Experimental and computational investigation of heat transfer in channels filled by woven spacers

• The effect of woven spacers on heat transfer and friction in channels was studied.
• Experiments were performed by Thermochromic Liquid Crystals and image processing.
• Numerical simulations were performed both for steady and unsteady flow.
• A good agreement was obtained for the Nusselt number and the friction coefficient.
• Results are relevant for the optimum design of Membrane Distillation (MD) modules.

Models of woven-type spacer-filled channels were investigated by Computational Fluid Dynamics (CFD) and parallel experiments in order to characterize the performance of Membrane Distillation (MD) modules. The case of overlapped spacers was analysed in a companion paper.Experiments were based on a non-intrusive technique using Thermochromic Liquid Crystals (TLC) and digital image processing, and provided the distribution of the local convective heat transfer coefficient on a thermally active wall. CFD simulations ranged from steady-state conditions to unsteady and early turbulent flow, covering a Reynolds number interval of great practical interest in real MD applications. A specific spacer aspect ratio (pitch-to-channel height ratio of 2) and two different spacer orientations with respect to the main flow (0° and 45°) were considered.Among the existing studies on spacer-filled channels, this is one of the first dealing with woven spacers, and one of the very few in which local experimental and computational heat transfer results are compared. Results suggest a convenience in adopting the 45° orientation for applications that can be operated at very low Reynolds numbers, since convenience decreases as the Reynolds number increases.

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