What is thermal conductivity?
What will be an ideal response?
The defining equation for thermal conductivity k is Fourier’s law of conduction;
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When a 12-V battery powers a single 6-ohm lamp,
A) 2 joules flow in the lamp each second. B) 6 joules flow in the lamp each second. C) 12 joules flow in the lamp each second. D) none of the above
A long, hollow cylinder is constructed from a material whose thermal conductivity is a function of temperature according to k = 0.15 + 0.0018 T, where T is in C and k is in W/(m K). The inner and outer radii of the cylinder are 12.5 and 25 cm, respectively. Under steady-state conditions, the temperature at the interior surface of the cylinder is 427°C and the temperature at the exterior surface is 93°C. (a) Calculate the rate of heat transfer per meter length, taking into account the variation in thermal conductivity with temperature. (b) If the heat transfer coefficient on the exterior surface of the cylinder is 17 W/(m2 K), calculate the temperature of the air on the outside of the cylinder.
GIVEN
• A long hollow cylinder
• Thermal conductivity (k) = 0.15+ 0.0018 T [T in °C, k in W/(m K)]
• Inner radius (ri) = 12.5 cm
• Outer radius (ro) = 25 cm
• Interior surface temperature (Twi) = 427°C
• Exterior surface temperature (Two) = 93°C
• Exterior heat transfer coefficient ( oh ) = 17 W/(m2 K)
• Steady-state conditions
FIND
(a) The rate of heat transfer per meter length (q/L) (b) The temperature of the air on the outside (T?) ASSUMPTIONS
• Steady state heat transfer
• Conduction occurs in the radial direction only
SKETCH
Euler’s equation integrated along a streamline results in Bernoulli’s equation provided the flow is:
(A) Incompressible, inviscid, steady, in an inertial reference frame (B) Constant density, steady, along a streamline, in an inertial reference frame (C) Incompressible, steady, along a streamline, in an inertial reference frame (D) Constant density, steady, along a streamline, inviscid, in an inertial reference frame
Four identical particles (mass of each = 0.40 kg) are placed at the vertices of a rectangle (2.0 m × 3.0 m) and held in those positions by four light rods which form the sides of the rectangle. What is the rotational inertia of this rigid body about an axis that passes through the mid-points of the longer sides and is parallel to the shorter sides?
A. 2.7 kg?m2 B. 3.6 kg?m2 C. 3.1 kg?m2 D. 4.1 kg?m2 E. 1.6 kg?m2