HW2Problem2

# HW2Problem2 - The hot channel in a PWR operates under the...

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Critical Heat Flux 19 1 The hot channel in a PWR operates under the conditions given below. Problem Parameters Maximum channel heat flux 474,500 Btu/hr-ft 2 Channel Mass Flux 2.48 x 10 6 lbm/hr-ft 2 Inlet 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 Assuming the W3 correlation is valid for this channel, determine the location and the value of the Minimum DNB ratio. You may assume an axial heat flux profile of the form + = e H z q z q ) ( sin ) ( 0 λ π SOLUTION The DNB ratio is defined to be ) ( ) ( z q z q DNBR c The minimum DNB ratio is most easily found by computing the DNB ratio over the channel height and searching for the minimum. Heat Flux The heat flux profile is in terms of two unknown parameters, the extrapolation distance λ and the amplitude 0 q . The extrapolation distance is determined by the axial peak to average ratio. The amplitude sets the magnitude of the heat flux. Extrapolation Distance The axial peak to average ratio is defined to be q z q F z ) ( max where max z is 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 ) ( max z q and q both contain the amplitude 0 q , this parameter cancels and the axial peak to average ratio is only a function of shape.

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