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che309-H3(report) - Abstract This experiment is about the...

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Abstract: This experiment is about the condensation on vertical tubes. If the temperature of the plate is below the saturation temperature of the vapor, condensate will form on the surface and under the action of gravity will flow down the plate. The main objectives of this experiment are as follow: 1. To investigate heat transfer to water flowing inside a vertical tube from steams condensing on the outside of the tube. 2. To study the film and dropwise condensation mechanisms. 3. To determine the heat flux and surface heat transfer coefficient. 4. To study and investigate the effect of air in the condenser. However, if the liquid wets the surface, a smooth film is formed, and the process is called film condensation . Where if the liquid does not wet the surface, droplets are formed and fall down the surface in some random fashion. This process is called dropwise condensation . The experiment was run twelve times for both the filmwise and dropwise condensation. The experiment was performed by measuring the temperature of the steam, the tube surface, the water inlet and the water outlet. These temperatures were measured for different flow rates for each type of condensers. And it found that for the same flow rates, the heat transfer and the surface heat transfer coefficients in dropwise condensation are higher than that in filmwise condensation. Because of the higher heat transfer rate, dropwies condensation would be preferred than film condensation, but it is extremely difficult to maintain since most surfaces 1
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become wetted after exposure to a condensing vapor over an extended period o0f time. The effect of air on the condensation was investigated, and it was found that the precence of air decreases the effectiveness of the condenser. Introduction: The transfer of heat, which accompanies a change of phase, is often distinguished by high rate. Heat flux high as 50 million Btu/h.ft2 has been obtained in boiling. Although condensation rates have not reached a similar magnitude, coefficient of heat transfer for condensation as high as 20,000 Btu/h.ft2.F have been reported. Condensation coefficients in ordinary commercial equipment are generally higher than in system where a change of phase does not occur. Condensation occurs when a saturate vapor comes in contact with a surface whose temperature is lower than the saturation temperature corresponding to the thermodynamic vapor pressure. However, heat transfer by condensation of vapors on a cold surface is a common industrial process. Condensation occurs usually on the outer surface of tubes in a shell and tube heat exchanger, and in most condensers the liquid inside the tubes which receives the heat is water. The vapor being condensed may consist of only one substance, as the case of steam being condensed in a power plant, or it may be a mixture of substances. The role of condensation using steam for power production, refrigeration and distillation, and to convey heat has a large history and its used in the industry and in these field are likely to continue 2
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into foreseeable future. During condensation, very high heat fluxes are
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