L21_Energy_Balance - 10/13/11 1 Energy Balance-Overall...

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Unformatted text preview: 10/13/11 1 Energy Balance-Overall Energy Balance-Overall 10/13/11 2 LEARNING OBJECTIVES By the end of this topic, you should be able to understand the following: Perform basic energy calculation 10/13/11 3 EXAMPLE 1 Suppose that an ideal gas at 300 K and 200 kPa is enclosed in a cylinder by a frictionless piston, and the gas slowly forces the piston so that the volume of gas expands from 0.1 to 0.2 m 3 . Calculate the work done by the gas on the piston if two different paths are used to go from the initial state to the final state. Path A: the expansion occurs at constant pressure (p=200 kPa) Path B: the expansion occurs at constant temperature (T=300 K) 10/13/11 4 EXAMPLE 1 V 1 =0.1 m 3 V 2 =0.2 m 3 State 1 State 2 By definition the work done by the system is negative. Path A: kJ v v p pdV Fds W v v state state 20 ) 1 . 2 . ( 10 200 ) ( 3 1 2 2 1 2 1- =- - =-- =- =- = 10/13/11 5 EXAMPLE 1 Path B kJ W kgmol n V V nRT dV V nRT pdV Fds W v v v v state state 86 . 13 2 ln ) 300 )( 314 . 8 )( 00802 . ( 00802 . ) 314 . 8 )( 300 ( ) 1 . )( 200 ( ln 1 2 2 1 2 1 2 1- =- = = = - =- =- =- = Total energy done by the system = (-20)+(-13.86)=-33.86kJ 10/13/11 6 EXAMPLE 2 Water is pumped from a storage tank into tube of 3.00 cm inner diameter at the rate of 0.001 m3/s. What is the specific energy of the water? Given the density of water is 1000 kg/mthe water?...
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This note was uploaded on 08/08/2009 for the course CHEMICAL 11189 taught by Professor Dr.azmi during the Spring '09 term at International University in Germany.

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L21_Energy_Balance - 10/13/11 1 Energy Balance-Overall...

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