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Lecture 10

Lecture 10. Introduction to Environmental Eng. Energy Flows and Balances. Energy Flows and Balances. Units of Measure BTU – British Thermal Unit Amount of energy required to heat 1 pound of water 1 degree Fahrenheit Calories

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Lecture 10

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  1. Lecture 10 Introduction to Environmental Eng. Energy Flows and Balances

  2. Energy Flows and Balances • Units of Measure • BTU – British Thermal Unit • Amount of energy required to heat 1 pound of water 1 degree Fahrenheit • Calories • Amount of energy required to heat 1 gram of water 1 degree Celcius • Joules • Kilowatt-Hours • All are measures of energy and are interchangeable

  3. Energy Balances and Conversion • Many types of energy • Heat, kinetic, potential, electrical • Engineers utilize one form of energy and place in another that can be used for work • This energy conversion is always less than 100% efficient

  4. Energy Balances and Conversion • A black box “energy balance” Rate of energy accum. = rate in – rate out + rate produced – rate of energy consumed Wasted Energy in Energy out Prod/cons.

  5. Energy Balances and Conversion • Energy can not be produced or consumed, just transformed • And energy systems can be at steady-state Rate in = Rate out + Rate Wasted

  6. Energy Balances and Conversion • Example • What is the efficiency of a gas powered car if gas has an energy content of 20,000 BTU/gal, a car uses 20 gallons per week and in that time produces 10 x 106 joules? • Energy In = 20 gal x 20,000 BTU/gal = 40,000 BTU x 1054 Joules/BTU = 42.16 x106 Joules Energy Out = 10 x106 Joules Efficiency = 10 x106 Joules/42.16 x106 Joules X 100 = 23.72%

  7. Energy Balances and Conversion • How is the Energy content of a source measured? • A bomb calorimeter • Source is placed in a steel ball, placed in a water bath • Pure Oxygen is added • The source is ignited and combusted • Change in the temperature of the water is the result of the energy content of the source

  8. Energy Balances and Conversion • Heat Energy Balance • Heat energy = mass of material x absolute temperature Analogous to mass flows 0 = heat energy IN – heat energy OUT 0 = [T1Q1 + T2Q2] – [T3Q3] • T = absolute temperature • 1 & 2 input streams, 3 output stream

  9. Energy Sources and Availability • Renewable Energy • Hydropower, Wood and other biomass, Solar power, Refuse and other waste materials • Non-renewable Energy • Nuclear Power, Coal, peat and other similar materials, Natural gas, Oil • How long will they last? 50, 30 20 years?

  10. Energy Balances and Conversion • Energy Equivalence • Arithmetic or Conversion Energy Equivalence • Energy production isn’t just based on the caloric content of the substance, • In considering energy production all other costs of production must be taken into account • How much more does it cost? What will the different infrastructure costs be? • Example methane gas from Wastewater treatment?

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