Experimental studies on a compression–absorption system for heating and cooling applications

An experimental study has been carried out on a single‐stage compression–absorption system for simultaneous heating and cooling with R22 and E181 (DMETEG) as the working fluid pair. An absorber, being the major component of the system, is designed to absorb the amount of vapour that can be handled by the selected refrigerant compressor. The designs of the other components of the system are based on the design result of the absorber. The experimental test results have been compared with the results obtained from the theoretical analysis of the system. Though the experimental results are found to match the theoretical results qualitatively, the performance of the experimental test rig is found to be lower than that of the theoretical predictions due to various heat losses from the system and non‐ideal compression. Copyright © 2007 John Wiley & Sons, Ltd.     

Microwave synthesis of phase-pure, fine silicon carbide powder

Fine, monophasic silicon carbide powder has been synthesized by direct solid-state reaction of its constituents namely silicon and carbon in a 2.45 GHz microwave field. Optimum parameters for the silicon carbide phase formation have been determined by varying reaction time and reaction temperature. The powders have been characterized for their particle size, surface area, phase composition (X-ray diffraction) and morphology (scanning electron microscope). Formation of phase-pure silicon carbide can be achieved at 1300 °C in less than 5 min of microwave exposure, resulting in sub-micron-sized particles. The free energy values for Si + C → SiC reaction were calculated for different temperatures and by comparing them with the experimental results, it was determined that phase-pure silicon carbide can be achieved at around 1135 °C.     

Development,characterization and erosion wear response of plasma sprayed fly ash–aluminum coatings

This paper describes the processing, characterization and the erosion wear response of a new class of metal–ceramic composite coatings deposited on metal substrates by plasma spraying. Coatings are developed on aluminum substrates using fly ash pre-mixed with aluminum powder in different weight proportions at various plasma torch power levels ranging from 9 to 18 kW DC. The coatings are characterized in terms of thickness, interface adhesion strength and deposition efficiency. Maximum adhesion strength of about 35 MPa is recorded with coatings deposited at 12 kW power level. It is noticed that the adhesion strength of fly ash coating is improved with pre-mixing of aluminum up to 15 wt.% in the feed material. To study the erosion wear behavior of the coatings, a plan of experiments based on the Taguchi technique is used to acquire the erosion test data in a controlled way. An orthogonal array and signal-to-noise ratio are employed to investigate the influence of the impingement angle, impact velocity, erodent size, stand-off-distance and the aluminum content in the feed stock on the erosion rate. The study reveals that the impact velocity is the most significant factor influencing the erosion wear rate of these coatings.     

REWETTING OF AN INFINITE SLAB WITH BOUNDARY HEAT FLUX

This paper deals with a numerical solution of the two-dimensional quasi-static conduction equation, governing conduction controlled rewetting of an infinitely long slab with one side flooded and the other side subjected to a constant heat flux. The solution gives the quench front temperature as a function of various model parameters such as Peclet number, Biot number, and dimensionless boundary heat flux. Also, the critical boundary heat flux is obtained by setting the Peclet number equal to zero, which gives the minimum heat flux required to prevent the hot surface being rewetted.     

Modification of polydimethylsiloxane with polyvinylpyrrolidone: Influence of reinforcing filler on physico‐mechanical properties

The present article reports an approach for the modification of hydrophobic polydimethylsiloxane (PDMS) with low molecular weight hydrophilic polyvinylpyrrolidone (PVP) via solution blending method to develop new PDMS‐based materials with improved mechanical performance and wettability which can be used in many biomedical applications. The influence of dimethyldichlorosilane treated fumed silica (FS) on physico‐mechanical properties of PDMS–PVP blends were investigated and analyzed. There was the significant improvement in mechanical, dynamic mechanical and thermal properties of PDMS–PVP blends, whereas, transparency and contact angle were slightly decreased after incorporation of FS into PDMS–PVP blends. Scanning electron microscopy revealed that the fourfold reduction in the average domain size of the dispersed PVP in the PDMS matrix in the presence of compatibilizer (PDMS‐PEO block copolymer) when compared with the uncompatibilized PDMS–PVP blend morphology. By incorporation of FS into the neat PDMS matrix, the onset of degradation (T_i), the maximum rate of degradation (T_max) and overall thermal stabilities increased significantly. On the other hand, by the addition of FS into to PDMS–PVP blends, the T_i and T_max remains unaffected, but overall thermal stabilities increased significantly. PDMS–PVP blends exhibited low contact angle (～45°) which confirmed the formation of the hydrophilic surface. POLYM. ENG. SCI., 56:491–499, 2016. © 2016 Society of Plastics Engineers     

Mechanical,dynamic mechanical,and thermal characterization of fly ash and nanostructured fly ash‐waste polyethylene/high‐density polyethylene blend composites

Disposal of polyethylene used as carry bags is the greatest challenge increasing day by day. Composite materials were prepared by mixing Fly ash (FA) and nanostructured fly ash (NFA) from thermal power station as filler and blends of Waste polyethylene (WPE)(carry bags) collected from municipal solid waste (MSW) with virgin high‐density polyethylene (HDPE) as matrix. Different modifications were induced to improve the overall properties of these composites. At first, the WPE/HDPE blend matrix was modified by grafting with maleic anhydride (MA) and the composite prepared with FA/NFA. Then, the WPE/HDPE‐FA/NFA composite as a whole was treated with electron beam irradiation at 250 kGy radiation dose and finally the FA/NFA filler was treated with radiation dose of 250 kGy and the composite prepared. Significant enhancement in tensile strength, flexural strength, flexural modulus, and hardness are observed for MA modified and irradiated composites, the increase being more prominent in irradiated composites. Furthermore, an increase in storage/loss moduli with enhanced thermal stability was observed with the addition of FA/NFA and upon modifications. The analysis of the tensile fractured surfaces by scanning electron microscopy was in well correlation with the mechanical properties obtained. In summary, after analyzing the effects of the three different modifications on mechanical, dynamic mechanical and thermal properties, the irradiation on to the WPE/HDPE‐FA/NFA composites investigated was selected as the most appropriate for future applications. POLYM. COMPOS., 37:3256–3268, 2016. © 2015 Society of Plastics Engineers     

Mechanical and barrier properties of polyvinyl chloride plasticized with dioctyl phthalate,epoxidized soybean oil,and epoxidized cardanol

Plasticized polyvinyl chloride (PVC) films were prepared by melt compounding and compression molding using epoxidized cardanol (EC), a biobased plasticizer and its plasticization effect was compared with epoxidized soybean oil (ESBO) and dioctyl phthalate (DOP). The mechanical, migration, thermal, and barrier properties of the plasticized films were compared. The effect of replacing DOP with EC on the properties of PVC films was also investigated. The tensile strength, elongation at break, tensile modulus and impact strength values of PVC/EC films were higher in comparison to PVC/DOP and PVC/ESBO films at a fixed plasticizer loading of 40 wt.%. Also, the films prepared with a mixture of DOP + EC showed higher tensile strength and elongation at break compared to that of films prepared with only DOP. The PVC/EC films showed good thermal stability and reduced oxygen transmission rate (OTR) compared to PVC/DOP films. The addition of graphene and nanoclay in the PVC/plasticizer system exhibited an increase in oxygen transmission. However, the oxygen barrier property of nano filler incorporated PVC/EC films was better than PVC/DOP films. All the films showed negligible water vapor transmission rate (WVTR).     

Morphological interpretations and micromechanical properties of polyamide-6/polypropylene-grafted-maleic anhydride/nanoclay ternary nanocomposites

Ternary nanocomposites were fabricated based on an optimized impact modified polyamide-6 (PA-6)/polypropylene grafted maleic anhydride (PP-g-MA) blend composition with varied concentrations (0–6 wt.% at a step of 2 wt.%) of organoclay, Cloisite 30B™. The morphological attributes such as state of intercalation/exfoliation/crystalline organization and fractured surface topography of the nanocomposites were characterized by transmission electron microscopy (TEM), wide angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) while the thermal characterizations were done by conducting differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The WAXD/DSC studies have revealed that the crystallinity of the nanocomposites remained unaffected. DMA revealed an increase in glass transition temperature (T_g) of the nanocomposites by ∼14–19 °C relative to the soft polypropylene (PP)-phase, by ∼7–12 °C relative to the neat matrix PA-6 and by ∼4–9 °C relative to the optimized impact toughened PA-6 matrix while simultaneously being accompanied by the appearance of a second phase T_g peak progressively at higher temperatures as a function of nanoclay content, indicating the reinforcement effects/restrictions imposed by the nanoclay layers to the polymer chain mobility. The bulk mechanical response of the nanocomposites such as tensile, flexural and impact properties were studied and its related micromechanics aspects have been investigated using composite theories such as Halpin-Tsai, Hui-Shia, Takayanagi and Pukanszky models to analyze the interfacial effects and its role on the stress transfer efficiency. SEM analysis of fractured surface indicated that the failure mode of the nanocomposites undergoes a switch-over from interfacial-effects assisted fibrillation controlled ductile deformation to nanoclay induced soft PP-phase stiffened semi-ductile response via shear-lips formation.     

Optimal design of flyash filled composite friction materials using combined Analytical Hierarchy Process and Technique for Order Preference by Similarity to Ideal Solutions approach

The performances of flyash based fibre reinforced-phenolic composites have been rigorously evaluated on a Krauss friction testing machine following PVW-3212 norms as per the “Economic Commission for Europe” (ECE) regulations and have been discussed in-terms of fade, recovery, performance friction coefficient, wear and disc-temperature rise. The present paper deals with tribo-performance analysis in-terms of sensitivity of the overall performance due to any fluctuations in six selected performance defining attributes (PDA) specifically with regard to friction-fade, friction-recovery, wear, disc-temperature rise and averaged friction performance. The relative weights of importance of the PDAs with respect to overall friction performance have been elicited by the Analytic Hierarchy Process (AHP). The ranking of the friction materials has been carried out by the Technique for Order Preference by Similarity to Ideal Solutions (TOPSIS). In the sensitivity analysis part, the weightage of the PDAs were systematically varied within a specified range to assess the response of different friction materials so as to optimally design materials for varied friction applications.     

Viscoelastic interpretations of erosion performance of short aramid fibre reinforced vinyl ester resin composites

Short aramid fibre reinforced vinyl ester resin based isotropic composites are fabricated with varying fibre weight fractions (20–50 wt%). The composites were evaluated for their erosion performance under a dynamic set of variables such as impingement angle (30°–90°), impact velocity (43–76 m/s), erodent size (250–600 μm) and stand-off distance (55–85 mm) following design of experiments (DOE) based on Taguchi analysis approach. The thermo-mechanical attributes such as storage modulus, loss modulus and damping properties as viscoelastic responses of the composites were investigated in the temperature range of 0–180 °C for their possible interpretations regarding reinforcement efficiency and energy dissipation aspects relevant to erosion process. An interrelation between the full-width half-maxima (FWHM) of loss modulus peak and erosion rate has emerged indicating the erosion to be mainly controlled by the fibre–matrix interfacial characteristics. The eroded surface morphology investigation by scanning electron microscopy (SEM) revealed the nature of wear-craters, material damage mode and other qualitative attributes responsible in facilitating erosion of the composites.