Systems with Dilute Raining Particles

Systems with Dilute Raining Particles 

In principle, practically all enhancement in convective heat or mass transfer is derived at the expense of increased pressure drop in moving the gas at 

This is shown schematically in Fig. 41. The downwardly directed curve on the left-hand side of Fig. 41 for the fixed bed implies that increased flow is by no means sufficient to raise the heat or mass-transfer factor proportionately to the increased pressure drop. Similarly, for single particles, neither a larger particle diameter nor a higher flow rate could compensate for the relatively limited increase in the transfer factor. 

Between the fixed-bed and single-particle curves lies the region for fluidized solids. For ideal fluidization, the flow rate can be varied by one to two orders of magnitude without affecting the value of NuPr 1/3 or ShSc 1/3, thus lead- 

It is thus evident that for processes in which resistance at the particle-fluid interface is the dominant rate-controlling step—when the value of hdp/ks or hDdp/Ds is small—operation near the single-particle region, that is, dilute-phase G/S contacting, is the preferred choice. 

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VIII. Systems with Dilute Raining Particles... 

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