E-PolyLearning

526. The purpose of providing expansion bellows in the shell of tubular exchanger is to
a. increase the heating load.
b. impart structural strength.
c. account for the uneven expansion of shell and tube bundles.
d. facilitate increase of shell length, if needed.
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Answer: (c).account for the uneven expansion of shell and tube bundles.

527. Grashhoff number is given by
a. gD³.β.Δtρ²/μ²
b. gD²βΔtρ/μ²
c. gD²βΔtP²μ
d. gD³βΔtP²/μ
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Answer: (a).gD³.β.Δtρ²/μ²

528. The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m².K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m².K. The overall heat transfer co-efficient at this time is
a. 1200W/m².K
b. 894W/m².K
c. 333W/m².K
d. 287 W/m².K
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Answer: (c).333W/m².K

529. 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
a. 2000
b. 4000
c. 5000
d. 6000
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Answer: (c).5000