Heat transfer , condensation and fog formation in crossflow plastic heat exchangers
-In this paper heat transfer of air-water-vapour mixtures in plastic crossflow heat exchangers is studied theoretically and experimentally. First, a model for heat transfer without condensation is derived, resulting in a set of classical differential equations. Subsequently, heat transfer with wall condensation and fog formation are considered in some detail. Separate attention is paid to the heat transfer and condensation of pure steam in the heat exchanger. Finally, the experiments performed are reported and the results compared with the models presented. From this comparison it can be learnt that the models are well able to predict the rate of heat transfer and phenomena such as condensation and fog formation.
Film models for transport phenomena with fog formation : with application to plastic heat exchangers and condensers
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An Ackermann-Colburn and drew type analysis for condensation of multicomponent mixtures
Abstract This paper considers design procedures for condensation of multicomponent mixtures. Using essentially a ‘film’ model, the rate relations for heat and mass transfer in the vapour and liquid phases are formulated and combined with differential material and energy balances to yield design equations. The mass transfer analysis includes the possibility of diffusional interactions. A sample design problem for condensation of a 6-component mixture is considered and the results with the complete analysis are compared with three other simpler approaches: (i) a model based on assuming negligible diffusional interactions and using uncoupled rate relations, (ii) the procedure suggested by Bell and Ghaly in which the mass transfer resistance is ignored but compensated for by over-estimation of the heat transfer resistance and (iii) an equilibrium design procedure in which the vapour and liquid phases are assumed to be in equilibrium. The results show that neglect of diffusional interactions might lead to severe underdesign. The Bell and Ghaly method gives a surprisingly good estimate of the condenser area required.