Heat transfer solution

                                                                   Homework 6

An ammonia water solution is added at a specified rate to a charge of a formaldehyde water solution.  The reaction is instantaneous, that is, as soon as the ammonia and formaldehyde mix they react forming HMT and water; the reaction is also highly exothermic.  A cooling jacket surrounds the reactor to cool the liquid.

Process Information:

Initial charge of formaldehyde water solution = 1000 kg

Mass fraction of formaldehyde in the original solution = 0.42

Initial temperature of formaldehyde water solution = 50 ^oC

Feed flow rate: ;  Ammonia mass fraction in feed:

Feed temperature:

Heat capacity of reactants and products:

Heat of reaction (assumed constant):

Overall heat transfer coefficient:

By the way, the jacket volume (volume of liquid in the jacket) is 2 m3.  Be careful with the units!

The feeding time is 130 minutes.

a)      Assume that the cooling water flow rate is so high that its temperature due to heat transfer hardly increases that is, its exit temperature is also.  Find the heat transfer area such that the reactor temperature just rises to  by the end of the feeding time.

b)       Assume now that the utility plant providing the cooling water is limited in its capacity, and we must remove the assumption of very high cooling flow and thus, constant cooling temperature.  It is necessary to find out the water flow rate that experiences no more than  increase in temperature, that is, the maximum exit water temperature cannot be over, and at the same time does not allow the reactor’s content to exceed  by the end of the feeding time.  Use the heat transfer area obtained in (a).