PART D - DYNAMIC FLUID FLOW
Reynolds number. The Reynolds number is a dimensionless quantity that does
not represent any particular unit.
Example: 4 inches divided by 4 inches = 1; in this case 1 does not
represent inches but a number that represents the ratio of 4 inches to 4
inches. The Reynolds number is a dimensionless quantity which can be
calculated using the following equation:
R
=
Reynolds number
Q
=
Flow rate in GPM
d
=
Inside diameter of pipe, in inches
K
=
Kinematic viscosity in centistokes (see Figure 1-1).
R = 3160 x Q
(where 3160 is a constant)
dxK
In this equation we use field data and we will concentrate on it in the
classroom. It is also the one used by the Army.
Reynolds number using design data.
V = Velocity in feet per sec
d = Inside diameter of pipe in ft
Y = Kinematic viscosity in feet squared (ft,,) per sec
R=Vxd
Y
Scientific Notation. Once you have obtained the Reynolds number you must be
able to use it. We know that the Reynolds number can tell you whether the
flow is laminar or turbulent. We can also determine a friction factor using
the Reynolds number. The friction factor relates to the resistance to flow
in pipeline operations. In our example using field data, we obtained a
Reynolds number of 144881. Because of the large number we will express it
in scientific notation. This is simply a way of expressing a number as a
decimal with one integer to the left of the decimal point times the
appropriate power of ten. For example: The number 144881 is expressed as
1.44x10 to the 5th power. In this case the decimal is moved 5 places to the
left 1.4x10 to the 5th power. The reverse is true for numbers less than
one, example: 0.00000064 becomes 6.4x10 to the (-) eighth. We just count 8
places to the right of the decimal.
Example: Determine the Reynolds number using field data, given the
following information:
Q = 350 gpm
D = 6.415 inches
Fuel = JP-4 at 50F
Figure 1-1 is a chart that gives you Kinematic viscosity for common military
fuels. Across the bottom of the chart from left to right is the temperature
in degrees Fahrenheit. On the left hand vertical side of the chart you will
find Kinematic viscosity in centistokes. First, locate 50 F on the bottom
12-10
QM 5099
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