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Since refrigeration appliances consume more than 15% of electrical energy over the globe, many solutions have been proposed to enhance the efficiency of these appliances. However, the solutions mostly rise the expenditure and complexity of the appliances, making these methods less feasible for manufacturing. Therefore, some inexpensive and less complicated modifications should be proposed to enhance the efficiency and performance of the appliances affordably. This paper presents a new solution using unutilized cooling capacity of evaporator for cooling compressor. The experimental exergy analysis of a domestic refrigerator in which the suction pipe absorbs heat from the compressor shell illustrates a 12.64% reduction in total irreversibility, as well as a 5% and 4% of increase in cooling capacity and coefficient of performance, respectively. Moreover, the appliance with the modified cycle needs 18.2% less refrigerant than the normal design. This idea would be an affordable and practical way to enhance the efficiency of refrigeration appliances as well as decrease the manufacturing costs. This study proposes recommended design guidelines for more efficient refrigeration appliances to be used in designing compressors.

We report on a study focusing on UV exposure conditions in three different types of chambers used for accelerated ageing of materials. The first chamber is equipped with four 300-W UVA/UVB mercury vapour lamps (Ultra-Vitalux/Osram). The second chamber uses four 40-W UVA fluorescent lamps (QUV-340/Q-Lab). The third chamber is Weather-Ometer Ci3000+ from Atlas with a 4500-W xenon arc lamp. UV irradiance prevailing in each chamber was measured using Bentham DM150 double monochromator spectroradiometer. The results were compared to measurements of solar spectral UV irradiance at Jokioinen, Finland, with a Brewer MkIII double monochromator spectrophotometer. The spectral shapes of the exposing UV radiation in the different chambers were found to notably differ from each other and from the solar UV spectrum. Both spatial inhomogeneities and temporal variability caused by various factors, like the ageing of the lamps, were detected. The effects were found to strongly depend on wavelength of the exposing UV radia...

The sedimentation stability and rheological properties of ionic liquid–based magnetorheological fluids comprising a mixture of micron- and nano-sized particles were experimentally studied. Three different fluids with the same total particle concentration of 15 vol% were prepared for testing: one containing only microparticles and two others in which 5 or 10 wt% of the microparticles were replaced by nanoparticles. The nanoparticles were surface stabilized against oxidation. For comparison purposes, silicon oil–based magnetorheological fluids with similar solid fractions were also prepared and tested. The results indicate that, with ionic liquid as a carrier fluid, the addition of nanoparticles at 10 wt% reduces the sedimentation rate almost by an order of magnitude from that without nanoparticles, while the reduction in the dynamic yield stress is only marginal. The ionic liquid–based fluids also had a better dispersion of particles.

This paper discusses shear viscosity measurements of polymer melts by the capillary rheometer. Particular emphasis is placed on investigating the effects of viscous heating and pressure dependence of viscosity in capillary flows. The capillary flow problem is addressed by means of numerical simulation using the finite element method to solve the equations of continuity, momentum and energy along with the viscosity model that accounts for the dependence on shear rate, temperature and pressure. Simulations clearly reveal that viscous heating and pressure dependence of viscosity can have a considerable impact on capillary rheometer experiments. On the other hand, as far as the pressure drop over the capillary is concerned, it is possible that these two contributing factors compensate for each other. Selected experimental data from the capillary rheometer are also presented and discussed in connection with the simulated results.

Rheological properties of polymer melts were studied using a slit die attached to an injection molding machine. The die has three exchangeable inserts to set the slit height to 0.75, 1.0, or 1.5 mm. The modular design eases the die cleaning, and measurements with variable slit heights enable the detection of possible wall slip. Two grades of polypropylene and two grades of polystyrene were studied using the slit die and the results were compared to those obtained using a capillary rheometer and a rotational rheometer in steady and dynamic modes. The examination of the selected polymers with different slits gave essentially the same results at each slit height, verifying the absence of wall slip. The agreement with the conventional off-line rheometer results was very good for all polymers studied. This suggests that a simple slit die construction can be used as an inexpensive rheometer to measure rheological properties of polymer melts for processing purposes. The thermo-mechanical history of the investigated melt in the in-line slit die experiments resembles that in actual melt processing and, therefore, determination of rheological properties under true processing conditions is possible.

A heat transfer model is constructed to derive the surface temperature of specimens in outdoor weathering. Data on thermal properties of materials and routinely collected weather data are used as inputs for the model. The model is validated against surface temperature data measured on samples of 11 different materials exposed to natural outdoor weathering in Jokioinen, Finland, over a period of 12 months. The agreement between the model and the surface measurements is more than satisfactory with a mean difference less than 0.5 K and a root-mean-square difference ranging from 0.4 to 1.4 K (0.1–0.5%), depending on material. The mean differences between the surface and ambient temperatures range from −0.1 to 1.3 K. Use of ambient temperature instead of sample surface temperature is shown to lead to severe misjudgements in estimations of reaction rates.

Polyamide and polystyrene particles were coated with titanium dioxide films by atomic layer deposition (ALD) and then melt-compounded to form polymer nanocomposites. The rheological properties of the ALD-created nanocomposite materials were characterized with a melt flow indexer, a melt flow spiral mould, and a rotational rheometer. The results suggest that the melt flow properties of polyamide nanocomposites were markedly better than those of pure polyamide and polystyrene nanocomposites. Such behavior was shown to originate in an uncontrollable decrease in the polyamide molecular weight, likely affected by a high thin-film impurity content, as shown in gel permeation chromatography (GPC) and scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer. Transmission electron microscope image showed that a thin film grew on both studied polymer particles, and that subsequent melt-compounding was successful, producing well dispersed ribbon-like titanium dioxide with the titanium dioxide filler content ranging from 0.06 to 1.12wt%. Even though we used nanofillers with a high aspect ratio, they had only a minor effect on the tensile and flexural properties of the polystyrene nanocomposites. The mechanical behavior of polyamide nanocomposites was more complex because of the molecular weight degradation. Our approach here to form polymeric nanocomposites is one way to tailor ceramic nanofillers and form homogenous polymer nanocomposites with minimal work-related risks in handling powder form nanofillers. However, further research is needed to gauge the commercial potential of ALD-created nanocomposite materials.

Extensional viscosity of a low-density polyethylene was measured at three temperatures in uniaxial extension by Sentmanat Extension Rheometer, and in contraction flow using the Cogswell analysis. The molecular stress function model was applied to describe the experimental results. The achieved maximum values from uniaxial transient tests were in accordance with the ones obtained by Cogswell method at similar strain level, and the molecular stress function model was able to describe the experimental transient uniaxial extensional data. The steady-state extensional viscosity was not reached in the experiments.

Transient extensional viscosity of low-density polyethylene was measured by Sentmanat extensional rheometer in combination with MCR301 rheometer (Anton Paar) at different temperatures. Issues related to the experimental procedure, namely fixing the sample and controlling the temperature, as well as correction for true sample dimensions in calculation of extensional viscosity of polymer melts, were discussed. The molecular stress function model was used to describe the experimental data. The results were in accordance with other test methods and theoretical description when the measurements were done without using the sample fixing clamps, careful temperature control was followed, and the experimental data were corrected for sample dimensions affected by thermal expansion and pre-stretching at the beginning of the test.

This study focused on determining the effects of molecular weight on the degradation of polylactide 96l/4d in melt spinning and the effects of melt processing on hydrolytic degradation. Three polylactides with different inherent viscosities were melt spun, and the fibres were studied in vitro. Results showed that during melt spinning high-molecular-weight polylactide degraded because polymer chains were subject to high shear stress and high melt temperatures, whereas a low-molecular-weight polylactide with low melt viscosity was not affected by melt processing. Most degradation occurred during the melting phase in the length of the extruder barrel. Lactide monomer, generated as the polymer degraded in the melt, significantly affected in vitro degradation such that the degradation rate was directly proportional to the lactide concentration of the polymer.

UV radiation conditions in a UV chamber equipped with four 300-W mercury vapour lamps have been characterized to assess the exposure received by the specimens aged in the chamber. Spectrally resolved measurements were performed on UV radiation emitted by new lamps and lamps operated for 4850 h in the chamber. An intensity decrease of as much as 75% with a strong wavelength dependency was detected. By linking the measurements with independent broadband measurements of the UV radiation field emitted by a single lamp, the UV dose rate distribution on the specimen plane of the chamber was derived. A method for true exposure accumulation estimation, accounting for the fading of the lamps, was developed. Accumulated UV radiation exposures on material samples in the chamber were derived and compared to long-term (1995–2007) average UV exposures received in natural sunshine at Jokioinen, Finland (lat. 60.4°N, long. 23.5°E, 104 m a.s.l.). Acceleration factors for the exposure in the UV chamber were derived in terms of doses integrated over different wavelength ranges. The acceleration factor was found to depend strongly on the wavelength range of the dose considered, presenting an extra challenge to the assessment of the artificial material exposure duration.

The relation between Pressure–Volume–Temperature (PVT) and rheological behaviour of several polymers including polypropylene, poly(methyl methacrylate), polyamide, polycarbonate, polystyrene and polystyrene/polycarbonate blends was studied. Pressure–viscosity coefficient b = ( ∂ ln η 0 / ∂ P ) was calculated by means of a revisited version of the Miller equation that accounts for pressure and temperature effect on Newtonian viscosity through the activation energy of flow and PVT parameters. Pressure–temperature dependent viscosities experimentally determined using pressure chamber capillary rheometry allow us to check the approach of the Miller equation. Incorporating the pressure effect in the Carreau–Yasuda model for η ( γ ˙ ) allows establishing the viscosity curves of thermoplastics over a wide range of shear rates and pressures.

Viscosity was measured for three amorphous polymers, PS, PMMA and PC, down to temperatures well below those normally available. Measurements were made in the dynamic mode and the Cox–Merz rule was applied to obtain the shear viscosity versus shear rate data. The Carreau–Yasuda viscosity model with WLF-type temperature dependence was found to provide good fits to the measured data over a wide range of temperatures.

New photocatalytic fibers made of sulfonated polyetheretherketone (SPEEK)/polypropylene (PP) are melt compounded and melt spun, first on laboratory scale and then on a semi-industrial scale. Fiber ...

Rheology and FTIR spectroscopy are compared as methods to study the degree of photodegradation in polypropylene (PP) and polystyrene (PS) sheets. The materials are hot pressed, artificially photo-aged with fluorescent lights for 4–2048 h and then measured with a rotational rheometer and FTIR. Both materials show a tendency for chain scission which can be seen as a reduction in viscosity. Changes in PP can be observed with both methods after 256 h of irradiation. Changes in PS become significant in rheology after 64 h but in FTIR only after 1024 h of irradiation. Due to the different chemical nature of the materials, the degradation of PS is rather linear with exposure, whereas the degradation of PP is more exponential. Using the zero shear viscosities obtained through extrapolations of the Cole–Cole and Carreau–Yasuda models, relative molecular weights are estimated with the aid of the power–law relationship between these two. These results are compared with the carbonyl indices determined from the FTIR spectra. Rheology is found to be a viable alternative for FTIR in certain situations. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42246.

Sulfonated polyetheretherketone (SPEEK) was synthesized via a mono-substitution reaction of PEEK in concentrated sulphuric acid and was blended with polypropylene (PP) in 2–10%w/w concentration to be used for the production of photoactive thermoplastic products. SPEEK and SPEEK/PP blends were characterized using FTIR, DSC, TGA, NMR, rheology, SEM, and EPR. Under UV-Vis irradiation, stable benzophenone ketyl (BPK) radicals were generated by hydrogen extraction from PP. By increasing the amount of SPEEK in the polymer blend a linear increase in the BPK radicals was achieved according to the EPR data. DSC and TGA tests indicated weaknesses in the thermal stability of SPEEK but according to the rheological tests this should not have a major effect on processabililty. The optimal amount of SPEEK in the blend was obtained at 5%w/w. This concentration provided a good compromise between radical concentration, material processability, and cost. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41509.

Using the high-order finite element method, we provide accurate predictions of the friction factor and the Nusselt number for the fully developed laminar flows of power-law-type non-Newtonian fluids in rhombic, isosceles-triangular, elliptical, and semielliptical ducts. Two kinds of thermal boundary conditions, commonly referred to as the H1 and T conditions, are considered. For each type of duct, computed results are presented for several aspect ratios with the power-law index ranging from 0.2 to 1.0. Mesh refinement tests with four different meshes are carried out for two specific duct configurations, indicating that the present predictions are remarkably insensitive to mesh density.

The performance of a single-screw extruder for the processing of cross-linkable low-density polyethylene in cable coating applications is examined. In particular, the aim is to demonstrate that the melt quality is markedly dependent on the melting efficiency. An instrumented 120 mm, 24 : 1 L/D extruder is used to perform the study. So-called pull-out tests are carried out for investigating the melting behavior inside an extruder. At the beginning of the melting zone, a typical Maddock melting mechanism is observed. Thereafter, as melting proceeds, the solid polymer becomes totally surrounded by melt according to the Lindt-Decker melting mechanism, and finally a solid-bed break-up occurs in many circumstances. This undesirable phenomenon can be avoided by screw cooling which, however, has its own drawbacks. In addition to the experimental work, numerical simulations of the melting behavior are conducted. The results provided by the simulation are in accord with the experimental findings.

A new approach for simulating the melting of polymers in extruders is presented. The key feature in the present treatment is that the melting evolution along the screw channel is obtained solely on the basis of the solution of relevant field equations, without making any presumptions regarding the mechanism of melting. Samples of calculation results are presented and discussed in order to illustrate the potential of the proposed method.

Forced convection heat transfer to hydrodynamically and thermally fully developed laminar flow of power-law non-Newtonian fluid in rectangular ducts has been studied for the H1 and T thermal boundary conditions. The solutions for the velocity and temperature fields were obtained numerically using the finite element method with quartic triangular elements. From these solutions, very accurate Nusselt number values were determined. Computations were performed over a range of power-law indices and duct aspect ratios.

The performance of a penalty-Galerkin finite element method with quartic triangular elements when applied to laminar natural convection in a square cavity with differentially heated vertical walk and adiabatic horizontal walls is studied. The numerical calculations were carried out for Rayleigh numbers of 104 105, 106, and 107 on several successively refined meshes. The computational results are presented in terms of velocity components, temperature, stream function, and Nusselt number. The numerical procedure adopted in the present study yields consistent performance with respect to mesh refinement, and comparisons with previously published results indicate fairly close agreements.

The finite-element method has been applied to solve numerically equations governing fully developed laminar flow of power-law non-Newtonian fluid in a rectangular duct. The resulting finite-element solutions for the velocity profile have been further utilized to obtain the numerical values of the friction factor-Reynolds number product for duct aspect ratios ranging from 0.05 to 1.0 and for power-law indices ranging from 0.2 to 2.0, i.e., both shear-thinning and shear-thickening cases are considered.

Modern polymeric materials possess an ever increasing potential in a large variety of outdoor objects and structures offering an alternative for many traditional materials. In outdoor applications, however, polymers are subject to a phenomenon called weathering. This is primarily observed as unwanted property changes: yellowing or fading, chalking, blistering, and even severe erosion of the material surface. One of the major weathering factors is UV radiation. In spring 2005, the Finnish Meteorological Institute with its research and industrial partners launched a five-year material research project named UVEMA (UV radiation Effects on MAterials). Within the framework of the project, a weathering network of seven European sites was established. The network extends from the Canary Islands of Spain (latitude 28.5°N) to the Lapland of Finland (latitude 67.4°N), covering a wide range of UV radiation conditions. Since autumn 2005, the sites of the network have been maintaining weathering platforms of specimens of different kinds of polymeric materials. At the same time, the sites have been maintaining their long-term monitoring programmes for spectrally resolved UV radiation. Within UVEMA, these data are used for explaining the differences between the degradation rates of the materials at each site and for correlating the UV conditions in accelerated ageing tests to those under the Sun. We will present the objectives of the UVEMA project aiming at deeper understanding of the ageing of polymers and more reliable assessments for their service life time. Methodologies adopted within the project and the first results of the project will be summarized.

A microscope add-on device to a 1.3 Mpix camera phone was selected as a demonstrator system for testing inmould integration of electronic substrates and plastic optics. Optical design of the device was quite challenging due to the fact that illumination system needed to be integrated with a double aspheric singlet lens structure as a single optical piece. The designed imaging lens resolution was adequate to resolve 10 mm features with a mobile phone camera. In the illumination optics the light from LEDs embedded into the plastic structure was collected and guided to the surface that was imaged. Illumination was designed to be uniform and adequately bright to achieve high resolution images with the camera phone. Lens mould design was tested by using injection moulding simulation software. The critical mould optical surfaces were designed as separate insert parts. Final shapes producing lens surfaces were tooled by diamond turning on nickel coatings. Electronic circuit board inserts with bonded bare LED chips and packaged SMD LEDs were assembled to the mould and then overmoulded with optical grade PMMA. Experiences proved that inmould integration of electronic substrates, bare LED chips and high resolution imaging optics in injection-compression moulding process is feasible. The yield of embedded packaged and also bare chip components was close to 100% after the right injection moulding process parameters were found. Prototype add-on system was characterized by testing the imaging properties of the device with a camera phone.

A recently developed approach to simulate the nonisothermal polymer melt flow in a single-screw extruder is validated against experimental data taken from the literature. Comparisons are made with eight sets of experimental results, and for each case several numerical runs are performed to provide some insight into the sensitivity of simulation outcomes to input material parameters (i.e., viscosity, density, thermal conductivity, and specific heat). In general, predictions for the pressure distribution along the extruder and for the mean melt temperature at the exit of the extruder compare favorably with pertinent experimental results. On the other hand, calculated estimates for the power consumption of an extruder are systematically lower than corresponding measured values.

A numerical study on the laminar flow and heat transfer behavior of viscoelastic fluids in rectangular ducts is conducted using the finite element approach. A Criminale-Ericksen-Fibley relation is applied to describe the viscoelastic character of the fluid, and a hydrodynamically and thermally fully developed flow with the H1 thermal boundary condition is considered. The finite element procedure employed yields essentially mesh-independent predictions with a fairly moderate computational effort. Computed results are presented and discussed in terms of the secondary flow field, the temperature field, the friction factor and the Nusselt number. In particular it is shown that the presence of a secondary flow markedly alters the temperature field and results in a substantial heat transfer enhancement with all duct aspect ratios considered.

Flow and heat transfer characteristics in a rectangular channel covered by an isothermally heated moving wall were studied for a non-Newtonian fluid obeying the power-law relationship under fully developed creeping flow conditions. The governing partial differential equations were solved using the finite element method together with a penalty formulation. A practical application behind the present study is the screw extrusion process. Several simplifications were, however, introduced into the analysis, and therefore the primary purpose of this study is not to characterize the flow and heat transfer in the actual screw extruder, but to present a first effort towards this goal. The most interesting result revealed by the analysis is that the recirculatory motion set up by the diagonally moving top wall has a pronounced influence on the heat transfer.

Effects of the plate material, surface roughness and measuring gap height on static and dynamic yield stresses of a magnetorheological (MR) fluid were investigated with a commercial plate?plate magnetorheometer. Magnetic and non-magnetic plates with smooth (Ra???0.3??m) and rough (Ra???10??m) surface finishes were used. It was shown by Hall probe measurements and finite element simulations that the use of magnetic plates or higher gap heights increases the level of magnetic flux density and changes the shape of the radial flux density profile. The yield stress increase caused by these factors was determined and subtracted from the measured values in order to examine only the effect of the wall characteristics or the gap height. Roughening of the surfaces offered a significant increase in the yield stresses for non-magnetic plates. With magnetic plates the yield stresses were higher to start with, but roughening did not increase them further. A significant part of the difference in measured stresses between rough non-magnetic and magnetic plates was caused by changes in magnetic flux density rather than by better contact of the particles to the plate surfaces. In a similar manner, an increase in gap height from 0.25 to 1.00?mm can lead to over 20% increase in measured stresses due to changes in the flux density profile. When these changes were compensated the dynamic yield stresses generally remained independent of the gap height, even in the cases where it was obvious that the wall slip was present. This suggests that with MR fluids the wall slip cannot be reliably detected by comparison of flow curves measured at different gap heights.

The morphology and rheological and mechanical properties of nanoclay-reinforced polypropylene nanocomposites were investigated with aid of transmission electron microscopy (TEM), thermo gravimetric analysis, rheometry, and mechanical tests. The organically modified silicate (montmorillonite) was used as a reinforcing material and maleic anhydride-grafted polypropylene oligomer as a compatibilizer to improve the clay dispersion and adhesion. The object of the study was to examine the effect of screw speed of the co-rotating twin-screw extruder on the clay exfoliation and nanocomposite properties. Also, the effect of compatibilizing agent was taken into account. The main result of the study was that nanocomposites showed both intercalated and exfoliated structures depending on the screw speeds of extruder. TEM images revealed that the dispersion of silicate layers was greatly influenced by the screw speed. However, even when the silicate layers were highly exfoliated, there was no remarkable effect on mechanical properties of the nanocomposite. POLYM. ENG. SCI., 46:995-1000, 2006.

The aim of this work was to study the solubility of chemical pulps and the effects of ZnO and NaOH concentrations on the solution properties. The pulps were mechanically shredded, pretreated using cellulase, and dissolved directly into aqueous sodium zincate. The solubility of pulp was observed visually by a microscope, and the viscosities of solutions were measured by a rotational rheometer and a ball-drop method.