 In this module of oxygen delivery system we will talk about the air flow rate. As we have seen in our previous module that the air current and the air flow inside the mentor is very critical. So, while calculating the kinetic parameters of the fermentation process the supply of the air is very very critical because the supply of the air that indirectly depend upon the supply of the oxygen to the organism. If the organism is highly aerobic and then that how effect on the growth parameters. So, we have to determine that what is the flow rate. So, as concern this the air flow rate is typically reported in term of the volume per volume per minute mean VVM. The first V is the volume of the air supplied to the how much volume of the and the second V is the volume of the fermentation medium and M is the time in minute. So, if we want to calculate the flow rate in mean in term of VVM. So, the volumetric air flow rate that how much litter of the air is supplied with unit time to the fermentor and then is a liquid volume that how much is the liquid volume in litter. So, both in both case litter over litter. So, note that as concern the unit. So, that is mostly L, L and M mean per litter per litter per minute mean how much litter of the air supplied to the how much litter of the fermentation media in one minute. So, if we want to calculate if we just an example if we supply a 5 litter air to the 5 litter medium in a 1 minute then the air flow will be 5 over 5 mean 1 L L M 1 VVM. So, that is why by this way we can calculate the flow rate in fermentation medium. So, in this slide you can see that F is the F A is the flow rate of the air A is specified to that and VL V is the volume of L mean liquid and fermentation liquid. So, the ratio between F A to F VL that is basically comes in term of VVM. So, by this term we can easily calculate the flow rate. So, if we know the flow rate into that and then we know the composition of that. So, oxygen delivery system also having coupled with oxygen probe. So, oxygen probe that sense the amount of the oxygen that is in the form of dissolved that is meant by dissolved oxygen. So, the oxygen probe sense the presence of the oxygen inside the medium. So, if we want to control that dissolved oxygen in some cases then that can be controlled by two method either by the increase of the flow rate or with increase the agitation. So, different modern fermenters have coupled with the systems of cascade. So, we can maintain the dissolved oxygen by this increasing the or decreasing of the flow rate or by increasing or decreasing the impeller speed. So, by using the cascade system we can control the dissolved oxygen in any fermentation process or that is very critical. If we can maintain the dissolved oxygen which is very complex and difficult because as the fermentation process proceed increase in the number of the cells and then there is a more demand of the oxygen. So, when there is a more demand we will discuss in detail in the next chapter of aeration and agitation. Then we balance that how much oxygen is needed to respire the one glucose one mole of the glucose.