|
|
 |
|
|
|
|
 |
|
|
|
- Superheated steam is used in a shell-and-tube heat exchanger to pre-heat an air stream that is being fed to a reactor. The steam enters at 240 degC and 475 kPa and exits at 175 degC at the same pressure; the steam flow rate is 25 kg/sec. The air enters at 25 degC, and flows at 100 kg/sec. Assume the heat exchanger operates without any heat losses.
Except where noted, assume ideal gases and use the heat capacity formulas in Table C.1 to answer the following
a. Compute the total enthalpy and entropy changes of the steam.
b. What is the output temperature of the air stream?
c. Compute the total entropy change of the air stream.
d. What is the total entropy change of the complete air/steam system?
e. Use the steam tables to answer part (a). Why are the results different?
- Consider two metal bars, one of heat capacity 0.5 J/K and at a temperature of 400 K and the other of heat capacity 1.0 J/K at 300 K. They are placed in thermal contact and an amount of heat |Q| flows from one to the other; their temperatures change uniformly. Develop expressions for:
a. The temperature of each bar as a function of |Q|.
b. The total entropy change of the system of two bars, as a function of |Q|.
Prepare a single plot showing all three quantities as a function of |Q|, for |Q| ranging from 0 to 60 Joules. To ensure that your entropy plot shows up on the scale needed by the temperature plot, plot the entropy times 20,000. What is the temperature of each bar at the maximum-entropy value of Q?
- Smith, van Ness & Abbott, problem 5.2.
- Answer: Power = 148.78 kW
- Smith, van Ness & Abbott, problem 5.9.
- Smith, van Ness & Abbott, problem 5.15.
- Answer: deltaS(total) = 6.02 J/mol-K
- Smith, van Ness & Abbott, problem 5.23.
|
|
