# A) A gas-fired heat exchanger uses gas with energy value of 40MJ / m^3 at a rate of 0.4 m^3/h and produces 50kg/h of water at a temperature of 70^oC from feed water at 20^oC. The rest of the question is in the picture attached.PLZ help?

##### 2 Answers

I got this

#### Explanation:

Let us calculate amount of heat required to raise the temperature of feed water at

Mass of water used in one hour

Rise in temperature

Useful heat

#=>Q_u=50xx(4.19xx10^3)xx50#

#=>Q_u=10475000\ J#

Heat produced by the gas in the heat exchanger in one hour

#Q_p=0.4xx(40xx10^6)#

#=>Q_p=16000000\ J#

Thermal efficiency of the heat exchanger

#eta=10475000/16000000=0.65# , rounded to two decimal places.

Thermal efficiency

#### Explanation:

Start by working out how much energy is required to heat 50 kg of water from

Specific heat capacity of water =

so 50 kg raised 50 degrees will need

Energy

Energy/hr in from gas

so thermal efficiency is