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Thermodynamics and Energy The First Law The Second Law Dimensions and Units Dimensions Units – English and SI

Thermodynamics and Energy The First Law The Second Law Dimensions and Units Dimensions Units – English and SI Example: In Europe, many tanks are rated in terms of hL ( hectaliters ). What is the equivalent of a 10,000 gallon tank in hL ? In cc’s?. Systems and Control Volumes

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Thermodynamics and Energy The First Law The Second Law Dimensions and Units Dimensions Units – English and SI

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  1. Thermodynamics and Energy The First Law The Second Law Dimensions and Units Dimensions Units – English and SI Example: In Europe, many tanks are rated in terms of hL (hectaliters). What is the equivalent of a 10,000 gallon tank in hL? In cc’s?

  2. Systems and Control Volumes System – Two types? Boundary – Four ways to characterize? Isolated system – What the heck is that? Properties of Systems Intensive and Extensive Specific Properties Examples…

  3. State and Equilibrium State Postulate: State of a simple, compressible system is completely defined by two independent, intensive properties Keywords: State, simple compressible, independent, intensive Process and Cycles Quasi-equilibrium Isothermal, isobaric, adiabatic

  4. Forms of Energy Microscopic or macroscopic Internal energy – Internal to what? Kinetic and potential energies Heat and Work Heat – temperature difference (3 forms) Work – anything else (shaft, electricity, boundary, spring, etc.) Sign conventions, path vs. point functions Characteristics of heat and work?

  5. Energy Efficiency Desired output / required input Heating value of a fuel Propagating efficiencies Example: Water Heater Gas: 55% Electric: 90% Why would gas be better?

  6. Problem 1 2 kg of water is contained within a tank at 20oC and 200 kPa. The water in the tank is heated at constant pressure with a 500 W electric resistance heater. How long must it run in order to heat the water to 50oC?

  7. Problem 2 2 kg of water is contained within a tank at 20oC and 200 kPa. The water in the tank is heated at constant pressure with a 500 W electric resistance heater. How long must it run in order to heat the water to 200oC?

  8. Problem 3 Air enters a nozzle at 300 kPa, 200oC and 30 m/s and leaves at 100 kPa and 180 m/s. The inlet area is 80 cm2. Determine: a. the mass flow rate through the nozzle b. the exit temperature of the air c. the exit area of the nozzle

  9. Problem 4 Steam flows steadily through an adiabatic turbine. The inlet conditions of the steam are 10 Mpa and 450oC. The exit conditions are 10 kPa and 92 % quality. The mass flow rate of steam is 12 kg/s. Determine: a. power output b. the turbine inlet area c. the isentropic efficiency of the engine

  10. Problem 5 During the “mash-in” step of the brewing process, the temperature of the “liquor” and grain mixture (which becomes the wort after mashing) is critical. In our brewery, we need to supply water at 54oC and 200 kPa at a rate of 140 gallons per minute. We have cold “liquor” at 20oC and 200 kPa and saturated (vapor) steam at 500 kPa. Determine the water and steam mass flow rates to achieve the desired hot water flow.

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