EE/MM/PH 301 Energy Supplies, Semester I, 2013The University of the South Pacific Serving the Cook Islands, Fiji, Kiribati, Marshall Islands, Nauru, Niue, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu, and Vanuatu. School of Engineering and Physics EE/MM/PH 301: ENERGY SUPPLIES FINAL EXAMINATION – SEMESTER I, 2013 Time Allowed 3 hours plus 10 minutes reading 100 marks (50% of final grade) INSTRUCTIONS 1. This exam has TWO sections. a. Section A: 20 marks b. Section B: 80 marks 2. Answer all questions in sections A and ANY 5 from section B. For section B, begin each answer on a separate sheet. 3. You can use calculators that have not been programmed. 4. The symbols carry their usual meaning unless otherwise stated. 5. Use the following data where necessary 1.60 × 10-19 C 1.38 × 10-23 J K-1 8.85 × 10-12 F m-1 3.00 × 108 m s-1 1.025× 103 kg m-3 Charge of the electron, e Boltzmann constant, k Permittivity of free space, 0 Speed of light in vacuum, c Density of seawater Total number of pages: 7 -1- EE/MM/PH 301 Energy Supplies. Each question carries 2 marks. A4. Sketch labeled I-V characteristics of a photodiode both in the dark and under illumination.7 eV. Name the processes by which ethanol and biodiesel are produced. Determine the type of conductivity of this sample at 300 K. A8. A5.5 x 1016 m-3 at this temperature. A1. Semester I. A7. Define the term Power Factor of an AC electric power system. A10. the intrinsic carrier density is 1. A2. -2- . Calculate the wavelength of the photons that will just be able to excite an electron from the top of the valence band to the bottom of the conduction band. and the type of vehicle engines they may be used in. How is pyrolysis different from gasification? What are the final products of these two processes? A9. 2013 Section A: Answer ALL questions. Briefly describe a method for the determination of the volumetric flow rate Q of a hydropower station. Define the term Air mass as applied to solar radiation. A6. The band gap of a CdSe sample is 1. List at least three non-power related benefits of an open cycle OTEC system. A3. Write an expression for the rated maximum power produced by a wind front of speed u0 and density passing across a turbine intercepting cross section area A. A silicon crystal is doped with 3 x 1019 m-3 Phosphorous atoms. For silicon. i) Sketch labelled band diagrams for the specimen before and after the contact was made.4 x 10 19 m-3. (a) Starting with the concept of global warming. [3 marks] -3- . [3 marks] (b) Two silicon specimen doped with 1.39 m2 V-1 s-1. [5 marks] (c) B2. electron mobility = 0. 2013 SECTION B: Answer ANY FIVE questions. hole mobility = 0.10 South) on June 20th 2013. Describe at least one example of such an activity that you have come across. Each question carries 16 marks.5 x1020 m-3 phosphorus impurity and 2. B1. [5 marks] (b) Determine the time of sunrise and sunset in Suva (latitude 18.EE/MM/PH 301 Energy Supplies. explain how renewable energy technologies and energy efficiency can help in climate change mitigation. (a) Briefly describe the following: i) Solar ponds [2 marks] ii) Thermosyphon effect based hot water systems [2 marks] iii) Selective absorbers [2 marks] The following data is given for intrinsic germanium at 300 K: Intrinsic carrier concentration ni = 2.0 x 1019m-3 boron impurity are used to form a p-n junction. Semester I.19 m2 V-1 s-1 Determine the conductivity of this sample. [10 marks] -4- .9 V and Im = 7. explain the operation of a p-n junction solar cell. Peak sun hours : 4 Consecutive no-sun days: 2 Inverter efficiency = 90 % Battery DoD = 60 % Inverter input voltage = 24 V Solar panel: 120 W. [3 marks] B3. Semester I.7 V and a reverse bias of 10.EE/MM/PH 301 Energy Supplies. Determine the number of solar panels and batteries needed for this system and sketch a diagram showing the arrangement. 12 V.5 V? [2 marks] v) Sketch and explain the I-V characteristics of this junction. 75 W each DC 112 Duty hour/day 6 AC AC AC 60 200 150 4 4 4 cycle Location: Nadi . (a) With the help of its equivalent circuit and band diagram. [6 marks] (8) A homeowner in Nadi would like to install a standalone solar PV system based on the following data: Load Data: Appliance AC/DC Watts 4 Lights 28 W each TV Computer 2 Fans. [3 marks] iv) What are the barrier heights under a forward bias of 0. 2013 ii) Sketch the band diagram when the junction is forward biased and explain the effect of biasing. Vm =16. [2 marks] iii) Calculate the barrier height when the junction is unbiased.1 A Battery rated capacity = 100 Ah. [5 marks] (c) With help of schematic diagrams. [3 marks] -5- . (a) i) Under what conditions is the combustion of biomass incomplete? Name two products that are formed that are not produced during complete combustion.EE/MM/PH 301 Energy Supplies. 2013 B4. [2 marks] iii) Starting from the First Law of Thermodynamics show that the work Weng done by a heat engine during one complete cycle is equal to the net heat Qnet. the average power carried forward in the wave per unit width across the wave front is given by P g 2 a 2T 8 where the symbols carry their usual meaning and given that the wavenumber of a deep water wave is k 2 g [7 marks] (b) Compare and contrast the operation of a PEM electrolyzer and a PEM fuel cell. explain the operation of the following ocean energy technologies: i) A tidal range power system ii) A Oscillating Water Column ( OWC) System [4 marks] B5. [2 marks] ii) Describe the difference between a Condensing Power Plant and a Combined Heat and Power (CHP) Plant. Semester I. (a) Show that for deep water waves. [4 marks] (c) A 2-jet Pelton Wheel produces an output power of 8. i) the speed vj of the water in the jets [2 marks] ii) area A of each jet. Determine . It plans to generate this using a thermal power plant that will use the timbermilling residues produced. If the head loss (due to friction) is 15 m.5 MW from a head of 315 m. Semester I. with the help of a schematic diagram. steam turbine and generator to be 80%. [2 marks] (b) Describe the difference between the Francis. 35% and 85% respectively [2 marks] ii) What is the Carnot efficiency of the heat engine if the boiler temperature is 350 oC and the condenser temperature is 30 oC? State why the actual efficiency is lower than the Carnot efficiency. and use the above expression for the input power at a hydropower station to decide which turbine you will use for a high head. and the turbine and generator efficiencies are 90% and 85% respectively. and Q is the volumetric flow-rate.EE/MM/PH 301 Energy Supplies. [2 marks] iii) B6. Take the efficiencies of the furnace. (a) What is the total mass of timber-milling residues (with energy content 10 MJ kg-1) required to operate this power plant continuously for one week (7 days)? [5 marks] Show that the power P that can be generated from water flowing down from a height H is given by P = ρ gQ H where ρ is the density of water. 2013 (b) A small timber-milling community requires 100 kW for its electrical power needs. and . a low head and a very low head. The speed of rotation of the runner is 300 rpm. how the energy conversion processes will take place. i) Show. Propellor and the Pelton Wheel turbines. [4 marks] -6- . The cut –out wind speed is 25 m s-1. [2 marks] ii) Explain why thermodynamically only about half the power in the wind can possibly be extracted. Semester I. [1 mark] THE END -7- .20 kg m-3.5 m s-1 and the rated wind speed is 16 m s1. the fraction of power extracted from the wind. [2 marks] ii) Explain the effect of blade spacing and rotation on the optimum power extraction efficiency. is given by: CP i) 4 a 1 a 2 Show that the maximum value of CP occurs when a = 1/3 [3 marks] ii) Show that the axial thrust FA for a horizontal axis machine is FA Au 2 2 . 2013 iii) the wheel diameter D? B7. a) [4 marks] A small scale (20 kW) wind turbine has a power coefficient of 0. The cut-in wind speed of the turbine is 4.Calculate the rotor diameter. c) 4 a 1 a 2 [6 marks] i) Sketch with well labelled axes the wind turbine operating regions and power performance (power curve) of a 20 kW wind turbine.3 at the rated wind speed of 15 m s-1. assuming the air density is 1.EE/MM/PH 301 Energy Supplies. [2 marks] b) The power coefficient CP.