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Multiple roll systems: Residence times and dynamic response
Author(s) -
Benjamin D. F.,
Anderson T. J.,
Scriven L. E.
Publication year - 1995
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.690411004
Subject(s) - coating , residence time distribution , residence time (fluid dynamics) , limiting , evaporation , materials science , residence , flow (mathematics) , mechanics , process engineering , composite material , mechanical engineering , engineering , thermodynamics , physics , geotechnical engineering , demography , sociology
In roll coating as in other coating processes the coating liquid often suffers changes in properties on the time of the coating flow, that is, from fractions of a second upward depending on the amount of recirculation and recycling. The agents of change may be chemical reaction, colloidal aggregation, or evaporation. Hence the mean residence time and the residence time distribution of the liquid are important to designers and operators of coating processes. Here, building on the examination of roll‐coating systems by Benjamin et al. (1995), the residence times of liquid coated by representative arrays of multiple rolls in the “forward roll” mode and relatively starved feed condition (neglecting the possibly significant effects of “rolling banks” and other internal recirculations when they are present) are analyzed. The dynamic response of these transfer coaters to step changes in the feed gap and to periodic gap changes, as from roll and bearing run‐out, are also analyzed. No reports of operating or laboratory experiments are available for comparison. Nevertheless the results make plain how these quality‐limiting features may depend don the number of rolls used; their sizes, speed, and arrangement, and the properties of the coating liquid.