Is the boiling heat flux necessarily higher in the

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Unformatted text preview: 33_ch10.qxd 9/4/2002 12:38 PM Page 554 554 HEAT TRANSFER 10–3C What is the difference between evaporation and boiling? 10–4C What is the difference between pool boiling and flow boiling? 10–5C What is the difference between subcooled and saturated boiling? 10–6C Draw the boiling curve and identify the different boiling regimes. Also, explain the characteristics of each regime. 10–7C How does film boiling differ from nucleate boiling? Is the boiling heat flux necessarily higher in the stable film boiling regime than it is in the nucleate boiling regime? 10–8C Draw the boiling curve and identify the burnout point on the curve. Explain how burnout is caused. Why is the burnout point avoided in the design of boilers? 10–9C Discuss some methods of enhancing pool boiling heat transfer permanently. 10–10C Name the different boiling regimes in the order they occur in a vertical tube during flow boiling. from 70 kPa and 101.3 kPa. Plot the maximum heat flux and the temperature difference as a function of the atmospheric pressure, and discuss the results. 10–14E Water is boiled at atmospheric pressure by a horizontal polished copper heating element of diameter D 0.5 in. and emissivity 0.08 immersed in water. If the surface temperature of the heating element is 788°F, determine the rate of heat transfer to the water per unit length of the heating element. Answer: 2465 Btu/h 10–15E Repeat Problem 10–14E for a heating element temperature of 988°F. 10–16 Water is to be boiled at sea level in a 30-cm-diameter mechanically polished AISI 304 stainless steel pan placed on top of a 3-kW electric burner. If 60 percent of the heat generated by the burner is transferred to the water during boiling, determine the temperature of the inner surface of the bottom of the pan. Also, determine the temperature difference between the inner and outer surfaces of the bottom of the pan if it is 6 mm thick. 10–11 Water is to be boiled at atmospheric pressure in a mechanically po...
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