An agitated-film evaporator 120 mm in inside diameter contains a four-blade agitator turning at 400 rpm. It is vaporizing ethylene dichloride from a polymer solution with an average viscosity of 100 cP. The properties of the liquid film are: k= 0.15 Btu/h·ft·°F; ρ = 60 lb/ft³; c_p = 0.3 Btu/lb·°F. 

(a) Estimate the heat-transfer coefficient of the agitated liquid film. 

(b) Compare your result with the data in Table 16.1 and comment on the discrepancy, if any.

Table 16.1

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TABLE 16.1 Typical overall coefficients in evaporators Type Long-tube vertical evaporators Natural circulation Forced circulation Agitated-film evaporator, newtonian liquid, viscosity I cP IP 100 P Overall coefficient U W/m². "C 1.000-2.500 2,000-5.000 2,000 1,500 600 Btu/ft-h-F 200-500 400-1,000 400 300 120