Biomedical Engineering Reference
In-Depth Information
4
2
4
⎡
⎤
1.056 * 200 * 7.5 * 10
−
6
⎡⎤
P
100 mmHg
1
mmHg
113.79 mmHg
=
+
−
=
⎢
⎥
⎢⎥
⎣⎦
2
2
10
⎢
⎥
⎣
⎦
For a real fluid, shear converts kinetic energy to thermal energy in a nonre-
coverable way, which is manifested as the net pressure loss. In practice, there are
additional losses termed minor losses in addition to the frictional pressure loss.
These minor losses are contributed by the entrance and exit effects (or inlets and
outlets) of the tubes; expansions and contractions due to different sizes of tubing
and catheters needed to adjust the flow rate; bends, elbows, tees, and other fittings
used in the flow system; and valves (open or partially closed) used for controlling
flow rate. Many times minor losses are the
largest
cause of frictional loss in a flow
system. Although there is no adequate theory to predict minor losses, a commonly
used empirical relation is
2
V
hK
g
=
L
L
2
where
K
L
is the minor loss coefficient. For many standard fittings,
K
L
is obtained
from the manufacturer or from a handbook. If there several fittings in the flow
system, all minor losses are summed to obtain the total loss. These minor losses are
added to the frictional loss in the tubes to obtain the total head loss as
2
2
lV
V
∑∑
h
=
f
+
K
(4.29)
L
L
Dg
2
2
g
where
f
is Darcy's friction factor and
l
is the length of the tube.
f
is typically ob-
tained using either a Moody plot or empirical correlations, which are described in
[4].
4.4.2 Energy Balance in the Body
Energy is used continuously in the body and is fundamental to the physiological
functions of the body such as body movement, functioning of the heart, respiration,
digestion, and functioning of the brain. Metabolism is the sum of many individual
chemical reactions by which cells process nutrient molecules and maintain a living
state. The metabolism is grouped into
anabolism
and
catabolism
. In anabolism, a
cell uses energy to generate complex molecules such as DNA, RNA, and proteins
needed by the cells and perform other life functions such as creating cellular struc-
tures. In catabolism, a cell breaks down complex molecules such as carbohydrates
and fats to simpler molecules to yield energy. Both processes are coupled to each
other, linked by energy sources such as adenosine triphosphate (ATP), nicotinamide
