Page 137 - Biomedical Engineering and Design Handbook Volume 2, Applications

116 MEDICAL DEVICE DESIGN

TABLE 4.2 Gas Conversion Factors (Volume and Flow)
Multiply by
To convert from To Formula Typical value
BP − pH O 310
2
ATPS BTPS ⋅ 1.080
BP − 47 273 + T
BP − pH O 273
2
STPD ⋅ 0.892
760 273 + T
BP − pH O
2
ATPD 0.971
BP
BP 310
ATPD BTPS ⋅ 1.113
BP − 47 273 + T
BP 273
STPD ⋅ 0.919
760 273 + T
BP
ATPS 1.030
BP − pH O
2
BP − 47 273
BTPS STPD ⋅ 0.826
760 310
BP − 47 273 + T
ATPS ⋅ 0.926
BP − pH O 310
2
BP − 47 273 + T
ATPD ⋅ 0.899
BP 310
760 310
STPD BTPS ⋅ 1.210
BP − 47 273
760 273 + T
ATPS ⋅ 1.121
BP − pH 2 O 273
760 273 + T
ATPD ⋅ 1.088
BP 273
BP = barometric pressure
T = temperature (°C)
ATPS = ambient temperature and pressure, saturated
ATPD = ambient temperature and pressure, dry
STPD = standard temperature and pressure, dry
BTPS = body temperature and pressure, saturated
The “typical values” assume a barometric pressure of 760 mmHg and a temperature of 24°C.
Standard pressure is 760 mmHg and standard temperature is 0°C (= 273 K).
Body temperature is 37°C (= 310 K).
Under ideal conditions, seldom encountered, gas flowing through a straight tube would exhibit
only laminar flow (the absence of all turbulence). In laminar flow, every molecule in the gas stream
has only axial velocity, and moves only in the direction of the bulk flow. Under conditions of com-
plete turbulence, the gas molecules move in all directions, with no net flow. Flows encountered in
practice exhibit some characteristics of both laminarity and turbulence (Fig. 4.3). Factors tending to
favor increasing turbulence include decreasing tube radius, increasing gas density, and increasing
bulk flow rate. Turbulence is increased by sharp angles and geometric obstructions in the gas stream.
Laminar flow is increased by having a straight, smooth-bore tube with a length at least 6 times its
diameter prior to flow measurement.