Optimal Mass Fraction Research Articles

Thermodynamic analyses of a modified ejector enhanced dual temperature refrigeration cycle for domestic refrigerator/freezer application

This paper presents a modified ejector enhanced dual temperature refrigeration cycle (MERC) with mixture refrigerant R290/R600a for domestic refrigerator/freezer application. The proposed cycle eliminates the vapor-liquid separator and allows low boiling component refrigerant R290 enters the freezer evaporator, which results in an enhancement of evaporating pressure at the same evaporating temperature. The thermodynamic modeling through energetic and exergetic analysis method is employed to evaluate the cycle performance of MERC and compared with that of basic ejector enhanced dual temperature refrigeration cycle (BERC). The simulation results show that the COP and qev of MERC are improved by 23.1% and 34.7% compared with BERC under the typical operating condition. And every component of MERC shows relatively lower level of exergy destruction than that of BERC, which has 22.9% improvement in exergy efficiency ηex. Overall, the MERC could achieve higher cycle performance when a lower cooling capacity ratio of freezer evaporator to refrigerating evaporator is demanded. Furthermore, the highest COPs and ηex could be obtained at the optimal R290 mass fraction of 0.7. The theoretical results reveal the practical application potential of MERC in the domestic refrigerator/freezer.

Carbon Particle-Doped Polymer Layers on Metals as Chemically and Mechanically Resistant Composite Electrodes for Hot Electron Electrochemistry

This paper presents a simple and inexpensive method to fabricate chemically and mechanically resistant hot electron-emitting composite electrodes on reusable substrates. In this study, the hot electron emitting composite electrodes were manufactured by doping a polymer, nylon 6,6, with few different brands of carbon particles (graphite, carbon black) and by coating metal substrates with the aforementioned composite ink layers with different carbon-polymer mass fractions. The optimal mass fractions in these composite layers allowed to fabricate composite electrodes that can inject hot electrons into aqueous electrolyte solutions and clearly generate hot electron-induced electrochemiluminescence (HECL). An aromatic terbium (III) chelate was used as a probe that is known not to be excited on the basis of traditional electrochemistry but to be efficiently electrically excited in the presence of hydrated electrons and during injection of hot electrons into aqueous solution. Thus, the presence of hot, pre-hydrated or hydrated electrons at the close vicinity of the composite electrode surface were monitored by HECL. The study shows that the extreme pH conditions could not damage the present composite electrodes. These low-cost, simplified and robust composite electrodes thus demonstrate that they can be used in HECL bioaffinity assays and other applications of hot electron electrochemistry.

Thermal Analysis of a Forced Flow Diffusion Absorption Refrigeration System for Fishing-Boat Exhaust Waste Heat Utilization

Ammonia water absorption refrigeration systems are effective in utilizing fishing-boat exhaust waste heat for cryopreservation. However, the liquid level control and the use of a solution pump characterized by small flowrate and high-pressure head result in poor reliability in the traditional system. Besides, the system must necessarily be designed anti-swaying and anti-corrosion. This paper proposes a forced flow diffusion absorption refrigeration system, in which an inherently leak-free canned motor pump and an ejector are employed to provide the driving forces of the gas and liquid loops. The approximate single pressure operation allows for a simple passive liquid sealing control without throttling valves. The system adopts an integrated cooling strategy which allows the system to operate under swaying conditions, and the external seawater cooled heat exchanger avoids internal corrosion and leakage. The thermal analysis shows the system is valid to be operated under wide operating conditions, and the coupled gas and solution circulation ratios determined the performance of the novel system. There is an optimal ammonia mass fraction difference in the gas loop to obtain the optimal COP. The COP reaches 0.4 when the temperatures at the outlets of the generator, evaporator, absorber, and condenser are 160, −15, 35, and 35°C, respectively. The novel system provides a reliable absorption refrigeration system design for fishing-boat applications.

Fabrication of highly thermal conductive and shape-stabilized phase change materials

Poor thermal conductivity and easy leakage in molten state into the surrounding of the thermal energy storage (TES) system are two major problems of organic phase change materials (OPCMs). This study focuses on the heat conduction enhancement and leakage-proof of the OPCM and a novel shape-stabilized OPCM with decyl alcohol (DA) as TES material, expanded graphite (EG) and nanoparticles as additives is developed. The optimal mass fraction of the porous EG, which serves as the shape-stabilizer and heat conduction enhancer, is determined to be 9% through vacuum drying method. Five different kinds of nanoparticles are selected to further improve the thermal conductivity. The experimental results suggest that the composite PCM DA/MgO/EG possesses the highest thermal conductivity, with a value of 1.873 W/(m·K), which is significantly increased by 11.570 times comparing to pure DA and 1.010 times higher than that of DA/EG. The mechanism of strengthening thermal conductivity by the coupling effect of EG and nano additives is revealed. According to DSC tests, the melting temperature and the melting enthalpy of the ternary composite PCM DA/MgO/EG are 1.1 °C and 194.6 J/g, respectively. The effect of additives on the phase transition temperature and enthalpy of PCMs is also investigated. Depending on the cyclic stability experiments, after 300 charging-discharging cycles, both the phase transition temperature and the melting latent heat of DA/MgO/EG have little change by comparison with those of uncirculated composites, which indicates excellent thermal stability of the material. Finally, the applicability of DA/MgO/EG composite is explored by cold insulation experiment. Overall, the composite in this work has promising prospects in cold chain logistics.

On the rheological properties of multi-walled carbon nano-polyvinylpyrrolidone/silicon-based shear thickening fluid

Abstract This study examines the rheological properties of shear thickening fluid (STF) enhanced by additives such as multi-walled carbon nanotubes (MWCNTs), polyvinylpyrrolidone (PVP), and nano-silica (SiO2) at different mass fraction ratios. The rheological properties of the liquid (MWCNTs–PVP/SiO2–STF) and the effect of the rheological properties of the STF under different plate spacing of the rheometer were investigated. The optimal mass fraction mixing ratio was also studied. The MWCNTs–PVP/SiO2–STF system with different PVP mass fractions was fabricated using ultrasonic technology and the mechanical stirring method. Then, the steady-state rheological test of the MWCNTs–PVP/SiO2–STF system was carried out with the aid of the rheometer facility. Dynamic rheological and temperature sensitivity tests on the MWCNTs–PVP/SiO2–STF system with 0.1 and 0.15% PVP mass fractions were performed. The rheological test results show that the MWCNTs–PVP/SiO2–STF system has a significant shear thickening effect when the PVP mass fraction is increased from 0 to 0.15%. When the PVP mass fraction is 0.1% and the plate spacing is 1 mm, the system exhibits the best shear thickening performance. This is based on the following facts: the viscosity can be achieved as 216.75 Pa s; the maximum energy storage and energy consumption capabilities can be observed. As a result, PVP can significantly enhance the shear thickening performance of the MWCNTs/SiO2–STF system.

Enhanced aquathermolysis of extra-heavy oil by application of transition metal oxides submicro-particles in relation to steam injection processes

In order to investigate the catalytic effects of transition metal oxides submicro-particles on aquathermolysis of Liaohe extra-heavy crude oil, the catalysts NiO, α·Fe2O3 and Co3O4 are used and evaluated during the experiments. The optimum mass fraction of the catalyst and water was determined to be 5.0 wt% and 30 wt%, respectively. The optimum reaction time for aquathermolysis was 24 h, and the optimum reaction temperature was 240 °C. The analysis results showed the heavy oil was upgraded dramatically by addition of the catalysts based upon viscosity reduction, saturate/aromatics/resins/asphaltenes analyses, elemental analysis, Fourier transform infrared spectroscopy and gas chromatography. All results show the heavy oil is in situ updated dramatically by catalytic aquathermolysis under the optimum operating conditions. A five-lump model is proposed for estimating kinetic parameters of aquathermolysis and agrees well with the experimental data.

Characterization of physical and mechanical properties of recycled jute fabric reinforced polypropylene composites

AbstractThis research designed to contribute to reduce the environmental impacts through the preparation of composites with recyclable materials to be used in different applications. To this end, composites have been developed based on jute recovered from packaging bags and polypropylene (PP) reclaimed from scraps obtained from the manufacture of PP yarns. The developed composites were then characterized. First of all, the optimum mass fraction was determined in order to achieve good mechanical performance. Several mass fractions (30%, 40%, 45%, 50%, 60%, and 70%) were experimented to find that the best characteristics were those of the biocomposite with 40% reinforcement (σ = 39.07 MPa, E = 4.60 GPa). With this ratio, jute–PP biocomposites were further developed with different jute architectures (Satin, Serge 2 × 2, Taffeta). A structural study of the different jute fabric wastes was carried out to confirm whether they are suitable for use with a thermoplastic matrix (i.e., at a processing temperature of ≥200°C). Tensile and bending tests were carried out on these composites to find out the effect of the weave structure of the reinforcement.

Hybrid nanoparticles-laden fluid based spiral solar collector: A proof-of-concept experimental study

Over-reliance on limited fossil resources to meet the ever-increasing energy demand has several consequences such as high prices, unpredictable supply, and adverse environmental and ecological impact. It is the need of the current time to explore sustainable renewable energy sources in order to mitigate the environmental consequences and match the increasing demand economically. Out of various sustainable renewable energy sources, solar energy stands out as one of the exemplary candidates. It is a clean energy source with no greenhouse gas (GHG) emissions and is available in abundance at many parts of the world. Prevailing studies corroborate the merit of nanofluids in harnessing solar energy. In this experimental study, thermal analysis of a novel spiral-shaped collector is conducted with both hybrid nanofluid-based volumetric absorption system (VAS) and surface-based absorption system (SAS). In the case of hybrid VAS, homogenous mixture of Al2O3 and Co3O4 with de-ionized water as base fluid is employed. The experimental results reveal that the maximum temperature rise and thermal efficiency of 9.8 °C and 50%, respectively, is obtained at nanoparticle mass fraction of 100 mg/L Al2O3 +100 mg/L Co3O4 which is the optimum mass fraction. Whereas, in the case of SAS, volumetric flow rate of 100 mL/h is the optimum volumetric flow rate at which the maximum temperature rise of 8.5 °C is achieved. Further, the effect of variation in volumetric flow rate and the incident flux on the thermal performance of both VAS and SAS is also presented. On comparing the performance of VAS with SAS under a similar condition a temperature rise and thermal efficiency of about 15.3% and 15%, higher is achieved in VAS than SAS (at optimum volumetric flow rate).

Experimental Study on Rare Earth and Magnesium Composite Treatment of 49MnVS3 Non‐quenched and Tempered Steel

Nowadays, under the context of severe resource shortage, it is urgent to develop non‐quenched and tempered steel. Herein, a new method of combining rare‐earth cerium (Ce) and magnesium (Mg) to treat the 49MnVS3 steel with low oxygen and rather high sulfur is proposed. The inclusions modification, microstructure evolution, and mechanical properties change of 49MnVS3 steel with different Ce and Mg content composite treatment are investigated by optical microscope (OM), scanning electron microscope (SEM)–energy‐dispersive spectrometer (EDS), electron probe microanalyzer (EPMA), and tensile and impact tests. The results indicate that the small spherical Ce–Mn–Mg–O–S composite inclusions replace the Al2O3wrapped MnS composite inclusions and elongated MnS inclusions after Ce and Mg joint treatment. After Ce and Mg composite treatment, the proportion of ferrite is significantly improved. Meanwhile, the interlamellar spacing of pearlite is refined. Attributed to modified inclusions and optimized microstructure, the strength and impact toughness are gradually enhanced. In contrast to Ce–Mg free steel, the impact energy of 4#steel with 0.0122 wt% Ce and 0.0012 wt% Mg addition is increased by 33%. In the current study, the optimal mass fractions of Ce and Mg are 0.0122 and 0.0012 wt%, respectively.

Effect of Mg on the microstructure evolution and mechanical properties of 5%TiB2/Al−4.5%Cu composites

Agglomeration behavior of TiB2 particles in 5%TiB2/Al-4.5%Cu composites (all compositions are in wt.% unless otherwise specified) is studied by adding different content of Mg to improve its strength and ductility, a widely used in-situ molten salt reaction process is used to produce the composites. The results show that addition of Mg could not only significantly segregate TiB2 particles but also further refine the α-Al grains and then improve the mechanical properties of the composites on the basis of TiB2 particles. Here, 0.5% Mg is considered the optimum mass fraction for dispersion, refinement, and modification of particles based on the results of investigation. The yield strength (YS), ultimate tensile strength (UTS), elastic Young’s modulus (EM), and Vicker’s hardness (VHN) of the composites in T6 heat treatment are increased to 375 MPa, 486 MPa, 88 GPa, and 167 HV - an improvement of 21.8%, 16.5%, 20.9%, and 9.4%, respectively, versus the original TiB2/Al-4.5%Cu composite (308 MPa, 417 MPa, 63 GPa, and 153 HV). The elongation of the composite is improved by 20.9%. These merits are mainly attributed to addition of Mg, which increases the surface-spread coefficient of TiB2 particles by reducing the surface tension of the Al melt, thereby improving the wettability.

Mechanical properties of graphene nanoplatelets reinforced epikote 828 under dynamic compression

In this experimental investigation, the influence of graphene nanoplatelets (GNPs) on the dynamic behavior of polymeric material such as diglycidyl ether of bisphenol A (DGEBA) epoxy is investigated using the Split Hopkinson Pressure Bar (SHPB). Nanocomposite samples with a different weight percentage of GNPs i.e. 0, 1, 2, 5 wt% were fabricated and tested under dynamic compression to understand the influence of nanofillers on the mechanical performance of the epoxy. The results established that changing the mass fraction of GNPs greatly influences the mechanical behavior of the epoxy and confirmed that the optimal mass fraction of GNPs was 1 wt% because of the good dispersion and viscosity. While, a further increase in the percentage of GNPs resulted in degradation of the mechanical strength of the material because of the agglomeration of graphene sheets, porosity, and their poor interfacial bonding. Moreover, each mass fraction of nanocomposites was tested at three different impact pressures i.e. 1.5, 2, and 4 bar. The main objective is to quantify the effect of the strain rate on the mechanical behavior and on the resulting damage modes. This study further confirmed that the high percentage of GNPs increases the viscosity of the epoxy resulting in porosity and void in the structure which generates high-localised stresses into the matrix causing premature failure under dynamic loading.

Impermeability of basalt fiber soil-cement

The influence of basalt fiber on the impermeability of soil-cement is studied by the tests of permeability, anti-chloride ion resistance and scanning electron microscope. The mixing basalt fiber mass fractions for different tests are 0, 0.5%, 1.0%, and 1.5%, respectively. The permeability coefficients and electric fluxes of basalt fiber soil-cements are obtained. Results show that the addition of basalt fiber can obviously enhance the impermeability of soil-cement. With the increase of basalt fiber content, both the permeability coefficient and the value of electric flux decrease. The optimal mass fraction of basalt fiber is 1.5%. The incorporation of basalt fibers can effectively connect the discrete soil particles and make the basalt fibers, soil particles and cement form a more stable whole.

Development and performance characterization of ultra-light foam thermal insulation material based on ordinary Portland cement modified by sulphoaluminate cement

In this study, an ultra-light ordinary Portland cement-based thermal insulation material (ULCFTIM) with an apparent density of less than 300 kg/m3 was developed using physical foaming technology. The problem of ULCFTIM collapse during the preparation process was solved by adding sulphoaluminate cement (SAC). The influence of SAC mass fraction and water-cement ratio on the thermal conductivity and compressive strength of ULCFTIM was researched. The experimental results show that increasing the SAC is beneficial to the compressive strength of ULCFTIM at 3 days, but decrease the compressive strength of ULCFTIM at 28 days. The optimal mass fraction for SAC in a cementitious material is 10%. With the water-cement ratio increases, the compressive strength first increases and then decreases, and the thermal conductivity decreases first and then stabilizes. When w/c values ranging from 0.26-0.30, ULCFTIM has a good performance with compressive strength between 0.185 MPa and 0.201 MPa and thermal conductivity between 0.701W ⋅m-1⋅K-1 and 0.714 W ⋅m-1⋅K-1.

Resizing Approach to Increase the Viability of Recycled Fibre-Reinforced Composites.

Most recycling methods remove the essential sizing from reinforcing fibres, and many studies indicate the importance of applying sizing on recycled fibres, a process we will denote here as resizing. Recycled fibres are not continuous, which dissociates their sizing and composite lay-up processes from virgin fibres. In this study, commercial polypropylene and polyurethane-based sizing formulations with an aminosilane coupling agent were used to resize recycled glass and carbon fibres. The impact of sizing concentration and batch process variables on the tensile properties of fibre-reinforced polypropylene and polyamide composites were investigated. Resized fibres were characterized with thermal analysis, infrared spectroscopy and electron microscopy, and the tensile properties of the composites were analysed to confirm the achievable level of performance. For glass fibres, an optimal mass fraction of sizing on the fibres was found, as an excess amount of film former has a plasticising effect. For recycled carbon fibres, the sizing had little effect on the mechanical properties but led to significant improvement of handling and post-processing properties. A comparison between experimental results and theoretical prediction using the Halpin-Tsai model showed up to 81% reinforcing efficiency for glass fibres and up to 74% for carbon fibres.

Fluid selection and advanced exergy analysis of dual-loop ORC using zeotropic mixture

The comprehensive performance of a dual-loop organic Rankine cycle (DORC) is mainly influenced by working fluid pairs and key components. Based on multi-objective optimization, we conducted the working fluid selection and advanced exergy analysis for the DORC system driven by flue gas at 300℃. The exergy efficiency, payback period (PBP), and annual CO2 emission reduction (AER) were selected as the objective functions. Operating parameters and mass fraction of mixtures were optimized by non-dominated sorting genetic algorithm-II (NSGA-II). A suitable fluid pair for the DORC system was selected from 13 candidate fluid pairs. Then, the improvement potential of each component was estimated based on advanced exergy analysis. The results show that there is an optimal mass fraction for different zeotropic mixtures. When cyclohexane/cyclopentane (0.2/0.8) and butane/pentane (0.65/0.35) are used for the high-temperature (HT) loop and low-temperature (LT) loop respectively, the DORC system can achieve the best performance. Its exergy efficiency and AER increase by 14.7% and 19.1% respectively, while PBP only increases by 2.6%, compared with the fluid pair of cyclohexane-butane. There is 261.9 kW endogenous avoidable exergy destruction in the DORC system, accounting for 53.5% of the total exergy destruction. The HT turbine (HTT) is the first component that needs technical modifications, followed by the HT evaporator (HTE), intermediate heat exchanger (IHE), and LT turbine (LTT).

A comparative thermodynamic analysis of Kalina and organic Rankine cycles for hot dry rock: a prospect study in the Gonghe Basin

Hot dry rock is a new type of geothermal resource which has a promising application prospect in China. This paper conducted a comparative research on performance evaluation of two eligible bottoming cycles for a hot dry rock power plant in the Gonghe Basin. Based on the given heat production conditions, a Kalina cycle and three organic Rankine cycles were tested respectively with different ammonia-water mixtures of seven ammonia mass fractions and nine eco-friendly working fluids. The results show that the optimal ammonia mass fraction is 82% for the proposed bottoming Kalina cycle in view of maximum net power output. Thermodynamic analysis suggests that wet fluids should be supercritical while dry fluids should be saturated at the inlet of turbine, respectively. The maximum net power output of the organic Rankine cycle with dry fluids expanding from saturated state is higher than that of the other organic Rankine cycle combinations, and is far higher than the maximum net power output in all tested Kalina cycle cases. Under the given heat production conditions of hot dry rock resource in the Gonghe Basin, the saturated organic Rankine cycle with the dry fluid butane as working fluid generates the largest amount of net power.

Numerical analysis of photothermal conversion performance of MXene nanofluid in direct absorption solar collectors

A newly direct absorption solar collector (DASC) based on MXene nanofluid is proposed herein. The excellent optical properties of MXene nanofluids are experimentally determined, and a three-dimensional steady-state numerical model is developed to investigate the synergistic effect of the optical properties of MXene nanofluids and the structural parameters of the DASC. The effects of volume flow rate, working temperature, and solar concentration ratio on the photothermal conversion performance of the DASC are also analyzed. The results show that the transmittance of the MXene nanofluid evidently decreases because of the enhanced absorption of solar radiation of MXene. With the addition of MXene, the photothermal conversion efficiency of the nanofluid rapidly increases and then slightly decreases. The optimal MXene mass fraction is inversely proportional to the collector height. A mere 100 ppm of MXene nanofluid can achieve a maximum intercept efficiency of 77.49%, which is 55.47% higher than that of the base fluid. This work demonstrates the potential for the application of MXene nanofluids in the utilization of solar energy.

Flame spray pyrolysis synthesis and H2S sensing properties of CuO-doped SnO2 nanoparticles

In this work, CuO-doped SnO2 (CuO/SnO2) nanoparticles with different CuO mass fractions (0–1.0 wt%) are synthesized by a flame spray pyrolysis (FSP) route and applied to fabricate thin-film gas sensors for H2S detecting. The nanoparticles are characterized by X-ray diffraction (XRD), N2-physisorption isotherms, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Within the 0–1.0 wt% CuO-doping concentrations, all of the nanoparticles predominantly exhibit a spherical structure with a diameter of 5–15 nm, and possess a quite large specific surface area (110–125 m2/g). These textural characterizations suggest that Cu atoms form substitution doping in polycrystalline SnO2 nanoparticles at low CuO levels (< 0.5 wt%), and they are segregated as CuO nanoclusters at high CuO concentrations (0.5–1.0 wt%). From gas-sensing measurements, the CuO doping significantly improves the H2S sensing performance of SnO2 nanoparticles, especially at the optimal CuO-doping mass fraction of 0.5 wt%. The optimal CuO-doped SnO2 gas sensor exhibits a highest response (Ra/Rg = 1056) under a condition of 10 ppm H2S atmosphere at 125 °C. This is probably because a large number of highly dispersed small CuO nanoclusters are supported on the surface of the nanoparticle for 0.5 wt% doping, forming abundant p-n junctions with SnO2. When the CuO/SnO2 composite is exposed to H2S, semiconducting CuO is converted to metallic-like CuS, thereby increasing electrical conductivity and resulting in a high response. In addition, the optimal sensor displays good cycle performance and high H2S selectivity against other toxic and flammable gases including NH3, H2 and CO. Therefore, the gas sensor of 0.5 wt% CuO-doped SnO2 made by the FSP shows a large potential for H2S detecting in practical industrial application.

Theoretical Study of a New Porous 2D Silicon-Filled Composite Based on Graphene and Single-Walled Carbon Nanotubes for Lithium-Ion Batteries

The incorporation of Si16 nanoclusters into the pores of pillared graphene on the base of single-walled carbon nanotubes (SWCNTs) significantly improved its properties as anode material of Li-ion batteries. Quantum-chemical calculation of the silicon-filled pillared graphene efficiency found (I) the optimal mass fraction of silicon (Si)providing maximum anode capacity; (II) the optimal Li: C and Li: Si ratios, when a smaller number of C and Si atoms captured more amount of Li ions; and (III) the conditions of the most energetically favorable delithiation process. For 2D-pillared graphene with a sheet spacing of 2–3 nm and SWCNTs distance of ~5 nm the best silicon concentration in pores was ~13–18 wt.%. In this case the value of achieved capacity exceeded the graphite anode one by 400%. Increasing of silicon mass fraction to 35–44% or more leads to a decrease in the anode capacity and to a risk of pillared graphene destruction. It is predicted that this study will provide useful information for the design of hybrid silicon-carbon anodes for efficient next-generation Li-ion batteries.

Microstructure and properties of laser clad Fe-based amorphous alloy coatings containing Nb powder

Fe-Cr-Mo-Co-C-B-Nb coatings with the Nb mass fractions of 0, 2, 4 and 6% were prepared on 45 steel by laser cladding. The surface and microstructural evolution, chemical compositions, phases and thermal behavior of the obtained coatings were analyzed using a scanning electron microscope (SEM) equipped with energy disperse spectroscopy (EDS), Electron Probe Microanalyzer (EPMA), x-ray diffraction (XRD), and differential scanning calorimeter (DSC), respectively. The effects of element Nb addition on the glass forming ability (GFA), microhardness and corrosion behavior of coatings were investigated. The results show that the addition of Nb improves the surface properties, corrosion resistance and GFA of the material significantly, but the presence of excessively high Nb elements will generate Nb-Mo phase, which reduces the plasticity of the coating. Besides, by analyzing the properties of the coating, the optimum mass fraction of Nb was determined to be 4%.