eml 3100 lec 8 energy eqn

eml 3100 lec 8 energy eqn - Thermodynamics We discussed the...

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UNIVERSITY OF FLORIDA Lecture No. 8 1 Thermodynamics We discussed the conservation of Energy last period, First Law is also called the “Conservation of Energy”. “During an interaction between a system and its surroundings, the amount of energy gained by the system must be exactly equal to the amount of energy lost by the surroundings.” Today. . .Conservation of Mass Principle: In – out = accumulation Or total mass entering the system less the total mass leaving the system equals the net change in mass. (AKA the continuity equation) m in – m out = m system Or on a time basis Mass rate in (kg/s) – mass rate out (kg/s) = rate of mass accumulation (kg/s)
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UNIVERSITY OF FLORIDA Lecture No. 8 2 Thermodynamics Note for flow in a conduit or pipe or any other constrained space: Mass flow rate (kg/s) = ρ V ave A Where ρ = the density of the fluid V ave = the average velocity of the fluid in the pipe A = cross sectional area of flow field Example: Water flows at an average velocity of 50 ft./min in a round pipe with an inside diameter of 2 inches. The density of water (from tabular data) is 62.4 lbm/ft 3
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UNIVERSITY OF FLORIDA Lecture No. 8 3 Thermodynamics The mass flow rate of water = ρ V ave A= ρ V ave π D 2 /4 62.4 lbm/ft 3 x 50 ft/min x (3.1416x4/(4x144)) x 1 min/60s = 1.23 lbm/s We can also talk about this in gallons per minute or gpm: 1.23 lbm/s x (1 gal/8.34 lbm) x 60s/min = 8.85 gpm
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eml 3100 lec 8 energy eqn - Thermodynamics We discussed the...

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