Page 149 - Modelling in Transport Phenomena A Conceptual Approach

PROBLEMS 129

the heart beats, it pumps out blood into the arteries. The blood pressure reaches
its maximum value, Le., systolic pressure, when the heart contracts to pump the
blood. In between beats, the heart is at rest and the blood pressure falls down to
a minimum value, diastolic pressure. An average healthy person has systolic and
diastolic pressures of 120 and 80mmHg, respectively. Human body has about 5.6
L of blood. If it takes 20s for blood to circulate throughout the body, estimate the
power output of the heart.
(Answer: 3.73 W)

4.13 Water is in isothermal turbulent flow at 20°C through a horizontal pipe
of circular cross-section with 10 cm inside diameter. The following experimental
values of velocity are measured as a function of radial distance r:

0.5 0.394
1.5 0.380
2.5 0.362
3.5 0.337
4.5 0.288

The velocity distribution is proposed in the form
(1 - i)
n
u, = v,,

where u,,, is the maximum velocity and R is the radius of the pipe. Calculate
the pressure drop per unit length of the pipe.
(Answer: 12.3 Pa/ m)

4.14 In Example 4.15, the length to diameter ratio is expressed as

Use the Chilton-Colburn analogy, i.e.,

StH pr2I3
2
and evaluate the value of LID. Is it a realistic value? Why?

4.15 Water at 10°C enters a circular pipe of internal diameter 2.5cm with a
velocity of 1.2 m/ s. Steam condenses on the outside of the pipe so as to keep the