A tank contains a viscous fluid that is being stirred with an agitator (turbine). Calculate the heat-transfer coefficient from a coil immersed in this agitated vessel.
Fluid:
Density, rho, 45 BTU per cubic foot
Viscosity, mu, 10 pound per foot per hour
Specific heat, c, is 0.7 BTU per pound per degree Fahrenheit
Thermal conductivity, k, 0.10 BTU per hour per foot per
degree Fahrenheit
System:
Vessel diameter, D, 8 feet
Agitator diameter, L, 3 feet,
Heat-transfer parameter, a, 1.5
Agitator speed, N, 150 revolutions per minute
Solution:
Heat-transfer coefficient from coil in agitated tank can be
found through a correlation in term of Nusselt number.
Nusselt number is a function again of Reynolds number and
Prandtl number. Please note that N is
9000 revolutions per minute in consistent units. Reynolds number is given as L squared times N times rho over
mu. This is found to be 3.645 times 105.
Prandtl number is c times mu over k and is equal to 70.
Nusselt number is a times Re0.667 times Pr0.333. This is found to be 3.163 times 104. Plugging in the values of k and D,
heat-transfer coefficient, h, is calculated to be 395 BTU per hour per square
foot per degree Fahrenheit.