Question $3$

$($Marks will be awarded if only if question is solved step by step with each equation and working$)$

a$)$ A countercurrent heat exchanger has fluid inlet temperatures for a hot

process fluid $(H)$ and a cold service fluid $(A)$ of $350K$ and

$290K$ respectively. After long service the exit temperatures for hot and

cold fluids are both $310K.$ The exchanger is cleaned, resulting in a

$10\%$ greater overall heat transfer coefficient. The exchanger is then

put into service with the same hot process fluid $($inlet temperature and

capacity flowrate as before$),$ but with cold service fluid $B$ having a new

inlet temperature of $300K.$ Assuming capacity flowrates of A and $B$

are the same, calculate new exit temperatures for both fluids.

In counterflow, the effectiveness is:

$=\{\frac{1-e^{-\text{N}\text{T}\text{U}[1-C_r]}}{1-C_r{e}^{-\text{N}\text{T}\text{U}[1-C_r]}}\}$ where NTU$=\frac{UA}{C_{\text{m}\text{i}\text{n}}}$