thermodynamics 2

1. Processes of Vapors

2. Constant Pressure (Isobaric)

3. • There are 10 kg/min of saturated liquid heated until the temperature was
306 C with the pressure remaining constant at 100 kPa. Determine (a) initial
and final enthalpy, kJ/kg (b) amount of heat absorbed, kJ/s (c) kW rating of
an electric heater required for an overall heat transfer of 90%.

4. Constant Volume (Isochoric; Isometric)

5. • A rigid tank contains 1 kg of saturated liquid-vapor mixture of water 100 kPa
Determine the amount supplied to completely vaporize the water if initially 1/4
of the mass is the liquid phase.

6. Constant Temperature (Isothermal)

7. If one kg of saturated liquid at 500 kPa is heated with the temperature
remaining constant until its pressure is 200 kPa. Determine (a) the amount of
heat transferred (b) the change of internal energy and enthalpy, kJ (c) work.

8. Constant Entropy (Isentropic)
- reversible adiabatic process

9. Steam enters an adiabatic turbine at 5 MPa and 450C and leaves at a pressure
of 1.4 MPa. Determine the work output of the turbine per unit mass of steam
flowing through the turbine if the process is reversible and changes in kinetic
and potential energies are negligible.

10. Reversible Polytropic process
𝑃𝑉𝑛 = 𝑐
𝑊
𝑛 =
𝑃2𝑉2 − 𝑃1𝑉1
1 − 𝑛
𝑄 = ∆𝑢 + 𝑊
𝑛
𝑄 = 𝑢2 − 𝑢1 +
𝑃2𝑉2 − 𝑃1𝑉1
1 − 𝑛
𝑊
𝑠 = 𝑄 − ∆ℎ − ∆𝐾𝐸
𝑊
𝑠 =
𝑛(𝑃2𝑉2−𝑃1𝑉1)
1−𝑛
= 𝑛 𝑊
𝑛

11. Five kg per second of steam at 5.9 Mpa and 500 C expand to 0.9 Mpa in a
polytropics process where 𝑃𝑉1.26 = 𝑐. Find (a) T2 ∆𝐻, ∆𝑈, ∆𝑆 (b)Wn (c)Wf if
∆𝐾 = −40𝑘𝐽/𝑠 (d) Q from non steady and steady flow.

12. Steady State Engineering Devices

13. Throttling Process: Throttling valves
Throttling valves are any kind of flow-restricting devices that cause a
significant pressure drop in the fluid, such as adjustable valves, capillary
tubes and porous plugs. Throttling valves are usually small devices, and
the flow through them maybe assumed to be adiabatic (Q=0) since
there is neither sufficient time of large area for any effective heat
transfer to take place. Also, there is no work (W=0), and the change of
potential energy if any is very small (∆PE=0). Even though the exit
velocity is often considerably higher than the inlet velocity, in many
cases, the increase in kinetic energy is insignificant (∆KE=0). Then the
conservation of energy equation for this single-stream device reduces
to h2 = h1, a constant enthalpy process

14. A throttling calorimeter is connected to a steam main in which the pressure is
15 bar. In the calorimeter P2 = 1 bar and T2 = 110 C. Compute the quality of
the percentage moisture of the steam sampled.

15. Turbine and Compressors
In steam, gas, or hydroelectric power plants, the device that drives the
electric generator is the turbine. As the fluid passes through the turbine, work is
done against the blades which are attached to the shaft. As a result, the shaft
rotates and the turbine produces work. Compressors, as well as pumps and fans,
are devices used to increase the pressure of a fluid. A compressor is capable of
compressing the gas to very high pressures. Pumps work very much like
compressors except that they handle liquids instead of gasses.

16. The power output of an adiabatic steam turbine is 50 MW and the inlet and exit
conditions of the steam are described in the figure. Compute (a) ∆H and ∆KE for
unit mass of steam (b) work done per unit mass of the steam flowing (c) actual
mass flow rate required.

17. Nozzles and Diffusers
These devices are commonly utilized in jet engines, rockets, space craft
and even garden hoses. A nozzle is a device that increases the pressure of a fluid
by slowing it down. Nozzles and diffusers perform opposite tasks. The cross-
sectional area of a nozzle decreases in the flow direction for subsonic flows and
increases for supersonic flows. The reverse is true for diffusers. The rate of
direction for subsonic flows and increases for supersonic flows. The reverse is
true for diffusers. The rate of heat transfer between the fluid flowing and the
surroundings is usually very small (Q=0), the work term for nozzles and diffusers
is zero since these devices involve no shaft (W=0). Nozzle and diffusers usually
involve very high velocities but fluid usually experiences little or no change in
potential energies (∆PE=0).

18. Steam at 250 psia and700 F steadily enters the nozzle whose inlet area is 0.2 ft2.
the mass flow rate of the steam through the nozzle is 10 lb/s. Steam leaves the
nozzle at 200 psia with a velocity of 900 ft/s. The heat loss through the nozzle per
unit mass of steam are estimated to be 1.2 Btu/lb. Determine (a) inlet velocity (b)
exit Temperature of the steam.

19. Mixing Chambers
In engineering applications, mixing two streams of fluids is not a rare
occurrence. The section where the mixing process takes place is usually referred
to as mixing chamber. The mixing chamber does not have to be a distinct
“chamber”. An ordinary T-elbow or Y-elbow in a shower, for example, serves as a
mixing chamber for the cold and hot-water streams. Mixing chamber are usually
well insulated (Q=0) and does not involve any kind of work (W=0). Also, the
kinetic and potential energies of the fluids are usually negligible. (∆KE=∆PE=0).

20. A supply of 5 kg/s ammonia at 500 kPa, 20°C is needed. Two sources are
available one is saturated liquid at 20°C and the other is at 500 kPa, 140°C.
Flows from the two sources are fed through valves to an insulated mixing
chamber, which then produces the desired output state. Find the two source
mass flow rates and the total rate of entropy generation by this setup.

21. Heat Exchangers
Heat exchangers are devices where two moving fluid streams exchange heat
without mixing. Heat exchangers typically involve no work (∆KE=∆PE=0). Heat
exchangers are intended for heat transfer between two fluids within the device,
and the outer shell is usually insulated to prevent any heat loss to the
surrounding medium.

22. Saturated steam at 100 kPa enters the condenser with a mass flow rate of 5
kg/s. The cooling water enters at 25 C and leaves with a temperature rise of 15
C. Neglect pressure drop and the change of kinetic and potential energies be
negligible, compute the amount of cooling water needed.