Calculate the maximum safe heat flux in the nucleate-boiling regime for water flowing at a velocity of 15 m/s through a 1.2-cm-ID tube 0.31-m-long if the water enters at 100 kPa pressure and 100°C saturated liquid.
GIVEN
? Nucleate boiling of water flowing through a tube
? Water velocity (V) = 15 m/s
? Tube inside diameter (D) = 1.2 cm = 0.012 m
? Tube length (L) = 0.31 m
? Water pressure (p) = 1 atm
? Water temperature (Tw) = 100°C
FIND
? The maximum safe heat flux in the nucleate boiling regime (q"max)
ASSUMPTIONS
? Steady state
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, for water at 100°C, 1 atm
From Appendix 2, Table 35, for steam at 100°C: pv = 0.5977 kg/m3
From Table 9.2: Surface tension at 100°C (s) = 0.0589 N/m
From Table 9.1: For water on copper, Csf = 0.0130
Assuming that by ‘safe’ we mean that the critical heat flux is not exceeded, we can use the Griffith
correlation, Figure 9.17. The critical pressure is Pc = 218.3 atm, P/Pc = 1/218.3 = 0.0046. From the
figure, the ordinate is therefore 6000
Since Ts = Tb, the parameter F simplifies to
You might also like to view...
The most important reason that an alpha particle can be stopped by a single sheet of paper while an electron of the same energy might not be stopped by hundreds of sheets of paper is that the alpha particle
A. Is a nucleus, while the electron is not. B. Moves more slowly than the electron. C. Interacts more strongly than the electron does. D. Has greater mass than the electron. E. Has more charge than the electron.
Which of the following best describes how the greenhouse effect works?
A) A planet's surface absorbs visible sunlight and returns this absorbed energy to space as infrared light. Greenhouse gases slow the escape of this infrared radiation, which thereby heats the lower atmosphere. B) Greenhouse gases absorb X rays and ultraviolet light from the Sun, and this absorbed radiation then heats the atmosphere and the surface. C) Greenhouse gases absorb infrared light coming from the Sun, and this absorbed sunlight heats the lower atmosphere and the surface. D) The greenhouse effect is caused primarily by ozone, which absorbs ultraviolet light and thereby makes the atmosphere much hotter than it would be otherwise.
John's mass is half the mass of Jill. They both start walking and John moves twice as fast as Jill. What is the ratio of the kinetic energy of Jill to the kinetic energy of John?
A) 4 B) 2 C) 1 D) 1/2 E) 1/8
A baseball is struck by a bat. While the ball is in the air, what objects exert forces on the ball?
1.Earth 2.Bat 3.Air 4.Bat, Air 5.Earth, Bat 6.Earth, Air 7.Earth, Bat, Air 8.There are no forces on the ball. 9.The answer depends on whether the ball is going up, going down, or at its highest point.