A watt is equal to
a. 746 horsepower.
b. one calorie.
c. one joule.
d. 1 J/s.
e. a unit of energy.
d
You might also like to view...
Vision Problems: What power contact lens must be used to correct the vision of a nearsighted person whose far point is 40 cm?
A. +2.5 diopters B. -2.5 diopters C. -3.6 diopters D. -4.0 diopters E. +4.0 diopters
Which of the following could have been habitable if the Sun had been twice as massive?
A. Mercury B. Neptune C. Venus D. Pluto E. Jupiter's moons
A puddle of water (n = 1.33) is covered with a very thin layer of oil (n = 1.20). How thick is the oil in the region that strongly reflects light with a wavelength of 497 nm?
a. 207 nm c. 458 nm b. 550 nm d. 229 nm
The electronic controls of a medical imaging device are housed in a compartment such that it dissipates heat to the ambient from a flat vertical plate surface, 15 cm wide and 20 cm high, to which fins are attached so as to enhance the heat transfer and improve the cooling of the electric systems. If 10 fins made of aluminum with a rectangular cross section are attached that extend over the full vertical height of the plate surface, where each fin is 0.15 cm thick with equal spacing of 1.5 cm along the width of the plate, determine the optimum fin height and the rate of heat transfer to the surrounding air. The room air temperature is at 20°C and the base temperature of the plate surface to which the fins are attached should not exceed 70°C.
GIVEN
? An electronic device with vertical aluminum fins in air
? Air temperature (T?) = 20°C
? Vertical Height of fin (H) = 0.2 m
? Width of surface (w) = 0.15 m
? Fin thickness(t) = 0.0015 m
? Maximum base temperatures: Tb= 70°C
? Fin spacing (s)= 1.5 cm=0.015 m
FIND
(a) Optimum fin height perpendicular to surface.
(b) Rate of heat transfer to surrounding air.
ASSUMPTIONS
? The fins are at a uniform temperature equal to the base temperature
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at the mean temperatures for each of the base temperatures
From Appendix 2, Table 12, the thermal conductivity of aluminum in the range of around 70°C
(ka) = 240 (W/(m K))