The Lewis symbol

would be characteristic of which group?



a.

6A



b.

2A



c.

3A



d.

5A

---

a

Physics & Space Science

Suppose a thin vertical flat plate 60-cm-high and 40-cm-wide, is immersed in a fluid flowing parallel to is surface. If the plate is at 40°C and the fluid at 10°C, estimate the Reynolds number at which buoyancy effects are essentially negligible for heat transfer from the plate if the fluid is: (a) mercury, (b) air, and (c) water. Then calculate the corresponding fluid velocity for the three fluids.

GIVEN
? A thin flat plate immersed in a fluid flowing parallel to its surfaces
? Plate height (H) = 60 cm = 0.6 m
? Plate width (w) = 40 cm = 0.4 m
? Plate temperature (Ts) = 40°C
? Fluid temperature (T?) = 10°C
FIND
? The Reynolds number and corresponding fluid velocity (U?) for buoyancy effects to be negligible,
if the fluid is: (a) mercury, (b) air, (c) water
ASSUMPTIONS
? Steady state conditions
SKETCH

PROPERTIES AND CONSTANTS
From Appendix 2, Tables 26, 28 and 13 at the mean temperature of 25°C

The thermal expansion coefficient of mercury can be estimated from

A CD player uses a laser with wavelength 900 nm. If the CD has a plastic coating with index 1.50, what is the wavelength in the plastic?

a. 600 nm c. 1350 nm b. 500 nm d. 750 nm

A 30-cm-OD pipe with a surface temperature of 90°C carries steam over a distance of 100 m. The pipe is buried with its center line at a depth of 1 m, the ground surface is –6°C, and the mean thermal conductivity of the soil is 0.7 W/(m K). Calculate the heat loss per day, and the cost of this loss if steam heat is worth $3.00 per 106 kJ. Also, estimate the thickness of 85% magnesia insulation necessary to achieve the same insulation as provided by the soil with a total heat transfer coefficient of 23 W/(m2 K) on the outside of the pipe.

GIVEN

FIND
(a) The heat loss per 24 hour day
(b) The value of the lost heat
(c) The thickness of 85% magnesia insulation necessary to achieve the same insulation
ASSUMPTIONS
Steady state conditions
Uniform thermal conductivity
Two dimensional heat transfer from the pipe
SKETCH

Since the big bang, but before now, a time existed where matter was not dominant

a. True b. False Indicate whether the statement is true or false