Question

When new, a heat exchanger transfers 10% more heat than it does after being in service for six months. Assuming that it operates between the same temperature differentials and that there is insufficient scale built up to change the effective surface area. The fouling factor of heat exchanger if the overall heat transfer coefficient is $200W/m^{2}Kis$

• A. $0.05K/W$
• B. $0.005K/W$
• C. $0.0005K/W$
• D. $0.5K/W$

Answer 1

The correct option is C $0.0005K/W$

$\frac{Q_n}{Q_0}=\frac{U_n{A}_n(\Delta T{)}_n}{U_0{A}_0(\Delta T{)}_0}$

$Since{A}_n=A_0,(\Delta T{)}_n=(\Delta T{)}_0$

$And{Q}_n=1.1Q_0$

$1.1=\frac{U_n}{U_0}$

$U_0=\frac{U_n}{1.1}=\frac{200}{1.1}=181.82$

Fouling factor

$F=\frac{1}{U_0}-\frac{1}{U_n}$

$=\frac{1}{181.82}-\frac{1}{200}=0.0005kW$