GATE2015-2-42

Question

A balanced counterflow heat exchanger has a surface area of $20$ $m^2$ and overall heat transfer coefficient of $20$ $W$/$m^2$-$K$. Air ($C_p$=$1000$ $J$/$kg$-$K$) entering at $0.4$ $kg/s$ and $280$ $K$ is to be preheated by the air leaving the system at $0.4$ $kg/s$ and $300$ $K$. The outlet temperature (in $K$) of the preheated air is

• A. $290$
• B. $300$
• C. $320$
• D. $350$