# Urgent chemical engineering. specific enthalpy. Help me please

kp3legend

## Homework Statement

Prior to entering a combustion furnace, air is heated up from ambient temperature (25 °C) to 250 °C. This change in temperature causes the specific enthalpy to change to 3745 J/mol. Assume that the pressure of the air leaving the heater is 150 kPa and the flow rate is 1.3 m3 /min. Assuming ideal behaviour, calculate the heat required in units of kW.

PV=nRT
H=U+PV
dH=Q

## The Attempt at a Solution

I can find P1 and V1 from the equation T1/T2=P1/P2 and V1/V2=P2/P1
P1=85.487 kpa
V1=136.863m^3

Last edited by a moderator:

## Answers and Replies

Mentor
Since you know the exit temperature and exit pressure, you should be able to determine the exit molar density using the ideal gas law. What is the exit molar density (moles/m^3)?

kp3legend
It will be 34.487 mol/m^3

Mentor
It will be 34.487 mol/m^3
If the exit molar density is 34.387 moles/m^3, and the exit flow rate is 1.3 m^3/min, what is the flow rate in moles/min?

kp3legend
It should be 1.3 x 34.387 = 44.7031 mol/min. I guess

Mentor
It should be 1.3 x 34.387 = 44.7031 mol/min. I guess

In the molar flow rate is 44.7 mol/min and the change in enthalpy per mole is 3745 Joules, how much heat is being added per min? How much heat is being added per second?

Chet

kp3legend
Omg thank you very much now I get it . but do you think I have to find H for the entering flow ?

Mentor
Omg thank you very much now I get it . but do you think I have to find H for the entering flow ?
What do you think?

1 person