Gazi niversitesi/Gazi University Mhendislik-Mimarlk Fakltesi/Faculty of Engineering and Architecture

Makina Mhendislii Blm/Mechanical Engineering Department Ankara/Trkiye

Instructor: Dr. Atilla Bykolu

31.03.2015

MM204E THERMODYNAMICS-II

HOMEWORK-II 2014-2015 SPRING

DUE ON APRIL 7th, 2015

(40%) 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 , 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 const1 2 ., (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

ln .pT

23033754

And that of liquid ammonia by

ln .pT

19 493063

(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?

Gazi niversitesi/Gazi University Mhendislik-Mimarlk Fakltesi/Faculty of Engineering and Architecture

Makina Mhendislii Blm/Mechanical Engineering Department Ankara/Trkiye

Instructor: Dr. Atilla Bykolu

MM204E THERMODYNAMICS-II

HOMEWORK-II 2014-2015 SPRING

DUE ON APRIL 7th, 2015

(40%) Q3. 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.

Fig. Q3. A refrigerator with two-stage compression and flash chamber

5

Condenser

W7-2

W1-7 Flash Chamber

(1-y7) kg

6

4

4

7

7

2

Q2-3

1 kg

1 Q8-1

Evaporator

3

y7 kg

7

7