TAILIEUCHUNG - Heat Transfer Handbook part 137

Heat Transfer Handbook part 137. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | CHAPTER 19 Direct Contact Heat Transfer ROBERT F. BOEHM University of Nevada-Las Vegas Las Vegas Nevada 1 Introduction 1 Sensible heat exchange General comments External convection to spheres Heat transfer inside spheres Evaporation and condensation General considerations Condensation of a vapor on or in a liquid Film condenser Condensation on liquid droplets Condensation on liquid jets Condensation in a liquid Evaporation of a liquid by a s Lirouou-O gy vapc r aas or liquid Droplet evaporation in a vapor or gas Droplet evaporation in a liquid Columns and other conaactors Spray columns Global treatments Differential treatment Melting and sand ao appliaaiions Baffled columns Packed columns Concluding comments Nomenclature References INTRODUCTION Direct contact heat transfer can occur whenever two substances at different temperatures touch each other physically. The implication is that there is not an intervening wall between the two substances. Heat transfer where there is a surface between the two streams is sometimes called indirect or the heat transfer device is one of 1359 1360 DIRECT CONTACT HEAT TRANSFER the closed types. The physical interaction of the two streams can accomplish heat transfer very efficiently. Without an intervening wall the energy transport between the two streams can take place across small thermal resistances. In addition the fact that a wall is not present can allow a mass transfer process to take place. In some cases this is a desirable phenomenon open cooling towers but in other cases it may not be. Costs are often more favorable for direct contact heat transfer devices than for their closed counterparts. Thie herrm d resistances present in closed heat exchaggers result in less heat transfer than might be accomplished in direct contact nnd thio often translates to lower operating costs for the latter. In addition the equipment to accomplish the .

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