ENERGY, WORK, AND HEAT ThermodynamicsExample:Determine the kinetic energy of 7 lbm of steam flowing through a pipe at a velocity of100 ft/sec.Solution:Using Equation 1-12.KEmv^{2}2g_{c}KE(7 lbm) (100 ft/sec)^{2}2(32.17 ft lbm/lbf sec^{2})KE(7 lbm) (10,000 ft^{2}/sec^{2})(64.34 ft lbm/lbf sec^{2})KE1088 ft lbfSpecificInternalEnergyPotential energy and kinetic energy are macroscopic forms of energy. They can be visualizedin terms of the position and the velocity of objects. In addition to these macroscopic forms ofenergy, a substance possesses several microscopic forms of energy. Microscopic forms of energyinclude those due to the rotation, vibration, translation, and interactions among the molecules ofa substance. None of these forms of energy can be measured or evaluated directly, buttechniques have been developed to evaluate the change in the total sum of all these microscopicforms of energy. These microscopic forms of energy are collectively called internal energy,customarily represented by the symbol U. In engineering applications, the unit of internal energyis the British thermal unit (Btu), which is also the unit of heat.The specific internal energy (u) of a substance is its internal energy per unit mass. It equals thetotal internal energy (U) divided by the total mass (m).(1-13)uUmwhere:u = specific internal energy (Btu/lbm)U = internal energy (Btu)m = mass (lbm)HT-01 Page 16 Rev. 0

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