BRAE 348 final
The amount of energy used for an activity depends on the energy required for that activity and the frequency of that activity. What are the two approaches listed from the book that address the efforts of energy conservation? (think broad category)
-Technical Fix -Lifestyle change
When your see a sticker at a gas pump that reads E10 which of the following is true.
-The gasoline from that pump is approved for use in all automobiles -The gasoline from that pump contains up to 10% Ethanol -Vehicles driving on this gasoline will have a reduction in miles per gallon of 3-4% compared to using 100% gasoline.
Electrical power plants dissipate about 2/3 of their input energy into the environment, primarily in the form of hot water at about 20C (35F) above ambient temperatures. What would be some of the challenges in using this "waste heat" for the heating of buildings near the power plant? (this has multiple correct answers to get full credit)
-The quality of warm water is low due to the low delta temperature (between the building and the water). It leads to very low efficiency -Capital costs would be high to build the piping network to get the warm water to the buildings and back to the power plant -Operating costs might be high because you would have to move a very large volume of water through the pipes to get enough heat from the warm water.
What things can be done to reduce the rate of heat transfer through a single pane window? (could be more than one answer)
-low-e coating -use a window shade -Insulating drapes plus valance
Newton's First Law of Motion states that: An object continues in a state of rest or motion with a constant velocity unless compelled to change by an unbalanced (net) outside force. Then why do objects stop after we push them (like rolling a ball on the floor)?
Because of the force of friction
Power
Energy/time
Removal of 99.9% of particles greater than 0.1 micron
Fabric filter
What is the definition of sustainable?
Utilizing resources today in a way that will allow future generations to meet their needs
Power
Watts Horse Power ft-lb/min
How does the "Angle of Incidence" effect the amount of energy that is absorbed by a solar panel?
When perpendicular to a surface there is the minimum amount of reflected light resulting in the highest amount of solar input being absorbed.
Why does deforestation contribute to global warming?
-Adds CO2 due to the burning process -Removes the CO2 sinks
Energy
-Calorie -Joules -BTU -Kilowatt-hr -ft-lb
What methods can be used to reduce infiltration in a house? (more than one answer)
-Caulking doors and windows -Sealing exterior electrical plates -Weatherstripping doors
Enhanced Oil Recovery
-Correct answer: Inject steam or CO2 into the reservoir -Pumps out from 35% - 45% of the original oil
Which of these statements describe renewable energy? Select all that apply.
-Energy that is derived indirectly from the sun -Energy that is naturally regenerated over a short time scale -Energy derived directly from the sun.
Why do you expect photochemical smog to be a greater problem in a city like LA than in a heavy industrialized city like Pittsburgh?
-LA has more sunlight -Reaction with NOx from automobile combustion process -hydrocarbons present from rush hour traffic pg 250-252
How does 1 gallon of gas become 20 Lb of CO2?
-Lastly multiply by the molecular weights to get from C to CO2 (44/12) -Next multiply by the carbon content fraction (about 85% carbon) -Start by converting 1 gal of gas to 6.4 Lb
Secondary Recovery
-Pumps out from 15% - 35% of the original oil -Water injection into the oil reservoir to increase pressure and output
Primary Recovery
-Pumps out up to 15% of the original oil -Mainly just pumping can get the oil out
Consider Example 17.1, page 539 in your textbook on the caloric value of gasoline compared to food. Using the same process what would be the cost per kcal for natural gas, which is valued at $1.95 per therm. Note: 1 Therm = 100,000 BTU
0.0077 ¢ per kcal
Suppose you want to lift 500 gallons of water to a storage tank at a height of 10 meters in a period of 5 hours using a solar panel and pump system like the one in activity. Determine the power rating of the pump (in Watts) and calculate the wattage of the solar panel required if the pump has an efficiency of 65%.
1) 10 Watt pump 2) 16 Watt solar panel
If the solar panels used on a Solar farm have an efficiency of 16 %, what area of land is needed, in hectares, to produce an output of 1092 MW? Assume that the mean insolation is 656 W/m2. and that there are 10,000 m2 per hectare. State your answer in Hectares and round to 2 decimal places
1,040.40 Use the equation from chapter 6: Power = Insolation * Efficiency * Area
Suppose you left a 119 watt light bulb on continuously for 37 days. If the electricity generation and transmission combined has an efficiency of 30%, calculate the total chemical energy (in JOULES) transformed at the power plant due to the light being left on? Recall: Joules are Energy, Watts are Power; Power is the rate of using energy State your answer in Mega Joules and round to 2 decimal places.
1,268.06 Given the watts of the light bulb and the period of time we can calculate the Energy (joules). We must also account for the efficiency. So we need to use more total energy than what is transformed to electricity. We need to divide the useful energy out by the efficiency to calculate the total energy. Total energy in = Useful energy out / efficiency. Also need to convert from Kw-hr to Joules (Table 3.4 pg 86)
How many hours will it take to heat 65 gallons of water from 55 to 132 degrees F with a 7 KW immersion heater (assuming no energy is lost to the environment)? State your answer in hours, round the value to 2 decimal places.
1.74 Use Q = m c (t2-t1) to solve for the energy required to heat the water. Then you need to convert Q into Kw-hr and divide by the size of the heater, in KW. This leaves you with hours. Remember KW is power and power is the energy/time or the rate at which energy is used. You can get m by multiplying the gallons by 8.3 Lb/gallon; c = 1 Btu/Lb/deg F; t2 and t1 are given. There are 3413 Btu / Kw-hr
Suppose the solar radiation is 809W m-2, and you can collect 16 % (efficiency) of the energy that falls on the reflecting surface of a solar hot dog cooker. If you need 235 watts to cook a hotdog, what is the minimum collector area required to cook a hotdog? Give your answer in meters and round your answer to 2 decimal places.
1.82 Use the equation Q = I * Eff * Area (page 182) I = insolation Here Q = energy required for the cooking (watts = energy/time) Eff = efficiency Area = size of the surface
Possible reserves
10%
A Boeing 777 airplane flying New York to San Francisco (3,000 miles) consumes 10632 gallons of jet fuel. If the plane is full with 371 passengers, then how much energy (kW-hr) is used for this trip per passenger? Assume energy content for jet fuel is the same as that for gasoline State your answer in kW-hr per person and round to 2 decimal places.
1041.18 Given the gallons consumed in total, you need to divide by the number of passengers. Assume jet fuel has the same energy content as gasoline, 1.25 x 10^5 BTU per gallon you can now convert to Kw-hr. Also need to convert from BTU to Kw-hr (Table 3.4 pg 86)
Emissions from heating, 1 therm of natural gas (100,000 Btu)
12 Lb CO2
A wall is made up of four elements, use table 5.2 to calculate the R-value. 0.5 inches of wood siding (lapped) 1 inch of plywood 3.5 inches of fiberglass insulation 1 inch of sheetrock
13.85
What is the potential energy of a 2 kg person sitting on a ladder 8 m off of the ground? State your Answer in Joules (J) rounded to 2 decimal places, and assume gravity is 9.8ms-2
156.80
A recent wind farm project in Idaho uses 6 turbines of 3 MW rating; 27 million kW-hr per year is expected from this site. What is the capacity factor for this project as a PERCENT (i.e., energy output divided by the rated capacity on an annual basis)? (answer as %)
17.12
A 53 W light bulb is accidentally left on for 9 days in a basement. If electricity costs 17 cents per kilowatt hour (¢/kw-hr), how much did this oversight cost? (final answer should be in rounded to the nearest CENT, not in dollars and cents, for example, if your final answer is $1.98, enter 198)
195
Emissions from the production of 1 Kw-hr electricity from coal
2 Lb CO2
A 1000 MW electric plant uses coal with 3.81 % sulfur content. How many tons of SO2 will be emitted into the air during the operation of the plant for 4 day(s)? (9000 tons of coal per day for a 1000 MW electrical plant) (also remember SO2 is heavier than S) State your answer in tons, rounded to 2 decimal places
2,743.20 Multiply the amount of coal 9000 tons/day times the %sulfur; this gives you tons of sulfur per day, convert that to SO2 by multiplying by the ratio of the molecular weight 64/32 (S=32; O2=32; SO2=64) and then multiply by the number of days.
Suppose that all of World's needs for oil were to be provided by that available from the estimated undiscovered oil reserves located in the Arctic circle, 91.4 billion barrels. How long (years) would that supply last using the current consumption, 90.4 million barrels per day (MBPD)? State your answer in YEARS and round to 2 decimal places.
2.77 Divide the total reserves in billions of barrels by the daily consumption in millions of barrels per day, divide by 365 days per year. Make sure you convert billions to millions.
Emissions from a car, per 1 gallon of gasoline
20 Lb CO2
A small Pump storage system has a water reservoir of 1000L that is set 9 feet above the ground. Potentially how much energy could be stored in the reservoir and recovered, if the attached hydropower generator has an Efficiency of 80%.
21,512 J
Consider an old house (from 1858) It has walls constructed of 2 inch hardwood planks, 0.5 inch lapped wood siding with 0.5 inch sheetrock on the inside. The size of the house is 40 ft wide, 27 ft long and 11 ft tall. Assume a flat roof covered with 1 inch plywood, asbestos shingles and 3.5 inches of fiberglass insulation. Assume 25% of the walls are covered with single pane windows. This old house is very leaky resulting in 3 exchanges per hour (k value). Assume no losses through the floor. The outside temperature is 45 degrees F cooler than the inside temperature. Considering only infiltration heating losses, calculate the heating needs in BTU/hr, and round your answer to 2 decimal places.
28,868.40 The total heat loss from a house is the sum of the conductive losses and the infiltrative losses. Here we are only calculating the infiltration losses. We use the equation from chapter 5, page 134 Q/t = 0.018 * Volume * K * delta T 0.018 is a constant and units are Btu / ft^3 / F Volume is the volume of the space or length * width * height K is the number of exchanges, new house have a K value of 0.5 - 1.5 old houses may have a K value of 4 - 6. This is the total volume exchanges per hour
If an electric clothes dryer has a power rating of 5946 watts and is used for 1.5 hour per day, how much money can be saved over 29 days by using the backyard clothes dryer (hang dry on a clothes line) instead. Assume electricity costs 11 cents per kw-hr. (answer should be is dollars($) rounded to 2 decimal places)
28.45 Calculate the Kw-hrs of savings and multiply that by the cost. dryer watts * hr/day * days = watt-hrs * 1/1000 = Kw-hr * cost = money saved
Given a wall is made up of four elements, find the rate of heat loss through the wall per square foot when the inside temp is 68 degrees F and the outside temp is 24 degrees F. (units will be BTU hr-1 ft-2) 0.5 in wood siding 0.5 inch plywood sheeting 3.5 inch fiberglass 0.5 inch sheetrock State your Answer in BTU hr-1 ft-2 and round to 2 decimal places.
3.44 Use the equation Q/t = 1/R * A * delta T. However, because we are not given an area, we divide both sides of the equation by Area. So use Q/(t*A) = 1/R * delta T. Q/t = heat flow rate A = area R = R value found by adding each individual R value from Table 5.2 for each component of the wall (should be 12.78 for this problem) delta T = temperature difference between inside and outside
How many Kg per year of carbon monoxide (CO) would your car emit to the atmosphere if it just conformed to the emissions standards for automobiles? (Assume you drive 10,000 miles per year)
30
If the world uses about 11.5 MBPD of oil, how many years would will the resource last. Assume that the proven world reserves are 129 x 109 barrels (bbl)? Round your answer to the nearest whole year.
31
A stream flowing at a rate of 78 kg/sec has a vertical drop of 7 meters. What is the maximum power that can be obtained from this stream? (in Watts) Assume maximum efficiency for hydro power is 80% (acceleration due to gravity is 9.8 m/s/s)
4,280.64
What is the rate of heat gain in a small hut kept at 74 degrees F when the outside temperature is 91 degrees F? Assume the hut is 10 ft wide by 9 ft long by 6 ft tall and the five exterior surfaces are made of 1 in softwood. (neglect losses through the floor, but not the ceiling) State your answer in BTU per hour and round to 2 decimal places.
4,324.80 Use the equation Q/t = 1/R * A * delta T. The area must be calculated by adding the area of each of the four walls and the area of the ceiling. This gives the total area of the hut that will experience conductive heat gains. The area of each wall is calculated by multiplying the length X height for two walls, the width X height for two walls and the length X width for the ceiling. Delta T is the temperature difference between the inside and outside temperature The R value is found in table 5.2 and is 1.25 ft^2-hr-F / Btu
How many pounds of coal(bituminous) have the same heating value as 41 gallons of gasoline? Hint: Use the heating values from Appendix B in your text. State your answer in pounds and round to 2 decimal places.
406.72 We need to look up the energy content of coal and gasoline (table 3.4 pg 86) 1 gallon of gasoline = 1.24 x 10^5 BTU 1 ton of coal = 25 x 10^6 BTU OR 1.25 x 10^4 BTU / pound So divide the two and multiply by the number of gallons of gasoline: Gal of gasoline * 1.24x10^5 BTU/gal * 1 Lb of coal/1.25x10^4 BTU
Consider an old house (from 1858) It has walls constructed of 2 inch hardwood planks, 0.5 inch lapped wood siding with 0.5 inch sheetrock on the inside. The size of the house is 42 ft wide, 30 ft long and 12 ft tall. Assume a flat roof covered with 1 inch plywood, asbestos shingles and 3.5 inches of fiberglass insulation. Assume 25% of the walls are covered with single pane windows. This old house is very leaky resulting in 3 air exchanges per hour (K value). Assume no losses through the floor. The outside temperature is 41 degrees F cooler than the inside temperature. Considering only conductive heating losses, calculate the heating needs in BTU/hr and round your answer to 2 decimal places.
41,562.22 The total heat loss from a house is the sum of the conductive losses and the infiltrative losses. Here we are only calculating the conductive losses. Use Q/t = 1/R * Area * Delta T; Q/t (total) = (1/R*A*Delta T) of the walls + (1/R*A*Delta T) of the ceiling+ (1/R*A*Delta T) of the windows You need to find the Q/t for the walls, the Q/t for the ceiling and the Q/t for the windows separately and then add them together. You must calculate the R value for the walls separately from the R value of the ceiling and the R value of the windows. Keep them separate. Also calculate the areas separately. There are 4 walls so find the area of each one and then add them together to get the total area. Area = length * height or width * height. The area of the ceiling is the length * width. Remember the wall area must be multiplied by 0.75 because the walls are only 75% of the space as the other 25% is taken up by windows. The wall area is multiplied by .25 or 25% to find the area of the windows.
What maximum output would you expect from a wind turbine with a blade diameter of 26 ft in a 31 mph wind? ( Answer in Kw )
47.53
A skateboard with a mass of 8 kg is moving at a speed of 10 meters per second on a level surface. It encounters a hill and rolls up until it stops. Ignoring friction, to what vertical height does it rise (in meters)? Hint energy transforms from kinetic energy to potential energy State your answer in meters and round to 2 decimal places.
5.1 KE = 1/2 M V^2 PE = MgH If all the energy gets transferred from KE to PE, then you can set the equations equal to each other and solve for H (height) Height will be in meters so use metric units and g = 9.8 m/s/s
Probable reserves
50%
A house in St. Cloud, MN in January needs 8619 BTU/hr for the hot water supply. What fraction of this requirement can be met by a flat plate collector (FPC) of area 16.4 ft2? Assume that the collector is tilted at an angle equal to the latitude and the system efficiency is 53.9 %. Use tables in Appendix D to determine the insolation and assume the solar energy can be stored to be used 24-hours a day. (State your answer as a percent and round to 2 decimal places)
6.03 Look up in appendix D for St.Cloud Minnesota and you should find 1410 Btu/ft^2/day Use Q = I * Eff * A We are given I, Eff, Area solve for Q. Then compare the heat provided by the FPC to the required heat for space heating needs. Calculated Q / required Q * 100% = percent of needed remember the 1410 is per day and the answer wants per hour
A household furnace has an output of 215399 BTU / Hr. What size electrical heating unit (in KW) would be needed to replace this? (think of unit conversions table 3.4 page 86) Round to 1 decimal place.
63.1 For this problem, you need to convert the BTU to Kw-hr, knowing that there are 3,413 BTU / (Kw-hr)
About how many BTUs of waste heat are dumped into the environment by a fossil fueled electrical generating plant that uses 10,000 BTUs of chemical energy during combustion? (Assume 35% efficiency)
6500
How many Btus of Heat energy are needed to raise the temperature of 4.4 gallons of water from 47 degrees F to 65 degrees F? Round your answer to 2 decimal places.
657.36 Use the equation Q = m c (t2-t1). Must convert the gallons of water to pounds. 1 gallon = 8.3 Lb. c = 1 Btu / Lb / deg F; you are given t2 and t1. Plug in and solve.
Assume that two cows produce daily enough manure to produce 0.75 m3 of biogas, and that the biogas is made up of 40% CO2 and 60% Methane. If a kitchen stove uses 50 cubic feet of natural gas per day, how many cows would be needed to produce enough fuel for the stove? (Round up to the nearest whole cow.)
7 cows
If a 1486 megawatt power plant is shut down for one day, what will be the loss in revenues if the utility could sell its electricity at 0.22 dollars per kw-hr?
7,846,080 Need to convert the power (MW) to energy (Kw-hr) by multiplying the MW by the number of hours it was shut down. Then multiply by 1,000 to convert Mw-hr to Kw-hr. Lastly, multiply by the value of 1 Kw-hr.
A (natural) gas-fired turbine generator for producing electricity has an efficiency of about 50%. How many cubic feet of Natural gas would be needed to produce 1000 MW of electricity for 1.2 year? State your answer in Million cubic feet, and round to 2 decimal places.
71,754.91 Because the conversion is 50%, you will need 2 times the amount of natural gas due to energy lost in the form of waste heat. We also need to remember there are 1000 Btus per cubic foot of natural gas. We also need to remember there are 3413 Btu / Kw-hr. Start with the 1000 MW convert that to Kw-hrs per year; Multiply by 24 hrs per day and by 365 days per year and 1000 Kw per MW; Now we have Kw-hr/year. Now divide by the efficiency (50% or 0.5). Now convert Kw-hr / year to Btu per year by multiplying by the 3413. Lastly divide by 1000 Btu / cubic foot and you have found out the required cubic feet.
A simple heat engine for driving a motor could make use of the warm air around New York City as an energy source. Energy could be taken in the form of heat from the atmosphere (assume 39 degrees C) and converted to mechanical action and the waste energy rejected as heat to the Hudson River (assume 14 degrees C). Calculate the maximum efficiency of such an engine using the equation for maximum efficiency found in your text. Hint: Be careful to use temperature in units of Kelvin State your answer as a percent and round to 2 decimal places.
8.01 Use the maximum efficiency equation we learned in chapter 4. Maximum Efficiency = (Temp Hot - Temp Cold) / (Temp Hot) * 100% Remember that temperatures must be converted to the absolute scale Kelvin. You must 273 to the degrees C and use that value for each temperature.
If 117 Btus of Heat Energy are added to 3 Lbs of water at 45 degrees F, what will be the final temperature of the water (in degrees F)? Round your answer to 2 decimal places.
84 Use the equation Q = m c (t2 - t1). We are given Q (in Btu), m (the Lb of water), c (for water = 1 Btu / Lb / deg F) and we know t1 (given initial temperature of the water). Plug in all the information and solve for t2.
Newton's Second Law of Motion states that the net force on an object is equal to the mass of the object multiplied by the acceleration of the object. In this question, the net force is the object's WEIGHT in Earth's gravity (use g = 9.8 m/s2) F = m a If a Giant Panda weighs 200 pounds, what is his weight in Newtons and mass in Kg?
890 Newtons; 90 Kg
Proven reserves
90%
What is the rate of emissions in Kg/hr of particulates from a power plant with an electrical output of 1000 MW that burns coal with an ash content of 2.3 %? This power plant has installed an electrostatic precipitator that removes 88 % of the ash. Remember to use 9000 British tons/day coal to get 1000 MW and that 1 British ton = 2000 lbs. State your answer in kg/hr and round to 2 decimal places
940.91 For this problem we start with 9000 tons per day and multiply by the ash content. Then we need to convert the tons per day to Kg per hour and then multiple by (100%-efficiency of the precipitator). This will give us the emission rate of ash to the environment in Kg/hr.
What is Irradiance?
A measure of instantaneous incident solar power per unit area.
The relative temperature difference between two objects influences the amount of heat transfer more than absolute temperature. Example: More heat is transferred between objects that are 40 degrees and 80 degrees than between 110 and 120 assuming the same materials and mass.
True
What is Insolation?
Amount of solar energy (radiation) reaching Earth during a given period of time per unit area.
Ethanol can be produced from ______ by using by using _______ to help in fermentation. Select the correct combination of words needed to fill in the blanks.
Cellulose, Enzymes
Removes up to 99% of particles greater than 5 microns
Cyclone collector
Removes about 50% of particles smaller than 1 micron
Electrostatic precipitator
Biomass
Renewable
Corn Ethanol
Renewable
Solar Panel provide AC power.
False
Wiring solar panels in parallel will allow for increased Voltage with the same Current as a single panel.
False
You can cool a kitchen by leaving the refrigerator door open.
False
According to the book, what is the definition of exponential growth?
Increase in growth is proportional to the amount present
What happens to the kinetic energy of a car as it rolls up an incline and stops? (Remember the seven forms of energy)
Kinetic energy (KE) is transformed to Potential energy (PE) and Thermal energy (TE).
Heat sources at high temperatures are more useful than those at low temperatures because an engine becomes more efficient as the delta T is larger (the change in temperature is larger).
True
Natural Gas
Non-Renewable
Oil
Non-Renewable
Coal
Non-renewable
Nuclear
Non-renewable
Weight in USCS units
Pounds force lbf
If the temperature of the earth rises enough so that the polar ice caps begin to melt, would this melting cause the global temperature to remain the same, drop or rise higher? Why? (consider feedback mechanisms)
Rise
Used for sulfur dioxide (a gas) removal
Scrubber
Usually the first device used to treat effluent gases
Settling Chamber
Uses dispersion as the primary removal technique
Tall stacks
Work
force*time
Mass in SI units
kilogram (kg)
Solar
renewable
