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Can the tank breathe for your cells?
Microbes making an API burn oxygen as fast as they grow. A fermenter's whole job is to dissolve oxygen into the broth faster than they use it, and carry away the heat they make. Choose an illustrative organism preset, size the vessel below, then play the batch clock. The prescribed growth curve demonstrates engineering relationships; it does not predict a real batch.
Running conditions
How the fermenter is sized
From the cells' oxygen appetite to the motor, the cooling and the sterilization time. Hover a step to light up the part it decides.
Oxygen: supply vs demand
Oxygen barely dissolves in water (≈ 7 mg/L at 30 °C, against a demand of grams per litre per hour). Bubbles and impellers have to refill it many hundreds of times an hour.
Oxygen the tank can deliver at each speed
Four levers when oxygen runs short
Speed raises kLa fastest but power grows with speed³. Air rate helps less and brings foam. Head pressure increases oxygen solubility and compressor duty: +0.5 bar ≈ +35 % driving force. Oxygen enrichment changes gas supply and operating costs; it is outside this air-only model.
Heat: the hidden limit
Every mole of oxygen the cells use releases about 460 kJ. At high cell density the cooling, not the oxygen, often sets the size of the batch.
Can the jacket keep up?
Scaling up from the pilot plant
Grow the same geometry from a pilot vessel and you cannot keep everything the same. Pick a rule and see what it costs.
Why it matters
Compare each rule against the stated pilot operating point. Constant power per volume, tip speed, estimated kLa and estimated mixing time generally require different speeds. Values at the speed limits are marked as unmatched. Validate transfer, mixing and cooling at the target scale.
Sterilization in place
Explore an illustrative isothermal hold calculation: assumed starting bioburden 10⁶ spores/mL, expected survivors 10⁻³ per vessel, and D₁₂₁ = 2 min. Heat-up, cool-down, cold spots and process-specific resistance are excluded. This is not a validated sterilization cycle.
Inside the fermenter
Tap a part to fly the camera to it.
Method: O₂ solubility from Henry's law with a 10 % salting-out allowance and a log-mean driving force over the liquid height; kLa from Van't Riet (1979) for coalescing or non-coalescing broths with a (μ)-0.2 viscosity correction; gassed Rushton power after Calderbank; flooding after Nienow; mixing time after Nienow/Grenville; metabolic heat 460 kJ/mol O₂ (Cooney); jacket U ≈ 450 W/m²K, coils ≈ 900 W/m²K; Del factor with D121 = 2 min for G. stearothermophilus. First-pass design numbers for learning and budgeting; validate against your vendor's and your process data.
Model assumptions & sources
Illustrative organism presets; normal dry-air flow at 0°C and 1 atm. Oxygen transfer and exhaust composition are solved together, with oxygen consumption bounded by the inlet supply. The dry-gas balance neglects CO₂ and water vapour. Air saturation is referenced to headspace pressure; hydrostatic pressure varies through the liquid.
kLa correlations, viscosity factors, turbulent power numbers, flooding screens and mixing-time estimates are assumptions. Production-scale values are extrapolations. Peak cooling duty uses requested aerobic demand; the batch heat gauge uses achievable oxygen uptake. Evaporative cooling is excluded. Coil geometry is illustrative.
Sterilization is an assumed hold-exposure example, not a cycle specification. Motor estimates require vendor confirmation of torque, starting loads and service margins.