example 13-1 - Example 13-1 Water at 70F and 40 psia enters...

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Example 13-1 Water at 70°F and 40 psia enters a long tube with a velocity of 1.4 ft/s. The outside of the tube is heated uniformly with a heat flux per unit surface area of 50,000 Btu/h·ft 2 . At distance L 1 along the tube, the water begins to boil. At L 2 , a two-phase mixture of water and steam exits with a quality of 0.3. Pressure may be assumed to be constant along the tube, which has a diameter of 2 in. Determine a) temperature, T 2 , at the point where the water begins to boil b) temperature, T 3 , at the tube exit c) the length L 1 d) the length L 2 Solution a) At point 2, the liquid is saturated, o 2 temperature(water, 40, 0) 267 F TP x == = = b) Point 3 is at the same pressure as point 2 and both are in the two-phase region, therefore
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o 32 267 F TT == c) From the first law for an open system 22 cv i e cv cv i i i e e e dE QW m h g z mh g z dt ⎛⎞ =−+ + + − + + ⎜⎟ ⎝⎠ ∑∑ ± ± ±± VV In this case, the first law reduces to ( ) 0 cv i e Qm hh =+ − ± ± For the first section of the tube between point 1 and 2, ( ) 12 =− ± ± 1 1 Btu enthalpy(water, 70, 40) 38.2 lbm hT P = = 2 Btu enthalpy(water,
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This note was uploaded on 04/06/2009 for the course ENGR 2250 taught by Professor Borca-tasciuc during the Spring '08 term at Rensselaer Polytechnic Institute.

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example 13-1 - Example 13-1 Water at 70F and 40 psia enters...

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