Question

Hot and cold streams of a fluid are mixed in a rigid mixing chamber. The hot fluid flows into the chamber at a mass flow rate of 5 kg/s with an energy in the amount of 150 kJ/kg. The cold fluid flows into the chamber with a mass flow rate of 15 kg/s and carries energy in the amount of 50 kJ/kg. There is heat transfer to the surroundings from the mixing chamber in the amount of 5.5 kW. The mixing cham- ber operates in a steady-flow manner and does not gain or lose energy or mass with time. Determine the energy carried from the mixing chamber by the fluid mixture per unit mass of fluid, in kJ/kg.

Answer 1

Answer:74.75 kJ/kg

Explanation:

Given

mass of hot fluid$(m_h)$=5 kg/s

Energy associated with it=150 kJ/kg

mass of cold fluid$(m_l)$=15 kg/s

Energy associated with it=50 kJ/kg

Energy lost=5.5 kW

Let the Enthalpy of outlet fluid be h

mass at outlet

$m=m_l+m_h=20 kg/s$

Using Energy Conservation

$m_h\times E_h+m_l\times E_l+Q=m\times h$

$5\times 150+15\times 50-5.5=20\times h$

h=74.75 kJ/kg