申論題

6. (30%) A team of engineers for a defense contractor are commissioned by the naval force of a global power to build a nuclear submarine. The specs for the submarine, as demanded by the navy in order to designate the submarine as the Los Angeles Class, is as follows,
 ●Weight: 7,000 tones (1 tone =1,000 kg)
●Top speed when submerged: 20 knots (~37 km/hr)
●Acceleration from rest to top speed when submerged: 1 minute
It is also estimated that all the friction experienced by a submarine submerged in sea water is 3.86 x 10⁶ N. Moreover, such a submarine is conventionally propelled by a steam-driven turbine, with the high-pressure steam generated from a boiler heated by the nuclear reaction. Now, you are assigned the most critical part of the project - design the heat exchange system for the power generation system of the submarine - and need to determine the operation condition of the heat exchanger. Before that can be done, several other operation parameters have to be known in advance.

(4) You decide to employ a counterflow, concentric tube heat exchanger for the purpose. Given the condition that the cooling fluid - water - is at 10℃ and the diameters of the outer annulus and inner tube are to be 45 cm and 25 cm, respectively, determine the respective convection heat transfer coefficients for cooling water and stean. (9 pts) Explain the physical meanings of Reynolds and Nusselt numbers, which are relevant for addressing the question. (2 pts)