During the volcanic eruption of Mt. Pelee in 1902, an incredibly hot "burning cloud" rolled down the mountain and incinerated the town of Saint-Pierre. From the damage done, the temperature in the cloud was estimated at 700°C. If the air temperature
was 20°C and a mole of air is 29 grams, estimate the molecular weight of the gas in the "burning cloud" that made it heavier than the surrounding air. (As a follow-on, estimate the most probable composition of the cloud. Some typical volcanic gases are H2S, SO2, H2SO4, CO2, NO.)
96, H2SO4 (sulfuric acid)
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Cathode rays are now known to be
A) electrons. B) visible light rays. C) protons. D) x-rays. E) short wavelength light rays.
When two elements form a eutectic phase diagram, in the eutectic reaction the atoms of the solid elements _____________.
Fill in the blank(s) with the appropriate word(s).
A light oil flows through a copper tube of 2.6-cm-ID and 3.2-cm-OD. Air flows perpendicular over the exterior of the tube as shown in the following sketch. The convection heat transfer coefficient for the oil is 120 W/(m2 K) and for the air is 35 W/(m2 K). Calculate the overall heat transfer coefficient based on the outside area of the tube (a) considering the thermal resistance of the tube, (b) neglecting the resistance of the tube but assume that fouling factors of 0.0009 (m2 K)/W and 0.0004 (m2K)/W have developed on the inside and on the outside, respectively.
GIVEN
• Air flow over a copper tube with oil flow within the tube
• Tube diameters: Inside (Di) = 2.6 cm = 0.026 m
Outside (Do) = 3.2 cm = 0.032 m
• Convective heat transfer coefficients: Oil h i= 120 W/(m2 K) Air h o= 35 W/(m2 K)
• Fouling factors: Inside (Rdi) = 0.0009 (m2 K)/W
Outside (Rdo) = 0.0004 (m2 K)/W
FIND
• The overall heat transfer coefficient based on the outside tube area (Uo),
(a) considering the thermal resistance of the tube, and
(b) neglecting the tube resistance
ASSUMPTIONS
• Uniform heat transfer coefficients
• Variation of thermal properties is negligible
SKETCH
PROPERTIES AND CONSTANTS
the thermal conductivity of copper (k) = 392 W/(m K) (at 127°C)
Two small charged objects repel each other with a force F when separated by a distance d. If the charge on each object is reduced to one-fourth of its original value and the distance between them is reduced to d/2 the force becomes:
A) F/16 B) F/8 C) F/4 D) F/2 E) F