Heat Engines
Heat Engines
1. The Energy Content of Fuels How heat is derived from fuels? For example, we may consider the burning process for heptane C7H16, colorless liquid constituent of gasoline CH16+1102→7CO2+8H2O+1.15×10° calories per100gCnH Carbon dioxide and water are the only material products of the reaction, and the energy liberated is in the form of heat The number at the right in the formula is the heat of combustion for heptane. Every fuel has a tabulated value for this quantity The heat of combustion is the definite maximum amount of energy available from a fuel which cannot be exceeded
How heat is derived from fuels? For example, we may consider the burning process for heptane, C7H16, colorless liquid constituent of gasoline. C7H16 + 11O2 → 7CO2 + 8H2O + 1.15x106 calories per 100g C7H16 Carbon dioxide and water are the only material products of the reaction, and the energy liberated is in the form of heat. The number at the right in the formula is the heat of combustion for heptane. Every fuel has a tabulated value for this quantity. The heat of combustion is the definite maximum amount of energy available from a fuel, which cannot be exceeded. 1. The Energy Content of Fuels
1. The Energy Content of Fuels Two basic purposes to obtain fossil fuels: to provide direct heating and lighting, and to power heat engines Direct heat, light Fossil fuels Electrical energy Heat engine Mechanical Transportation. Figure 3.1 The general pathways by which we utilize energy from fossil fuels
1. The Energy Content of Fuels Two basic purposes to obtain fossil fuels: to provide direct heating and lighting , and to power heat engines Figure 3.1 The general pathways by which we utilize energy from fossil fuels
2. The Mechanical Equivalent of Heat Unit for heat energy: 1 Btu (raise the temperature of one pound of water by one degree Fahrenheit) Unit for mechanical energy: 1 foot-pound (raise one pound of water one foot higher) Which one is larger? 1 Btu =778 foot-pound You can lifting a one-pound weight 778 feet into the air with the energy released by the burning of only one match Capture the heat energy of the fuel and turn it into mechanical energy The possibility of easing human labor by utilizing heat sources has been the driving force behind a long history of development of what we now call heat engines
2. The Mechanical Equivalent of Heat Which one is larger? 1 Btu = 778 foot-pound You can lifting a one-pound weight 778 feet into the air with the energy released by the burning of only one match. Capture the heat energy of the fuel and turn it into mechanical energy. The possibility of easing human labor by utilizing heat sources has been the driving force behind a long history of development of what we now call heat engines. Unit for heat energy: 1Btu (raise the temperature of one pound of water by one degree Fahrenheit) Unit for mechanical energy: 1 foot-pound (raise one pound of water one foot higher)
3. The Thermodynamic of Heat engines A heat engine is any device that can take energy from a warm source and convert a fraction of this heat energy to mechanical energy Heat source hot Q1 Figure 3.2 a thermodynamic diagram of a heat engine operating between a heat source and heat sink Work output at a lower temperature The work HEAT ENGINE Aw= Cnot-Qcold) output must equal the difference between the heat energy extracted from the source and that rejected to the sink- the Principle of Energy Heat sink Conservation old
3. The Thermodynamic of Heat Engines A heat engine is any device that can take energy from a warm source and convert a fraction of this heat energy to mechanical energy. Figure 3.2 A thermodynamic diagram of a heat engine operating between a heat source and heat sink at a lower temperature. The work output must equal the difference between the heat energy extracted from the source and that rejected to the sink – the Principle of Energy Conservation