Particle Loss Mechanisms
There are several factors affecting particle loss in transport tubing and these have been discussed in Application Note 81(3). A function of these factors is to ensure that turbulent flow is maintained, thus ensuring that particles are transported with maximum efficiency. The Reynolds number (Re) is a function of turbulence and it is widely recognized that turbulent flow exists where Re is greater than 4000(5).
Re was calculated for each of the three Lasair III counters under review as well as two, fixed location Airnet II particle sensors.
It can be seen in Table 2 that turbulent flow exists in the transport tubing to the Lasair III particle counter, irrespective of flow rate chosen. This verifies that the losses due to particle transport are minimized. It does not mitigate from all losses however, and therefore further testing is required to demonstrate empirically what those losses are.
V : fluid velocity
D : tube diameter
ρ : fluid density
µ : fluid viscosity
At 20 °C and 101.325 kPa, dry air has a density of 1.2041 kg/m3.
At 15 °C, the viscosity of air is 1.78 x 10-5 kg/(m∙s).
Laminar flow occurs when Re < 2300 and turbulent flow occurs when Re > 4000.
J.P. Holman. Heat Transfer, McGraw-Hill, 2002, p. 207.
The next installment will outline the testing parameters used to demonstrate losses in 2 m tubing. To download the full paper, click here.
- ISO 14644-1, Cleanrooms and associated controlled environments – Part 1: Classification of air Cleanliness, 2015.
- EU Guidelines to Good Manufacturing Practice, Medicinal Products for Human and Veterinary Use, Annex 1 – Manufacture of Sterile Medicinal Product, 2008.
- An Analysis of Acceptable Particle Losses in Transport Tubing, PMS Application Note 81 (2007).
- Environmental Monitoring of Cleanrooms in Vaccine Manufacturing Facilities, World Health Organization, Final Draft March, 2010.
- J P Holman, Heat Transfer, McGraw-Hill, 2002, p 207.