Browsing by Author "Marek, Jaromír"

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    A novel method for producing bi-component thermo-regulating alginate fiber from phase change material microemulsion
    (SAGE PUBLICATIONS LTD, 1 OLIVERS YARD, 55 CITY ROAD, LONDON EC1Y 1SP, ENGLAND, 2019-11-01) Wang, Yan; Yao, Juming; Zhu, Guocheng; Militký, Jiří; Marek, Jaromír; Venkataraman, Mohanapriya; Zhang, Guoqing
    A novel method for fabricating thermo-regulating alginate fiber by wet spinning from phase change material (PCM) microemulsions was proposed and carried out. In order to synthesize the PCM microemulsion successfully, different emulsifiers (alkylphenol polyoxyethylene ether (OP-10), sodium dodecyl sulfate (SDS) and their mixture) were added into the stock solution system. The solution systems with emulsifiers were observed under optical microscope and evaluated by using a differential scanning calorimeter (DSC); the results showed that only the solution system with the mixture of OP-10 and SDS transformed into PCM microemulsion, corresponding to the success of fiber formation by wet spinning. In addition, the microemulsion had a stable thermal property based on the DSC result, in which the latent heat capacity remained at 97.3% after 100 cycles of heating and cooling. The thermo-regulating alginate fiber was evaluated in terms of morphology, thermogravimetric (TG) analysis and differential scanning calorimetry. The results showed that the fiber had a smooth surface and porous structure in the cross-section, the bimodal TG curve of alginate fiber indicated that the PCM was successfully embedded into fiber and the DSC results demonstrated that the thermo-regulating alginate fiber had a comfortable phase change temperature of 25-35celcius, and an acceptable phase change enthalpy of about 20 J/g.
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    Desalination Performance Assessment of Scalable, Multi-Stack Ready Shock Electrodialysis Unit Utilizing Anion-Exchange Membranes
    (MDPI, 2020-01-01) Čížek, Jan; Cvejn, Petr; Marek, Jaromír; Tvrzník, David
    Incumbent electromembrane separation processes, including electrodialysis (ED) and electrodeionization (EDI), provide competitive techniques for desalination, selective separation, and unique solutions for ultra-pure water production. However, most of these common electrochemical systems are limited by concentration polarization and the necessity for multistep raw water pre-treatment. Shock electrodialysis (SED) utilizes overlimiting current to produce fresh, deionized water in a single step process by extending ion depleted zones that propagate through a porous medium as a sharp concentration gradient or a shock wave. So far, SED has been demonstrated on small scale laboratory units using cation-exchange membranes. In this work, we present a scalable and multi-stack ready unit with a large, 5000 mm2 membrane active area designed and constructed at the Technical University of Liberec in cooperation with MemBrain s.r.o. and Mega a.s. companies (Czechia). We report more than 99% salt rejection using anion-exchange membranes, depending on a dimensionless parameter that scales the constant applied current by the limiting current. It is shown that these parameters are most probably associated with pore size and porous media chemistry. Further design changes need to be done to the separator, the porous medium, and other functional elements to improve the functionality and energy efficiency.
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    Optimizing porous material in shock electrodialysis unit
    (DESALINATION PUBL, 36 WALCOTT VALLEY DRIVE,, HOPKINTON, MA 01748 USA, 2019-12-01) Marek, Jaromír; Čížek, Jan; Tvrzník, D.
    Shock electrodialysis (SED) is a new electromembrane process for water desalination. The principle is similar to electrodeionization - the product should be ultrapure water, but the inlet water can be the same quality as the inlet to electrodialysis. The ion exchange resin is substituted by porous media and used ion exchange membranes are just of one type (i.e., two cation exchange membranes or two anion exchange membranes). The use of porous media is essential. Many physical and chemical phenomena including electroosmotic flow, electroconvection, surface conduction combined in the moment lead to the phenomena of a "-shock wave" and SED, respectively. The mechanism of the wave is represented by the formation of a sharp border in the water stream between the highly concentrated and ion-free zone. The whole process was studied by Prof. Martin Bazant's group at MIT, Department of Chemical Engineering. The aim of this particular study is characterization and experimental testing of porous material as an essential component of SED. A variety of organic and synthetic porous materials were tested by various analytical methods and in the SED laboratory unit itself. The work reports an overview of commonly available and appropriate materials analogous to the glass frit used in the first prototypes developed by Bazant's group. Considering the physical properties and behavior in experimental conditions and based on the results exhibiting stable desalination, we suggest the optimal porous material as well as the housing for this media. Finally, it is represented by quality of products, hydrodynamic resistance, prize of the porous material, availability and also by workability (machinability) for appropriate shape and also construction stability.
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    Preparation and evaluation of thermo-regulating bamboo fabric treated by microencapsulated phase change materials
    (2019-08-01) Zhang, Guoqing; Cai, Changwei; Wang, Yilai; Liu, Guojin; Zhou, Lan; Yao, Juming; Militký, Jiří; Marek, Jaromír; Venkataraman, Mohanapriya; Zhu, Guocheng
    Two types of microencapsulated phase change materials (ENPCMs) were synthesized by polymerization. The core material of ENPCM was n-octadecane and the shell materials were polymethyl methacrylate-butyl acrylate and polymethyl methacrylate-butyl acrylate-hydroxyethyl methacrylate. Subsequently, the synthesized ENPCMs were applied onto bamboo fabric by the dip and dry method. The properties of ENPCMs were analyzed in terms of surface morphology, size distribution and latent heat; the treated bamboo fabrics were evaluated in terms of surface morphology, hydrophilicity, washing fastness and heat storage capacity. The results showed that polymethyl methacrylate-butyl acrylate/n-octadecane (PMBO) microcapsules had an irregular shape, while polymethyl methacrylate-butyl acrylate-hydroxyethyl methacrylate/n-octadecane (PMBHO) microcapsules were spherical, and the mean diameters of both microcapsules were less than 1 mu m. The latent heat of phase change material (PCM) microcapsules was almost the same at a thermal storage capacity of 110 J/g. There were many more and more even PMBHO microcapsules deposited on bamboo fabric than that of PMBO microcapsules deposited on bamboo fabric. Bamboo fabrics treated by both microcapsules were hydrophilic, and the hydrophilicity of fabric treated by PMBHO microcapsules was even better. The ratio of PCM microcapsules to bamboo fabric was about 1:4, and the latent heat of treated bamboo fabrics was about 20 J/g. Moreover, the treated bamboo fabrics exhibited excellent washing fastness due to the strong binding strength between the highly hydrophilic microcapsules and bamboo fibers. Approximately 72% of PCM microcapsules were retained on the fabric after 15 washing cycles.
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    Thermal Behaviour of Multi-layer Composite Containing PEG and Laponite as PCM
    (TEXTILE BIOENGINEERING & INFORMATICS SOCIETY LTD, TBIS 2010 SECRETARIAT MN104, HONG KONG POLYTECHNIC UNIV, HONG KONG SAR, 0000, PEOPLES R CHINA, 2019-01-01) Yang, Kai; Venkataraman, Mohanapriya; Wang, Yuan-Feng; Xiong, Xiao-Man; Yang, Tao; Wiener, Jakub; Militký, Jiří; Mishra, Rajesh; Marek, Jaromír; Zhu, Guo-Cheng; Yao, Ju-Ming
    Polyethylene glycol (PEG) and laponite were prepared together as PCM and a multi-layer composite containing this PCM was developed, consisting of a PCM loaded layer, a nano barrier layer and a protective layer. SEM was used to observe the structure of multi-layer composites containing PCM, with better adhesion observed between the PCM loaded layer, the nano barrier layer and the protective layer. DSC revealed the melting temperature, the cooling temperature and the enthalpy of PEG and laponite as PCM. The multi-layer composite containing PCM was obtained. Laponite functionalized as a nucleating agent to accelerate the crystallization of PEG and 15wt% LP in PCM resulted in a disordered PEG molecular. The composites with more laponite had the higher thermal insulation.