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Unformatted text preview: - sometimes molar form of energy balance more convenient . . 1 2 . 2 2 2 W Q gh m H N gh Nm U dt d k K k k + + + + = + + = H = molar enthalpy m = molecular weight- can often simplify energy balance by assuming changes in potential and kinetic energy &lt;&lt; changes in internal (thermal) energy k K k k K k k k gh M H M = = + 1 2 . 1 . 2 - exceptions o fluid velocity near velocity of sound (at sea level, 70 F = 344 m/s) o change in height is very large o system temperature is nearly constant (small thermal energy change) Returning to general energy balance- once have developed general eqn for instantaneous energy balance, can integrate to get value of energy change between 2 different times (t 1 ,t 2 ) . . 1 2 . 2 2 2 W Q gh H M gh M U dt d k K k k + + + + =...
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- Spring '11