Heterogeneous photoreactor modeling is a task complicated by the integro-differential\ud nature of the Radiation Transfer Equation (RTE) when scattering phenomena are important.\ud In the present work, a novel “Six Flux Model” (SFM) is proposed, which may be\ud regarded as a step forward with respect to the previously proposed “Two Flux Model”\ud (TFM). In order to validate the newly proposed model, Monte Carlo simulations of an\ud indefinite plane-slab photoreactor have been performed. As no simplifying assumptions\ud are involved in this case, the information obtained may be regarded as “pseudoexperimental,”\ud and therefore compared with the predictions of both TFM and SFM\ud models. Results show that the novel SFM is able to closely match the exact solution of the\ud RTE better than the TFM, still retaining the TFM advantage of a simple closed-form\ud solution, that is, ease of use, clearer effect of model parameters, and so forth

No abstract

No abstract

No abstract

The interest towards the use of Membrane Distillation (MD) processes for seawater desalination has been rising recently due to the ease of coupling MD with waste and/or solar thermal energy. Notwithstanding the flexibility of the process and its potential for further developments in membrane performances, one of the main drawbacks is the thermal efficiency reduction caused by temperature polarization. Because of such phenomenon, only a small amount of the driving force potentially available for the separation process, i.e. the temperature difference between evaporating and condensing fluids, is actually used for the separation. In order to reduce temperature polarization a study on the effects of spacer and channel geometry has been performed using Computational Fluid Dynamics (CFD) techniques. A simple reference geometry has been built to simulate the flow and temperature fields of a portion of a Spiral Wound MD module channel. Results show how spacers can significantly affect temperature gradients within the channel, therefore modifying the effective driving force between the faces of the membrane. The main features, which an optimal spacer should possess, have been thus indicated.