How to Calculate Mass of Steam in a Heat Exchanger?

[marialo]

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...

 

[Valkarie]

The mass of steam fed into the exchanger can be calculated using the ideal gas law. The ideal gas law states that PV = mRT, where P is the pressure, V is the volume, m is the mass, R is the gas constant and T is the temperature. Using this equation, you can calculate the mass of steam fed into the exchanger by plugging in the temperature, pressure, and volume of the steam.

 

[piercas]

I understand your struggle with this homework problem. It can be challenging to set up calculations for heat exchanger problems, but with some guidance, you should be able to solve it.

First, let's review the given information. We have two streams entering the heat exchanger: propane gas and superheated steam. The propane gas enters at 40 degrees C and 250 kPa, and exits at 240 degrees C. The superheated steam enters at 300 degrees C and 5.0 bar and exits as a saturated liquid at the same pressure.

To determine the mass of steam fed (kg), we need to use the mass balance equation. This equation states that the mass entering the system must equal the mass exiting the system, plus any accumulation or depletion within the system. In this case, we can assume that there is no accumulation or depletion of either stream within the heat exchanger.

Let's assume that the mass of propane gas entering the heat exchanger is m1 (kg) and the mass of steam entering is m2 (kg). Using the mass balance equation, we can write:

m1 = m2

Now, we need to use the ideal gas law to relate the pressure, temperature, and mass of each stream. The ideal gas law states that PV = nRT, where P is pressure (Pa), V is volume (m^3), n is the number of moles, R is the universal gas constant (8.314 J/mol.K), and T is temperature (K). Rearranging this equation, we can solve for the number of moles:

n = PV/RT

Since we know the pressure, temperature, and volume (which can be determined from the flow rate and density) of each stream, we can calculate the number of moles of propane gas and steam entering the heat exchanger.

Now, we can use the molar mass of each substance to convert the number of moles into mass. The molar mass of propane is 44.1 g/mol, and the molar mass of water (the main component of steam) is 18.0 g/mol. Using these values, we can calculate the mass of propane gas and steam entering the exchanger.

I hope this explanation helps you solve the problem and understand the steps involved. Remember to always use the given information and relevant equations to solve engineering problems. Good luck!