Contribution to Defining Pressure Drop/Zur Definition des Zugwiderstandes

With constant volumetric flow rate F at the end of the test specimen the pressure drop is dependent on the absolute pressure under which the volumetric flow rate is measured. The correlation between pressure drop Dp at the test specimen and volumetric flow rate F can be adequately described by

in which k is a constant for a certain object measured and p* designates the pressure under which the volumetric flow rate F is measured. p1 and p2 are the absolute pressures at the test specimen entrance and exit respectively. For the definition of draw resistance it results from this that the Coresta suggestion that p1 = 1 atm 760 Torr be determined as reference pressure is inexpedient for practical purposes. It would be more expedient to determine p* = p2 = 1 atm 760 Torr, i. e. that pressure is determined as reference pressure under which the volumetric flow rate F is measured at the end of the test specimen. The simple correction formulae resulting for this with fluctuating atmospheric pressure are quoted.