A long power transmission cable is buried at a depth (ground-to-cable-centerline distance) of 2 m. The cable is encased in a thin-walled pipe of 0.1-m diameter, and, to render the cable superconducting (with essentially zero power dissipation), the space between the cable and pipe is filled with liquid nitrogen at 77 K. If the pipe is covered with a super insulator (ki = 0.005 W/mK) of 0.05-m thickness and the surface of the earth (kg = 1.2 W/mK) is at 300 K, what is the cooling load (W/m) that must be maintained by a cryogenic refrigerator per unit pipe length?

Consider a power plant with water as the working fluid that operates on an ideal rankine cycle. it has a net power output of 45mw. superheated steam enters the turbine at 7mpa and 500°c (h=3411.4 kj/kg; s=6.8 kj/kg k) and is cooled in the condenser at a pressure of 10 kpa by running cooling water from a lake through the tubes of the condenser at a rate of 2000 kg/s. (a) show the cycle on a t-s diagram (a right schematic is fine - you do not need to calculate the temperatures at each point); (b)-determine the work done by the turbine and the pump in kj/kg; (c)-the mass flow rate of water used by the power plant; (d)-the thermal efficiency of the cycle; (e)-the temperature rise of the cooling water. assume the cooling water is incompressible with cp 4.18 kj/kg°c.