SECTION A : 100 MARKS BAHAGIAN A : 100 MARKAH INSTRUCTION: This section consists of FOUR (4) structured questions. Answer ALL questions. ARAHAN: Bahagian ini mengandungi EMPAT (4) soalan berstruktur. Jawab SEMUA soalan. QUESTION 1 SOALAN 1 a) Heat can be transferred in three different modes such as heat conduction, heat convection and heat radiation. Haba boleh dipindahkan dalam tiga mod berbeza seperti haba konduksi, haba olakan dan haba radiasi. i. Define heat conduction, heat convection and heat radiation. Takrifkan haba konduksi, haba olakan dan haba radiasi. [6 Marks] [6 Markah] ii. Write the relevant equation for each mode. Tuliskan persamaan yang untuk setiap mod. [6 Marks] [6 Markah] b) The main objective to learn heat transfer is to extend thermodynamic analysis through the study of the modes of heat transfer and development of relations to calculate heat transfer rates. State TWO (2) limitations of thermodynamics to heat transfer. 2 SULIT
Objektif utama untuk mempelajari pemindahan haba adalah untuk melanjutkan analisis termodinamik melalui kajian mod pemindahan haba dan melalui pembangunan hubungan untuk mengira kadar pemindahan haba. Senaraikan DUA (2) kekurangan termodinamik daripada pemindahan haba. [4 Marks] [4 Markah] CLO2 C2 c) Consider a 1.25 m high and 2.5 m wide double pane window consisting of two 3.25 mm thick layers of glass (k = 0.78 W/m C) that is separated by a 12.5 mm wide stagnant air space (k = 0.026 W/m C). The air resistance is 0.1538 C/W. Calculate each of the individual thermal resistance. Take the convection heat transfer coefficient on the inner and outer surfaces of the window to be h 1 = 10 W/m 2 C and h 2 = 25 W/m 2 C, and disregard any heat transfer by radiation. Pertimbangkan tingkap dua panel 1.25 m tinggi dan 2.5 m lebar yang terdiri daripada dua 3.25 mm lapisan tebal kaca (k = 0.78 W/m C) dipisahkan oleh ruang udara tetap (k = 0.026 W/m C). Rintangan udara ialah 0.1538 C/W. Kirakan setiap rintangan terma. Pekali pemindahan haba olakan bagi permukaan dalaman dan luaran ialah h 1 = 10 W/m 2 C and h 2 = 25 W/m 2 C, dan abaikan sebarang pemindahan haba oleh radiasi. [9 Marks] [9 Markah] QUESTION 2 SOALAN 2 a) Heat transfer through a liquid or gas can be by conduction or convection depending on the presence of any bulk fluid motion. Pemindahan haba melalui cecair atau gas boleh terjadi melalui konduksi atau olakan bergantung kepada kehadiran pergerakan pukal cecair. 3 SULIT
i. Convection heat transfer is depends on the fluid properties. State THREE (3) fluid properties of convection heat transfer. Pemindahan haba olakan bergantung kepada sifat cecair. Senaraikan TIGA (3) sifat cecair pemindahan haba olakan. [6 Marks] [6 Markah] ii. State ONE (1) similarity and difference of physical mechanism between heat conduction and heat convection. Senaraikan SATU (1) persamaan dan perbezaan mekanisme fizikal di antara haba konduksi dan haba olakan. [4 Marks] [4 Markah] CLO2 C2 b) A 15 cm diameter and 30 cm high cylindrical bottle contains cold water at 6ºC. The bottle is placed in windy air at 27ºC. The water temperature is measured to be 14ºC after 50 minutes of cooling. At the average temperature, the properties of water are given in density = 999.7 kg/m 3 and specific heat = 4194 J/kg ºC. Disregarding radiation effects and heat transfer from the top and bottom surfaces, calculate the heat transfer coefficient. Botol silinder bergaris pusat 15 cm dan 30 cm tinggi mengandungi air sejuk pada suhu 6ºC. Botol itu diletakkan di udara berangin pada suhu 27ºC. Bacaan suhu air adalah pada 14ºC selepas 50 minit penyejukan. Pada suhu purata, sifat-sifat air yang diberi adalah kepadatan = 999,7 kg/m 3 dan haba tentu = 4194 J /kg ºC. Tanpa menghiraukan kesan radiasi dan pemindahan haba dari permukaan atas dan bawah, kirakan pekali pemindahan haba. [15 Marks] [15 Markah] 4 SULIT
QUESTION 3 SOALAN 3 a) Heat radiation is different from heat conduction and heat convection due to radiation characteristics. List FOUR (4) characteristics of heat radiation. Haba radiasi adalah berbeza daripada haba konduksi dan haba olakan disebabkan oleh ciri-ciri radiasi. Senaraikan EMPAT (4) ciri haba radiasi. [8 Marks] [8 Markah] C2 b) Stefan-Boltzmann law can be used for radiation emission. Explain briefly radiation emission. Hukum Stefan-Boltzmann boleh digunakan untuk pelepasan radiasi. Terangkan secara ringkas pelepasan radiasi. [7 Marks] [7 Markah] CLO2 C3 c) A 3 mm thick glass window transmits radiation between λ = 0.3 and 3.0 µm and is essentially opaque for radiation at other wavelengths. Determine the fraction of radiation transmitted through a 2 m x 2 m glass window from blackbody sources at temperature 5800 K. 3 mm tingkap kaca tebal memancarkan radiasi antara λ = 0.3 dan 3.0 μm dan pada dasarnya legap untuk radiasi pada jarak gelombang yang lain. Tentukan pecahan radiasi yang dihantar melalui 2 m x 2 m tingkap kaca daripada sumber blackbody pada suhu 5800 K. [10 Marks] [10 Markah] 5 SULIT
QUESTION 4 SOALAN 4 a) Heat exchangers are classified according to flow arrangement and type of construction. Penukar haba diklasifikasikan mengikut susunan aliran dan jenis pembinaan. i. Name the simplest type of heat exchanger. Namakan jenis penukar haba yang paling mudah. [2 Marks] [2 Markah] ii. State TWO (2) types of flow arrangement of cross flow in compact heat exchanger. Senaraikan DUA (2) jenis susunan aliran di dalam aliran silang penukar haba padat. [4 Marks] [4 Markah] CLO2 C2 b) Water at an average temperature of 110 C and an average velocity of 3.5 m/s flows through a 5 m long stainless steel tube (k = 14.2 W/m C) in a boiler. The inner and outer diameters of the tube are D i = 1.0 cm and D o = 1.4 cm, respectively. The properties of water at 110 C are; density = 950.6 kg/m 3, dynamic viscosity = 0.255 x 10-3 kg/m s, thermal conductivity = 0.682 W/m 2 K and Prandtl Number = 1.58. If the convection heat transfer coefficient at the outer surface of the tube where boiling is taking place is h o = 8400 W/m 2 C, calculate the overall heat transfer coefficient, U i of this boiler based on the inner surface area of the tube. Air pada suhu purata 110 C dan halaju purata 3.5 m/s mengalir melalui tiub keluli tahan karat yang panjang 5 m (k = 14.2 W/m C) di dalam dandang. Garis pusat dalaman dan luaran tiub adalah D i = 1.0 cm dan D o = 1.4 cm, masing-masing. Sifat air pada suhu 110 C adalah; ketumpatan = 950.6 kg/m 3, kelikatan dynamik = 0.255 x 10-3 kg/m s, konduktiviti terma = 0.682 6 SULIT
W/m 2 K dan Nombor Prandtl = 1.58. Jika pekali pemindahan haba olakan pada permukaan luar tiub di mana mendidih sedang berlaku adalah h o = 8400 W/m 2 C, kirakan pekali pemindahan haba keseluruhan, U i dandang ini berdasarkan kawasan permukaan dalam tiub. [19 Marks] [19 Markah] SOALAN TAMAT 7 SULIT
Formula list / Senarai formula CONDUCTION The elementary thermal resistance relations: CONVECTION The average friction coefficient relations for flow over a flat plate: The average Nusselt number relations for flow over a flat plate: The average Nusselt number for cross flow over a cylinder and sphere: 8 SULIT
RADIATION Stefan Boltzmann law: E b (T ) = σt 4 ; σ = 5.670 x 10-8 W/m 2 K 4 Spectral blackbody emmisive power; Wien s displacement law: HEAT EXCHANGER Overall heat transfer coefficient U or a total thermal resistance R, expressed as: The effects of fouling on both the inner and the outer surfaces of the tubes of a heat exchanger can be accounted for by: LMTD method, the rate of heat transfer 9 SULIT
10 SULIT