 4×10−3 poise).
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Solution
See the expression of maximum velocity at centre of tube, vmax=(p1−p2)R24ηL ∴(P1−P2)=4ηLvmaxR4
=(4×4×10−3)(10−3)(0.66×10−3)(2×10−6)2 =2.64×103 N/m2=hρg h=2.64×103ρg =2.64×10313.6×103×9.81 m of Hg =0.0195 m of Hg =19.5 mm of Hg