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Effect of radial temperature variation on axial mixing in pipes
Author(s) -
Hawthorn R. D.
Publication year - 1960
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690060319
Subject(s) - laminar flow , reynolds number , mechanics , thermodynamics , turbulence , mixing (physics) , thermal diffusivity , isothermal process , axial compressor , flow (mathematics) , laminar flow reactor , isothermal flow , chemistry , viscosity , tube (container) , pipe flow , materials science , open channel flow , physics , composite material , gas compressor , quantum mechanics
In a pipe reactor axial mixing results in a distribution of residence times of fluid elements in the reactor. Taylor and others have discussed methods of predicting the extent of axial mixing for isothermal flow in pipes; however, in a reactor the heat of reaction and its supply or removal at the wall can cause significant radial variation of temperature and temperature‐dependent physical properties. Thus the velocity profile in a reactor may differ from that in a pipe through which fluid flows at constant temperature. This paper presents an analysis of the effects of radial temperature variations on effective axial diffusion coefficients. In laminar flow it is found that radial temperature variation may increase or decrease the effective diffusivity two‐ to threefold from that calculated for isothermal flow. At Reynolds numbers greater than 10,000 the diffusivity calculated for constant temperature flow does not differ significantly from that for flow through a reactor tube (with radial temperature variation) at the same Reynolds number, calculated with the viscosity evaluated at the wall temperature. In turbulent flow at Reynolds numbers less than 10,000, the effect of radial temperature variation is important but can be estimated only roughly.