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Reactor Design II

Reactor Design II. Heat transfer. Metabolic Heat Production. When cells grow they also produce a heat of reaction of about 2.3 kcal/gram of cells produced. Heat Production Rate. The heat production rate can be related to the rate of cell growth or the O2 consumption rate (OUR).

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Reactor Design II

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  1. Reactor Design II Heat transfer

  2. Metabolic Heat Production • When cells grow they also produce a heat of reaction of about 2.3 kcal/gram of cells produced.

  3. Heat Production Rate • The heat production rate can be related to the rate of cell growth or the O2 consumption rate (OUR).

  4. Scale-up Problem • Removing the heat from the reactor becomes more difficult the larger the reactor. 10 x

  5. Production and Removal Rates • Heat is produced at the same rate per liter regardless of scale • Heat is removed according to the available surface area.

  6. Small vs Large Reactor Design Issue

  7. Surface Area vs Volume • For jacketed reactors, the surface area per liter of reactor drops at a rate proportional to V-1/3 SA = K/V1/3 At large volumes (over 1000 L) this leads to difficulties removing the metabolic heat.

  8. Heat Management • There are 3 reasonable options for managing the heat. • Increase the heat transfer area Rate of heat removal = UA(Treactor – Tjacket) • Increase the temperature difference (by lowering Tjacket) • Reduce the heat production rate by growing the cells more slowly (reduce m)

  9. Jacket Heat Transfer Coefficient • A reasonable overall heat transfer coefficient between the jacket and tank is: U = 100 BTU/ft2-F-hr

  10. Jacket Area • The area for heat transfer in reactors is dictated by the area of the jacket. Jacket area

  11. Cooling Coils • To add more heat transfer surface area to a given reactor size, cooling coils are added. Cooling coils

  12. Cooling Coils • Cooling coils have some negatives • The job of cleaning the reactor and proving it is clean is much harder • The coils may create dead zones to getting oxygen to the cells • The coil material usually cannot be copper so conductive heat transfer may be an issue.

  13. Cooling Liquid • The cooling solution temperature is limited • Tap water minimum is about 10 C. • Glycol chilling loops can go down to -20 C, but are expensive to operate. Cross contamination must be avoided.

  14. Growth Rate vs Heat Production • The heat production rate is lowered by lowering the specific growth rate Rate of heat production (per unit volume)= mXDH Heat production per gram cells is fairly constant m drops 50% for each 8 -10 C temperature drop Cell mass per unit volume

  15. Growth Rate • Mammalian cells grow slowly and rarely have heat production issues • It may be better to grow bacterial cells at lower temperature to prevent protein misfolding.

  16. Summary • In large reactors, metabolic heat management becomes as or more important than O2 transfer. Consideration must be made of: • Adding heat transfer area • Changing cooling fluid • Growing cells at a slower rate

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