Which of the following is not suitable for studying biological material?
(a) An optical microscope
(b) A high-voltage TEM
(c) A STM
(d) An AFM
(c) A STM
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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)
Astronomers use roman numerals to indicate the ionization state of a gas. Ionized hydrogen is indicated by which of the following symbols?
A) H II B) H2 C) H I D) E) H III
The walls of cells are referred to by biologists as
A) linings B) coats C) shells D) membranes
An object of mass m with a certain initial speed on a horizontal surface comes to rest after traveling a distance of 10 m
If the coefficient of kinetic friction between the object and the horizontal surface is 0.20, what is the initial speed of the object? Use g = 10 m/s2. A) 9.8 m/s B) 6.3 m/s C) 3.6 m/s D) 7.2 m/s E) 8.9 m/s