Modeling and optimization of hollow fiber DCMD module for desalination

Cheng, Li-Hua; Wu, Ping-Chung; Chen, Junghui

doi:10.1016/j.memsci.2008.02.065

Cited by 82 publications

(68 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, it should be noted that these modules were tested under the same flow rate, thus both Re f and Re p decreased significantly with increasing packing density  . Based on 24 hydraulic calculations, the Re f ranged from 4700 ( =3.5%) to 1100 ( =40%) and the Re p decreased accordingly because of the increasing number of fibers. Therefore, the hydrodynamic conditions at the membrane surface deteriorated from loosely packed to tightly packed modules.…”

Section: Fiber Packing Densitymentioning

confidence: 99%

“…It has been shown that the hollow fiber module could potentially have the least temperature polarization among various module configurations [21]. 6 However, there are limited reports available on improving fluid dynamics and designing hollow fiber modules for MD applications in the open literature [22][23][24][25]. Some relevant studies have focused on the effect of packing density, flow maldistribution and hydrodynamic behavior in the shell side of hollow fiber modules, based on studies of various gas-liquid/ liquid-liquid contactors [26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

“…Generally, in order to increase membrane area and reduce module fabrication costs, larger module housings, higher packing density and/or longer fiber length are preferred in industry [32]. However, it has been observed in MD studies that the thermal efficiency can be impacted negatively by increasing packing density and fiber length because the distillate tends to be heated up along the fibers [10,33]. In addition, the risk of membrane pore wetting increases with the increasing fiber length due to the imposed hydrostatic pressure drop along the module length [22].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Performance improvement of PVDF hollow fiber-based membrane distillation process

Yang

Wang

Shi

et al. 2011

Journal of Membrane Science

229

144

View full text Add to dashboard Cite

The performance of membrane distillation depends on both membrane and module characteristics. This paper describes strategies to improve the performance of hollow fiber membrane modules used in Direct Contact Membrane Distillation (DCMD).Three different types of hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membrane (unmodified, plasma modified and chemically modified) were used in this study of Direct Contact Membrane Distillation (DCMD). Compared to the unmodified PVDF hollow fiber membrane, both modified membranes showed greater hydrophobicity and mechanical strength, smaller maximum pore sizes and narrower pore size distributions, leading to more sustainable fluxes and higher water quality (distillate conductiviy < 1µs·cm -1 ) over a one month test using synthetic seawater (3.5 wt% sodium chloride solutions).Comparing the plasma and chemical modification the latter has marginally better performance and provides potentially more homogeneous modification.MD modules based on shell and tube configuration were tested to identify the effects of shell and lumen side flow rates, fiber length and packing density. The MD flux increased to an asymptotic value when shell-side Re f was larger than 2500, while the permeate/lumen side reached an asymptotic value at much lower Re p (>300). By comparing the performance of small and larger modules, it was found that it is important to utilize a higher shell-side Re in the operation to maintain a better mixing near the membrane surface in a larger module.Single fiber tests in combination with heat transfer analysis, verified that a critical fiber 3 length existed that is the required length to assure sufficient driving force along the fiber to maintain adequate MD performance. In addition, for multi-fiber modules the overall MD coefficient decreased with increasing packing density, possibly due to flow maldistribution.This study shows that more hydrophobic membranes with a small maximum pore size and higher liquid entry pressure are attainable and favorable for MD applications. In order to enhance MD performance various factors need to be considered to optimize fluid dynamics and module configurations, such as fiber length, packing density and the effect of module diameter and flow rates.

show abstract

Section: Fiber Packing Densitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Performance improvement of PVDF hollow fiber-based membrane distillation process

Yang

Wang

Shi

et al. 2011

Journal of Membrane Science

229

144

View full text Add to dashboard Cite

show abstract

“…From Figure 1, we observe that it is easier to put more effective area into the hollow fibre module with less restriction than that of the flat sheet module, however, turbulence promoters are likely to be required to reduce temperature polarisation. One of the main impediments of the hollow fibre module is its typically low flux, which is generally 1-4 L.m -2 h -1 at 40-60°C [4][5][6]. This is much lower than that of the flat sheet membranes with fluxes of 20-30 L.m -2 h -1 [7].…”

Section: Introductionmentioning

confidence: 99%

“…Cross section of principal layer e. Cross section of outer skin layer wetting, i.e. large molecule will not pass through the pores and cause wetting of the membrane, and it also can improve antifouling effect [19,20] and thereby improve the performance performance [5]. The BJH adsorption pore size distribution measure in range of 0.0017-0.3 μm is presented in Figure μm and the other appears where the pore size is larger than 0.16 μm, corresponding to results found in the SEM image 7c.…”

mentioning

confidence: 99%

Performance of asymmetric hollow fibre membranes in membrane distillation under various configurations and vacuum enhancement

Zhang

Duke

et al. 2010

Journal of Membrane Science

View full text Add to dashboard Cite

Hollow fibre membrane distillation (MD) modules have a more compact structure than flat sheet membrane modules, providing potentially greater advantage in commercial applications. In this paper, a high-flux asymmetrically-structured hollow fibre MD module was tested under various conditions. The results show that increasing velocity and temperature are positive for flux, and salt rejection was more than 99% over the entire experimental range. The hollow fibre module also showed great variation in flux when altering the hot feed flow from the lumen side to the shell side of the fibre, and this phenomenon was analysed based on the characterisation of the asymmetric structure of the hollow fibre. The largest mass transfer resistance was determined to be in the small pore size skin layer on the outer surface of the membrane, and having the hot feed closest to this surface provided the greatest vapour pressure difference across this high resistance mass transfer layer. The results also show that placing the suction pump on the permeate outlet increased the flux by lowering the pressure within the pore and hence increased the rate of vapour mass diffusion. A maximum flux of 19 Lm -2 h -1 was obtained at 85˚C when hot feed was entering the shell side, and the mass transfer coefficient was relatively constant across the entire temperature range when operated at high velocities. These outcomes suggest that asymmetric hollow fibre MD modules should be operated with hot brine feed closest to the high resistant skin layer, and that vacuum enhanced MD further increases vapour transport and flux.

show abstract