EMH 332/3 Applied Thermodynamics [Termodinamik Gunaan]

Transcription

1 -1- UNIERSITI SAINS MALAYSIA First Seester Exaination 2012/2013 Acadeic Session January 2013 EMH 332/3 Applied Therodynaics [Terodinaik Gunaan] Duration : 3 hours Masa : 3 ja Please check that this paper contains SIX (6) printed pages, ONE (1) page appendix and SIX (6) questions before you begin the exaination. [Sila pastikan bahawa kertas soalan ini engandungi ENAM (6) ukasurat bercetak, SATU (1) ukasurat lapiran dan ENAM (6) soalan sebelu anda eulakan peperiksaan.] Appendix/Lapiran : 1. Forula for Internal Cobustion Engine [3 pages/ukasurat] INSTRUCTIONS : Answer FIE (5) questions only. You ay answer all questions in English OR Bahasa Malaysia OR a cobination of both. [ARAHAN : Jawab LIMA (5) soalan sahaja. Calon boleh enjawab seua soalan dala Bahasa Malaysia ATAU Bahasa Inggeris ATAU kobinasi kedua-duanya.] Answer to each question ust begin fro a new page. [Jawapan untuk setiap soalan estilah diulakan pada ukasurat yang baru.] In the event of any discrepancies, the English version shall be used. [Sekiranya terdapat sebarang percanggahan pada soalan peperiksaan, versi Bahasa Inggeris hendaklah diguna pakai.] Table for Property Tables Booklet is provided. Jadual Sifat Bendalir Terodinaik adalah dibekalkan. 2/-

2 -2- Q1. [a] Due to soe leakages of air into condenser of the stea plant, explain briefly how these probles being solved and the losses involved. Disebabkan kebocoran udara easuki penyejuk bagi loji sti, terangkan secara ringkas bagaiana asalah diatasi dan kehilangan yang terlibat. [b] A vessel of capacity contains a ixture of air and stea which is 75% dry. If the pressure is 700 kpa and the teperature is 117 o C, deterine the ass of water present, the ass of dry saturated vapor, and the ass of air. Sebuah kebuk berkapasiti engandungi capuran udara dan wap yang ana 75% kering. Jika tekanan adalah 700 kpa dan suhu adalah 117 o C, tentukan jisi air wujud, jisi bagi wap tepu, dan jisi air. 0.5 kg of saturated air is contained in a rigid tank along with water vapor at 160 o C and 1 MPa. Calculate the aount of heat required to be transferred to cool the ixture to 80 o C, and the oisture will be condensed in this process. 0.5 kg bagi udara tepu terkandung dala sebuah tangki tetap bersaa dengan wap pada 160 o C dan 1 MPa. Kirakan julah haba yang diperlukan bagi enyejuk capuran kepada 80 o C, dan lebapan yang akan tersejuk di dala proses ini. (40 arks/arkah) Q2. [a] Copare and explain briefly a sweating phenoena occurs on the glass surface filled by ice cubes at 50% and 90% relative huidity respectively with the atospheric condition of 101 kpa and 25 o C. Banding dan terangkan secara ringkas fenoena berpeluh berlaku pada perukaan gelas yang diisi oleh kiub ais asing-asing pada kelebapan relatif 50% dan 90% dengan keadaan atosfera 101 kpa dan 25 o C. (20 arks/arkah) [b] Using the scheatic, propose five (5) criteria required in design an effective air conditioning syste for a ediu sized factory floor that ainly assebles sensitive electronic products. Menggunakan skeatik, cadangkan lia (5) kreteria yang diperlukan dala reka bentuk sebuah siste penyaan udara untuk sebuah kilang bersaiz sederhana terutaanya bagi easang produk elektronik yang peka. (40 arks/arkah) 3/-

3 -3- Cold air at 30% relative huidity, 8 o C, is heated to 31 o C and the pass through huidifier cooler until it reaches 21 o C. Deterine: (i) The heat input (ii) The ass of water added (iii) The final relative huidity (iv) If the cold air as at 35% relative huidity, 8 o C, estiate the percentage different of heat input. Udara sejuk pada kelebapan relatif 30%, 8 o C, dipanaskan kepada 31 o C dan di alir elalui penyejuk lebapan sehingga encapai 21 o C. Tentukan: (i) Haba asukan (ii) Jisi air yang ditabah (iii) Kelebapan relatif akhir (iv) Jika udara sejuk pada kelebapan relatif 35%, 8 o C (40 arks/arkah) Q3. [a] Saples X and Y is the liquid and gas fuels respectively. Propose and explain how the calorific values of these fuels are deterined. Sapel X dan Y asing-asing adalah cecair dan gas. Cadang dan terangkan bagaiana nilai kalori bagi bahan api ini ditentukan. [b] A 500 g of Kerosene (C 12 H 26 ) is used in the cobustion, calculate both the stoichioetric air-fuel ratio required and for the cobustion with 20% access air. 500 g kerosin (C12H26) digunakan dala pebakaran, kirakan kedua-dua nisbah udara-bahan api stoikhioetrik dan bagi pebakaran dengan 20% lebihan udara. Methane and air enter a cobustor at atospheric pressure and 25 o C in the ratio ole air/ole ethane. After cobustion the products, including carbon dioxide and carbon onoxide, are at 227 o C and the water fored in the vapor state. Calculate the heat absorbed or released in kj/kol ethane. Metana dan udara easuki sebuah pebakar pada tekanan atosfera dan 25 o C dengan nisbah ol udara/ol etana. Selepas pebakaran produk, terasuk karbon dioksida dan karbon onoksida adalah pada 227 o C dan air terbentuk dala keadaan wap. Kirakan haba terbekal atau terbebas dala kj/kol ethan. (40 arks/arkah) 4/-

4 -4- Q4. [a] Using the diagra, differentiate the four-stroke and two-stroke spark ignition engines. Menggunakan gabarajah, bezakan enjin cucuhan bunga api lenjang-epat dan lenjang-dua. [b] Briefly discuss the phenoena is known as knock in a gasoline engine. Bincangkan dengan ringkas fenoena yang dikenali sebagai knock di dala sebuah enjin gasoline. (20 arks/arkah) A Mitsubishi truck used an air Diesel engine cycle with a copression ratio of 17. Air is at 30 o C and 100 kpa at the beginning of the copression process and at 1800 K at the end of the heat addition process. Accounting for the variation of specific heats with teperature, deterine: (i) The cut-off ratio (ii) The heat rejection per unit ass, and (iii) The theral efficiency. Sebuah trak Mitsubishi enggunakan kitar enjin udara Diesel dengan nisbah apatan adalah 17. Udara adalah pada 30 o C dan 100 kpa pada perulaan proses apatan dan pada 1800 K diakhir proses penabahan haba. Mengabil kira bagi perubahan haba tentu dengan suhu, tentukan: (i) Nisbah cut-off (ii) Haba terbebas per unit jisi, dan (iii) Kecekapan tera (50 arks/arkah) Q5. [a] In the indicated diagra, briefly discuss the perforance ap at different piston speed for Diesel engine. Dala gabarajah penunjukkan, bincang secara ringkas peta prestasi pada perbezaan halaju piston bagi enjin Diesel. 5/-

5 -5- [b] A three-liter 6 four-stroke spark ignition engine has copression ratio of 9.0. During a test at 3700 rev/in, the brake torque reading fro a dynaoeter is 200 N. At this speed, air enters the cylinders at 101 kpa and 30 o C. The air-fuel ratio easured is 14.5:1 and the echanical efficiency of the engine is 92%. The engine cylinder bore is the sae as the stroke length. The fuel calorific value is 44 MJ/kg, calculate the (i) Cylinder bore and stroke length (ii) Mean piston speed (iii) Clearance volue for one cylinder (iv) Brake power (v) Indicated power (vi) Brake ean effective pressure (vii) Indicated ean effective pressure (viii) Mass flow rate of fuel into the engine (ix) Brake theral efficiency Sebuah enjin epat lenjang 6 cucuhan bunga api tiga-liter epunyai nisbah apatan 9.0. Seasa ujian dijalankan ke atas enjin pada kelajuan 3700 pusingan/in, bacaan tork brek yang diperolehi daripada dynaoeter ialah 200 N. Pada kelajuan ini, udara easuki selinder pada 101 kpa dan 30 o C. Nisbah udara-bahan api yang diukur adalah 14.5:1 dan kecekapan ekanikal ialah 92%. Jara bagi enjin silinder adalah saa dengan lejang. Nilai kalori bahan api adalah 44 MJ/kg, kirakan: (i) Jara dan lejang (ii) Halaju purata oboh (iii) Isipadu kelegaan bagi sebuah silinder (iv) Kuasa brek (v) Kuasa tertunjuk (vi) Tekanan berkesan purata brek (vii) Tekanan berkesan purata tertunjuk (viii) Kadar aliran jisi bahan api ke dala enjin (ix) Kecekapan tera brek (70 arks/arkah) Q6. [a] Using the diagra, differentiate the reciprocating and rotary positive displaceent air copressor. Menggunakan gabarajah, bezakan peapat udara sesaran positif berlejang dan putaran sesaran positif. (20 arks/arkah) [b] In the indicated diagra, briefly discuss the correlation between the voluetric efficiency and pressure ratio for a ulti stage copressor. Dala gabarajah petunjuk, bincangkan secara ringkas korelasi antara kecekapan isipadu dan nisbah tekanan bagi sebuah peapat pelbagai peringkat. 6/-

6 -6- A two stage air copressor consists of three cylinders having the sae bore and stroke. The delivery pressure is 707 kpa and the FAD is /in. Air is drawn in at 101 kpa, 15 o C and intercooler cools the air to 38 o C. The index of copression is 1.3 for all three cylinders. Neglecting clearance, calculate: (i) the interediate pressure (ii) the power required to drive the copressor (iii) the isotheral efficiency Sebuah peapat udara dua peringkat terdiri daripada tiga silinder yang epunyai jara dan lejang yang saa. Tekanan hantaran adalah 707 kpa dan FAD adalah /in. Udara disedut asuk pada 101 kpa, 15 o C dan penyejuk antara peringkat enyejuk udara kepada 38 o C. Indeks apatan adalah 1.3 bagi keseua tiga silinder. Abaikan had ruang, kirakan: (i) Tekanan perantaraan (ii) Kuasa yang diperlukan bagi eandu peapat (iii) Kecekapan isotera (50 arks/arkah) -oooooooo- 7/-

7 The copression ratio, r: r ax in Forula for Internal Cobustion Engine APPENDIX 1/LAMPIRAN 1 The ean effective pressure, MEP MEP ax W net in v ax w net v in The indicated ean effective pressure, pi p i net _ area _ of _ diagra cons tan t length _ diagra Work done per cycle = p i A L The indicated power, ip: ip pi AL ( cycles/ tie) For four-stroke engine: ip p i ALNn 2 For two-stroke engine: ip p ALNn i Where n is the no. of cylinders. Brake power (bp) This is to easure the engine output. The engine is connected to the break or dynaoeter. T= WR The brake power is then given by bp 2NT [1/3]

8 APPENDIX 1/LAMPIRAN 1 Friction power (fp) and echanical efficiency, The difference between ip and bp: Fp = ip bp The echanical efficiency: bp ip For ulti cylinder engines such as four cylinder engine, the bp bp ( ip1 L1 ) ( ip2 L2 ) ( ip3 L3 ) ( ip4 L4 ) Break ean effective pressure (bep) The bp is obtained using dynaoeter, bp ip For a four-stroke engine, bp pi ALNn 2 or pb ALNn bp where pb pi 2 For the frictionless engine, the bep p b ALNn 2 2 NT Thus, p b K T where K = constant The overall efficiency of the engine is given by the brake theral efficiency, BT fuel bp Q net, v [2/3]

9 APPENDIX 1/LAMPIRAN 1 Specific fuel consuption, sfc The specific fuel consuption (sfc) is the ass flow rate of fuel consued per unit power output, sfc bp fuel The indicated theral efficiency, IT is defined as IT fuel ip Q net, v oluetric Efficiency, S [3/3]