Page V ■ 20 
Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
: \ 
D— -pu'c' 
(5.25) 
The velocity/concentration correlation, like the equivalent velocity/enthalpy correlation of 
equation 5.17, also follows a gradient hypothesis. In this case turbulent concentration diffusivity 
is calculated by: 
D t = 
M-t 
Sc T 
(5.26) 
Both the laminar and turbulent Schmidt numbers have a value of 1 .0. 
In this project, levels of the two considered animal emission gases, namely C02 and NH3, were 
determined by the analysis of the distribution of such a concentration throughout the cages and 
room volume. 
In the cases where the whole animal room was considered, the levels of C02 and NH3 generated 
by the animals were small enough such that the concentration could be represented as a passive 
concentration. In particular, the density change produced by the presence of the gases could be 
considered insignificantly small. However, in the cage wind tunnel simulations, the level of C02 
injected into the cages was such that the gas affected the density of the gas/air mixture. The 
density of the gas/air mixture in these cases was calculated as follows: 
The density formula is based on the Ideal Gas Law: 
Density = 
effective _ molecular _ weight x (T + datum_pressure) 
Rx(T + datum_temperature) 
where R (universal gas constant) = 8314.4 
datum_pressure = 1.0133E5 Pa 
datum_temperature = 273.13 K 
(5.27) 
When the molecular weight of the concentration is different to that of the air, the effective 
molecular weight is calculated as: 
