Effect of module design and flow patterns on performance of membrane distillation process

Abstract

h i g h l i g h t sEffect of fiber configurations and flow patterns on MD performance has been studied. Undulating fibers show best performance in terms of flux at low feed flow rates. Helical modules and intermittent flows exhibit better energy efficiency. Intermittent and pulsatile flows are the best optimum. a b s t r a c tThe present study highlights the effect of different hollow fiber membrane configurations and flow patterns on performance of membrane distillation (MD) process. The modules with helical and wavy conformations have been tested under various hydrodynamic conditions and their performance has been compared with conventional straight fiber modules. The effect of flow patterns has been studied by applying the intermittent and pulsating flows to straight hollow fiber membranes. A flux enhancement of 47% and 52% with respect to the straight fibers has been observed for helical and wavy configurations, respectively, though packing density of such modules is significantly less than their straight counterparts. For intermittent flow, an improvement of $30% has been recorded. The difference is more prominent at low flow rates and approaches to the straight fiber performance under steady flow at high Reynolds numbers (Re) for all hollow fiber configurations and flow patterns studied. The intermittent flow and wavy fibers exhibit an energy efficiency enhancement of $180% and $90% over their conventional counter parts, respectively. In terms of surface and volume based enhancement factor and packing density, intermittent and pulsating flow exhibited the most optimal performance.

Enhancement of Flux Performance in PTFE Membranes for Direct Contact Membrane Distillation

“…These indicators are either affected by membrane or process parameters. In order to optimize MD performance, the membrane parameters that need to be considered are (i) the thickness, pore size, and porosity to increase flux, the chosen average pore sizes lie in the range of 100-1000 nm [12][13][14][15][16], (ii) the wetting resistance, i.e., hydrophobicity of the pores to maintain purity of the product [17,18], (iii) the module design [19], the heat conduction of the material, membrane thickness, and porosity to increase energy efficiency [12,20], and (iv) thickness and porosity to increase structural endurance [21]. Comparatively less important is the latter indicator since the differential pressure applied in an MD process is low (usually <500 mbar, including hydraulic pressure), and, therefore, structural integrity is often sacrificed for the optimization of the remaining performance indicators [17].…”

Specific energy requirement of direct contact membrane distillation

“…In order to incorporate these features, membranes with different porosities, pore sizes, materials and hydrophobic characteristics have been fabricated, making it interesting to compare the process performance of these membranes with commonly used commercial membranes prepared for other separation purposes. Process design improvements in MD mainly focus on improving heat and mass transfer (Yang et al, 2011a;Ali et al, 2015;Phattaranawik et al, 2001) and energy recovery (Geng et al, 2014;Lin et al, 2014). Temperature polarization (TP), defined as the difference in bulk and membrane surface temperatures, plays an important role in governing heat and mass transport across the membrane (Ali et al, 2013).…”

Titanium white sulfuric acid concentration by direct contact membrane distillation

“…Membrane distillation (MD) using a porous membrane to separate liquid and vapor, thus achieving desalination or separation of volatile/non-volatile components is a potential candidate for acid recovery [8][9][10]. Tomaszewska et al used MD to concentrate sulfuric (H 2 SO 4 ), phosphoric (H 3 PO 4 ), hydrochloric (HCl) and nitric (HNO 3 ) acids [11].…”