Heat and Mass Transfer in Food Processing

In a counterflow plate heat exchanger pasteurizing milk, hot water enters at $85^\circ\text{C}$ and exits at $65^\circ\text{C}$. Cold milk enters at $45^\circ\text{C}$ and exits at $75^\circ\text{C}$. The temperature differences at the two ends are $\Delta T_1 = 85 - 75 = 10^\circ\text{C}$ and $\Delta T_2 = 65 - 45 = 20^\circ\text{C}$. Given $\ln(2) = 0.693$, the Log Mean Temperature Difference ($LMTD$) in degrees Celsius is: