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Atomic force microscopy (AFM) images of central channel surface. (a) Root mean square (RMS) roughness = 29.55 nm (grain masked for roughness calculation) (ID10); (b) RMS roughness = 68.58 nm (ID20). For detailed parameters see Table 1.
Source publication
The increasing research in the field of polymeric multi-channel membranes has shown that their mechanical stability is beneficial for a wide range of applications. The more complex interplay of formation process parameters compared to a single-channel geometry makes an investigation using Design of Experiments (DoE) appealing. In this study, seven-...
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Context 1
... two-dimensional elevation plots of the central channel inner surface of the selected PVDF/MCM membranes are shown in Figure 4. In both samples, ridges and valleys parallel to the channel/spinning direction become apparent. ...
Context 2
... particularly the PVP molecular weight plays a role in the morphology (see Figure 3), the difference in M W PVP may explain the deviation of surface roughness as well. The values for M W PVP were 10 kDa and 55 kDa for Figure 4a,b, respectively. Although the trend in P and R indicates less interconnected porous networks when the PVP molecular weight is increased, the actual pore size at the surface may be higher for longer PVP chains, as observed in Figure 4 and implied by Singh et al. [71]. ...
Context 3
... values for M W PVP were 10 kDa and 55 kDa for Figure 4a,b, respectively. Although the trend in P and R indicates less interconnected porous networks when the PVP molecular weight is increased, the actual pore size at the surface may be higher for longer PVP chains, as observed in Figure 4 and implied by Singh et al. [71]. Morevoer, the PVDF content was 18 wt.% ...
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Citations
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Passive daytime radiative cooling (PDRC) is an innovative and sustainable cooling technology that holds immense potential for addressing the energy crisis. Despite the numerous reports on radiative coolers, the design of a straightforward, efficient, and readily producible system remains a challenge. Herein, we present the development of a hierarchical aligned porous poly(vinylidene fluoride) (HAP-PVDF) film through a freeze-thaw-promoted nonsolvent-induced phase separation strategy. This film features oriented microporous arrays in conjunction with random nanopores, enabling efficient radiative cooling performance under direct sunlight conditions. The incorporation of both micro- and nano-pores in the HAP-PVDF film results in a remarkable solar reflectance of 97% and a sufficiently high infrared thermal emissivity of 96%, facilitating sub-environmental cooling at 18.3 °C on sunny days and 13.1 °C on cloudy days. Additionally, the HAP-PVDF film also exhibits exceptional flexibility and hydrophobicity. Theoretical calculations further confirm a radiative cooling power of 94.8 W·m−2 under a solar intensity of 1000 W·m−2, demonstrating a performance comparable to the majority of reported radiative coolers.
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Introduction
This study compared the absorbency capacity of paper points (PPs) to positively charged and non-charged Polyvinylidene Fluoride (PVDF) membranes (PVDFMs) and investigated the ability of PPs and PVDFMs to bind and remove endotoxin.
Methods
Three commercially available PPs were compared to PVDFM (Millipore Sigma, Burlington, MA, USA) prototype points. We recorded the initial dry weight for each PP and PVDFM using a digital balance to ±0.0001 precision for the absorbency. PPs and PVDFMs were then immersed in deionized water and weighed to obtain the wet weight. The absorbency was calculated with the formula: Percent increase = [(wet weight – dry weight)/dry weight] x 100. For endotoxin removal, we first quantified endotoxin remaining in wells after immersing PPs and PVDFMs in a 24 well-plate containing 10 endotoxin units/mL (EU/ml) of E. coli O55:B5 (Lonza, MD). We then extracted and quantified endotoxin from PPs and PVDFMs. Endotoxin was quantified using the KQCL test.
Results
The absorbencies for the positively charged and non-charged PVDFMs were higher than the PPs (p<.05), with no difference between them (p>.05). The positively charged PVDFMs bound and removed endotoxin than non-charged PVDFMs and the PPs (p<.05). Moreover, the non-charged PVDFMs bound and removed more endotoxin than any PPs (p<.05).
Conclusions
PVDFM prototype points are more absorbent than PPs. Moreover, the positively charged PVDFM points are more effective in binding and removing endotoxin than non-charged PVDFMs and PPs. This study suggests that positively charged PVDFMs with 0.22 μm pore size could potentially replace PPs used in endodontics.
The prediction of pressure and flow distributions inside porous membranes is important if the geometry deviates from single- bore tubular geometries. This task remains challenging, especially when considering local porosity variations caused by lumen- and shell-side membrane skins and macro- and micro-void structures, all of them present in multibore membranes.This study analyzes pure water forward and reverse permeation and backwashing phenomena for a polymeric multibore membrane with spatially-varying porosity and permeability properties using computational fluid dynamics simulations. The heterogeneity of porosity distribution is experimentally characterized by scanning electron microscopy scans and reconstructed cuboids of X-ray micro-computed tomography scans. The reconstructed cuboids are used to determine porosity, pore size distribution, and intrinsic permeability in the membrane’s porous structure in all spatial directions. These position-dependent properties are then applied to porous media flow simulations of the whole membrane domain with different properties for separation layer, support structure, and outside skin layer. Various cases mimicking the pure water permeation, fouling, and backwashing behavior of the membrane are simulated and compared to previously obtained MRI measurements.This work reveals (a) anisotropic permeability values and isoporosity in all directions and (b) differing contributions of each lumen channel to the total membrane performance, depending on the membrane-skin’s properties. This study encourages to pertain the quest of understanding the interaction of spatially distributed membrane properties and the overall membrane module performance of multibore membranes.
The prediction of pressure and flow distributions inside porous membranes is important if the geometry deviates from single-bore tubular geometries. This task remains challenging, especially when considering local porosity variations caused by lumen- and shell-side membrane skins and macro- and micro-void structures, all of them present in multibore membranes.
This study analyzes pure water forward and reverse permeation and backwashing phenomena for a polymeric multibore membrane with spatially-varying porosity and permeability properties using computational fluid dynamics simulations. The heterogeneity of porosity distribution is experimentally characterized by scanning electron microscopy scans and reconstructed cuboids of X-ray micro-computed tomography scans. The reconstructed cuboids are used to determine porosity, pore size distribution, and intrinsic permeability in the membrane’s porous structure in all spatial directions. These position-dependent properties are then applied to porous media flow simulations of the whole membrane domain with different properties for separation layer, support structure, and outside skin layer. Various cases mimicking the pure water permeation, fouling, and backwashing behavior of the membrane are simulated and compared to previously obtained MRI measurements.
This work reveals (a) anisotropic permeability values and isoporosity in all directions and (b) differing contributions of each lumen channel to the total membrane performance, depending on the membrane-skin’s properties. This study encourages to pertain the quest of understanding the interaction of spatially distributed membrane properties and the overall membrane module performance of multibore membranes.
Liquid desiccant air conditioning systems (LDAS) are an energy-efficient and eco-friendly alternative to conventional air conditioning systems. The performance of a LDAS significantly depends on its simultaneous heat and mass transfer components, namely dehumidifier and regenerator. These components are referred to as liquid desiccant energy exchangers (LDEEs) since the working fluids (air and desiccant) exchange both heat and moisture. There has been a lot of research on LDEEs over the last two decades to improve their performance, thereby enhancing the efficiency of the LDAS. The main objective of this comprehensive review paper is to summarize the developments of LDEEs. The desiccant material, and design, operating, and performance parameters of LDEEs are explained in detail. Even though a lot of research has been done on LDEEs, they are not much utilized in the practical heating, ventilation, and air conditioning (HVAC) systems. To address this issue, future research should prioritize its focus on (i) practical problems of LDEEs such as cross contamination, and leakage and blockage of the membrane, (ii) long term performance study in the practical systems, (iii) noncorrosive and inexpensive solution, (iv) compatible material for efficient heat and mass transfer, and (v) generalized design and performance control methodology. The discussions presented in this communication will be useful to ascertain the crucial research gaps that need to be addressed by future research studies.
