Water flows through a shower head steadily at a

rate of $10$ L$/$min$.$ An

electric resistance heater placed in the water pipe heats the water

from $16$ C to $43$ C$.$ Taking the density of water to be $1$ kg$/$L$,$ determine

the electric power input to the heater $,$ in kW$.$

In

an effort to conserve energy, it is proposed to pass the drained

warm water at a temperature of $39$ C through a heat exchanger to

preheat the incoming cold water. If the heat exchanger has an

effectiveness of $0\mathrm{.}50($that is$,$ it recovers only half of the energy that

can possibly be transferred from the drained water to incoming cold

water$),$ determine the electric power input required in this case.

If

the price of the electric energy is Rs $.8\mathrm{.}5/$kWh $,$ determine how much

money is saved during a $10$ minute shower as a result of installing this

heat exchanger