Advanced Thermal Energy Systems Based On Paraffin Waxes Applicable In Building Industry

Thermal energy storage systems are crucial for reducing dependency on fossil fuels and minimizing CO2 emissions. The building sector is a major sector responsible for producing high levels of CO2 in most countries (including Qatar). Thermal energy storage can be accomplished either by using sensible heat storage or latent heat storage components. Latent heat storage is more attractive than sensible heat storage because of its high storage density with smaller temperature fluctuations.[1] The materials able to utilize latent heat which can undergo phase changes (usually solid to liquid changes) at relatively low temperatures, while absorbing or releasing high amounts of energy are called phase change materials (PCMs).[2] Most promising PCMs are paraffin waxes which contain saturated hydrocarbon mixtures. They are frequently used due to their numerous advantages such as high latent heat of fusion, negligible super-cooling, and chemical inertness.[3,4] In this contribution, thermal properties of the PCMs based on linear low density polyethylene (LLDPE), different types of paraffin waxes with melting points, 25 oC and 42 oC, and expanded graphite (EG) were characterized by unique transient guarded hot plate technique (TGHPT), which allow to identified thermal properties of large sized samples[5] in comparison with commonly used ifferential scanning calorimetry (DSC). It was confirmed that all prepared PCMs were able to store and release huge amount of thermal energy. The 25 % increase of capacity to store and release a thermal energy was observed by PCMs contains paraffin wax with melting point 25 oC in comparison with paraffin wax with melting point 42 oC. Also reproducibility of storage and release heat of the PCMs by repeating of heating and cooling process has been demonstrated. Moreover, the increase of the EG content in the PCMs led to the increase of thermal conductivity from 0.24 W/mK for PCMs without EG to 1.3 W/mK for PCMs contain 15 wt.% of EG. Additionally, life cycle assessment of prepared PCMs has been demonstrated to identify the effects of these new materials on the Qatar environment. Our results indicate that using of PCMs in building industry can reduce emission of CO2 up to 10%.qscienc

Reinforcement of copolyamide membranes for water treatment applications

Clean water is the key element for all living organisms to sustain life. However, due to the rapid industrialization and large increase in the population, the contamination of water resources is important issue occurred globally as well as locally here in Middle East region [[1]]. From past few decades, various techniques for treating the wastewater have been developed. Among others, filtration techniques are a commonly used to eliminate contamination of water caused by various materials such as heavy metals, dyes, oil, bacteria etc. Robust, capable membranes are crucial for effective filtration process and various polymeric materials have been studied in last decades. Among others, polyamides membranes have been used as membranes due to their favourable properties such as good thermal and mechanical stability [[2]], which make them suitable for the designing of fibres, mats and membranes. Compared to many commercially available filtering membranes that are produced by conventional fabrication techniques such as phase inversion technique, the pore size distribution of electrospun fibrous membranes can be conveniently tailored in the range of sub-microns up to a few micrometers via simply adjusting the material and process parameters of electrospinning and related post-processes. In addition, electrospun filtering media are also capable of maintaining a high porosity, which guarantees the high-flux liquid filtration.One of the approach to further improved efficiency, mechanical performance and lifetime of membranes is using various fillers.Nanocelluloses are particularly interesting because of their environmental friendliness, high mechanical performance, flexibility, low-cost, versatility, and tailorable surface functionalities. The size, structure, and functional groups of nanocelluloses are dependent on the source of cellulosic fibres and preparation method [[3]].Other nanofillers, very recently discovered with large potential in water treatment applications are MXenes. MXenes are a new class of 2D metal carbides and carbonitrides, which are both conductive as well as hydrophilic [[4]]. MXenes have general formula Mn+1Xn, derived from MAX phases, where M is an early transition metal, A is an A-group element, mostly IIIA and IVA, or groups 13 and 14, and X is either carbon and/or nitrogen, by chemical etching in HF or NH4HF2 solutions, where n = 1, 2 or 3. The unique structure of MXenes offers combination of excellent mechanical properties, hydrophilic surface, transparency and metallic conductivity. Herein, we used electrospinning to prepared novel membranes based on copolyamide 6,10 reinforced by nanocellulose prepared from Qatari date palm waste and MXene 2D nanofillers which dramatically improved mechanical performance and separation efficiency of the membranes compared to neat copolyamide membranes. Prepared membranes were able to separate oil (vegetable and diesel) from water with efficiency over 96 % regarding of membrane composition and separation conditions. Additionally membranes exhibited good lifetime with maintaining high efficiency of separationqscienc

Purification of emulsified oily polluted waters with modified melamine foams

Oil and gas industry operations produce tremendous amounts of wastewater (produced water; PW). Tertiary treatment of the PW in the final treatment stage is challenging due to the presence of colloids with sizes < 500 nm and a low concentration target for the effluent of <10 mg/L. This study was focused on the purification of colloidal PW with modified melamine foams (MFs) and ferric chloride. The modified MFs exhibited superhydrophobic and superoleophilic character due to increasing roughness and complexation of Fe3＋ ions within the MF structure. The modified MF showed separation efficiencies up to 86 ± 3% for emulsions containing 120 ppm carbon. The Fe3＋ cations changed the hydrophilicities of the foams and made them highly hydrophobic, and they also contributed significantly to the adsorption of negatively charged species, such as crude oil droplets modified with an anionic surfactant (sodium dodecyl sulfate). The demulsification mechanism involved multiple diffusion processes run over different time scales, including diffusion of an emulsion into the foam and diffusion of the oil droplets within the foam, combined with parallel adsorption of the oil droplets onto the solid skeleton of the foam. The adsorption capacity of the MFs increased linearly with increasing initial concentration of crude oil content in the PW. The MFs were reusable for six consecutive cycles.This research was made possible by a grant from the Qatar National Research Fund under its National Priorities Research Program (award number NPRP12S-0311-190299 ) and by financial support from the ConocoPhillips Global Water Sustainability Center (GWSC), Qatar and Qatar Petrochemical Company (QAPCO) . The paper's content is solely the responsibility of the authors and does not necessarily represent the official views of the Qatar National Research Fund or ConocoPhillips and QAPCO.Scopu

Materials and Technologies for the Tertiary Treatment of Produced Water Contaminated by Oil Impurities through Nonfibrous Deep-Bed Media: A Review

This review covers various aspects of the treatment of emulsified oil/water mixtures and is particularly focused on tertiary treatment, which means the reduction of the oil content from 70&ndash;100 ppm to below 10 ppm, depending on national regulations for water discharge. Emulsified oil/water mixtures frequently occurs in water treatment processes because, in the petroleum industry, chemically enhanced oil recovery leads to the production of a vast amount of oil-emulsified wastewater. This review is focused on various aspects of tertiary treatment via granular deep-bed filtration. The importance of polymeric materials, as well as carbon nanostructures, which may be an alternative to the current media have been highlighting. The particular potential of polymers is based on their broad availability and low price (particularly for polyolefins), the simple treatment of their surfaces through a variety of chemical and physical methods to design surfaces with tailored surface free energy (wettability), and the porosity. Polymer technology offers a variety of well-established methods for designing foams with tailored porosity, which, together with appropriately tuned surface energy and controlled roughness, would open new avenues for the production of foamy media for efficient oil/water separation. Additionally, a crucial inventions in deep-bed filtration is discussed

Evaluation of photothermal conversion performance of shape-stabilized phase change materials using a heat flux evolution curve

Phase change materials are promising alternatives for solar energy harvesting by photothermal conversion and thermal energy storage. In this work, a shape-stabilized phase change material (PCM) was prepared by hot-melt blending of paraffin wax (PW), high-density polyethylene (HDPE), and expanded graphite (EG) to investigate the photothermal conversion and storage performance using a heat flux evolution curve. This study introduced the heat flux evolution curve for the first time to accurately measure phase change duration, which is otherwise underestimated by the conventional temperature curves. The impact of various component compositions on thermal conductivity, energy storage density, PCM leakage, and photothermal conversion efficiency was evaluated experimentally. The results showed that the addition of 20 wt% EG enhanced the thermal conductivity of the composite by 305%. The total energy storage density of the composite varied in the range of 116.7-138.5 J/g during the photothermal conversion study. The composite with 15 wt% EG and 50 wt% PW exhibited a photothermal conversion efficiency of 79.8% when calculated from the temperature evolution curve and 61.8% from the heat flux evolution curve. This difference in efficiency indicates that the temperature evolution curve accounts only for the phase change of PCMs at the point of temperature measurement, while the heat flux evolution curve estimates the phase change of whole PCMs in the composite. Therefore, this work not only provides a shape-stabilized phase change material for the effective utilization of solar energy but also provides some guidelines to accurately calculate the photothermal conversion efficiency.This work was made possible by the Award NPRP13S-0127-200177 from the Qatar National Research Fund (a member of The Qatar Foundation). SEM measurements of the samples were accomplished in the Central Laboratories Unit, at Qatar University. The statements made herein are solely the responsibility of the authors.Scopu

Evaluation of photothermal conversion performance of shape-stabilized phase change materials using a heat flux evolution curve

Phase change materials are promising alternatives for solar energy harvesting by photothermal conversion and thermal energy storage. In this work, a shape-stabilized phase change material (PCM) was prepared by hot-melt blending of paraffin wax (PW), high-density polyethylene (HDPE), and expanded graphite (EG) to investigate the photothermal conversion and storage performance using a heat flux evolution curve. This study introduced the heat flux evolution curve for the first time to accurately measure phase change duration, which is otherwise underestimated by the conventional temperature curves. The impact of various component compositions on thermal conductivity, energy storage density, PCM leakage, and photothermal conversion efficiency was evaluated experimentally. The results showed that the addition of 20 wt% EG enhanced the thermal conductivity of the composite by 305%. The total energy storage density of the composite varied in the range of 116.7–138.5 J/g during the photothermal conversion study. The composite with 15 wt% EG and 50 wt% PW exhibited a photothermal conversion efficiency of 79.8% when calculated from the temperature evolution curve and 61.8% from the heat flux evolution curve. This difference in efficiency indicates that the temperature evolution curve accounts only for the phase change of PCMs at the point of temperature measurement, while the heat flux evolution curve estimates the phase change of whole PCMs in the composite. Therefore, this work not only provides a shape-stabilized phase change material for the effective utilization of solar energy but also provides some guidelines to accurately calculate the photothermal conversion efficiency

Impact of the Processing-Induced Orientation of Hexagonal Boron Nitride and Graphite on the Thermal Conductivity of Polyethylene Composites

Emergent heat transfer and thermal management applications require polymer composites with enhanced thermal conductivity (κ). Composites filled with non-spherical fillers, such as hexagonal boron nitride (hBN) and Graphite (Gr), suffer from processing-induced filler orientations, resulting in anisotropic κ, commonly low in the through-plane direction. Here, the effects of extrusion and compression molding-induced orientations on κ of hBN- and Gr-filled polyethylene composites were investigated. The effect of extrusion on the hBN orientation was studied using dies of various shapes. The shaped extrudates exhibited hBN orientations parallel to the extrusion flow direction, which prompted additional hBN orientation during compression molding. κ of the composites produced with shaped extrudates varied from 0.95 to 1.67 W m−1 K−1. Pelletizing and crushing the extrudates improved κ, by exploiting and eliminating the effect of extrusion-induced hBN orientations. Gr-filled composites showed better κ than hBN composites due to the higher intrinsic conductivity and bigger particle sizes. A maximum κ of 5.1 and 11.8 W m−1 K−1 was achieved in composites with oriented hBN and Gr through a thin rectangular die and stacking the sheets to fabricate composites with highly oriented fillers

Thermophysical Characterization of Paraffins versus Temperature for Thermal Energy Storage

Latent heat storage systems (LHSS), using solid–liquid phase change materials (PCMs), are attracting growing interest in many applications. The determination of the thermophysical properties of PCMs is crucial for selecting the appropriate material for an LHSS and for predicting the thermal behavior of the PCM. In this context, the thermophysical characterization of four paraffins (RT21, RT27, RT35HC, RT50) at different temperatures, including the solid and liquid phases, is conducted in this investigation. This work is part of a strategic technological brick in the CERTES laboratory of the Paris Est University to build a database for phase change material properties. It contains the measurements of the thermophysical, optical and mechanical properties. It will serve as input for the numerical simulations to study the behavior of PCMs in LHSS. The temperatures and the latent heats of the phase transitions as well as the thermal dependence of the specific heat of the paraffins were evaluated by differential scanning calorimetry (DSC). In addition, the DSC measurements under successive thermal cycles revealed good reliability of the paraffins. Thermogravimetric analysis (TGA) was performed, and the results highlighted the thermal stability of the paraffins. Moreover, the evolutions of the thermal conductivities and diffusivities with temperature were measured simultaneously using the hot disk method. A discontinuity of the thermal conductivities was observed near the melting temperatures. Furthermore, the measurements of the densities of the paraffins at different temperatures were carried out. The volume changes and the coefficients of thermal expansion were assessed. The obtained outcomes of this study were compared with the available bibliographical data

Novel flexible piezoresistive sensor based on 2D Ti3C2Tx MXene

Stretchable and wearable strain-sensing devices are appropriate for motion detection, biomedical monitoring, human-machine interaction. These pressure sensors are working based on numerous electrophysical phenomena's such as piezoelectric, capacitive and piezoresistive reactions towards mechanical stretching [1]. Piezoresistive sensors are highly favored due to their features like high sensitivity, fast response, easy fabrication and low energy requirement. They are generally fabricated using a suitable polymeric matrix and electrically conductive fillers, such as graphite, graphene or carbon nanotubes. MXenes are a relatively new family of (2D) transition metal carbides, nitrides or carbonitrides, produced by the selective chemical etching of "A" from MAX-phases, where M is a transition metal, A is a group IIIA or IVA element and X is C or N. These nanomaterials are first reported in 2011 by the Gogotsi and Barsoum groups [2]. These materials have received tremendous attention from the scientific community due to their excellent physiochemical properties, electrical conductivity and hydrophilicity [3]. Herein, we report the preparation, characterization and piezoresistive individualities of semiconductive, electrospun mats composed of copolyamide 6,10 and Ti3C2Tx. We observed that the relative resistance of the sensor increased with an increase in the Ti3C2Tx content, and the materials with higher electrical conductivity showcased a significantly higher sensitivity to applied pressure until reaching the percolation limit. (font size can be increased