# GATE2015-2-42

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

1. $290$
2. $300$
3. $320$
4. $350$

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