Question

Hot oil at $110°C$ heats water from $30°C$ to $70°C$ in a counter-current double-pipe heat exchanger. The flow rates of water and oil are 50 kg/min and 100 kg/min, respectively, and their specific heat capacities are $4.2 kJ/(kg\cdot °C)$ and $2.0 kJ/(kg\cdot °C),$ respectively. Assume the heat exchanger is at steady state. If the overall heat transfer coefficient is $200 W/(m²\cdot °C),$ the heat transfer area in $m²$ is

• A. 17.9
• B. 1.1
• C. 5.2
• D. 35.2

Official answer: 17.9