In a ship with a main engine of $8000$ kW power and $30\%$ thermal efficiency, $60\%$ of the total waste heat comes from the chimney.

is thrown away. It is desired to obtain hot water at $80$ C from the exhaust gas. Add distilled water to the boiler at $30$ C$.$

taken at temperature. The main engine exhaust gas outlet temperature is $600$ C and the chimney atmosphere outlet temperature is $220$ C$.$

The boiler working order is considered to be $2$ passes $-2$ stages plate separation. Body diameter $150$ cm$,$ inner pipe diameter

When the inner pipe wall thickness is taken as $10$mm$,$ the inner pipe wall thickness is $2$mm and the body length is $3$ meters,

a$)$ Find the total heat transfer amount.

b$)$ Find the total heat transfer coefficient.

c$)$ Find the number of pipes to be used. $(2$ passes $=1$ pipe$).$