Thermodynamics HW Solutions 818

Thermodynamics HW Solutions 818 - needed to vaporize a unit...

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Chapter 10 Boiling and Condensation 10-30 Cold water enters a steam generator at 15 ° C and is boiled, and leaves as saturated vapor at T sat = 100 ° C. The fraction of heat used to preheat the liquid water from 15 ° C to saturation temperature of 100 ° C is to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat losses from the steam generator are negligible. Properties The heat of vaporization of water at 100 ° C is h fg = 2257 kJ/kg and the specific heat of liquid water at the average temperature of (15+100)/2 = 57.5 ° C is C kJ/kg 184 . 4 C ° = pl (Table A-9). Analysis The heat of vaporization of water represents the amount of heat
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Unformatted text preview: needed to vaporize a unit mass of liquid at a specified temperature. Using the average specific heat, the amount of heat needed to preheat a unit mass of water from 15 C to 100 C is determined to be Water, 100 C Steam generator Water, 15 C Steam 100 C kJ/kg 355.6 = C ) 15 C)(100 kJ/kg 184 . 4 ( preheating = = T C q pl and kJ/kg 6 . 2612 6 . 355 2257 preheating boiling total = + = + = q q q Therefore, the fraction of heat used to preheat the water is ) (or 2612.6 6 . 355 preheat to Fraction total preheating 13.6% 0.136 = = = q q 10-30...
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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