On the coupled condensation-evaporation in pillow-plate condensers: Investigation of cooling medium evaporation

Abstract Pillow-plate heat exchangers (PPHE) represent a promising alternative to conventional equipment, e.g., in the process industries; however, the lack of published design methods still hinders their widespread application. The present work represents a first step towards investigation of a particular PPHE operation mode, which comprises process medium condensation between adjacent pillow plates and simultaneous cooling medium evaporation in the plates. An experimental set-up was built and used for heat transfer experiments, in which 1,1,1,2-tetrafluoroethane evaporated in both thermosyphon and forced-convection operation mode. The focus was on the investigation of heat transfer during the evaporation process in the wavy pillow-plate channel, and the (virtual) enthalpy of condensation was imitated using dissipation of electrical current in the walls of a single pillow plate. Along these lines, two-phase heat transfer coefficients for the evaporating fluid flow in the inner channels of the plates were determined. The results reveal a promising heat transfer performance, which can be utilised to increase energy efficiency in the process industries. A correlation proposed by Kandlikar for saturated two-phase flow boiling heat transfer inside tubes was found suitable for the prediction of heat transfer in pillow plates, with slight underestimation. The results of this study can further be applied for the description of a number of heating and cooling processes.