Heat Transfer
Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid

for fluids in tubulent flow
when Grashhoff number is very important
none of the listed here
for fluids in laminar flow

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Heat Transfer
In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m².s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m²/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is

4000
5000
6000
2000

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