Aheat engine has a solar collector receiving 600 btu/hr per square foot, inside which a transfer medium is heated to 800 r. the collected energy powers a heat engine that rejects heat at 100 f if the solar collector is 50 square foot large, what is the power output of the heat engine (in hp)? note: [1hp=2544 btu/hr]

Ahe-xe mixture containing a 0.75 mole fraction of helium is used for cooling electronics in an avionics application. at a temperature of 300 k and atmospheric pressure, calculate the mass fraction of helium and the mass density, molar concentration and molecular weight of the mixture. if the cooling capacity is 10 l, what is the mass of the coolant?