 In this module, we will talk about the third part of the oxygen delivery system. First part was the compressor, second was the air sterilization system and the third one is the sparser. What is sparser? And what is the role in oxygen delivery system? The air sparser is used to break the incoming air into the small bubbles. So, when there is a steam of the air coming through compressor and then entered through air sterilization system and then enters into the fermentation medium. So there are the small pores or the slit either that have a round either they may be a slit. So they are different design and the shape of the sparser. In a daily life you can see the stove. So how the gas, natural gas comes out from your stove. So you have a different design and different shape of that just to give equal distribution in the hole. So by the same way in fermentation system the sparser having the same having the equal distribution of the air into the fermentation vessel and having giving a proper size and the shape of the bubbles. So in case of the pores sparser, porous sparser sometime it the sparser is a slit like. So there are the different types. So we can say that the sparser is basically the device that control the bubble size. But later on these bubble can be further having the link with the impeller system as we have talked about while talking the agitation system and their role of radial impellers and axial impellers and what are the shear effect to creating the bubble size. But the sparser has its own role for making the bubbles properly and equally distributed into the fermentation medium. So in this slide you can see that here you can see there is a sparser and that having 1, 2, 3, 4 and 5 different points from where the air can oozes out. And the upper to this aeration sparser then there is a impeller agitation system. So when the sparsers facilitate to distribute the air bubbles into the fermentation media and then that have a proper distance from the impeller system that will control their bubbles and their distribution into side that. So that why when they collide with this system then there is a shear effect. So that is why this whole system aeration and agitation system work together. So as concerned the sparser ring that should be exactly situated below the impeller. So that is why that help to have a direct contact with the air bubbles that is why that help and to facilitate the breakdown of those impeller into the smaller size. So that is the role of placing the sparser just below the impellers. So as concerned the shear forces that an impeller generate play a major role in determining the bubble size. So if the impeller speed as concerned the distance from the sparser to the impellers on other hand the speed of the impeller is also having a role in the formation of the bubble size as well as the distribution of the bubbles. So if we say in this slide you can see that just imagine if the impeller speed is very slow and then the air bubbles when they exit and oozes out from the sparser they just go just and having a less time to retain inside the fermentation medium. But in case when the impeller speed is very high what happen then they facilitate having the equal distribution and a proper distribution of the air bubbles. So when there is a proper distribution and then each bubble have a maximum retaining time into the fermentation medium. So when there is a less time of the retention of the air bubble into the medium it means then there is a less chance of the oxygen solubility. But when there is a more time retained in the fermentation medium then there is a more chance of oxygen solubility inside the fermentation medium. So because the oxygen delivery system the more object behind this is just to supply the oxygen demand. So if the air bubble just passes through the fermentation medium just without dissolving the oxygen then there is no need of that. So that is why it is very critical the speed of the impellers and the pressure inside the sparser. So another consequence of the two slow impeller speed is the flooded impellers because sometimes when there is the slow speed and then there is a more flood of the air bubbles and there is a column of the air is produced and that is also having less chance of the contact of the air bubbles to the fermentation medium. So under these conditions the bubble will accumulate and collects under the impeller leading to the formation of the large bubbles. So the small bubbles aggregate to having a form of bigger bubbles. So when there are bigger bubbles then there is a less surface area. So that is the way. So in other case a similar phenomena will happen when a ratio rate is too high in that case then oxygen transfer efficiency will also low. So the air pressure and then the impeller speed these are the both factors which can either have a positive fact or a negative fact in case of the optimum condition then the proper working of the oxygen delivery system along with the combination of the impeller speed in a fermentation vessel.