MS2230 TERMODINAMIKA TEKNIK I

TUGAS KELOMPOK KE 3

Dikumpulkan hari Senin, 2 Maret 2015 (jam dan tempat sesuai perjanjian dgn dosen

kelas)

1. Sebuah sistem turbin gas sederhana (siklus terbuka) bekerja secara isentropik. Udara

masuk kompresor dengan tekanan dan temperatur masing-masing adalah 100 kPa(abs)

dan 30 0C. Tekanan dan temperatur gas masuk turbin masing-masing adalah 2000 kPa

dan 1000 0C. Diketahui data-data udara: R = 287 J/kg.K , cp = 1 kJ/kg.K, dan cv = 0,718

kJ/kg.K.

(a) Gambarkan diagram blok turbin gas tersebut lengkap dengan nama komponen-

komponen utamanya.

(b) Gambarkan siklus kerja turbin gas tersebut pada diagram temperatur terhadap entropi

(diagram T vs S).

(c) Hitung daya turbin yang dihasilkan jika laju massa udara masuk kompresor 10 kg/s

(abaikan laju massa bahan bakar).

(d) Hitung temperatur gas keluar turbin.

(e) Hitung efisiensi termal dari sistem turbin gas tersebut.

2. Udara memasuki mesin turbojet pada temperatur 240 K, tekanan 0,85 bar, dan kecepatan

masuk 1.100 km/h. Rasio tekanan pada kompresor adalah 8. Temperatur fluida memasuki

turbin adalah 1.200 K dan tekanan pada sisi keluar nosel adalah 0,8 bar. Kerja yang

dihasilkan turbin seluruhnya digunakan oleh kompresor. Difuser dan nosel bekerja secara

isentropik, sedangkan efisiensi isentropik kompresor dan turbin secara berurutan adalah

0,8 dan 0,9. Untuk kondisi tunak, hitunglah tekanan pada setiap tingkat keadaan [bar] dan

kecepatan fluida keluar dari nosel [m/s]. Gunakan asumsi yang diperlukan.

3. A Brayton cold air standar cycle (ASC) has a turbine isentropic efficiency of 92% and a

compressor pressure ratio of 14. The compressor and turbine inlet temperatures are 40oC

and 1100oC, respectively. Determine the compressor isentropic efficiency that causes

overall thermodynamic thermal efficiency of the system to be exactly zero.

4. A test on an open loop Brayton cycle combustion gas turbine produces the following

results:

Net power output = 180.5 hp

Air mass flow rate = 20.0 x 103 lbm/h

Air inlet temperature = 80oF

Inlet air pressure = 14.5 psia

Compressor exit pressure = 195 psia

Compressor isentropic efficiency = 85%

Combustion chamber heat addition = 4.00 x 106 Btu/h

Using a cold air standar analysis and assuming k = 1.4, determine

a) The cycle thermal efficiency.

b) The turbine inlet temperature.

c) The isentropic efficiency of the turbine.

d) The back work ratio of the system.

5. Air enters an Otto cycle internal combustion engine at 90.0 kPa and 15.0°C. The engine

has a compression ratio of 8.00 to 1. During the combustion process, 3000. kJ per kg of

air is added to the air. Assuming a reversible engine, determine

(a) the pressure and temperature at the end of each process of the cycle,

(b) the engine’s cold air standar cycle thermal efficiency, and

(c) the mean effective pressure of the engine.

6. An ideal Otto cycle with air as the working fluid has a compression ratio of 8. The

minimum and maximum temperatures in the cycle are 540 and 2200 R. Accounting for

the variation of specific heats with temperature, determine:

(a) the amount of heat transferred to the air during the heat addition process, in Btu/lbm

(b) the thermal efficiency, and

(c) the thermal efficiency of a Carnot cycle operating between the same temperature

limits.

7. An air-standard Diesel cycle has a compression ratio of 16 and a cutoff ratio of 2. At the

beginning of the compression process, air is at 95 kPa and 27oC. Accounting for the

variation of specific heats with temperature, determine:

(a) the temperature after the heat-addition process, in K,

(b) the thermal efficiency, and

(c) the mean effective pressure, in kPa.

8. A four-cylinder 4.5-L diesel engine that operates on an ideal Diesel cycle has a

compression ratio of 17 and cutoff ratio of 2.2. Air is at 27oC and 97 kPa at the beginning

of the compression process. Using the cold-air standard assumptions, determine how

much power the engine will deliver at 1500 rpm.

9. A Bryton cycle with regeneration using air as the working fluid has a pressure ratio of 8.

The minimum and maximum temperatures in the cycle are 310 and 1150 K. Assuming an

isentropic efficiency of 75% for the compressor and 82% for the turbine and an

effectiveness of 65% for the regenerator, determine:

(a) the air temperature at the turbine exit, in K,

(b) the net work output, in kJ/kg, and

(c) the thermal efficiency, in %.

10. Motor Diesel dengan volume langkah 3000 cc. Proses pada setiap silinder dimodelkan

sebagai siklus Diesel ideal dengan rasio cut-off nya adalah 2,5. Tingkat keadaan udara

pada awal kompresi ditetapkan dengan p1 = 95 kPa , T1 = 22oC, dan V1 = 3170 cc. Hitung

kerja netto siklus dalam kJ, dan daya yang dihasilkan motor, dalam kW, jika siklus

beralngsung pada 1000 rpm.

Selamat bekerja.