Water $\left(C_{p}=4.18 \mathrm{~kJ} / \mathrm{kg} . \mathrm{K}\right)$ at $80^{\circ} \mathrm{C}$ enters a counterflow heat exchanger with a mass flow rate of $0.5 \mathrm{~kg} / \mathrm{s}$. Air $\left(C_{p}=1 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\right)$ enters at $30^{\circ} \mathrm{C}$ with a mass flow rate of $2.09 \mathrm{~kg} / \mathrm{s}$. If the effectiveness
of the heat exchanger is 0.8 , the $\mathrm{LMTD}$ (in ${ }^{\circ} \mathrm{C}$ ) is
(A) 40
(B) 20
(C) 10
(D) 5
Water $\left(C_{p}=4.18 \mathrm{~kJ} / \mathrm{kg} . \mathrm{K}\right)$ at $80^{\circ} \mathrm{C}$ enters a counterflow heat exchanger with a mass flow rate of $0.5 \mathrm{~kg} / \mathrm{s}$. Air $\left(C_{p}=1 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\right)$ enters at $30^{\circ} \mathrm{C}$ with a mass flow rate of $2.09 \mathrm{~kg} / \mathrm{s}$. If the effectiveness
of the heat exchanger is 0.8 , the $\mathrm{LMTD}$ (in ${ }^{\circ} \mathrm{C}$ ) is
(A) 40
(B) 20
(C) 10
(D) 5