Question

A continuous flow water heater (geyser) has an electrical power rating $=2kW$ and efficiency of conversion of electrical power into heat $=80\%$. If water is flowing through the device at the rate of $100cc/sec$, and the inlet temperature is ${10}^{\circ }C$, the outlet temperature will be :

• A. ${12.2}^{\circ }C$
• B. ${13.8}^{\circ }C$
• C. ${20}^{\circ }C$
• D. ${16.5}^{\circ }C$

Answer 1

The correct option is B ${13.8}^{\circ }C$

$1cc$ of water has a mass of $1g$.

Flow rate is $m=100g/s$

$Q=2000\times 0.8=1600W$ or J/s ,since the efficiency is 80%

$Q=mc\Delta T$ , where m is mass flow rate in kg/s

$1600=100\times 4.2\times (T-10)\Rightarrow T={13.8}^{o}C$