Question

Caster oil at ${25}^{o}C$ flows at a velocity of 0.1m/s past a flat plate, in a certain process. If the plate is 4.5m long and is maintained at a uniform temperature of ${95}^{o}C$ the thermal boundary layer thickness if the following data is available
$\rho =956.8KG/m^3,\alpha =7.2\times {10}^{-8}{m}^2/s,$
$K=0.213W/mK,v=0.65\times {10}^{-4}{m}^2/s$
Pr = 903,
$\delta$ = Thickness of hydrodynamic boundary layer = 270.4mm

• A. 28 mm
• B. 900 mm
• C. 0.9 mm
• D. 99.8 mm

Answer 1

The correct option is A 28 mm

$Re=\frac{VL}{v}$

$=\frac{0.1\times 4.5}{0.65\times {10}^{-4}}=6923<5\times {10}^5\left(laminar\right)$

For external and laminar flow

$\frac{{\delta }_h}{{\delta }_t}=(Pr{)}^{\frac{1}{3}}$

${\delta }_t=\frac{{\delta }_h}{(Pr{)}^{1/3}}$

$=\frac{270.4\times {10}^{-3}}{(903{)}^{1/3}}=27.97\times {10}^{-3}m$

= 28 mm