To totally convert a given amount of mechanical energy into heat is
A) possible.
B) impossible.
C) need more information
D) none of the above
Answer: A
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A metal-clad electrical heating element of cylindrical shape, as shown in the sketch below, is immersed in water at atmospheric pressure. The element is a 5-cm-OD, and heat generation produces a surface temperature of 300°C. Estimate the heat flux under steady state conditions and the rate of heat generation per unit length.
GIVEN
? Cylindrical, electrical heating element
? Heat generation produces a 300°C surface temperature
FIND
(a) Heat flux
(b) Rate of heat generation
ASSUMPTIONS
? The system operates at atmospheric pressure
? The heater surface is black
SKETCH
PROPERTIES AND CONSTANTS
Inspection of the boiling curve in Figure (9.1) indicates that at 300°C surface temperature, the heating system must operate in the film boiling regime. Hence, a vapor layer covers the surface of the heater and it is appropriate to evaluate the physical properties at the mean film temperature of (100 + 300)/2 = 200°C.
From Appendix 2, Table 35
From Appendix 2, Table 13
A one-pass condenser-heat exchanger, shown in the sketch, has 64 tubes arranged in a square array with 8 tubes per line. The tubes are 1.22 m long and are made of copper with an outside diameter of 1.27 cm. They are contained in a shell at atmospheric pressure. Water flows inside the tubes whose outside wall temperature is 98°C. Calculate (a) the rate of steam condensation and (b) the temperature rise of the water if the flow rate per tube is 0.0454 kg/s.
GIVEN
? One-pass condenser heat exchanger with 64 tubes in a square array
FIND
(a) Rate of steam condensation
(b) Water temperature rise
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, the properties of saturated water at the film temperature (100 + 98)/2 = 99°C are
If distance is speed × time and light takes 8 minutes to travel from the Sun to Earth and over 4 hours to travel from the Sun to the planet Neptune, what is the distance from the Sun to Neptune?
a. 5 AU b. 30 AU c. 30 ly d. 5 ly e. 0.6 ly
The geologic time scale is broken up into time units of different sizes based on eons, eras, periods, and epochs.
Indicate whether the statement is true or false