Hybrid photovoltaic/thermal (PV/T) systems provide both electrical and thermal energy. The development of seawater-proof PV/T systems can enlarge the, by now, very limited PV/T application fields to a new one: sustainable reverse osmosis (RO) desalination. There, the PV/T systems' disadvantage of heat at low temperature level can redound to its advantage: the RO freshwater output is increased at elevated seawater temperatures while the PV efficiency is improved due to cooling with seawater. In this paper, the development of a novel seawater-proof PV/T system with the aim of low cost and high electrical and thermal performance is presented. Low-cost is achieved by using standard components combining a polypropylene thermal absorber with a commercial PV system. Experimental investigations on a PV/T prototype include thermal and electrical efficiency characterization at different fluid temperature levels, mass flow rates and ambient conditions. The results are compared the state-of-theart PV/T systems.
a b s t r a c tMotivation of this paper is the hypothesis of permeate flux enhancement due to the dynamic operation of Reverse Osmosis (RO) systems powered by fluctuating renewable energies or by active control. Therefore, in this paper the influence of laminar pulsating flows in spacer filled channels with two porous walls is considered and numerically analysed using the opensource Computational Fluid Dynamics (CFD) tool OpenFOAM. Three different 2-D spacer configurations typically found in literature are investigated: Cavity, Submerged and Zig-Zag. The simulations are performed using typical conditions for seawater desalination. A literature review about dynamically operated membrane systems showed that the results achieved in previous studies are contradictory. Most of them were experimentally or numerically performed in open channels at different conditions. A comparison of the results is therefore difficult. As a first approach this study discusses the dynamics of the mass transfer through the membrane using an analysis based on Biot number. For the CFD simulations, boundary conditions based on the Solution-Diffusion model are implemented and validated with literature data. It shows good agreement at steady state conditions for typical seawater and brackish water desalination conditions. A qualitative analysis of the flow patterns shows that the flow is mainly disturbed in the decelerating phase of the pulsation cycle, which increases the mixing inside the channel. Different local concentration profiles at the membrane and Sherwood number profiles showed that especially in the middle part of two cylinders the mass transfer is significantly influenced whereas at the attachment points of cylinder and membrane, the influence is only marginal. At Womersley numbers of Wo = 17.7 the concentration profiles along the membrane are highly disturbed and the patterns change significantly, also qualitatively. The influence of the Amplitude Ratio is lower than that of the influence of the Womersley number.
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