During open-heart surgery, a patient's blood is cooled down to $25^{\circ}C$ from $37^{\circ}C$ using a concentric tube counter-flow heat exchanger. Water enters the heat exchanger at $4^{\circ}C$ and leaves at $18^{\circ}C$. Blood flow rate during the surgery is $5\; L/\text{minute}$.
Use the following fluid properties:
$$\begin{array}{|c|c|} \hline
\text{Fluid} & \text{Density}(kg/m^{3}) & \text{Specific heat}(J/kg-K) \\ \hline \text{Blood} & 1050 & 3740 \\ \hline \text{Water} & 1000 & 4200 \\ \hline \end{array}$$
Effectiveness of the heat exchanger is _____________ (round off to $2$ decimal places).