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# MM204E HW3 2019-20 SPRING

```Gazi &Uuml;niversitesi/Gazi University
M&uuml;hendislik Fak&uuml;ltesi/Faculty of Engineering
Makina M&uuml;hendisliği B&ouml;l&uuml;m&uuml;/Mechanical Engineering Department
Ankara/T&uuml;rkiye
Instructor: Dr. Atilla Bıyıkoğlu
04.05.2020
MM204E THERMODYNAMICS-II
HOMEWORK-III
2019-2020 SPRING
DUE ON MAY 11th, 2020
(30%) Q1. A vessel is divided into three compartments (a), (b) and (c) by two partitions. Part
(a) contains hydrogen and has a volume of 0.1 m3, part (b) contains nitrogen and
has a volume of 0.2 m3 and part (c) contains carbon dioxide and has a volume of
0.05 m3. All the three parts are at a pressure of 2 bar and a temperature of 13oC.
The partitions are removed and the gases are allowed to mix. Determine (a) the
molecular weight of the mixture, (b) the characteristics gas constant for the
mixture, (c) the partial pressures of each gas, (d) the reversible adiabatic index γ,
and (e) the entropy change due to diffusion. The specific heats of hydrogen,
nitrogen and carbon dioxide are 14.235, 1.039 and 0.828 kJ/kgK, respectively.
The above gas mixture is then reversibly compressed to a pressure of 6 bar
according to the law, 𝑝𝑣 1/2 = 𝑐𝑜𝑛𝑠𝑡. (f) Determine the work and heat interactions
in magnitude and sense, and (g) the change in entropy.
(20%) Q2. The vapor pressure, in mm of mercury, of solid ammonia is given by
3754
3063
, and that of liquid ammonia by ln p  19.49 
ln p  23.03 
T
T
(a) What is the temperature of the triple point? What is the pressure?
(b) What are the latent heats of sublimation and vaporization?
(c) What is the latent heat of fusion at the triple point?
(20%) Q3. Moist air at 30oC, 2 bar, and 59% relative humidity enters a heat exchanger
operating at steady state with a mass flow rate of 600 kg/h and is cooled at
essentially constant pressure to 20oC. Ignoring kinetic and potential energy
effects, determine the rate of heat transfer from the moist air stream, in kJ/h.
Gazi &Uuml;niversitesi/Gazi University
M&uuml;hendislik-Mimarlık Fak&uuml;ltesi/Faculty of Engineering and Architecture
Makina M&uuml;hendisliği B&ouml;l&uuml;m&uuml;/Mechanical Engineering Department
Ankara/T&uuml;rkiye
Instructor: Dr. Atilla Bıyıkoğlu
MM204E THERMODYNAMICS-II
HOMEWORK-III
2019-2020 SPRING
DUE ON MAY 11th, 2020
(30%) Q4. An ammonia refrigeration cycle works between a condenser saturation
temperature of 50oC and an evaporator temperature of -50oC. The liquid
entering the throttle valve is saturated. The vapor entering the compressor has
an entropy of 5.365 kJ/kgK, i.e. it will reach saturation at -2oC,
(a) Show the cycle on a T-s diagram Calculate the refrigeration effect and the
coefficient of performance.
(b) The cycle is modified as shown in Fig. Q3. The temperature in the flash
chamber is -2oC, and the saturated vapor bled off is mixed with the saturated
vapor leaving the first-stage compressor. Show the modified cycle on a T-s
diagram. Calculate the correct amount to be bled, the refrigeration effect,
and the coefficient of performance. Note: All quantities to be based on 1 kg
passing through the condenser.
Condenser
1 kg
2
3
Q2-3
W7-2
5
y7 kg 4
7
7
7
7
6
Flash Chamber
W1-7
(1-y7) kg
4
1
Q8-1
Evaporator
Fig. Q3. A refrigerator with two-stage compression and flash chamber
NOTE: Report your homework with a cover page and submit the pictures of the manual
solution pages in the word and deliver it electronically to [email protected] within the
date range specified as a single document, specifying your name and homework number.
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