Question

In a counter flow heat exchanger, the temperature rise of the cold fluid is equal to the temperature drop of the hot fluid. The effectiveness $\left(ϵ\right)$ of the heat exchanger is

• A. None of these
• B. $ϵ=\frac{1-exp(-2NTU)}{2}$
• C. $ϵ=\frac{NTU}{1+NTU}$
• D. $ϵ=1-exp(-NTU)$

Answer 1

The correct option is C $ϵ=\frac{NTU}{1+NTU}$

$(\Delta T{)}_c=(\Delta T{)}_h$

$\Rightarrow C=1$ (capacity ratio)

$\therefore$ $ϵ=\frac{NTU}{1+NTU}$ for a counter flow heat exchanger