Renewable Energy Technology Exam, Exercises of Environmental Science

Download Renewable Energy Technology Exam and more Exercises Environmental Science in PDF only on Docsity! 1 EXAMINATION Renewable Energy Technology MJ2411 2015/01/14 1400-1800 This exam paper contains five problems. You need to attempt all these problems. Total points allocated for this examination are 60 points. This is equal to 60% of the total of RET evaluation. (The remaining 40% is accounted from Quiz Examinations, Quiz 1 AND Quiz 2 conducted previously) A help document (9 pages) is provided with the examination. It contains information such as equations, formulas and property data. You are permitted use the following during the exam, • Provided help document • A scientific calculator • Pens, pencils and erasers • A dictionary This is a closed-book exam. Therefore, you are NOT permitted to use any other materials; books, notes or electronic resources or any other help materials. You need to write your solution in the provided papers. Please write only on one side of the paper. When you start a new problem always start with a new page. Write your name, your student number, question number and page number on each page. Energy Technology 2 The Exam grade of the course is decided based on your aggregated total of this examination and the quizzes. This part of the examination gives 60 points Quizzes (previously held) account 40 points Total 100 points Exam Grade: 91 - 100 A 82 - 90 B 68 - 81 C 54 - 67 D 50 - 53 E 47 - 49 Fx 0 - 46 F A – E, are exam pass grades. If you receive the grade Fx you can upgrade your grade to E by completing additional assignment. In such a case you need to contact the course responsible not later than one week after the result is released. If there is no intention from you, Fx will become F automatically 2 weeks later. The Final grade of the course is decided based on the Exam grade and Project grade of each individual and determined according to the following matrix. EXAM A B C D E P R O JE C T A A B B C D B A B C C D C A B C D D D B B C D E E B C C D E Good luck! 5 e) Calculate the lower heating value (LHV) of moist wood after the dryer in MJ/kg (2 points) f) Calculate the amount of diesel required for running the engine with 100% diesel in litres/year (2 points) g) Calculate the yearly wood consumption before the gasifier if it replaces 90% of diesel in ton/year (2 points) h) Calculate the gas flow rate out of the gasifier in mn 3/h (1 point) i) What would be the amount of water removed in the dryer (ton/year) (1 point) j) What would be the annual electrical power consumption of the drying process (kWh/year) (1 point) k) What is the percentage of electricity consumed for drying process? (%) (1 point) l) What alternative is available to consider for reducing the internal energy consumption of drying process (considering that the electrically driven mechanical drying is currently employed)? (1 point) Q2. Wind Power Question (10 points) Wind power system Wind energy is one of the most attractive renewable energy sources and is growing largely in the current global energy context. To establish a wind turbine at a specific location, several technical parameters are necessary to be determined. Considering such a situation, answer the following. a) For a given location, the wind speed at 10 m and 50 m heights above ground has been measured to be 4 m/s and 6.8 m/s respectively. Find the wind speed at 90 m height. (5 points) b) A wind turbine has a 1 MW rated power output at standard air density (15 ᵒC, 1 atm). Estimate the change of rated power if the turbine operates at a freezing temperature of -10 ᵒC.(3 points) c) Again for the 1MW turbine, estimate the change of the rated power relative to the sea level conditions, if the turbine is installed at 2000 m altitude above the sea. Use the below graph for determining the variation of air density with altitude.(2 points) (Take R = 286.9 J/kg K) 6 Q3. Solar Energy (15 points) Problem Description: The Energy Department at KTH plans to reduce its carbon dioxide emissions by maximizing its energy efficiency. As part of the design, solar energy will be used to produce hot water. For hot water production of the Energy Department, a solar thermosyphon system has been purchased. The system has a collector for heating the water with a frontal area of 100m². The system has a water tank with 4000 liters of water. The collector is a single glass type with an average transmission τG ∗ of 0.9. The absorption coefficient of the collector αA ∗ is 0.95, the U-value on the front is 4.5 W/(m² K) and on the back 0.5 W/(m² K). The collector can be considered perfectly insulated (adiabatic) at the sides. The collector efficiency factor F’ can be assumed as 0.94 and the mean ambient temperature as 18°C. For the calculation of the thermosyphon measurement data of the DNI (direct normal irradiation = beam radiation) form May 1st 2004 as shown in Figure 1 should be considered. Due to an error in the measurement system the clock time is unknown. Use your knowledge of the solar time to relate solar and clock time. In order to simplify the calculations this day can be can be divided into morning, noon and afternoon (sections I, II, and III) with mean irradiance levels of 300 W/m², 625 W/m², and 350 W/m², respectively. The noon section can be considered twice as long as the morning and evening sections (these two are equally long). 7 The solar collector of the thermosyphon system is placed due south with an inclination angle βc to harness the maximum amount of solar energy during an entire year. As the direct beam radiation is quite strong on this particular day the impact of the diffuse radiation can be neglected. Additionally, it can be assumed that the cosine effectiveness of the solar collector is constant during the day and equal to the cosine effectiveness of the collector at solar noon. Important assumptions: 1. There are no losses in the water tank and no usage of water either. The water temperature in the morning is the same as outdoor temperature 18°C. 2. After each section of the day the water in the tank is mixed to obtain a uniform temperature (the end temperature of each segment represents the starting temperature of the next one). 3. The mean fluid temperature in the collector can be assumed as equal to the arithmetic mean value of the start and end temperature of the water in the tank. Figure 1 Direct normal irradiance for Stockholm, May 1st, 2004