A heater is rated at 1200 watts for a 120-volt source.If two heaters are connected in parallel across the 120-volt source, the total power in watts drawn from the source is
a. 600 b. 1200.
c. 2400 d. none of the above.
c
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A well-clothed person walks into a large auditorium that is empty. If the auditorium walls are at an average temperature of 55ºF and the average surface temperature of the person’s clothes is 85ºF, estimate the net radiation heat transfer between the person and the auditorium walls. An average person can be assumed to have a surface area of 19.4 ft^2 (1.8 m2^).
What will be an ideal response?
A solar collector design consists of several parallel tubes each enclosed concentrically in an outer tube that is transparent to solar radiation. The tubes are thin walled with the inner and outer cylinder diameters of of 0.10 and 0.15 m respectively. The annular space between the tubes is filled with air at atmospheric pressure. Under operating condition the inner and outer tube surface temperatures are 70°C and 30°C respectively.
(a) What is the convective heat loss per meter of tube length?
(b) If the emissivity of the outer surface of the inner tube is 0.2 and the outer cylinder
behaves as though it were a black body, estimate the radiation loss.
(c) Discuss design options for reducing the total heat loss.
GIVEN
? Thin walled concentric tubes with air atmospheric pressure between them
? Inner tube diameter (Di) = 0.1 m
? Outer tube diameter (Do) = 0.15 m
? Inner tube temperature (Ti) = 70°C = 343 K
? Outer tube temperature (To) = 30°C = 303 K
? Outer surface emissivity of inner tube (E) = 0.2
FIND
(a) The convective loss pe meter of tube (qc/L)
(b) The radiative loss (qr/L)
(c) Discuss design options for reducing the total heat loss
ASSUMPTIONS
? Steady state
? Tubes are horizontal
SKETCH
PROPERTIES AND CONSTANTS
Which sequence of events is in the correct chronological order?
A. Quarks form, protons form, protons and electrons recombine into atoms, helium is produced. B. Protons form, helium is produced, protons and electrons recombine into atoms, quarks form. C. Protons form, quarks form, protons and electrons recombine into atoms, helium is produced. D. Quarks form, protons form, helium is produced, protons and electrons recombine into atoms.
A jet flies at 1.4 times the speed of sound. What is the half-angle of the conical shock wave formed?
A) 46° B) 44° C) 30° D) 36°