Two objects are placed in a room with a temperature of 20°C. Object A has a temperature of 70°C, while object B has a temperature of 140°C. They have the same emissivity, but different areas
What should the ratio of the area of object A to that of object B be if the net power emitted by both objects is the same? A) 2.0
B) 3.4
C) 5.2
D) 17
E) 21
B
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In our solar system, Jovian planets are
A) large, made mostly of gases and liquids with low densities, and found far from the Sun B) small, made of pure rock with high densities, and found close to the Sun C) large, made of pure gases with low densities, and found far from the Sun D) small, made mostly of rock and iron with high densities, and found close to the Sun
Evacuated Magdeburg hemispheres are each
A) sucked together. B) pushed together by the atmosphere. C) held together by tension.
For a certain patient, the build-up of fatty tissue on the wall of an artery has decreased the arterial radius by 10%
By how much would the pressure provided by the heart have to be increased to maintain a constant volume of blood flow? Model the blood as an ideal incompressible fluid. A) 48% B) 52% C) 46% D) 54%
An 20 cm-diameter horizontal steam pipe carries 1.66 kg/min of dry saturated steam at 120°C. If ambient air temperature is 20°C, determine the rate of condensate flow at the end of 3 m of pipe. Use an emissivity of 0.85 for the pipe surface. If heat losses are to be kept below 1 per cent of the rate of energy transport by the steam, what thickness of fiberglass insulation is required? The rate of energy transport by the steam is the heat of condensation of the steam flow. The heat of vaporization of the steam is 2210 kJ/kg.
GIVEN • A horizontal steam pipe in air • Pipe outside diameter (D) = 20 cm= 0.2 m • Mass flow rate of steam (ms) = 1.66 kg/min=0.0277 kg/s • Steam temperature (Ts) = 120°C =393 K • Ambient air temperature (T?) = 20°C= 293 K • Emissivity of pipe surface (?) = 0.85 • Heat of vaporization (hfg) = 2210 kJ/kg FIND (a) Rate of condensate flow (mc) at the end of 3 m of pipe. (b) Thickness of fiberglass insulation (S) to keep loss below 1% of the energy transport by steam ASSUMPTIONS • Steady state • Air is still • Thermal resistance of the convection in the pipe and of the pipe wall are negligible • The surroundings behave as an enclosure at T? • Insulation is foil covered, its emissivity ? 0.0 PROPERTIES AND CONSTANTS the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4) Thermal conductivity of fiberglass (ki) = 0.035 W/(m K) for dry air at the mean temperature of 70°C Thermal expansion coefficient (?) = 0.00291 1/K Thermal conductivity (k) = 0.0288 W/(m K) Kinematic viscosity (?) = 17.1*10-6 m2/s Prandtl number (Pr) = 0.71