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Fig. 7.3. The use of heat transfer surfaces normal to the air flow direction within packed beds (a) as used in the Prophyta bioreactor (Luth and Eiben 1999) and (b) as used in the PlaFractor bioreactor (Suryanarayan and Mazumdar 2000; Suryanarayan 2003). In each case the substrate beds are in light gray and the heat transfer plates are in dark gray. The white regions represent empty spaces for air flow. Solid arrows represent the flow of cooling water and dashed arrows represent the flow of air

Plafractor

Fig. 7.4. The phenomenon of channeling. (a) The desirable situation, with uniform flow across the whole cross section of the bed. (b) Preferential flow between the bed and the wall in the case in which the bed pulls away from the wall. (c) Preferential flow through a crack in the bed. (d) Microscale view of a channel, showing how the preferential flow through the channel arises due to two sources of resistance to flow through the bed of particles, namely the tortuous path through the bed and the fact that the space between the particles is partially filled with biomass. Note that in extreme cases of channeling, there may be no bulk flow through the inter-particle spaces, with mass transfer being limited to diffusion and heat transfer to conduction

Fig. 7.4. The phenomenon of channeling. (a) The desirable situation, with uniform flow across the whole cross section of the bed. (b) Preferential flow between the bed and the wall in the case in which the bed pulls away from the wall. (c) Preferential flow through a crack in the bed. (d) Microscale view of a channel, showing how the preferential flow through the channel arises due to two sources of resistance to flow through the bed of particles, namely the tortuous path through the bed and the fact that the space between the particles is partially filled with biomass. Note that in extreme cases of channeling, there may be no bulk flow through the inter-particle spaces, with mass transfer being limited to diffusion and heat transfer to conduction

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