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Problem 12.3. Evaluation ofpool boiling conditions at high pressure (Section 12.4) 1. A manufacturer has free access on the weekends to a supply of 8000 amps of 440 V electric power. If his boiler operates at 3.35 MPa, how many 2.5 cm diameter, 2 m-long electric emersion heaters would be required to utilize the entire available electric power? He desires to operate at 80% of critical heat flux. 2. At what heat flux would incipient boiling occur? Assume that the water at the saturatiorn temperature corresponds to 3.35 MPa. The natural convection heat flux is given by qNc 2.63(AT)125 kW/m2 p- 3.35 MPa Tsat 240°C htg 1766 kJ/kg px = 813 kg/m3 pv 16.8 kg/m3 σ = 0.0286 N/m k = 0.0628 W/m°C Assume that the maximum cavity radius is very large. You may use the Rohsenow correlation for nucleate pool boiling taking G, 0.0130 in Equation 12.18c. 3 Equation 12.18c: ds Cf 147sat Answers: 1. N- 6 (based on Ce-0.18 in Equation 12.31) 2. q,"- 4.19 kW/m2 2/3 q" L μ.cp1 (12118b) to 1/3 1/2 I 「sat (12.18c) fg 11/4 σίρι-p.jg (12.31) where C 0.149 This equation form is plotted in Figure 12.10, where the lead constant has been optimized by various investigators (0.13 for Zuber [50], 0.16 for Kutateladze [30] and 0.18 for Rohsenow [35] and differs slightly from the 0.149 value of Equation 12.31. This correlation with C 0.149 works well if the horizontal surface is reason- ably large and no liquid enters from the sides of the plate.

Answer 1

드 8000 X440 Зу 12 卉 te

Caleadoli 2 13 Cn