Unformatted text preview: 1. 4. NEEP 411: HW#7
Single Phase Heat Transfer; Heat Transfer with Change in Phase
Due: Friday, November 11th, 2011 In our expression for natural circulation through a PWR, we had a frictional loss term
in the denominator of our dimensionless ﬂow/power expression: L 1/3 F=[ﬂATo pg 0 P]
[l The term in is a frictional loss term, which we took as 10 x the cold leg frictional loss. The purpose of this ﬁrst problem is to evaluate that term a bit more rigorously. Suppose we consider the frictional loss around the loop as having these components: (a) The frictional loss in the cold leg as calculated in class (b) The frictional loss in the hot leg (same pipe diameter and length as the cold leg)
(0) The frictional loss in the annular gap of the downcomer. Take the ﬂow area based on a 20 cm thick annulus with inner radius 1.85 m and outer radius 2.05 m. Take
the height of the downcomer as 4 m. Note that all 18,000 kg/s passes through the downcomer.
(d) The frictional loss in the assembly region. Take the average assembly geometry and ﬂowrate as representative, as used to calculate the singlephase, forced—ﬂow heat transfer coefficient. The assemblies are 3.5 m high. (e) The frictional loss in the steam generator. Assume the steam generator has 4500
tubes of inner diameter 2.54 cm each. Neglect any ﬂow distribution effects from
the U—tube and base the estimated drop on the vertical legs 10 m up and 10 m down in your calculations. Remember to account for property differences between the cold leg (15.5 MPa, 290 OC) and the hot leg (15.5 MPa, 320 °C). What is the greatest source of pressure loss
among these five sources, and what is the total frictional loss? Using the result from Problem 1, ﬁnd the dimensionless flow and power ratios that
give us P/F = 1. In his discussion of bubble dynamics in Ch 11, El—Wakil provides this expression
(Eqn 11—2) for the liquid superheat required to nucleate bubbles: T—T : 20—];m sat
hfgpgrc Assuming a nucleation site of radius rc = 1 um, what is the difference in superheat
between atmospheric pressure (0.101 MPa) and PWR system pressure (15.5 MPa)? 1L4, El—Wakil ...
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 Fall '09

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