Adiabatic heat exchanger problem

[marialo]

Adiabatic heat exchanger problem... Please Help!

I have this proplem as a homework assignment and I'm a bit stuck as houw to set it up. Here it is:

Propane gas enters a continuous adiabatic heat exchanger at 40 degrees C and 250 kPa and exits at 240 degrees C. Superheated steam at 300 degrees C and 5.0 bar enters the exchanger flowing countercurrent,y to the propane and exits as a saturated liquid at the same pressure.

I know how to draw the process flowchart, but the problem also asks to include in the labeling the mass of the steam fed (kg). I have no idea how to figure this out. Is it in some table, or chart?

Please Help, 'cause i am stumped!

-Thanks in advance...

 

[mark-ashleigh]

Adiabatic heat exchanger

Couple of questions for you: Do you own a copy of the si steam tables? Are you familiar with heat balances?

Ok, i will try and point you in the right direction .

Q= Of the steam = Q of the water

Thus Q=McpDT m= mass of water/steam Kg Cp=Specific heat Dt= (Outlet Temp - Inlet)

So call steam 1 and Water 2

M1*cP*DT1=M2*cp*DT2

OR we can say that Q=m*Hf-Hg and take the data from the steam tables for steam as we know the conditions in and out! once we know Q ofcourse...lol ( H is Empalthy)

Good luck , hope this is some help...half asleep so probs wrote crap! lol

 

[mark-ashleigh]

i didn't mean water i meant propane...lol

 

[GCT]

The problem seems to relate to the Joules-Thompson effect...

 

[Astronuc]

"adiabatic heat exchanger" implies the heat is transferred from the hot fluid to the cold fluid. The change in energy of the hot fluid = change in energy of the cold fluid, or rather rate of energy transfer from the hot fluid = rate of energy transfer to the cold fluid.

$$\dot{m_h}\,c_p_h\,\Delta{T_h}$$ = $$\dot{m_c}\,c_p_c\,\Delta{T_c}$$ where h and c are hot and cold, $$\dot{m}$$ is mass flow rate, c_p is specific heat and $$\Delta{T}$$ is the change in temperature. Or instead of $$c_p\,\DeltaT$$, one could use the change in specific enthalphy directly, which one can find in a thermodynamic table as a funtion of temperature and pressure for the given fluid.

 

[mark-ashleigh]

Thats what i said...lol, but in laymen terms! :P