Thermodynamics ENERGY, WORK, AND HEATExample:Determine the specific internal energy of 12 lbm of steam if the total internal energy is23,000 Btu.Solution:Using Equation 1-13.uUmu23,000 Btu12 lbmu1916.67 Btu/lbmSpecificP-VEnergyIn addition to the internal energy (U), another form of energy exists that is important inunderstanding energy transfer systems. This form of energy is called P-V energy because itarises from the pressure (P) and the volume (V) of a fluid. It is numerically equal to PV, theproduct of pressure and volume. Because energy is defined as the capacity of a system toperform work, a system where pressure and volume are permitted to expand performs work onits surroundings. Therefore, a fluid under pressure has the capacity to perform work. Inengineering applications, the units of P-V energy, also called flow energy, are the units ofpressure times volume (pounds-force per square foot times cubic feet), which equals foot-poundsforce (ft-lbf).The specific P-V energy of a substance is the P-V energy per unit mass. It equals the total P-Vdivided by the total mass m, or the product of the pressure P and the specific volume n, and iswritten as Pn.(1-14)PnPVmwhere:P = pressure (lbf/ft2)V = volume (ft3)n= specific volume (ft3/lbm)Vmm = mass (lbm)Rev. 0 Page 17 HT-01
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