Four hundred kg/h of steam from a low pressure turbine at 12.5 atm. and 250 c goes into a feed water heater which preheats the water entering the economizer in a boiler. the steam is comes out of the feed water at 200 c. the water at a flow rate of 500 kg/h enters the feed water heater at 20c. calculate the feed water exit temperature.

Explanation:

According to the heat relationship,

    Heat given by steam = heat taken by water

Hence,     =

where, = specific heat

Value of at 250^{o}C and 12.5 atm is 2.326 .

And, at 200^{o}C and 12.5 atm is 2.743 .

Therefore, average =

                                          = 2.5345 kJ/Kg^{o}C

As the given data is as follows.

      = 400 kg/hr, = = , = 500 kg/hr

            = 4.186

Hence, putting the given values into the above formula as follows.

            =

  =

As we know that,

Thus, we can conclude that the new temperature of water is .