CHAPTER 4 Mass Transport in Bioreactor
Chapter 4 Mass Transport in Bioreactor O2 O2
4.1.The oxygen demand The oxygen demand ro=Xgo=X Liquid Bulk Cells with liquid film :Gas: phase liquid phase Gas film Liquid film Schematic presentation of the oxygen pathway from the bulk gaseous phase to the enzymes in the cell.kl-k5 represent mass transfer constants
x o o o Y r Xq X / = = 4.1. The oxygen demand The oxygen demand
4.2.The oxygen transport Gas phase Liquid film Bulk liquid C=C米 0<C<C￥ C=0 一6 Distance Oxygen concentration gradients at the gas-liquid interface.Cg is the oxygen concentration in the gas phase(about 300 mg/L).At the liquid side of the interface(=0)the dissolved oxygen concentration C*is given by Henry's law.It is about 7 mg/L in water in equilibrium with air.Depending on the oxygen consumption rate in the liquid different concentration gradients(a-d)will appear through the liquid film with the thickness
4.2. The oxygen transport
A-surface (m2) eql Oxygenfte-DA 6-thickness(m) AC-the concentration difference over the film(mol m-3) D-the diffusivity of the gas in the film(m2 h-1) eq2 KL- 2.8↓ eq3 △C=C*-C △c-The force(molm3) eq4a=∑A/V a-The specific interface area(m-) By substituting eqs.2-4 into eq.1,OTR is given by: OTR=KLa(C*-C)OTR-The oxygen transfer rate(mol m3h1)
OTR-The oxygen transfer rate(mol m-3 h-1) KL = D C =C*−C a = A/V A-surface (m2 ) δ-thickness (m) △C-the concentration difference over the film (mol m-3 ) D- the diffusivity of the gas in the film (m2 h -1 ) OTR=KL a (C*-C) 1. D 2.δ C Oxygenflux DA = ΔC-The force( mol m-3) a-The specific interface area(m-1 ) By substituting eqs.2-4 into eq.1 , OTR is given by: eq1 eq2 eq3 eq4
OTR=K4C-C K air,stirrer and speed,viscosity ◆A small gas bubble ◆ C* oxygen carrier temperature and pressure ◆C recom binent DNA
OTR=KL a (C*-C) ◆ KL air, stirrer and speed, viscosity ◆ A small gas bubble ◆ C* oxygen carrier temperature and pressure ◆C recombinent DNA