Document ID: chunk:federal_register_of_legislation:F2023L00129:reg:13:p50
Version: federal_register_of_legislation:F2023L00129
Segment Type: reg
Provision Reference: reg 13 (pt 50/56)
Character Range: 430823–433675

shall be plotted as a function of venturi inlet pressure. For critical (choked) flow, Kv will have a relatively constant value. As pressure decreases (vacuum increases), the venturi becomes unchoked and Kv decreases, which indicates that the CFV is operated outside the permissible range.
9.5.3.1. Data analysis
 The airflow rate (qvCVS) at each restriction setting (minimum 8 settings) shall be calculated in standard m3/s from the flowmeter data using the manufacturer's prescribed method. The calibration coefficient shall be calculated from the calibration data for each setting as follows:
  (88)
 Where:
qvCVS is the airflow rate at standard conditions (101.3 kPa, 273 K), m3/s
T is the temperature at the venturi inlet, K
pp is the absolute pressure at venturi inlet, kPa
 The average KV and the standard deviation shall be calculated. The standard deviation shall not exceed ±0.3 per cent of the average KV.
9.5.4. Calibration of the subsonic venturi (SSV)
 Calibration of the SSV is based upon the flow equation for a subsonic venturi. Gas flow is a function of inlet pressure and temperature, pressure drop between the SSV inlet and throat, as shown in equation 53 (see paragraph 8.5.1.4.).
9.5.4.1. Data analysis
 The airflow rate (QSSV) at each restriction setting (minimum 16 settings) shall be calculated in standard m3/s from the flowmeter data using the manufacturer's prescribed method. The discharge coefficient shall be calculated from the calibration data for each setting as follows:
  (89)
              Where:

                  QSSV is the airflow rate at standard conditions (101.3 kPa, 273 K), m3/s

                  T is the temperature at the venturi inlet, K

                  dV is the diameter of the SSV throat, mm

rp is the ratio of the SSV throat to inlet absolute static pressure =
rD is the ratio of the SSV throat diameter, dV, to the inlet pipe inner diameter D
 To determine the range of subsonic flow, Cd shall be plotted as a function of Reynolds number Re, at the SSV throat. The Re at the SSV throat shall be calculated with the following equation:
                      (90)
               With

                (91)

               Where:

                  A1 is 27.43831 in SI units of

                  QSSV is the airflow rate at standard conditions (101.3 kPa, 273 K), m3/s

                  dV is the diameter of the SSV throat, mm

μ is the absolute or dynamic viscosity of the gas, kg/ms
b is 1.458 x 106 (empirical constant), kg/ms K0.5
S is 110.4 (empirical constant), K
 Because QSSV is an input to the Re equation, the calculations shall be started with an initial guess for QSSV or Cd of the calibration venturi, and repeated until QSSV converges. The convergence method shall be accurate to 0.1 per cent of point or better.
 For a minimum of sixteen points in the region of subsonic flow,