A piece of wood 350 mm × 350 mm and 15 mm thick conducts heat through its thickness under steady state conditions. The rate of heat flow is measured to be 14.0 watts when the temperature difference is 28 C°
Determine the coefficient of thermal conductivity for this wood A) 9.2 × 10-4 J/(m?s?C°)
B) 270 J/(m?s?C°)
C) 16 J/(m?s?C°)
D) 0.061 J/(m?s?C°)
E) 33 J/(m?s?C°)
D
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The primary method of joining thermosetting polymers is with ___________.
Fill in the blank(s) with the appropriate word(s).
In the context of supernovae, briefly explain how synchrotron radiation is produced
What will be an ideal response?
A shell-and-tube heat exchanger with the characteristics given below is to be used to heat 27,000 kg/h of water before it is sent to a reaction system. Saturated steam at 239 kPa absolute pressure is available as the heating medium and will be condensed without subcooling on the outside of the tubes. From previous experience, the steam-side condensing coefficient can be assumed constant and equal to 11,300 W/(m2 K). If the water enters at 16°C, at what temperature will it leave the exchanger? Use reasonable estimates for fouling coefficients. Exchanger specifications
- Tubes – 2.5-cm-OD, 2.3-cm-ID, horizontal copper tubes in six vertical rows
- Tube length = 2.4 m
- Total number of tubes = 52
- Number of tube-side passes = 2
GIVEN
Shell-and-tube heat exchanger - water in copper tubes, saturated steam is shell Water flow rate m w= 27,000 kg/h = 7.5 kg/s Steam pressure = 2.36 atm = 239 kPa Steam-side coefficient h o= 11,300 W/(m2 K) Water entrance temperature: Tw,in = 16°C Tube diameters
? Do = 2.5 cm = 0.025 m
? Di = 2.3 cm = 0.023 m Tube length (L) = 2.4 m Number of tubes (N) = 52 Number of tube passes = 2
FIND
The water exit temperature (Tw,out)
ASSUMPTIONS
Length given is total tube length for both passes
SKETCH
PROPERTIES AND CONSTANTS
the temperature of saturated steam at 239 kPa (Ta) = 125°C
for water at 20°C
Thermal conductivity (k) = 0.597 W/(m K)
Kinematic viscosity (?) = 1.006 × 10–6 m2/s
Prandtl number (Pr) = 7.0 Density (?) = 998.2 kg/m3 Specific heat (cp) = 4182 J/(kg K), the thermal conductivity of copper (kc) = 392 W/(m K) at 127°C
The most striking example of solar variability was the
A) Dust Bowl drought of the 1930s. B) Maunder Minimum from 1645-1715. C) Sporer Minimum that doomed the Anasazi. D) fall of Rome. E) Joseph's seven lean years in the Old Testament.