A sodium-potassium alloy (78 percent K) is to be circulated through ¹/₂-in.-ID tubes in a reactor core for cooling. The liquid-metal inlet temperature and velocity are to be 580°F and 32 ft/s. If the tubes are 3 ft long and have an inside surface temperature of 720°F, find the coolant temperature rise and the energy gain per pound of liquid metal. Properties of NaK (78 percent K) are as follows: 

ρ = 45 lb/ft³         k = 179 Btu/ft·h·°F         μ = 0.16cP         c_p = 0.21 Btu/lb·°F