68cpl tsat ts 2257 103 jkg 068 2314 103 jkg 4206 jkg

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Unformatted text preview: for Example 10–4. cen58933_ch10.qxd 9/4/2002 12:38 PM Page 542 542 HEAT TRANSFER l l l 965.3 kg/m3 0.315 10 3 kg/m · s 0.326 10 6 m2/s l/ l Cpl kl 4206 J/kg · °C 0.675 W/m · °C Analysis (a) The modified latent heat of vaporization is h* fg hfg 0.68Cpl (Tsat Ts) 2257 103 J/kg 0.68 2314 103 J/kg (4206 J/kg · °C)(100 80)°C For wavy-laminar flow, the Reynolds number is determined from Eq. 10–27 to be Re Revertical, wavy 4.81 3.70 Lkl (Tsat l h* fg Ts) g 1/3 0.820 2 l 3.70(3 m)(0.675 W/m · °C)(100 90)°C (0.315 10 3 kg/m · s)(2314 103 J/kg) 1/3 0.82 9.81 m/s2 6 2 2 (0.326 10 m /s) 1287 4.81 which is between 30 and 1800, and thus our assumption of wavy laminar flow is verified. Then the condensation heat transfer coefficient is determined from Eq. 10–25 to be h Re kl g 1/3 1.08 Re1.22 5.2 2 l 1287 (0.675 W/m · °C) 9.81 m/s2 1.08(1287)1.22 5.2 (0.326 10 6 m2/s)2 hvertical, wavy 1/3 5848 W/m2 · °C The heat transfer surface area of the plate is As W L (3 m)(2 m) 6 m2. Then the rate of heat transfer during this condensation process becomes · Q 30° hAs(Tsat Ts) (5848 W/m2 · °C)(6 m2)(100 80)°C 7.02 105 W (b) The rate of condensation of steam is determined from Steam 100°C · m condensation · Q h* fg 7.02 2314 105 J/s 103 J/kg 0.303 kg/s That is, steam will condense on the surface at a rate of 303 grams per second. 80°C EXAMPLE 10–5 FIGURE 10–31 Schematic for Example 10–5. Condensation of Steam on a Tilted Plate What would your answer be to the preceding example problem if the plate were tilted 30° from the vertical, as shown in Figure 10–31? cen58933_ch10.qxd 9/4/2002 12:38 PM Page 543 543 CHAPTER 10 SOLUTION (a) The heat transfer coefficient in this case can be determined from the vertical plate relation by replacing g by g cos . But we will use Eq. 10–30 instead since we already know the value for the vertical plate from the preceding example: h hvert (cos )1/4 hinclined (5848 W/m2 · °C)(cos 30°)1/4 5641 W/m2 · °C The heat transfer surface area of the plate...
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This note was uploaded on 01/28/2010 for the course HEAT ENG taught by Professor Ghaz during the Spring '10 term at University of Guelph.

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