An ice chest (see sketch) is to be constructed from Styrofoam [k = 0.033 W/(m K)]. If the wall of the chest is 5-cm-thick, calculate its R-value in (m2 K)/(W cm).
GIVEN
- Ice chest constructed of Styrofoam, k = 0.0333 W/(m K)
- Wall thickness 5 cm
FIND
(a) R-value of the ice chest wall
ASSUMPTIONS
(a) One-dimensional, steady conduction
SKETCH
From Section 1.6 the R-value is defined as
The thermal conductivity in engineering units is
and the thickness is
From the problem statement, it is clear that we are asked to determine the R-value on a ‘per-icm’
basis. Dividing the above R-value by the thickness in inches, we get
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A thin-wall jacketed tank, heated by condensing steam at one atmosphere contains 91 kg of agitated water. The heat transfer area of the jacket is 0.9 m2 and the overall heat transfer coefficient U = 227 W/(m2 K) based on that area. Determine the heating time required for an increase in temperature from 16°C to 60°C.
GIVEN
• A thin wall jacketed tank, heated by condensing steam
• Steam pressure = one atmosphere
• Mass of water in the tank = 91 kg
• The heat transfer area (A) = 0.9 m2
• The overall heat transfer coefficient (U) = 227 W/(m2 K) based on that area
• Temperature increases from 16°C to 60°C
FIND
• Determine the heating time required
ASSUMPTIONS
• Uniform water temperature due to agitation
• Thermal capacitance of the tank wall is negligible
SKETCH
