The diffusivity of human insulin is 77 µm2 /s in water at 37◦ C. Assuming the protein to be spherical, what is its effective radius? How does this compare to its crystal structure dimensions (77.22 x 77.22 x 77.22 Å)? Hint: The mean frictional drag coefficient for a sphere of radius R = 6πµR

Water at the rate of 1 kg/s is forced through a tube with a 2.5 cm inner diameter. the inlet water temperature is 15°c, and the outlet water temperature is 50°c. the tube wall temperature is 14°c higher than the local water temperature all along the length of the tube. what is the length of the tube?