Question

Saturated vapor is condensed to saturated liquid in a condenser. The heat capacity ratio is $C_r=\frac{C_{min}}{C_{max}}$. The effectiveness $\left(\epsilon \right)$ of the condenser is

• A. $\frac{1-exp[-NTU(1+C_r\left)\right]}{1+C_r}$
• B. $\frac{1-exp[-NTU(1-C_r\left)\right]}{1+C_r[-NTU(1-C_r\left)\right]}$
• C.
  $\frac{NTU}{1+NTU}$
• D.
  $1-exp(-NTU)$

Answer 1

The correct option is D

$1-exp(-NTU)$
For parallel

$\epsilon =\frac{1-exp[-NTU(1-C_r\left)\right]}{1+C_r}$

For condenser,

$C_{max}=\infty$

$C_r=0$

$\epsilon =\frac{1-exp[-NTU]}{1}$

$\therefore$ (d) is the correct option.

Considering counter-flow heat exchanger

$\epsilon =\frac{1-exp[-NTU(1+C_r\left)\right]}{1-C_{r}exp[-NTU(1+C_r\left)\right]}$

$\therefore C_r=0$

1-exp(-NTU)

$\therefore$ Again (d) is the correct option.