The evaporation of fluids on the inside and outside of tube bundles has been studied extensively by the authors and others for many years. Most of this work has been on bundles with tube diameters of commercial interest in the range 12-19 mm. The recent drive towards process intensification has awakened interest in much smaller systems down to truly compact arrangements with tubes of less than 3 mm diameter. In this work the advantages and disadvantages of shell side versus tube side evaporation are examined in the context of reducing tube diameter. Other things being equal, tube side evaporation is best for heat transfer, but pressure drop is greatest in this configuration and fouling may be a factor to be considered. Design relationships for exchangers with small tubes based on current research by the authors and othere on boiling both inside and outside the tubes are explored. The work should be of direct interest to designers considering the use of compact shell and tube exchangers for evaporation duty.
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