Reynolds number sheet thickness

The thickness of the liquid sheet on the drum is independent of the pressure applied between the applicator roller and the drum. It depends largely on the viscosity and the surface tension of the liquid as well as on the ratio of rotational speeds of the drum and roller and the nip width. A stable thickness can be achieved for medium viscosity shear-thinning liquids at moderate Reynolds number. Re (the ratio between momentum and viscous forces), low capillary number, Ca (the ratio of the viscous force and surface tension), and low rotational speed ratio." A smaller Ca (<0.01) or a larger surface tension extends coating stability to higher rotation speeds. A stable sheet is established between a minimum and a maximum drum speed and at a critical ratio of rotational speeds of the applicator roller and the drum. The sheet formed beyond the eritical point is unstable, leading to ribbing and may entrain air bubbles as well especially if the liquid contains excessive surfactants." This rarely occurs in drum dryer operation because both the rotation speed and the ratio of rotation speeds are low (linear speed of drum surface rarely exceeds 0.3 m/s). 

The fin plates are shaped from 0.15 to 0.6 mm thick aluminium sheets by periodical distortion. The fin height, i.e. the clearance between the neighbouring partition plates, ranges between 3.8 and 12 mm. The distortions form channels with diameters ranging between 1.2 and 4.5 mm. The Reynolds number calculated on the basis of this diameter lies between about 500-10 000, i.e. the flow is in the transition range between laminar and turbulent In order to improve the turbulence and thus the heat transfer, additional obstacles are installed. To this end, fins are either perforated or are serrated and periodically displaced against each other with a certain clearance. 

This is the case of a square rubber sheet 1 cm thick with 10-cm sides, initially at 160°C, immersed in stirred air at 20°C on both sides, in a vertical position. The Reynold s number should be used and evaluated, and from the valne obtained for this number, it is possible to calculate the Niisselt number. 

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