Question

For a steam condenser, the steam condenses on the outer surface of the tubes at condensation temperature 50${}^o$C . Water enters the tube at
20${}^o$C and leaves at 35.95${}^o$C. What is the NTU for the heat exchanger?

• A. Can't be determined from given data
• B. 0.5317
• C. 0.9569
• D. 0.7586

Answer 1

The correct option is D 0.7586


Given heat exchanger is a condenser,

$C_h=C_{max}=\infty$

$C_{min}=C_c$

$Effectiveness=\frac{C_c}{C_{min}}\frac{[t_{c2}-t_{c1}]}{[t_{h1}-t_{c1}]}$

$=\frac{t_{c2}-t_{c1}}{t_{h1}-t_{c1}}$

$=\frac{35.95-20}{50-20}=0.5317$

Effectiveness of condenser,

$ϵ=1-exp[-NTU]$ (Since C = 0)

$\Rightarrow 0.5317=1-exp[-NTU]$

$\Rightarrow exp[-NTU]=1-0.5317=0.4683$

$\Rightarrow -NTU=lo{g}_{e}0.4683=-0.7586$

$\Rightarrow NTU=0.7586$