Air at 40oC, 1 bar and a volumetric flow rate of 60 m^3/min enters an insulated control volume operating at steady state and mixes with helium entering as a separate stream at 100oC, 1 bar and a volumetric flow rate of 30 m^3/min. A single mixed stream exits at 1 bar. cp,i for air and helium is 1.005 and 5.193 kJ/kg.K, respectively. Ignoring kinetic and potential energy effects and heat transfer and external work, determine for the control volume,
a) the temperature of the exiting mixture,
b) the entropy change from the entrance to exit per second.
First calculate the mass flow rates from the given volumetric flow rates.