Comparative study on the heat transfer performance of micro-grooved anodized thermosyphon with R134a,R600a and R717 for low-temperature applications

Journal of Mechanical Science and Technology - A comparative heat transfer performance of an internally grooved anodized thermosyphon with eco-friendly refrigerants is presented in this study....     

Optimisation of process parameters for electroless nickel plating on SS316L for refrigeration systems

Nowadays, refrigeration systems are important for industrial and domestic applications. The coefficient of performance of a vapour compression refrigeration system can be improved if a reduction in the work of compression can be achieved by a suitable technique for a specified heat removal rate. The present study investigates the effect of material coating of electroless nickel (EN) plating. The friction and wear experiments were performed using a four-ball machine tribo tester. Controlling the EN plating parameters plays an important role in the quality of coating. It depends on the wear scar rate of the coated material. So it is necessary to optimise the process parameters of EN plating. The experimental studies have been conducted under varying pressure, load and time on quality characteristics. In this paper, optimisation of process parameters using response surface methodology technique for EN plating was discussed.     

Dielectric and conducting behavior of pyrene functionalized PANI/P(VDF‐co‐HFP) blend

Herein, we present the dielectric and electrical conductivity properties of the partially miscible polymer blend prepared using pyrene functionalized polyaniline (pf‐PANI) and poly(vinylidene fluoride‐co‐hexafluoro propylene) (PVDF‐co‐HFP). The blend mostly retains the fluorescent nature of pf‐PANI as well as can be moldable and possesses good damping property. The dielectric properties have been investigated as a function of temperature at three different frequencies and the plausible origin of polarization responsible for dielectric behavior in this blend has been identified. The experimental results of dielectric measurements are compared with theoretical models and discussed. The surface morphology of the samples has been examined with a scanning electron microscope. The electrical conductivity has also been studied as a function of temperature and explained in terms of hopping of charge carriers/interconnected networks. The combined dielectric and conductivity results together with scanning electron microscope micrographs, reveal that there is hindrance to achieve percolation threshold even after pf‐PANI addition of 57 vol % and subsequent thermal treatment. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44077.     

Rauhut–Currier‐Initiated Organocascade Reaction: Synthesis of Substituted Dispirocyclohexanes through a [2+2+2] Strategy Between 2‐Arylideneindan‐1,3‐diones and Activated Alkenes

For the synthesis of multisubstituted dispirocyclohexane derivatives, a Rauhut–Currier‐initiated organocascade reaction between 2‐arylideneindan‐1,3‐diones and activated alkenes in the presence of diazabicyclo[2.2.2]octane (DABCO) was demonstrated. The functionalized dispirocyclohexanes with a wide range of substituents were obtained in satisfactory to excellent chemical yields (58–99%) with high chemo‐ and diastereoselectivities (>95:5 dr). This organocatalytic reaction proceeded smoothly through Michael/Michael cyclization, which involves the formation of three new carbon‐carbon bonds with simultaneous construction of two all‐carbon spiro quaternary centers.

     

An electrostatic powder spray process for manufacturing thermoplastic composites

Manufacture of thermoplastic composites is expensive because of the difficulty of impregnating the resin into the fibers. Powder processing shows great promise as an impregnation technique for cost-effective manufacturing. This paper discusses an electrostatic powder spray impregnation technique that uses glass fibers. A geodesic fiber spreader is used to spread the fibers locally in the region of maximum powder deposition. A negative corona electrostatic spray gun is employed to charge and direct the powder for coating both sides of the spread fiber tow. The process has been used to impregnate glass fibers with poly(aryl ether ketone ketone) powder. The effect of the powder mass flow, corona voltage, and fiber tow velocity on powder deposition has been investigated. Particle image velocimetry is utilized to determine particle velocities. Compression molded panels have been produced and tested in three point bending.     

Recent Advances in Reactive Extrusion Processing of Biodegradable Polymer‐Based Compositions

This review reports on recent advances in the design of biodegradable polymers built from petroleum and renewable resources using reactive extrusion processing. Reactive extrusion represents a unique tool to manufacture biodegradable polymers upon different types of reactive modification in a cost‐effective way. Partially based on our ongoing research, ring‐opening polymerization of biodegradable polyesters will be approached as well as the chemical modification of biodegradable polymers, particularly natural polymers. The development of environmentally friendly polymer blends as well as (nano)composites from natural polymers, including natural fibers and nanoclays, through reactive extrusion, as an efficient way to improve the interfacial adhesion between these components, will be also discussed.

     

Melt‐stable poly(1,4‐dioxan‐2‐one) (co)polymers by ring‐opening polymerization via continuous reactive extrusion

Bulk polymerization of ?‐caprolactone (CL), 1,4‐dioxan‐2‐one (PDX), and mixtures of PDX and CL was carried out by initiation with Al(O^secBu)₃ in a co‐rotating twin‐screw extruder through a fast single‐step process. Both homopolymerizations and copolymerization of PDX and CL proceed very rapidly and reach almost complete (co)‐ monomer(s) conversion as soon as 8 mol% of CL are added in the feed. Even though poly(1,4‐dioxan‐2‐one) (PPDX) is known to thermally degrade mainly through unzipping depolymerization promoted from the hydroxyl end‐groups and yielding PDX monomer, it turns out that the thermal stability of PPDX chains is substantially improved by the copolymerization of PDX with limited amounts of CL. Interestingly, DSC analysis of the so‐obtained P(PDX‐co‐CL) copolymers has demonstrated that a CL molar fraction as high as 11 mol% does not prevent the crystallization of the resulting copolymer, which retains a melting temperature close to 95°C. This last observation has been explained by the formation of a blocky‐like copolymer structure, in which short PPDX and PCL sequences are randomly distributed. POLYM. ENG. SCI., 45:622–629, 2005. © 2005 Society of Plastics Engineers.     

The Use of D-optimal Design for Modeling and Analyzing the Tribological Characteristics of Journal Bearing Materials Lubricated by Nano-Based Biolubricants

Response surface methodology (RSM) based on a D-optimal design was employed to investigate the tribological characteristics of journal bearing materials such as brass, bronze, and copper lubricated by a biolubricant, chemically modified rapeseed oil (CMRO). The wear and friction performance were observed for the bearing materials tested with TiO₂, WS₂, and CuO nanoadditives dispersed in the CMRO. The tests were performed by selecting sliding speed and load as numerical factors and nano-based biolubricant/bearing materials as the categorical factor to evaluate the tribological characteristics such as the coefficient of friction (COF) and specific wear rate. The results showed that RSM based on a D-optimal design was instrumental in the selection of suitable journal bearing materials for a typical system, especially one lubricated by nano-based biolubricant. At a sliding speed of 2.0 m/s and load of 100 N, the bronze bearing material with CMRO containing CuO nanoparticles had the lowest COF and wear rate. In addition, scanning electron microscopy (SEM) examination of the worn bearing surfaces showed that the bronze bearing material lubricated with CMRO containing CuO nanoadditive is smoother than copper/brass bearing material.     

A systematic approach to preliminary polymer process development: modeling and design

A general and complete methodology is presented to facilitate systematic modeling and design of polymer processes during the early development period. To capture and handle the subjective type of uncertainty, embedded in the preliminary process development, fuzzy theories are used as a basis to model and design the process in the presence of ambiguity and vagueness. Physical membership functions are developed for mapping the relation between process variables and the associated fuzzy uncertainties. Based on the qualitative results generated using our previously proposed “linguistic based preliminary design method,” the process modeling can be followed even in the absence of any process governing equations. The modeling is carried out by establishing an appropriate fuzzy reasoning system which provides a specific functional mapping that relates input process variables to one (or more than one) output performance parameter(s). A reduced yet feasible domain is generated by our qualitative design scheme to constrain the process variables. Now, any optimization routine can then be employed to search for a proper process design. We demonstrate the effectiveness of the proposed methodology by its application to a typical compression molding process.     

Collecting Statistics over Runtime Executions

By collecting statistics over runtime executions of a program we can answer complex queries, such as “what is the average number of packet retransmissions” in a communication protocol, or “how often does process P₁ enter the critical section while process P₂ waits” in a mutual exclusion algorithm. We present an extension to linear-time temporal logic that combines the temporal specification with the collection of statistical data. By translating formulas of this language to alternating automata we obtain a simple and efficient query evaluation algorithm. We illustrate our approach with examples and experimental results.