A once$-$through water cooling system exists for a $75$ kW air compressor.

The flow rate is $12\frac{l}{m}in.$ Water enters the compressor at $18C$ and leaves at $105C.$ If water and sewage

cost $$\frac{1\mathrm{.}50}{?}$ kilolitre and energy costs $$\frac{5\mathrm{.}00}{G}J,$ calculate the annual water savings $($litres and dollars$)$ and

annual energy savings $($GJ and dollars$)$ if the water could be used as boiler makeup water. Assume the

water cools to $32C$ before it can be used and flows $8760$ hours$/$year$.$ Assume a boiler efficiency of $70\%.$

In designing a PV panel, individual cells producing $0\mathrm{.}5$ volts and $1$ ampere are to be used. The need is for a

small dc water pump drawing $12$ volts and $3$ amperes. Design the necessary array include any voltage$-$

regulating device or storage devices.