Question

In a counter flow heat exchanger, for the hot fluid the heat capacity = 2 kJ/kgK, mass flow rate = 5 kg/s, inlet temperature $={150}^{\circ }C$, outlet temperature $={100}^{\circ }C$. For the cold fluid, heat capacity = 4 kJ/kgK, mass flow rate = 10 kg/s, inlet temperature $={20}^{\circ }C$. Neglecting heat transfer to the surroundings the outlet temperature of the cold fluid in ${}^{\circ }C$ is

• A.
  7.5
• B.
  32.5
• C.
  45.5
• D.
  70.0

Answer 1

The correct option is B

32.5
Given data:
$c_{ph}=2000J/KgK;$ $m_h=5kg/s;$

$c_{pc}=4000J/KgK;$ $T_{hi}={150}^{\circ }C$

$m_c=10kg/s$

$T_{ci}={20}^{\circ }C;$ $T_{co}=?$

Heat lost by hot fluid = Heat gained by cold fluid

$m_h{c}_{ph}(T_{hi}-T_{ho})=m_c{c}_{pc}(T_{co}-T_{ci})$

$5\times 2000\times (150-100)$

$=10\times 4000(T_{co}-T_{ci})$

$\therefore T_{co}={32.5}^{\circ }C$