Consider a vertical 20-cm-tall flat plate at 120°C suspended in a fluid at 100°C. If the fluid is being forced past the plate from above, estimate the fluid velocity for which natural convection becomes negligible (less than 10%) in: (a) mercury (b) air (c) water.

GIVEN

? A vertical flat plate suspended in a fluid

? Plate temperature (Ts) = 120°C

? Fluid temperature (T?) = 100°C

? Fluid is being forced past the plate from above

? Plate height (H) = 20 cm = 0.2 m

FIND

? The fluid velocity (U?) for which natural convection has a less than 10% effect in

(a) mercury (b) air (c) water

ASSUMPTIONS

? Steady state

SKETCH



PROPERTIES AND CONSTANTS

From Appendix 2, Tables 26, 28 and 13


From Equation (8.55), for laminar forced convection over a flat plate, the effect of buoyancy will be

less than 10% if



Solving for the fluid velocity





The Reynolds numbers for these fluid velocities are



These Reynolds numbers are all within the laminar regime (mercury is approaching the transition to turbulence). Therefore, the use of Equation (8.55) was valid.

Physics & Space Science

You might also like to view...

A boy on a bicycle rides in a circle of radius at speed If the boy rides at the same radius by what factor must he change his speed in order to triple his centripetal acceleration?

A. 3.0 B. 0.58 C. 0.33 D. 1.7 E. 0.11 F. 9.0

Physics & Space Science

The microstructure of the grains of solid ? and ? phases that form in the lead-tin eutectic reaction is _____________ of the ? and ? phases.

Fill in the blank(s) with the appropriate word(s).

Physics & Space Science

On a PV diagram where pressure is in atmospheres and V is in liters the area is measured in liter- atmospheres. What is the number of Joules in 1.00 liter-atmosphere?

A. 101.3 B. 83.1 C. 65.2 D. 22.4 E. 15.7

Physics & Space Science

Latent Heats: How much heat must be added to a 8.0-kg block of ice at -8°C to change it to water at 14°C? The specific heat of ice is 2050 J/kg ? C°, the specific heat of water is 4186 J/kg ? C°, the latent heat of fusion of ice is 334,000 J/kg, and 1 cal = 4.186 J.

A. 780 kcal B. 140 kcal C. 180 kcal D. 810 kcal E. 730 kcal

Physics & Space Science