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Boiling Heat Transfer 17 1The hot channel in a PWR operates under the conditions given below. Compute and compare the outer clad temperature distribution assuming the Jens-Lottes and Thom correlation in the nucleate boiling region and the Bergles and Rosenhow correlation in the mixed boiling region. You may assume an axial heat flux profile of the form ⎟⎟⎠⎞⎜⎜⎝⎛+′′=′′eHzqzq)(sin)(0λπProblem ParametersMaximum channel heat flux 474,500 Btu/hr-ft2Channel Mass Flux 2.48 x 106lbm/hr-ft2Inlet Temperature 552 F Channel Pressure 2250 psia Rod Pitch 0.496 inches Rod Diameter 0.374 inches Rod Height 144 inches Axial Peak to Average Ratio 1.5 SOLUTION Heat FluxThe heat flux profile is in terms of two unknown parameters, the extrapolation distance λand the amplitude 0q′′. The extrapolation distance is determined by the axial peak to average ratio. The amplitude sets the magnitude of the heat flux. Extrapolation DistanceThe axial peak to average ratio is defined to be qzqFz′′′′≡)(maxwhere maxzis the position of maximum heat flux in a particular channel, and q′′is the axially averaged heat flux in the same channel. Note, that since for any given channel )(maxzq′′and q′′both contain the amplitude 0q′′, this parameter cancels and the axial peak to average ratio is only a function of shape. The position of maximum heat flux is that location such that 0max=′′zqdzdFor this heat flux profile, the maximum heat flux occurs at 2H, such that 500,474)(maxmax0=′′=′′=′′qzqqBtu/hr-ft2. The axially averaged heat flux is defined to be
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