A 2.5-cm sphere is to be maintained at 50°C in either an airstream or a water stream, both at 20°C and 2 m/s velocity (see Problem 5.27). Compare the rate of heat transfer and the drag on the sphere for the two fluids.
Problem 5.27
Only of the energy dissipated by the tungsten filament of an incandescent lamp is in the form of useful visible light. Consider a 100-W lamp with a 10-cm spherical glass bulb, as shown in the sketch. Assuming an emissivity of 0.85 for the glass and an ambient air temperature of 20°C, what is the temperature of the glass bulb?
